EFFECTS OF UNSTABLE SURFACE CLOSED KINETIC CHAIN EXERCISES ON HAMSTRING:QUADRICEP RATIO AND NEUROMUSCULAR ACTIVATION

Abstract

PURPOSE: To examine the effects of performing closed-kinetic chain exercises on an unstable surface on the hamstring:quadricep ratio and motor unit recruitment in males and females. METHODS: Ten males (20.1 + 1.1 yrs) and ten females (21.2 + 2.1 yrs) performed closed kinetic chain exercises (CKCs) including a front lunge (FL), side lunge (SL), and single-leg squat (SLSQ). Each of the CKCs were performed twice on both a stable (SS) and unstable surface (US). Electromyography (EMG) of the vastus lateralis (VL) and biceps femoris (BF) was recorded on the dominant leg. Raw EMG recordings were normalized to maximal voluntary isometric contractions (MVICs) and analyzed for root mean square (RMS). The hamstring:quadricep ratio (H:Q) was calculated using RMS as: BF/VL. Data were analyzed using mixed-design repeated-measures ANOVA. RESULTS: No significant differences were observed between males and females during the FL (p = 0.666), SLSQ (p = 0.589), or SL (p = 0.768). During the FL, a main effect of condition was observed for H:Q (F = 10.832; p = 0.004) and RMS of VL (F = 17.462; p < 0.001) with a lower H:Q during US (0.362 + 0.072) compared to SS (0.48 + 0.1) and greater RMS of the VL during US (31.98 + 2.99) compared to SS (29.4 + 3.21). No main effect of condition for RMS of BF was observed (F = 0.184; p = 0.673). During the SLSQ, a main effect of condition was observed for H:Q (F = 12.662; p = 0.002) and RMS of VL (F = 6.646; p = 0.019), with lower H:Q during US (0.423 + 0.109) compared to SS (0.538 + 0.129) and greater RMS of VL during US (48.412 + 5.53) compared to SS (42.627 + 3.84). A main effect of condition was also observed for the BF (F = 14.983; p = 0 .001), with a significant decrease during US (15.051 + 3.56) compared to SS (20.631 + 4.51). During the SL, a main effect of condition was observed for H:Q (F = 8.909; p = 0.008) and RMS of VL (F = 75.454; p < 0 .001) with a greater H:Q during US (0.493 + 0.055) compared to SS (0.378 + 0.043) and lower RMS of VL during US (35.497 + 3.406) compared to SS (40.884 + 3.791). A main effect of condition was also observed for the BF (F = 17.808; p < 0 .001), with a significant increase during US (12.641 + 2.478) compared to SS (8.777 + 2.339). CONCLUSIONS: While no significant differences were observed between males and females, data suggest that performing CKCs on an unstable surface results in changes in H:Q and motor unit recruitment of the BF and VL.