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Article Title

THE RELATIONSHIP BETWEEN PERFORMANCE DECREMENTS AND PEAK EMG AMPLITUDE FOLLOWING RESISTANCE EXERCISE OVERREACHING

Abstract

Adam J. Sterczala1, Justin X. Nicoll1, and Andrew C. Fry1. 1Dept. of Health, Sport and Exercise Sciences, University of Kansas, Lawrence, KS; e-mail: adam.j.sterczala@ku.edu

Training and sport specific performance decrements are the hallmark of overtraining and overreaching, however the physiological cause of these decrements are unclear. Fatigue studies have demonstrated the effects of resistance exercise on neuromuscular activity; however, few studies have examined the effects of overtraining or overreaching on neuromuscular parameters. PURPOSE: To analyze the relationship between overreaching induced changes in performance and neuromuscular activity. METHODS: Eight resistance-trained men (n = 8; X ± SD; age = 22.6 ± 2.1 yrs) were assigned to the overreaching group as part of a larger study evaluating the effects of a nutritional supplement on overreaching. Following two weeks of resistance training twice per week, subjects trained twice per day for 7.5 days, performing ten sets of five repetitions using 70% 1RM. Performance and neuromuscular measures were collected before (PRE) and after (POST) the 7.5 day overreaching period. Performance measured included peak and average force during a back squat performed at the training load, as well as back squat one-repetition maximum. Neuromuscular activity was assessed via peak sEMG amplitude in the vastus lateralis during a seated leg extension isometric contraction performed with the knee positioned at a 90° angle. Pearson product-moment correlation coefficients (r) were calculated to evaluate the relationship between performance and neuromuscular changes induced by the overreaching period. RESULTS: The relationship between PRE to POST changes in sEMG peak amplitude and peak force were significant at the p = .05 level (r = .804). Analysis of the relationship between changes in sEMG peak amplitude and average force yielded an r value of .661, significant at the p = .10 level. Similarly, the relationship between changes in the sEMG peak amplitude and 1RM was significant at the p = .10 level (r = .627) CONCLUSION: The results of this investigation suggest that overreaching induced performance changes may, in part, be due to changes in neuromuscular activity. The observed changes in sEMG peak amplitude may to due to changes in motor unit recruitment or motor unit firing rates. Future investigations employing decomposition EMG (dEMG) may be able to further elucidate the effects of overreaching and overtraining on neuromuscular activity.

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