Final Post of 2012

This will likely be the last blog post of 2012.  I'm planning on staying off the computer the next few days and enjoying the holidays with my family.  As I look back in 2012, many amazing things happened in the world of sports, too many to name.  One of the most remarkable and quickest recoveries from ACL reconstruction is Adrian Peterson.  Peterson tore the ACL and MCL in his left knee on December 24, 2011.  He underwent reconstruction for both ligaments only six days later in Birmingham.  The procedure was performed by Dr. Andrews.

Now, the typical rehabilitation time after an ACL reconstruction for an athlete is around 8-12 months, although this can vary, depending on the athlete, sports, and position.  While most athletes can return to competition within a year of the injury, the majority of them take around 2 years to return to their pre injury performance level.  Probably due to a combination of Peterson's athletic ability, motivation to return to play, and great work by the Vikings' sports medicine staff, he was able to return for the season opener on September 9th, a little over 8 months after his surgery.  This was remarkable considering the stress placed on the knee of a running back.  Peterson is on pace to rush for over 2,000 yards this year, a feat that has only been accomplished 6 other times in NFL history.  Peterson also has a chance to break the all time single season rushing record.  This is truly a remarkable accomplishment, and most of the credit has to go to Peterson.  The rehabilitation following ACL reconstruction is long, tough, and demanding, and for him to do what he has done less than a year after the surgery is very impressive. 

LCL sprain

Last Sunday, Robert Griffin III suffered a fairly uncommon knee injury, the lateral collateral ligament (LCL) sprain.  The lateral collateral ligament connects the femur to the fibula on the lateral (outside) part of the knee.  It is smaller and thinner than the medial collateral ligament, and it feels like a small pencil.

Most of the time in football, players are hit on the lateral side of their knee, which places a lot of tension on the medial side of the knee and can cause a MCL sprain (think about breaking a pencil, the side that is getting longer is normally the side that breaks).  The lateral side of the knee is much more exposed which increases the number of MCL sprains.  In order to sustain a LCL sprain, a person would likely have to be hit on the medial side of the knee.  That's what happened during Griffin's injury.  As he was falling to the ground, the defender hit him directly on the medial side of the knee, causing the LCL sprain.  The LCL isn't as critical to knee stability as the other 3 knee ligaments, but for a running quarterback like Griffin, it is a bad injury.  He missed this past Sunday's game and could be out a few more weeks as the ligament heals and he goes through rehabilitation.

Motor Variability and Equivalence

Another argument in the case against the term "muscle memory" are the concepts of motor variability and motor equivalence.  When we perform even the simplest tasks, such as reaching and pressing a button, we will never move in exactly the same pattern.  Why?  There is much variability in terms of which joints to use, how to use the joints, which muscles to use, what order to recruit the muscles in, and how much force to produce.  Although the movements will look similar, they will never be exactly the same.  The fact that we can move in a similar motion but use different patterns of joint actions and muscle activation is called motor equivalence.

If you look at some of the elite quarterbacks in the NFL, or elite pitchers in MLB, you will notice that they all have a similar throwing motion, but there are a lot of differences between them.  The pictures of Brett Favre and Peyton Manning above demonstrate this.  Also, if you watch a single quarterback make several throws over the course of a practice or game, you will notice some differences.  These differences are a good thing, because they allow us to adapt to changes in the environment.  But this variability also presents a challenge, and helps explain why elite level athletes often times fail.  If muscle memory truly existed, we would be able to repeat the same motion every single time without mistakes.  The human body would essentially function like a computer.  We know that this isn't the case.

Dislocated Rib and SC Joint Sprain

During Monday's night NFL game, Steelers quarterback Ben Roethlisberger was sacked and landed right on the posterior aspect of his right elbow.  The defender also landed directly on his left shoulder.  He suffered a sprain of the sternoclavicular (SC) joint of his throwing shoulder.  This is where the clavicle meets the sternum.  It was likely caused by his humerus being forced up into his clavicle when he landed on the ground.  This is not a very common injury, but it can be very painful, especially for a quarterback.  Anytime you move your humerus (upper arm), the clavicle will rotate as well, so this would cause pain at the SC joint.  This is the injury that essentially ended Brett Favre's iron man streak two years ago.

Roethlisberger also had another injury that is not very common, and that is a dislocated rib.  I haven't found an article that says exactly which rib is dislocated, but my guess would be it is one of the first 3 or 4 ribs, due to the mechanism of injury.  It is unclear if the dislocation occurred where the rib attaches to the thoracic vertebrae in the back, or where it attaches to the sternum in the front through hyaline cartilage (probably the anterior attachment to the sternum).  In any case, it is a very painful injury, and even simple activities are difficult, such as breathing, because the ribcage moves when we breathe.  There is some concern about him taking another hit before the injury heals and the rib puncturing an internal organ.  Due to the pain and likelihood of a serious injury, he will probably not play for several weeks. 

Update on Marcus Lattimore

Recent reports are that Marcus Lattimore had successful knee surgery last Friday.  The report mentions that several ligaments had to be repaired, although it doesn't specify if these repairs were reconstructions (I'm 100% sure the ACL was a reconstruction), or a suture.  However, he did not have any fractures to his femur, patella, or tibia, and at this time he will not need any additional surgery.  This is good news and should definitely increase his chances of making a return to the football field.

Comparing Marcus Lattimore's Knee Injury to Willis McGahee's Knee Injury

I wrote last week about the knee injury Marcus Lattimore sustained during a recent game against Tennessee.  It has been reported that he tore all four knee ligaments, which will require extensive reconstruction, surgery, and rehabilitation.  This injury is very similar to one sustained by Willis McGahee almost 10 years ago, so I thought I would compare the two.

The mechanism of injury for both injuries is eerily similar.  As you can see, both of them are hit on the anterior aspect of the knee by a defender, in a very similar fashion.  Lattimore was also hit from behind, which probably contributed to him tearing all four knee ligaments.  McGahee tore his ACL, PCL, and MCL with his injury.  McGahee had to have his entire ACL reconstructed because it essentially tore in the middle and there was no hope for repair.  But, his PCL and MCL tore near their insertion into the bone, so instead of having to reconstruct those ligaments with a different piece of tissue, doctors were able to suture the ends back into the bone.  This was a bit of encouraging news for McGahee considering he tore 3 of his primary knee ligaments.

It is not known the exact location of the tears in the ligaments of Lattimore's knee.  More than likely, his ACL will require a complete reconstruction.  The location of the tear in the other ligaments will determine if a suture can be performed, such as in McGahee's case, or if those ligaments will be reconstructed as well.  The more complete tears that Lattimore has, the longer and more difficult has rehabilitation will be.  But, Willis McGahee has provided a very good blueprint for Lattimore and his sports medicine team to follow.

Horrible Injury

If you watch college football, then you have probably seen or heard about the injury to South Carolina running back Marcus Lattimore.  During the play above, Lattimore dislocated his knee, and tore all four primary knee ligaments.  This type of injury will require extensive surgery and rehabilitation, but Willis Mcgahee was able to make a comeback from a similar injury.  I'm going to post some pictures of his knee after the injury at the bottom of this post, so if you have a weak stomach, you may not want to look at them.

As you can see in the picture above, Lattimore is being tackled from behind, and while his right foot is planted in the ground, he is hit just above the knee on the medial (inside) side of the femur.  These forces causes the femur and tibia to lose their normal articulation with each other, resulting in a knee dislocation.  Because of the large amount of force required to dislocate the knee, the ligaments of the knee are often damaged during a dislocation.  In Lattimore's case, the forces were so large that it tore all four ligaments of the knee: the medial (tibial) and lateral (fibular) collateral ligaments on the sides of the knee, and the anterior and posterior cruciate ligaments inside of the knee.  There have also been reports that he fractured his femur and patella as well, but I have not been able to confirm them.

If you look at the two pictures below, you can clearly see his lateral (outside part) femoral condyle, which you normally cannot see because it articulates (touches) with the top of the tibia.  You can also see that his femur and tibia are not aligned normally, it appears that the tibia (lower leg) is rotated internally.  Anytime someone has a knee dislocation, it is treated as a medical emergency because of the blood vessels and nerves that run behind the knee that could be injured.  I have not seen any reports of this occurring as a result of his injury.  Lattimore is looking at a very long road to recovery, but considering he is an elite athlete, the modern advances that have been made in sports medicine, and his desire to return to competition, I would not bet against him.

Pre-Programmed Reactions: Part II

One type of pre-programmed reaction is the corrective stumbling reaction.  Some times when we are walking, we encounter some type of obstacle or perturbation that affects our balance and may cause us to fall.  The corrective stumbling reaction is present to help prevent us from falling, that is, to maintain our balance until the nervous system has to prepare and initiate a voluntary response to help correct for the perturbation. 

If we are walking and our swing leg (the one that is off the ground) hits something (a curb, step, object, etc.), the correct stumbling reaction creates a flexor response in the leg muscles of the swing leg that will lift the leg up over the obstacle.  If the stance leg (the one that is on the ground) steps on something uneven, or hits something, it creates an extensor response in the muscles of that leg that will shorten the amount of time it is on the ground, allowing the person to place the other leg (the swing leg) on the ground quickly, which will increase the chances of maintaining balance and not falling down.  This pre-programmed reaction will take place approximately 50-100 ms after the person encounters the perturbation, and hopefully will prevent the person from falling.  In the picture above, this reaction helped prevent some of the runners from falling, but did not occur fast enough or cause a great enough response to prevent some of the other runners from falling.

Pre-programmed reactions: Part I

We have recently discussed reflexes and their role in movement.  We said reflexes are an involuntary response to a specific stimulus.  One example was the tendon tap reflex: the doctor taps your patellar tendon with a hammer, and you extend your knee.  Another example is the stretch reflex: when a muscle is stretched, it activates the muscle spindles that cause a reflexive contraction of the same muscle group.  What if we need a bigger, more sustained response to a certain stimulus?  That is where pre-programmed reactions come in.

Like reflexes, pre-programmed reactions are an involuntary response to a specific stimuli.  However, there are some differences between the two.  It takes about 35-40 ms (milliseconds) after a stimulus is presented for the reflexive contraction to take place.  A pre-programmed reaction takes place about 50-100 ms after the stimulus is presented, and it is followed by a voluntary muscle contraction.  Generally, the reflex is a quick burst of muscle activity that does not have many long lasting effects.  The pre-programmed reaction is a stronger muscle contraction and may involve several muscle groups that cross many different joints.  Pre-programmed reactions can also be modified by instructions.  If a person is told that a perturbation is upcoming, and to try not to resist the perturbation, the pre-programmed reaction will be smaller than if they have received no instructions.  Likewise, instructions can be given to increase the pre-programmed response after a perturbation.  This indicates some involvement of the brain with pre-programmed reactions, which is not the case with reflexes.

Later this week, we will discuss some examples of pre-programmed reactions.  The picture above is a hint (think about what happens when you stumble).

Update on Chris Carpenter

At the end of August, I wrote a post talking about thoracic outlet syndrome and the surgery Cardinals pitcher Chris Carpenter underwent to help with the syndrome.  They basically removed his first rib on his right side of the body and released some of the muscles in his neck to relieve the pressure on his brachial plexus (the group of nerves running from his neck to his arm).  Since there were only about 2-3 months left in the season, the plan was for Carpenter to start rehab and get ready to pitch again in 2013. 

Well, apparently Carpenter did not get the memo about this plan.  He was very aggressive with his rehab, and began throwing off a mound with about 4 weeks left in the regular season.  He was able to make 3 starts before the end of the regular season, and tonight will make his second start of the postseason.  All of this is very remarkable, for several reasons.  One, this is not a common procedure performed on baseball pitchers, so the actually recovery and rehabilitation time was a bit of an unknown.  However, for Carpenter to pitch less than 3 months after having a rib removed says a lot about him and the Cardinals medical staff.  Two, Carpenter is 37 years old, and he pitched over 270 innings last year.  We all know that the older we get, the longer it takes the body to heal.  Now everyone heals at different rates, but it is a big unknown after surgery.

If you follow the Cardinals, baseball, and/or Chris Carpenter, then you know he is one of the toughest players in baseball, and also has a remarkable postseason resume.  There aren't many players that would have been able to make this comeback.  Hopefully he can continue to pitch well for a few more starts and the Cardinals can win another World Series.

Neural Control of Movement Part VI: Reflexes

What is a reflex?  If you ask 10 different people, there is a good chance you will get 10 different answers.  Many different and imperfect definitions of reflexes exist.  For example, if the car in front of you suddenly stops, and you quickly step on the brake, is that a reflex?  Well, if we go by the textbook definition of a reflex, which is an involuntary muscle contraction or coordinated patterns of muscle contraction and relaxation elicited by a specific stimuli, it is not a reflex.  You have a choice of whether or not to press the brake pedal (sometimes people don't and rear end the car in front of them).  Reflexes are involuntary movements that are very difficult or almost impossible to override.

There are many different types of reflexes.  One of the simplest and most familiar is the Tendon (T) tap reflex.  Everyone has had this reflex tested at one time or another.  You sit on the end of the exam table with your knee flexed (bent) at about 90 degrees, and the doctor taps your patellar tendon with a mallet.  What should is happen is that after the tap, the knee should extend (straighten).  Why does this happen?  When the doctor taps the tendon, it activates the muscle spindles, which send signals to the CNS that the muscle (the quadriceps) is lengthening.  In order to counteract this lengthening, the CNS will activate the alpha motoneurons of the quadriceps, causing the muscle to shorten in order to counteract the lengthening.  The entire process should take around 35 milliseconds (thousandths of a second).

What is the purpose of this reflex?  Its functional significance is very small.  We aren't walking and moving around often where we get "hit" on a tendon and need a reflexive response.  However, this is a fairly easy reflex to elicit, meaning that it is a useful diagnostic tool for a doctor.  He or she is making sure the reflex is present, and that there is a normal response, and not an exaggerated or diminished response.  This would indicate some type of neurological disorder.  We will talk about more complicated reflexes and their significance in the future.

Hey Roger Goodell, want to really get serious about player safety?

Roger Goodell and the NFL have supposedly started to "crack" down on player safety.  This includes larger fines for hitting defenseless players, especially quarterbacks, especially in the head, and cracking down on bounty programs.  Why is a player penalized and fined for hitting a quarterback in the head?  Because of the potential injury the quarterback may suffer.  So, why isn't the NFL doing more to protect all players from injury head/neck injuries?

I blogged a few weeks back about what seems to be an increase in head and neck injuries this year in the NFL and college football.  I watch many games, and the biggest thing I have seen that puts these players at risk for injury is 1) lowering their head (flexing the neck) when making a tackle (see picture above), and 2) a defender projecting himself head first into an offensive player (it just happened in the Rams/Cardinals game. Very scary but fortunately the players was able to walk off the field).  The second holds the greater risk for a potential head and/or neck injury.  Once the defender leaves the ground, they cannot change their motion until they a) hit the ground or b) hit another player.  Too many times a player dives headfirst to make a tackle and the top of his head makes contact with an opposing player or a teammate.  So, if this type of tackle can lead to the worst possible type of injury, why are players still allowed to do it?  I realize it is something they have probably been doing since they first started playing football, but they risk/reward just isn't worth it.  Is it worth making a tackle this way when the possible consequence could be a concussion or neck injury?  Isn't the NFL concerned about the quality of life for it's players after football?  I am not saying that this would eliminate all head or neck injuries in football, but it would sure cut down on a lot of them.  If you watch any videos of recent injuries like these, in almost all of them the player either puts his head down or projects himself headfirst into a defender or teammate.  I am in no way saying that these players deserve to be injured.  It just seems that more should be done to eliminate this potentially hazardous technique.  We don't teach pitchers to throw at other players heads because of the risk of injury. Youth baseball players are not allowed to slide headfirst because of the injury risk. Why are we letting football players put themselves in danger when the outcome could be disastrous?

I still do not have a simple solution for this.  I think it has to start with the youth leagues and work its way up.  But, if NFL players were penalized and fined for diving headfirst into another player, I imagine some of them would stop doing it, and if even just one head/neck injury is prevented, the it is worth it. 

Neural Control of Movement Part V: Recurrent Inhibition

Last week we talked about reciprocal inhibition, in which the CNS would inhibit the muscles of the one muscle group because their shortening would cause the opposite muscle group to lengthen.  This week, we are going to talk about recurrent inhibition, in which the CNS actually inhibits muscle fibers of the same muscle that is contracting.  This is known as recurrent inhibition, and the inhibitory neuron found in the spinal cord is called a Renshaw cell.

So, how does recurrent inhibition work?  The Renshaw cells are located near the cell bodies of the alpha motoneurons in the spinal cord.  When the alpha motoneurons are excited and send signals to the muscle fibers to contract, the Renshaw cells are also excited.  These Renshaw cells make inhibitory connections on these same alpha motoneurons, thus preventing them from sending more signals down to the muscle fibers.

Now, why would the CNS want to inhibit the same neurons that are causing a muscle to contract?  Well, it gives the CNS more control over the movement.  One way to increase force/decrease force/maintain force is to control the number of muscle fibers that are activated.  Renshaw cells can serve this function by inhibiting alpha motoneurons and limiting the number of muscle fibers involved in the movement.  However, this may not always be the most effective strategy.  The Renshaw cells can be inhibited (turned off) by descending inputs in the spinal cord, so that they cannot inhibit the alpha motoneurons, which would allow for the activation of more motor units and muscle fibers.

Neural Control of Movement Part IV: Reciprocal Inhibition

When we think about movement, we often focus on the central nervous system sending excitatory signals (turning things on) through the alpha motoneurons to the muscles so they will contract.  However, in order to control the motion and prevent unwanted movements, the nervous system also has to inhibit (or turn off) certain neurons to keep them from firing in order to prevented unwanted muscles from contracting.  This process is called inhibition.
There are two main types of inhibition: recurrent inhibition, and reciprocal inhibition.  Recurrent inhibition turns off alpha motoneurons that connect to the same muscle fibers that are contracting, and reciprocal inhibition turns off alpha motoneurons that control the opposing muscle group.  On the surface, reciprocal inhibition is the easiest to understand.  For example, if you are trying to actively flex your elbow (think about a dumbbell curl), you would use the elbow flexors (brachialis and biceps brachii).  You do not want your elbow extensors (triceps brachii) to turn on, because that would work against the desired movement.  So, through reciprocal inhibition, the nervous system will inhibit the alpha motoneurons that connect to the muscle fibers of the elbow extensors, in essence shutting them off. 

Another example of reciprocal inhibition is through the muscle spindles.  If a muscle is lengthening to much and too fast, the muscle spindles will send signals to the CNS.  In order to prevent the muscle from any further lengthening, the CNS will inhibit the alpha motoneurons of the opposing muscle group (that is causing the stretch to occur), and excite the alpha motoneurons of the muscle that is lengthening, so that the muscle will contract and shorten.  This inhibition of the opposing muscle group is know as reciprocal inhibition.  I will talk about recurrent inhibition during the next post.

Neural Control of Movement Part III: Golgi Tendon Organs

A couple of weeks ago, we talked about a special type of proprioceptive receptor called muscle spindles.  Muscle spindles detect changes in muscle length and velocity of lengthening, and send signals to the CNS.  This helps the nervous system know about changes in joint angles and muscle length, and can help protect the muscle from lengthening too much and too fast.

Another type of proprioceptive receptor found in muscle (actually between the muscle and tendon) is the Golgi Tendon Organ (GTO).  These receptors are sensitive to changes in muscular force.  Whenever a muscle contracts (shortens), tension is developed within the muscle and tendon, which activates the GTO, causing it to send signals to the CNS.  Thus, the GTO provides feedback to the CNS about the amount of force a muscle is producing.  If a muscle is producing too much force, and is at risk of injury, the CNS can send inhibitory signals back down to the muscle so it will stop contracting and relax, thus reducing the amount of force.  Unlike the muscle spindles, which are are sensitive to changes in muscle length and the rate of change, GTOs are only sensitive to changes in muscle force, not the rate of change.

So, the muscle spindles send information to the CNS about  muscle length and the velocity of lengthening, and GTOs send information about muscular force.  This information allows the nervous system to make quick adjustments so we can move more efficiently and safely.   

Neck Injuries

It seems that this football season, especially last weekend, has seen a very high number of neck injuries.  Devon Walker, a defensive back for Tulane, sustained a cervical spine fracture this past Saturday when he attempted to make a tackle and collided helmet to helmet with a teammate.  Walker had surgery but the extent of the damage is not yet known.  Hopefully he will make a full recovery.

The question is, why are we seeing so many head/neck injuries in football?  Obviously football is a contact sport and there are hundreds of violent collisions every game.  These players are very massive and move at high velocities, meaning they generate a large amount of momentum that is transferred between the players during a collision.  Injuries are going to happen.  Now, I have never played or coached football, I've only worked with football teams as an athletic trainer, and I watch a lot of football.  Through my observations, it seems that many football players attempt to make tackles, or attempt to "run into" a tackler with their necks in a flexed position (think about looking down).  This is the worst possible position for the neck to be in during a collision.  Cervical (neck) flexion removes the natural curvature from the cervical spine, and places the vertebrae in direct alignment.  When the head makes contact with another person, the force is transferred from the head straight down the vertebrae, essentially creating a domino effect.  If there is enough force, an injury such as a cervical vertebrae fracture can occur, which can potentially damage the spinal cord.

I do not think there is a simple solution to this problem.  The best way to avoid this injury would be to tackle with the head up, or to teach the defender to be able to see the person they are tackling.  I've seen several examples of defenders "launching" themselves headfirst into the offensive player.  However, I think a lot of these players have been tackling with their heads down for so long, that it is a difficult habit to break, especially in heat of the game when they have to make a play.  Hopefully improvements will continue to be made to equipment and more research will be conducted to help answer these questions.

Remembering 9/11

It is hard to believe that today is the 11th anniversary of the terrorist attacks of 9/11.  I thought I would do something different with the blog today due to the 11 year anniversary of the day the terrorists attacked our country and many brave men and women lost their lives.  I was a sophomore at Southern Miss on 9/11/2001, and had just finished a morning workout at the Payne Center when the news broke.  It seemed surreal at the time, and it still does.  I was working as a student athletic trainer with the football team, and it was very difficult for anyone to focus on football for a few days, and all the games for that weekend were canceled.  Looking back, it was definitely the right thing to do, although later on I do believe sports played an important part in helping our country heal.  Amy and I had a chance to visit ground zero in New York a couple of years ago, and even though the rebuilding process is underway, you could still sense that something terrible had happened there.  Let's just remember everyone that lost their lives that day or later due to the attacks, and all the brave men and women that are fighting for our freedom.

Neural Control of Movement Part II: Muscle Spindles

When we think about muscles, we often think about the contractile components, actin and myosin, that attach and slide past each other, causing a muscular contraction.  But, there is another component of the muscle that is critical for coordinated movement, and that is the muscle spindle.  In the picture above, the extrafusal muscle fibers are the ones that contract and develop force, while the muscle spindle contains the intrafusal muscle fibers, afferent neurons, and gamma motor neurons.

There are three types of intrafusal fibers: dynamic bag fibers, static bag fibers, and chain fibers.  When muscle lengthens (think about when a muscle is stretched), the intrafusal fibers send signals to the spinal cord through the Group Ia and Group II afferent neurons, which relays information about how much the muscle is lengthening and how fast the muscle is lengthening.  The greater the lengthening or speed of lengthening, the more signals will be sent.  The gamma motor neurons send signals to the muscle spindles from the CNS (central nervous system) that can increase or decrease the sensitivity of the muscle spindle.  The gamma motor neurons help the CNS control the gain of the muscle spindles.

Why are muscle spindles important?  There are two big reasons.  1) The muscle spindles send information to the CNS about muscle length, which helps the nervous system know how joint angles are changing and where the different body parts are located in space.  For example, if you extend (straighten) your elbow, this lengthens the biceps brachii muscle.  The muscle spindles in the biceps will send signals to the CNS, indicating that the muscle is lengthening.  If the biceps is lengthening, then the elbow has to be moving into an extended (more straight position).  Also, if you were to flex (bend) your knee, this would lengthen the quadriceps, which activate the muscle spindles, indicating that the muscle is lengthening and the knee if flexing.  2) Muscle spindles also help protect the muscle from injury due to the muscle lengthening too much and too fast.  If a muscle is lengthening too much and too fast, the CNS can send signals to the muscle for it to contract and shorten.

So, muscle spindles play a crucial role in providing feedback to the CNS about muscle length and speed of lengthening.  This information helps the body know how joint angles are changing, and it can serve to help protect the muscle against injury.

Neural Control of Movement Part I: Please Do Not Say Muscle Memory

This semester, I am teaching a class called "Neural Control of Human Movement."  This is a very challenging course for both myself and the students, because the nervous system is very complex.  To me, it is the most complex and difficult system in the body to understand.  I am going to do a series of blog posts discussing how the nervous system works with the muscular system to produce coordinated movement.

When we think of voluntary movement, such as walking, running, hitting or catching a baseball, etc., we often focus primarily on the muscles and the bones involved in the movement.  What we fail to consider is that none of this motion would be possible without the nervous system.  This simplified view of movement has given rise to a very commonly misused term called "muscle memory."  I hear sportscasters, coaches, and even so called scientists use this term often, and every time I hear it I cringe.  The ESPN segment called
"Sports Science" was airing the other day and the host used the term "muscle memory" to describe how a baseball player caught a ball. 

Why is "muscle memory" not correct?  The biggest reason is that there is no memory structure in the muscle.  A skeletal muscle cannot contract unless it is stimulated by the nervous system.  Now, it is true that through practice and experience, movements become more coordinated, efficient, and require less attentional demands, and many people want to label this as "muscle memory."  The next few blog posts will discuss the interaction between the nervous system and the skeletal system, and the actual processes that occur that lead to an improvement in performance that involves both the nervous and muscular systems.

Thoracic Outlet Syndrome

I was talking with my Dad the other evening about St. Louis Cardinals pitcher Chris Carpenter and his return from surgery to relieve his symptoms due to thoracic outlet syndrome (TOS).  This is not a very common injury, but it can lead to a lot of pain and weakness, which is obviously a major problem for a baseball pitcher.  I will outline the basic principles of TOS below.

Before talking about the syndrome, we first need to define the thoracic outlet.  If you look at the top picture, you will see a group of nerves coming out of the spinal cord, and running down between the scalene muscles, behind the clavicle, and in front of the first rib, and then down into the arm.  This group of nerves is known as the brachial plexus.  The opening between the scalene muscles and the ribcage is the thoracic outlet.  There are also blood vessels not pictured above that pass through this space.  Any time there is a nerve or group of nerves passing through a tight space, there is a chance that some of the structures can "press" on the nerves, which can lead to pain, tingling, numbness, and weakness in the affected area.  In TOS, it could be the scalene muscles, the clavicle, or the first rib pressing on the nerves.

What causes TOS?  There are many potential causes, including a fractured clavicle, tightness or scar tissue in the scalene muscles, the presence of an extra first rib (yes, some people actually have 13 instead of 12 pairs, but the presence of an extra rib does not necessarily lead to TOS), pressure from the normal 1st rib, repetitive stress, such as repeating the overhead throwing motion, or poor posture.  The signs and symptoms include pain along the side of the neck, the upper arm, and possibly the lower arm.  Numbness, tingling, and weakness in the shoulder and arm may also be present.  These symptoms are similar to other conditions, such as a herniated disc, which can make diagnosing TOS difficult.

In the case of Chris Carpenter, his TOS was likely caused due to the repetitive stress of the overhead throwing motion.  He had similar symptoms back in 2008, but they did not resurface again for several years.  His symptoms first resurfaced during spring training, when he was diagnosed with a herniated disc.  He was prescribed rest followed by strengthening exercises for the neck, shoulder, and arm.  After a couple of months of rehab, he attempted to pitch again, but could not because the pain returned.  He was then referred to a specialist who made the diagnosis of TOS and recommend surgery to remove his first rib and release some of the scar tissue around the scalene muscles (I am not sure if he had an extra first rib or not).  He has responded well since the surgery and is attempting to pitch again this year, but at the least he should be healthy to start next season (or relatively healthy for a 37 year old pitcher).

In many cases, therapy and postural changes can relieve most of the symptoms of TOS.  Surgery is often seen as a last option, because it does carry some risks since the surgeon has to operate close to many nerves.  

Gruesome injury

Last Thursday night during a preseason NFL game, Tennessee Titans wide receiver Marc Mariani suffered a compound fracture of his tibia and fibula while returning a punt.  I'm going to place the picture of the injury and video at the bottom of the post in case you don't want to see it.  This was a very bad injury.  It likely resulted in an open fracture, where the broken bone(s) punctures the skin.  This can lead to complications from infection because of the open wound.  What type of loading caused this injury?

The type of loading that caused this injury was bending.  Bending occurs when there is tension (think about making an object longer and skinnier) on one side of the bone, and there is compression  (think about making an object shorter and wider) on the other side of the bone.  To fully understand the injury, you must watch this video.  As Mariani is moving forward, his left foot is stepped on by one of his teammates.  This stops the momentum of his foot.  However, his lower leg and the rest of his body continues to move forward due to their inertia.  His lower leg makes contact with the other players leg a few inches above his ankle.  This stops the momentum of his lower leg, but the rest of his body continues to move forward.  The point of contact between Mariani's lower leg and his teammates lower leg basically acts as a fulcrum, and the bending forces placed on the tibia and fibula exceed the strength of the bones, and they fail (break).  Adult bone is weaker in tension than compression, so the fracture likely started on the side opposite of where his leg made contact with his teammate's leg.

Human bone is very strong, and it can withstand a large amount of force before breaking.  In these cases of extreme fractures on the football field, it is often times an example of all the forces being lined up in just the right positions to cause a fracture like this.  If Mariani's teammate had not stepped on his foot, there is a good chance he would not have sustained an injury at all.  The Titans are reporting that surgery went well, and hopefully he will have a chance of returning to the field next year.

The Stephen Strassburg Debate

If you are a major league baseball fan, then you have probably heard that the Washington Nationals plan on shutting down their ace pitcher, Stephen Strassburg, after he pitches around 170-180 innings this year.  What is their rationale for doing this?  Strassburg is a young pitcher, and he had ulnar collateral ligament reconstruction surgery (Tommy John surgery) a little less than 2 years ago.  Their theory is that by limiting the number of innings he pitches in his first full year of pitching after the surgery, they will help prevent him from becoming injured in the future.  Is this the right approach to take? 

The Argument for shutting him down: There is no doubt that the overhead throwing motion used by baseball pitchers places a lot of stress on the shoulder and elbow.  Most of these pitchers begin pitching at a relatively young age, and the cumulative stress of every inning pitched, bullpen session, and warm-up throws can lead to a degradation of the soft tissue of the shoulder and elbow.  A torn UCL is often times not the result of one traumatic event, but an accumulation of small tears in the ligament that cause it to weaken over time and eventually rupture during the execution of a pitch.  Also, labrum (the cartilage lining of the socket of the shoulder) tears in pitchers often occur due to the repetitive stress placed on the joint from throwing thousands of pitches.  This is why the Nationals want to shut Strassburg down.  He is relatively young, he already had one major surgery, and has the potential to win many games for them in the future.  By shutting him down early, they will help prevent excessive stress from being placed on his arm, and they are counting on this to keep him healthy in the future.

The Argument against shutting him down: From a purely baseball prospective, the goal is to win as many games as possible, make it into the playoffs, and win the World Series.  The Washington Nationals are not a franchise rich in postseason history.  This is their best chance to make it to the World Series.  The franchise has only been to the playoffs one time in their history.  Strassburg is one of the best pitchers in baseball, and to have a good chance of winning in the postseason, you really need your best players to play.  Also, there is no evidence to suggest that by shutting Strassburg down, he will not have a major injury in the future.  There have not been any studies conducted to investigate this question.  Also, Strassburg recently had his UCL reconstructed, so at this point, it should be very strong.  The Nationals should have a good team for the next few years, but in sports, you never know how many chances you are going to have to win a championship.

What would I suggest?  If it were me, I think I would continue to let him pitch, but would closely monitor his pitching mechanics for signs of fatigue and breakdown.  If Strassburg started to make changes to his throwing motion because he was fatigued due to all the pitches he has thrown this season, I would consider shutting him down or giving him a break.  The Nationals could also limit his innings over the last few weeks of the season so he could pitch a few games in the postseason without throwing an excessive number of innings.  However, you have to admire the Nationals organization for taking a pro-active stance on the number of innings they are going to allow him to pitch.  It seems like a majority of the time teams place winning ahead of player safety (especially football), so it is refreshing to see a team take a stand like this.  Hopefully it works out for Strassburg and he is able to have a long and relatively injury free career.  Even if Strassburg does not sustain another major injury for the rest of his career,  it will not be possible to cite his shutdown this year as the cause.  There are too many factors that effect whether or not an athlete sustains an injury to credit one singular event.

First day of classes

Today marks the first day of classes at Mississippi State University.  The first day is always an exciting time, and probably scary for some of the students.  I was talking with my wife the other day, and since we both started Kindergarten at age 5 back in 1987, we have either been in school or working at a university for the past 26 years.  We both love our jobs and interacting with the students.  I tell all my students that I want them to be successful and will do anything I can to help them succeed. 

I am teaching 3 courses this semester, and 2 of the classes are ones I have not taught previously.  I am teaching anatomical kinesiology for the 9th time during my 4 years at Mississippi State, and it is easily one of my favorite classes.  It is basically an overview of musculoskeletal anatomy starting with the foot and working up the body to the head and then down to the shoulder, elbow, and wrist.  My goal for the students by the end of the semester is that when they see a person performing a movement, they can name the joints that are involved, and the muscles that the person is using to accomplish the goal of the movement.

A new class I am teaching this semester is neural control of human movement.  I have previously taught motor development and motor learning, so I have some experience teaching about the nervous system.  To me, the nervous system is the most important system in the body, especially when it comes to human movement.  The nervous system is probably the most complex system as well, which makes the course challenging but fun.  There are many neural processes that occur during voluntary movement that we are not even aware of the majority of the time, and even the smallest disruption can cause errors in movement.  I am planning on starting another series of blog post on neural control very shortly.

The third class I am teaching this semester is a freshman seminar based on the television show "House."  This is a one hour course designed for students that are new to Mississippi State.  I have been a big fan of the show House and all the different medical mysteries on the show.  We are going to examine some the cases on the show and see how realistic they are.  We will also discuss why the doctors choose specific diagnostic tests.  It should be a lot of fun and a learning experience for all of us.

On the research side, we are about to begin a study this Wednesday investigating the relationship between ankle laxity ("looseness in the ankle joint"), balance, and landing kinetics (forces).  The study will examine people that have never sustained an ankle sprain, people that sprain their ankles frequently, and people that have sprained their ankle before but do not have any long term problems.  We are trying to see if there are differences in these variables between these different groups.  Several undergraduate students are taking a prominent role in this study.

All in all, it should be an exciting semester.  I am going to do my best to post at least two blog posts a week, so be sure to check back regularly. 

Just what are the benefits of PED use for baseball players?

Yesterday, major league baseball announced that San Francisco Giants outfielder Melky Cabrera tested positive for excessive testosterone, earning him a 50 game suspension.  Now, the debate has begun again, just like it does anytime an athlete tests positive for PED use, as to just how much of an advantage he or she gained by taking the banned substance.  The problem is, there is no clear answer to this question.

The reason this question cannot be definitively answered is that there is no way to isolate the effects of certain PEDs in a controlled laboratory setting (also, it would be nearly impossible to receive approval to conduct a study where these types of drugs were given to human participants).  There are numerous factors that effect the performance of a baseball player, including, but not limited to, hand-eye coordination, amount of practice/experience, motivation to perform, psychological status, muscular strength, muscular flexibility, etc.  While it is true that Cabrera's batting average has increased 91 points in two years, the effect that the excessive testosterone had on this increase cannot be determined.  Every other factor that could cause improvement in batting average cannot be controlled in order to isolate the effects of the testosterone. 

Now, I am not advocating the use of performance enhancing drugs.  They definitely can help cause increase in muscular strength, and they definitely have some very bad side effects, and they should not be allowed in athletics, as using them is a form of cheating.  However, scientists and researchers cannot quantify specifically how much of an advantage these drugs give an athlete.  Also, the punishment for a first time offense in both MLB and the NFL is not severe enough to discourage athletes from experimenting with PEDs.

Running with a fractured fibula

Although the Olympics are over, there is still time to examine some of the things that occurred over the past two and a half weeks.  One of the most impressive was US sprinter Manteo Mitchell finishing has leg of the men's 4 x 400 meter relay despite the fact that he was running on a fractured fibula.  How was he able to do this?  There are many factors that come into play, including his psychological condition and motivation, pain tolerance, and the fact that he is a world class elite athlete.  The only factors that I am able to analyze are the anatomical and biomechanical factors.

The fibula is the smaller, thinner bone located on the lateral (outer) side of your lower leg.  At the proximal (top) end, it articulates with the tibia (knee), and at the distal (bottom) end, it articulates with the tibia and helps form the ankle.  The "bump" on the lateral side of your ankle is the lateral malleolus, which is part of the fibula.  Due to the placement and size of the fibula, it does not play as large of a role in force absorption and weight bearing as the larger tibia does.  In fact, about 10-15 % of the force from the ground during walking and running is absorbed by the fibula, and the other 85-90% is absorbed by the tibia.  Even though it does not absorb as much force as the tibia, it is still a critical bone to transfer force from the foot and ankle up to the knee, and without a fibula, it would be nearly impossible to walk or run.  If Mitchell had fractured his tibia, he likely would not have been able to finish the race.  Since he fractured his fibula, he was able to finish, which was a very impressive accomplishment, not only because of the intense pain he was in, but also because the fractured fibula disrupted the normal transfer of force between the ground, and his foot, and ankle, and lower leg.  This is just speculation, but there is probably not a high percentage of people that would be able to continue running with a fractured fibula.

Biomechanics and the Olympics:Part X

Since the Olympics are ending on Sunday, this will be the last post of the series.  Again, with track and field being the focus of the Olympics this past week, some of these athletes are putting up really fast times.  Newton's third law is a critical factor in a person's capability to run fast.  Newton's third law is the law of action/reaction: "for every action there is an equal and opposite reaction."

In order for a person to walk or run, they exert a force from their foot into the ground.  The ground will push back with the same amount of force, but in the opposite direction.  This force from the ground is known as the "ground reaction force" and can be measured in a laboratory setting using an instrument called a force platform.  This force is measured in three directions: 1) vertical (straight up and down), 2) anterior-posterior (forward and back), and 3) medial-lateral (side to side). 

The way a person moves is influenced by the magnitude of the force applied as well as the direction the force is applied in.  If you want to jump as high as possible, you push straight down into the ground, and the ground pushes you straight up.  Almost all of the ground reaction force is in the vertical direction.  If you want to jump for maximum horizontal distance, you will apply a force both down and back into the ground, and the reaction force will push you up and out (consider a long jumper, they are trying to jump as far as possible, which has both a horizontal and vertical component).  When a person is running, they have a greater posterior ground reaction force when the foot hits the ground, and a greater anterior reaction force when they push off, which will propel them forward.  If a sprinter wants to increase his or her running velocity, he or she will need a greater anterior ground reaction force than posterior ground reaction force.  These sprinters are able to apply a large amount of force into the ground, at the optimal angle, in order to maximize the ground reaction force and run at very fast velocities. 

Biomechanics and the Olympics: Part IX

Another scary moment at the Olympics the other day occurred when pole vaulter Lazaro Borges had his pole snap during an attempt.  As you can see in the picture above, he was very fortunate not to be injured by this unfortunate accident.  Pole vaulting can be a potentially dangerous sport, as often times the athletes are attempting to use a pole to project themselves over a 15-17 foot high bar.  Why did Borges' pole break during this attempt?

When a structure is loaded, it will deform to a certain extent before it starts to break, and if the a load is still applied to the structure, it will eventually fail and rupture.  Think about holding a tree limb and applying a force to it.  Eventually, the limb will start to break, and if you continue loading it, it will rupture completely and become two separate parts.  We could plot a stress-strain curve for different materials (metal, glass, bone, muscle, tendon, etc.) to examine how they will behave when they are loaded.  Stress is similar to the load applied to the material, and strain is the amount of deformation.  The stress-strain curve is comprised of three main parts: 1) the elastic region 2) the plastic region 3) and the ultimate failure point.  If a material is loaded within the elastic region, it will undergo deformation, but it will return to its original shape once the load is removed.  If it is loaded past the elastic region into the plastic region, the material will start to show some small tears (microtrauma), and will not return completely to it's original shape after the load is removed.  If a material is loaded to or past the ultimate failure point, it will completely rupture and tear (break into two or more pieces). 

Now, the pole used in pole vaulting is highly elastic, which is beneficial because it will deform extensively and store potential energy which will be used later to project the vaulter over the bar.  Most of the time in pole vaulting, the pole is not loaded past its elastic limit, and no permanent deformation occurs to the bar.  Think about using a rubber band, if you pull the band back (but not too far), and then let it go, it releases a lot of energy and returns to its original shape.  If you pull the band back past its elastic limit, then it starts to show some little tears, and if you keep pulling the rubber band back, which increases the stress on the band, it will eventually break.  This is what happened to Borges' pole.  It was loaded past the elastic and plastic limits, to the ultimate failure point, and it broke.  Why did it happen on this attempt?  There are a few possible explanations.  Perhaps his pole had been loaded previously past its elastic limit to its plastic limit, and had already sustained some small deformation, and was weaker for this attempt.  It might have been due to pole placement and how the load was applied to the pole (unfortunately the video has been removed from the internet).  The fortunate thing is the he was not seriously injured.  In many of the Olympic sports,  the athletes are moving at very high velocities, producing a large amount of force, and sometimes have implements that they use or obstacles that are in their way.

Biomechanics and the Olympics: Part VIII

In my opinion, one of the most difficult events in track and field is the hurdles.  To get an idea, try running as fast as you can and jumping over an imaginary object every 10 meters.  It's not easy to do, and even more difficult when you add in a 42 inch (106.7 cm) high hurdle for men and a 33 inch (83.8 cm) high hurdle for women.  It is a skill that requires speed, strength and flexibility.  What joint actions are required in order to clear a hurdle?

If you watch hurdling, some athletes lead with their right leg, and some lead with their left leg, but it is always the same leg that leads.  In the picture above, the athlete in the middle uses her right leg to push off, and her left leg to land on.  We can call the right leg the propulsive leg, and the left leg the landing leg.  The propulsive leg has to produce enough force to project the runner and their legs up and over the hurdle.  This propulsive foot is not in contact with the ground for a very long time, but, the muscles in the right leg must apply a great enough force to the ground to get the runner over the hurdle.  The amount of force applied multiplied by the time interval over which the force is applied is known as impulse.  The primary muscles used during this propulsive phase are the hip extensors (gluteus maximus and hamstrings), the quadriceps, and the gastrocnemius and soleus (calf) muscles.

Once the athlete is in the air, they must now clear the hurdle.  If you look at the athlete's left leg in the picture above, the hip is flexed (moved in front of the torso) while the knee if fully extended (nearly straight).  This places a large amount of tension on the hamstrings; if the athlete does not have good flexibility in this muscle group, they will have difficulty clearing the hurdle and will have a greater risk of injury.  Once the lead leg clears the hurdle, the trail leg also has to clear.  The knee of this leg is in a flexed (bent) position, while the hip is going first extend (go back behind the torso), then abduct (move out to the side), and then flex to clear the hurdle. 

After clearing the hurdle, the athlete is now going to land on the lead or landing leg.  Impulse becomes important again, because the foot/ankle/lower leg has to absorb the impact forces from the ground, which will be applied over a very short time period, and then apply a force to the ground to propel the body forward to continue running.  This running and jumping cycle will be repeated several times (depending on the length of the race) over the course of the event, and one poor jump where the athlete hits the hurdle can take them from 1st place to last place (see the picture below from the men's race).  In order to be successful at this event, the athletes must be able to run at a very high velocity, be able to produce enough force to jump over the hurdle, must have enough flexibility to clear the legs over the hurdle, and must be able to absorb the impact forces when they land.  This is a very demanding event that requires a very specific skill set.

Biomechanics and the Olympics: Part VII

I was asking my wife what today's topic should be when I came across this video of weightlifter Matthis Stenier dropping 432 pounds directly onto his neck (video courtesy of Deadspin.com).  Before you read any further, watch the video (disclaimer: it looks worse than it really is, but if you have a weak stomach, you may not want to watch it).  This video itself contains numerous possibilities for discussion, but let's talk about Newton's second law of motion, since we have previously discussed the first law.

Newton's second law of motion is the law of acceleration, represented by the equation F=ma, where F is force, m is mass, and a is acceleration.  This equation tells us that an object's acceleration is directly proportional to the force applied to it and inversely proportional to the object's mass.  Steiner is attempting to perform a lift called the snatch, where he must lift the weight over his head, and then stand up.  During his failed attempt, he was attempting to lift 432 pounds.  This weight represents a force, since weight is the result of gravity acting on the mass of an object.  To calculate the weight of an object, you multiply the object's mass by the acceleration due to gravity (-9.81 m/s^2).  Pounds is the US unit of measuring force, in the metric system, a Newton is the unit used to measure force.  One pound is equal to -4.45 N, so in this example, the barbell had a weight of -1,922.4 N.  We can also calculate this weight by multiplying the mass of the barbell (195.95 kg) by the acceleration due to gravity (-9.81m/s^2), which also gives us approximately -1,922.4 N.  In this example, the negative sign indicates that the force is acting in the downward direction, which is the case with weight, which always pulls us or objects towards the ground.

For Steiner to lift the barbell off the ground, he must exert a force in the upward direction to the barbell greater than 1, 922.4 N, or 432 pounds.  If the force he exerts is less than or equal to the weight of the barbell, no movement will occur.  Steiner is clearly able to exert a force greater than this because he is able to move the barbell over his head.  The muscular force he generates is greater than the weight of the barbell, and the muscles shorten, allowing him to begin the movement.  This causes an acceleration of the barbell in the upward direction.  When Steiner gets the weight over his head, he pauses for a second, and the barbell does not move.  At this point, the force he is exerting is equal to the weight of the barbell, and the muscles develop tension while remaining at a constant length.  Since the forces are balanced, there is no acceleration.  After this short pause, Steiner begins to stand up, meaning he is exerting a force greater than the weight of the bar.  However, he is not able to complete the lift, and because he is now exerting less force than the weight of the bar, the bar is now moving in the downward direction right onto his neck.  Now, the barbell has an acceleration in the downward direction.  Normally, after we have lifted something and are attempting to lower it back down, we do so in a controlled manner, in order to avoid injury and slamming it on the ground.  The muscles gradually develop tension as they lengthen to control the movement.  Steiner was not able to do this (which is very difficult since he was lifting 432 pounds).  It is difficult to tell from this angle exactly what happened, but I have two theories.  1) He was lifting too heavy of a weight and simply could not continue to produce enough force to lift it over his head or 2) the barbell moved too far back behind his head, causing a tremendous amount of tension on his shoulders and elbows, to the point where if he did not drop the weight, he likely would have dislocated one of those joints.  It was probably a combination of these factors as well as fatigue.

I am happy to report that he was not seriously injured, and actually attempted another lift.  Weightlifting can be a very dangerous sport, especially when attempting to lift something this heavy.  My advice is to leave these kinds of lifts to the professionals, and if you are attempting to lift something over your head, be very careful.

Biomechanics and the Olympics: Part VI

Sometime yesterday afternoon (although NBC didn't show the race until later last night), Usain Bolt cemented his place as the world's fastest man by again winning the 100 meter race, with a time of 9.63 seconds.  As you can see in the picture above, Bolt is clearly a few meters ahead of his closest competitors.  What makes Bolt so fast?  Well, there are a number of factors, but today I am going to talk about his stride length, step length, and stride frequency.

Stride length is the amount of distance covered from the touchdown of one foot (let's see left foot strike) until the left foot touches the ground again.  Step length is the distance covered from the touchdown of one foot (left foot) until the touchdown of the other foot (right foot).  Bolt clearly has an advantage here because he is taller than the other sprinters.  I went back and watched the race in slow motion and it took Bolt 41 steps, or 20.5 strides, to run 100 meters.  The third place finisher, American Justin Gatlin, took 44 steps or 22 strides to complete the 100 meters.  Simply put, Bolt covers a much greater distance with each step and stride than any other competitor, giving him a distinct advantage.  On average, Bolt covers 2.44 meters with each step, which is roughly equal to 8 feet, and 4.88 meters per stride, or nearly 16 feet.  Justin Gatlin covers 2.27 meters per step, which is equal to 7.45 feet per step.  These numbers are just the average stride and step lengths over the entire race.  Since each runners takes a shorter stride at the start of the race, the actual stride and step lengths are going to be greater towards the middle and end of the race.

Another critical factor in determining running velocity or speed is stride frequency, which can also be broken down into step frequency.  Stride frequency is the number of strides taken during a given time frame, typically strides per second.  In this race, Bolt took 20.5 strides over 9.63 seconds.  This averages to 2.13 strides per second, or 4.26 steps per second.  For Justin Gatlin, he took 22 strides over 9.79 seconds, which averages to 2.25 strides per second, or 4.5 steps per second.  This means that Gatlin is able to swing his legs through the running gait cycle (put his foot on the ground, and swing it back and then forward to the ground again) at a faster rate than Bolt.  But, because Bolt is able to take such a longer stride and step than any of the other sprinters, he still finishes the race faster than them.  Based on Bolt's stride length and stride frequency, and Gatlin's stride length, Gatlin would have to increase his stride frequency to 2.28 strides (4.56 steps) per second to equal Bolt's time of 9.63 seconds.  Simply put, Bolt is very difficult to beat when he is dedicated to his training and focused on the race.

Biomechanics and the Olympics: Part V

Now that the focus of the Olympics has shifted to track and field, and more specifically the men's and women's 100 meter race, one of the critical factors in winning this race is the reaction time of the sprinters.  Often times, just like in swimming, these races are decided by a few hundredths of a second, and a poor start can be the difference between first place and last place.

Reaction time is the amount of time it takes the body to prepare and initiate a response to a stimulus.  There are three different types of reaction time (RT).

1. Simple RT: there is one stimulus/signal, and only one response to be made to the stimulus.  This is what happens at the start of a race in track and swimming.
2. Choice RT: there are several stimuli/signals, and each one requires a different response.  A traffic light is a good example.  Each color signal requires a different and timely response to avoid an accident, although one could debate what response is to be made to a yellow light.
3. Discrimination RT: there are several stimuli/signals, but the person is only going to respond to one specific signal.  A quarterback calling out the snap count is a good example of this; he is going through several different signals, but the offensive players are only responding to one specific signal and should ignore the rest.

The start of a track race involves simple RT, because the only signal the runners are paying attention to and responding to is the starting gun.  The faster the runners can respond to this signal and begin to move, the greater the chance they have of winning the race.  Reaction time can be broken down into two components, pre-motor time and motor time.

1. Pre-motor time is the amount of time from the onset of the stimulus (the sound of the gun) until electrical activity is detected in the muscle groups used to perform the movement.  This time can be measured using electromyography (EMG), which typically involves placing electrodes over the muscle in order to record the electrical signal associated with the muscle contraction.  What happens during this pre-motor time?  Well, the auditory signal has to be detected by the sensory receptors in the ear, this signal has to travel to the brain for processing, and the brain has to send signals down to the appropriate muscle groups.
2. Motor time is the amount of time from the onset of electrical activity in the muscle until the first movement is detected.  It takes time to develop tension in the muscle and transmit this tension from the muscle to the tendon to the bone for movement to occur.  This time is also known as the electromechanical delay of the muscle.

The take away message is that it takes time for the body to prepare and initiate a response, even to simple signals.  As movement complexity and the number of signals and possible responses increase, reaction time also increases. In all sports, a shorter (faster) reaction time typically leads to a greater chance of success. 

For the elite level sprinters in the Olympics, this entire process takes between 100-200 milliseconds (a millisecond is a thousandth of a second).  This does not seem like a large amount of time, but in a short sprint of 100 or 200 meters (or even 400 and 800 meters), a few milliseconds can make a large difference.  I am not an expert in track, but I know these sprinters spend a lot of practice time working on their starts.