A Practical Experiment in Muscle Fiber Activation

Tom Kelso
Strength and Conditioning

A few years ago we conducted an informal experiment to determine the effect of speed of exercise movement on muscle fiber (motor unit) recruitment. Please understand that the test was not conducted using standard research methods (number of subjects, lack of a control group, statistical analysis, etc.), but I do believe it had some interesting outcomes.


The Testing Phase

First, we determined a one repetition maximum (1 RM) barbell bench press of a group of male and female college athletes. On two non-adjacent days they used 60% of their 1 RM and performed a "fast" and "slow" movement speed test to determine the extent of motor unit activation on each day.


On day one, the athletes were instructed to move the 60% resistance as fast as possible, both concentrically and eccentrically, and for as many repetitions (reps) possible. Naturally, I do not recommend this speed of execution when training. However, for the sake of this test, we did deviate from the norm. We did assure the athletes minimized any bouncing of the resistance off the chest and any resting in the locked-out position. The number of reps obtained and the total time it took to reach muscular fatigue were recorded.


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