Jacob M. Smith, Kylee West, Jordan Brown, Brianna Simmons, Austen Arnold, Derick Anglin, Tanya Miller, Jessica Mutchler, Sam Wilson, Nicholas Siekirk. Georgia Southern University, Statesboro, GA.

Recent evidence has questioned the utility of eccentric (ECC) exercise in the prevention of hamstring (HS) strains. Inter-leg recruitment strategies influence the intervention’s success PURPOSE: To examine whether bilateral eccentric exercises display asymmetric recruitment strategies METHODS: Prior to maximum voluntary contractions (MVC), ten trained college-aged participants performed dynamic mobility drills. Isometric dynamometry measured participant’s peak torque (pTorq) for the gluteus maximus (Gmax) and medial gastrocnemius (MG) in prone. The pTorq was obtained for the knee in seated posture with isokinetic dynamometry set at 60o/sec and 120o/sec to measure concentric (CON) and ECC pTorq of the quadriceps (Q) and HS. Ipsilateral strength ratios (CON60oQ/ECC120oHS) were compared bilaterally with paired t-test. Surface electromyography (sEMG) during ECC exercise was bilaterally recorded from the MG, semitendinosus (ST), biceps femoris (BF) and GMax and was normalized to pTorq output during MVCs (%MVC). ECC exercise variations included (n = 3) reps of the Nordic Hamstring Exercise (NHSE), NHSE at 7o decline (NHSE7o) and Razor Curl in randomized order. Separate 3-way (variation, rep, side) RMANOVAs were conducted on each muscle. RESULTS: Contralateral differences in strength ratios were not detected, MD = 0.06 ft-lbs; 95% CI: -0.31 to 0.18, d = 0.15. Data suggested an interaction between variation, rep, and side for the MG; F(1.75, 15.76) = 3.07, n2 = 0.254. A large main effect of side was detected for Gmax; F(1, 9) = 11.58, n2 = 0.563. The participant R Gmax (95% CI: 31.07% to 84.25%) had greater %MVC than L (95% CI: 20.98% to 57.45%), a MD = 18.44% (95% CI: 6.18% to 30.71%). A large main effect of exercise variation was detected for ST, F(1.17, 10.51) = 3.23, n2 = 0.264 and BF, F(1.42, 12.78) = 4.48, n2 = 0.332. The Razor curl mEMG was reduced in ST and BF vs. NHSE7 o; ST [MD = -7.29% (95% CI: -13.00% to -1.58%)], BF [MD = -17.00% (95% CI: -30.57% to -3.42%)]. CONCLUSIONS: Data suggests recruitment strategies bias the R GMax across eccentric exercise variations. Furthermore, these findings support the pursuit of larger scaled investigations to examine recruitment strategies during eccentric HS exercise.

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