Effects Of Fatigue On Hamstring:quadricep Ratio And Neuromuscular Activation During Closed Kinetic Chain Exercises

Abstract

PURPOSE: To examine the effects of fatigue on the hamstring:quadricep ratio and motor unitrecruitment during closed kinetic chain exercises. METHODS: Ten males (20.1 + 1.1 yrs) and ten females ( 21.2 + 2.1 yrs) cycled at 110% of theirPhysical Working Capacity Fatigue Threshold (PWCFT) until exhaustion (TTE). Participants alsoperformed three closed kinetic chain (CKC) exercises before (PRE) and after (POST) the TTE, includinga front lunge (FL), side lunge (SL), and single leg squat (SLSQ). Each of the four CKC exercises wereperformed twice PRE and twice POST. Electromyography (EMG) of the vastus lateralis (VL) and bicepsfemoris (BF) was recorded on the dominant leg. Raw EMG recordings were normalized to maximalvoluntary isometric contractions (MVICs) and analyzed for root mean square (RMS). Thehamstring:quadricep ratio (H:Q) was calculated using RMS as:BF/VL. Data were analyzed usingmixed-design repeated-measures ANOVA. RESULTS: During the FL, a main effect of time was observed for the H:Q (F = 10.199;p = 0.005) andRMS of the VL (F = 17.462;p < 0.001). Specifically, H:Q was lower at POST (0.388 + 0.081) comparedto PRE (0.451 + 0.091) and RMS of VL was higher at POST (33.435 + 3.113) compared to PRE (27.937+ 3.004). No main effect of time (F = 6.275;p = 0.22) for RMS of the BF was observed. During theSLSQ, a main effect of time was observed for the H:Q (F = 7.498;p = 0.014) and RMS of the VL (F = 13.380;p = 0.002). Specifically, H:Q was lower at POST (0.392 + 0.087) compared to PRE (0.527 + 0.119) and RMS of VL was higher at POST (50.683 + 4.056) compared to PRE (41.457 + 4.391). Nomain effect of time (F = 0.238;p = 0.632) was observed for RMS of the BF During the SL, a main effectof time was observed for H:Q (F = 7.526;p = 0.013) and RMS of the VL (F = 9.548;p = 0.006).Specifically, H:Q was higher at POST (0.493 + 0.097) compared to PRE (0.354 + 0.098) and RMS of VLwas lower at POST (37.24 + 1.072) compared to PRE (49.644 + 1.083). No main effect of time (F = 0.766;p = 0.392) was observed for RMS of the BF. CONCLUSIONS: Fatigue may impact the H:Q ratio during closed-kinetic chain exercises These datasuggest that changes in the H:Q ratio may be dependent on fatigue-related changes in motor unitrecruitment of quadricep muscles.