Kinesiology and the 2016 Olympics Part IV: False Starts and Reaction Time

With the Olympics shifting away from the pool and towards the track, you might notice that a race starts but they stop it immediately, call all the runners back, and make them start again.  Also, the runner that started early is disqualified from the race. Sometimes, it is obvious that a runner starts before all the others and is disqualified.  Other times, it may be tough to tell that a runner started too soon.  So, how do they know that a runner "anticipated" the starting gun and started too soon? 

The starting blocks the athletes use have sensors in them that detect the amount and timing of the force applied to them by the runners' feet.  If the force applied to the blocks exceeds a certain threshold (I haven't been able to locate what this threshold is) in less than 0.1 (100 ms) seconds after the gun is fired, the runner is called for a false start and disqualified from the race.  This happened here to Usain Bolt in at the 2011 World Championships.  Why is this rule in place and why was 0.1 seconds chosen?

The purpose of the rule is to prevent the athlete from anticipating the firing of the starting gun and gaining an advantage on their opponents.  Most humans can react voluntarily to a stimulus (auditory, visual, etc) in about 120-150 ms.  Now, well trained athletes can react quicker than this because of their training, and there have been calls to lower the threshold to 90 ms (0.09 seconds).  Why does it take these athletes anywhere from 100-150 ms to start the race after the hear the firing of the gun? The answer lies in the nervous system and muscular system.

When responding to an auditory stimulus, the signal has to travel from the ears through sensory neurons to the brain.  Since this is a simple reaction time scenario (only one stimulus and one response), the brain can quickly process this signal and activate the alpha motoneurons that control the muscles in the legs, but it will still take some time for these signals to get from the brain down the motoneurons and to the muscles.  The time it takes from when the gun is fired to when the signal reaches the appropriate muscles is called the pre-motor time.  Once the signal reaches the muscle, it still takes time for chemical and mechanical process to occur within the muscle, force to be developed, and movement to occur.  This is known as the motor time.  Although it takes time for both of these processes to occur, it is remarkable to me the human body can respond so quickly.  However, if it occurs too quickly at the start of the race, the athlete will be disqualified.