Ballantyne, B. T., & Shields, R. K. (2006). Muscle fatigue alters neuromuscular performance during resisted weight bearing exercise. Medicine and Science in Sports and Exercise, 38(5), Supplement abstract 2404.

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This study examined the effect of muscle fatigue on voluntary and reflexive patterns of muscle activation and performance accuracy while tracking a visual target during the weight bearing lateral step down exercise. A specially designed apparatus was used to provide controlled resistance to knee motion during the lateral step down exercise. Motion of the knee was measured as Ss were asked to track a sinusoidal target waveform as accurately as possible during the exercise. Absolute, constant, variable, and endpoint errors were calculated to evaluate tracking performance. Random perturbations were delivered in 20% of the trials by unexpectedly releasing the resistance during the flexion phase of the exercise. Quadriceps and hamstring muscle activity were recorded during both perturbed and unperturbed trials. Females (N = 12) were tested before and after completing a repetitive submaximal eccentric quadriceps fatigue protocol. A second group of 12 females served as controls.

Muscle fatigue increased the level of quadriceps muscle activity throughout most of the exercise, more during flexion than extension. Muscle fatigue also resulted in a reversal in the direction of the constant errors during the extension phase of the exercise, causing Ss to lag behind the target. Unexpected perturbations elicited long latency responses characterized by facilitation of the quadriceps and inhibition of the hamstrings. Muscle fatigue increased the amplitude of this response.

Implication. These results indicate that muscle fatigue alters patterns of coordinated muscle activity, which may render subjects less able to cope with unexpected perturbations during activities that require a high degree of accuracy. Unless muscles are fatigued (trained) in the action they are to perform, specific conditioning, and therefore an effect on performance, will not occur.

[This study highlights the need to develop specific physical fitness for baseball pitching. That fitness would stall the onset of fatigue allowing more precision pitches to be executed before a pitcher would have to consciously change pitching deliveries and eventually combat fatigue in an obvious manner.]

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