Berk, S. E., Kinzey, S. J., Kravitz, L., & Cole, J. L. (1999). The effect of voluntary fatigue on the involuntary muscle activity of selected arm muscles. Medicine and Science in Sports and Exercise, 31(5), Supplement abstract 865.

"Reflexes are actions that serve to protect and stabilize the human body. Fatigue is the result of the body exhausting its readily available reserve of fuel that enables the muscle to work. It is not clearly understood how skeletal muscle reflexes are affected when the body reaches a state of fatigue." (p. S192)

The effect of fatigue on the reflexive responses of arm muscles was investigated in male American football players (N = 18). Ss completed six trials to fatigue. The exercise consisted of holding a 5-pound weight via a rope and handle. Ss had to react to an unannounced 20-cm drop of the weight, which caused rapid elbow extension.

Muscle activity, joint acceleration, or angular displacement did not change across trials. It is possible that a failure to reach peripheral fatigue, biochemical changes in the muscles, test methodology, and/or inter-subject differences influenced the study's results. However, this type of activity protocol did not influence performance dynamics.

In the latter periods of athletic events, when the number of injuries rise, it is possible that the reflexive protection in the muscles is not altered but that a delay in cognitive processing or attention is the cause of the injuries.

Implications. Injuries may be mediated by cognitive/attentional factors more than fatigue in intermittent collision sports.

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