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Where Is The Error?

Reaction Time, Movement Time, Device Time and Honing In                                                                                                                

In 1927 at Cornell University, Exercise Physiologist and Nobel Laureate, Archibald Vivian Hill took large coils of wire and used them to detect magnets worn by sprinters as they raced by them.  He calculated velocity and acceleration by knowing the distance between the coils.


Today electronics are commonplace in trying to remove error from measuring sprinting performance.

The greatest error in hand timing is at the start.  This is the reaction time of the person timing.  Reaction time is the time it takes for the timer to perceive that the movement of the runner has occurred and decide to respond.  The response will be to press the start button on the stop watch.  By using electronics the error of the timers’ reaction time is eliminated.

Movement time is the time from when the response has been mentally engaged by the coach to perform the required muscle movement of pressing the button.  This is the actual pushing of the button to start the stop watch by moving the finger.  Movement time is very quick and has little variation between coaches.

Device Response Time is relative to the quality of equipment that you are using.  Mechanical devices take time to engage even after the coach has acted.  A stiff clunky stop watch versus a smooth quick slick device.

The fastest stop watch is the “attosecond stopwatch” used in physics for atomic particles.  The good news is that the variance between stop watches is negligible and for coaching purposes all stop watches can be construed as ultrafast.

Stopping the stop watch can have very little error as long as the timer has a selected point of stopping and all the timers agree that they are going to engage the watch at the same point i.e., the athletes back as he crosses the finish line.  Honing in on the runner as they head to the finish line and knowing the decision point can reduce the reaction time to an insignificant part of the total time.


All coaches should agree on exactly what movement by the athlete will constitute engaging their watch.

All coaches should agree on what constitutes the finish.

All timing for testing should be done by more than one coach.

All coaches should meet about the human error in timing.

Suggestions for Posting Results

Post all of the times

Post none of the times and individually tell each athlete

Post the average time

Throw out the high and low times and post results

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