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EFFECTS OF NEUROMUSCULAR FATIGUE ON MAXIMAL AND RAPID STRENGTH CHARACTERISTICS OF THE SHOULDER EXTERNAL ROTATORS

Abstract

Kyrsten L. Smith1, Eric C. Conchola2, & Ryan M. Thiele1

1Kansas State University, Manhattan, Kansas, 2University of Central Oklahoma, Edmond, Oklahoma

Deficits in muscular strength following fatiguing exercise may lead to a diminished ability to dynamically stabilize the joint. Due to the increased mobility of the glenohumeral joint, it is important to investigate recovery responses of the stabilizing muscles following a bout of fatiguing exercise. PURPOSE: Investigate the effects of submaximal intermittent isometric contractions on maximal and rapid strength recovery of the shoulder external rotators in college-aged males. METHODS: Fourteen (mean ± SD: age = 24.3 ± 3.3 yrs) males participated in a familiarization trial followed by a submaximal intermittent isometric fatigue session, separated by 7(±1) days. Experimental session began with maximal voluntary contractions (MVCs) followed by a fatigue-inducing protocol consisting of intermittent isometric contractions of the shoulder external rotators using a 0.6 duty cycle (6s contraction, 4s relaxation) at 50% of MVC until volitional fatigue. For each MVC, peak torque (PT), peak rate of torque development (RTDpeak), early (0-50 milliseconds, RTD50), and late (0-200 milliseconds, RTD 200) RTD were examined. MVCs were again performed at 0, 7, 15, and 30 min post-fatigue. A one-way repeated measures ANOVA was used to analyze all torque data. RESULTS: Significant main effects for time were observed for all maximal (PT) and rapid (RTDpeak, RTD50, and 200) strength variables (P=0.001). PT was greater at Pre compared to Post 0 (P=0.001), and Post 7 (P=0.009), however no differences were observed at all other recovery time points (P > 0.05). Early and late rapid strength was significantly lower at only Post 0 compared to Pre for RTDpeak, RTD50, and RTD200 (P=0.001), however no differences were observed at all other recovery time points for rapid strength (P=0.079–0.955). CONCLUSION: Differences in maximal and rapid strength recovery of the external rotator muscles were observed following a volitional intermittent isometric fatigue protocol. Specifically, maximal strength (PT) was decreased up to 15 minutes post-exercise, while rapid strength exhibited a quicker recovery. The observed deficits in maximal and rapid strength may result in a diminished ability to stabilize the glenohumeral joint during repetitive fatiguing tasks, potentially leading to an increased risk of musculoskeletal injury.

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