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.

Biomechanics and the Olympics: Part IV

Many different Olympic sports involve rotational motion of the entire body, with the most popular probably being diving and gymnastics (trampoline too, that is crazy!).  When we examine motion, one of the first things we have to look at is the inertia of the object or the person.  Inertia is resistance to change in motion, and is measured by an object or a person's mass.  The greater the inertia of an object or person, the greater the force that is required to start, stop, or change the object or person's motion (this is Newton's first law of motion; objects in motion stay in motion and objects at rest stay at rest unless acted upon by an outside force).  For example, if you were going to lift a 25 kg block off the floor and a 50 kg block off the floor, it would take more force to lift the 50 kg block, because it is more massive and has more inertia.  The force applied to an object or person has to be greater than its inertia in order to cause a change in motion.  When we examine rotational motion, such as the flips, tucks, twists, and spins that occur in diving and gymnastics, we have to consider the mass moment of inertia of the person.  The mass moment of inertia is resistance to change in rotational motion, and is the mass of the person and the way the mass is distributed about the axis of rotation.  In these rotational motions, we can consider the axis of rotation to be the center of gravity.  The further away from the axis the mass is located, the greater the mass moment of inertia, and the closer to the axis the mass is located, the smaller the mass moment of inertia.  When the divers and gymnasts want to increase their rotational velocity, they get into a tucked position, such as in the picture above.  This brings the athlete's mass towards the axis of rotation, and reduces the mass moment of inertia.  When the athlete wants to slow down and decrease their rotational velocity (when they are about to enter the water or land), they come out of a tucked position into a more extended position (in the picture below), which will increase their mass moment of inertia and reduce their rotational velocity.  The same principle is demonstrated with figure skaters; when they want to rotate at a high angular velocity, they get into a crouched position and bring the arms in towards the body, and when they want to slow down, they get into a more upright position.  Since track and field is now in full swing, the next few posts will examine some of those events.

Biomechanics and the Olympics: Part III

 In my opinion, some of the best athletes in the world are gymnasts.  The combination of strength, power, flexibility, balance, and stamina are a rare combination.  All of the events are extremely difficult, but the one I find the most fascinating is the balance beam.  The balance beam has a width of 10 cm (3.9 inches).  There are many factors when it comes to maintaining balance, but two of the most critical are the base of support and the center of gravity.  The majority of the time during human locomotion, our base of support is our feet.  In the second picture below, the gymnast's base of support is her hands and chin.  We can change our base of support in order to be in a more stable position or a less stable position.  A wider base of support is better for stability and balance, but does not allow for a great deal of mobility (try walking with your feet spread far apart, you can't move very quickly, but you are less likely to fall over), while a narrower base of support is better for mobility but does place us in a less stable position.  The second factor is the center of gravity.  This is the balance point for the body, or the point where the weight of the body acts.  The center of gravity is slightly lower in females versus males in a standing position.  When we move, the location of the center of gravity will change.  In order to remain in a stable position, the line from the center of gravity (directed towards the ground) must remain within the base of support.  Consider what happens when you are standing in an upright position and start to lean forward.  As you lean forward, your center of gravity moves forward.  If you lean forward far enough, your center of gravity will move outside of your base of support, and if you don't take a step forward to change your base of support, you will fall.  Now, consider how a gymnast moves when she is performing a routine on the balance beam.  The shape of the balance beam automatically reduces the size of the base of support, making it difficult not to fall.  Many people, including myself, would have difficulty just walking across the beam.  When you factor in all the different moves, jumps, and landings the gymnasts have during their routine, which constantly changes the location of their center of gravity, it is truly remarkable what they are able to do on the balance beam.  Many of the gymnasts use their hands as their base of support during the routine, which increases the difficulty.

Biomechanics and the Olympics: Part II

 There is little doubt about the greatness of Michael Phelps and it is truly remarkable all the Olympic medals he has won.  However, it is the race that he barely lost that caused him much frustration.  During the Men's 200 meter butterfly two days ago, South Africa's Chad le Clos beat Phelps by five hundredths of a second.  The race was very close and Phelps had a slight lead on le Clos coming into the wall at the end.  However, instead of taking another half stroke before touching the wall, Phelps decided to go ahead and reach for the wall, while le Clos did take a half stroke.  The announcer commented that Phelps lost the race because he did not have any momentum at the end.  This was only partially correct.  Momentum is the product of a person's (or objects) mass and velocity (think speed with a direction).  Any time a swimmer is moving, they have momentum.  When they are not moving, either before or after the race, they do not have any momentum.  The faster a person is moving, the more momentum he or she has.  In order to increase momentum, it requires a reactive force in the same direction you are moving in.  In order to change momentum to the opposite direction, it requires a reactive force in that direction.  When swimmers complete a turn, they push into the wall, and the wall pushes back in the opposite direction, thus giving them momentum in that direction.  Back to the finish.  When Phelps decided not to take another stroke or half stroke into the wall, he was not applying any force to the water to increase his momentum.  Due to the drag force from the water, which acts in the opposite direction that the swimmer is moving in, Phelps was losing momentum.  le Clos, by taking another half stroke, was able to produce more force and increase his momentum, thus allowing him to touch the wall right before Phelps.  If you remember the 2008 Beijing Olympics, Phelps won this same event by one hundredth of a second because he did take an additional half stroke.  These are incredible athletes, and often times the difference between winning a losing can be just a few hundredths of a second.  Phelps did not lose because he did not have any momentum, he lost because he was losing momentum while le Clos was gaining momentum.  The video of the race can be found at this link at around the 30 minute mark.

Biomechanics and the Olympics: Part I

With the 2012 London Olympic games underway, I thought it would be a good time to do a series of blog posts and discuss biomechanics and the role it plays in analyzing and improving the performance of Olympic athletes.  My former doctoral adviser and mentor, Dr. Wendi Weimar, an associate professor at Auburn University, got me interested in analyzing movement several years ago when I was a Master's student at Auburn.  Dr. Weimar is highly skilled at watching an athlete perform a motor skill, or just watching a person walking down the street, and then analyzing their performance or walking gait.  She has worked with several former and current Olympians that attended Auburn, and as a graduate student, I had the unique opportunity to assist her.  We had an underwater video camera that was used to capture the swimmer's motion from a unique position, and then we were able to use a motion analysis program called Dartfish to analyze variables such as the swimmer's body position, joint angles, and the mechanical efficiency of the movement.  In many of these Olympic events, the difference between winning a medal or coming in last place is only a few hundredths or tenths of a second, so even the smallest biomechanical details are critical.  Over the next few days, I am going to take some of the sports in the Summer Olympics and discuss biomechanical factors related to the skill.  If you would like to read more about Dr. Weimar and her work, please click on the link below.

Weimar specializes in the science behind Olympic sport