Gender Differences after Downhill Running for Voluntary Isometric Contractions of Knee Extensor Muscles using Surface EMG

Abstract

Introduction: We examined gender differences for performance and surface electromyograms (sEMG) of knee extensors 1hr after downhill running. Methods: Maximal voluntary isometric force (MVIF) and sEMG of vastus lateralis (VL) and vastus medialis (VM) muscles during 50%MVIF were measured in 8 males (22±4yr, 75.8±6.1kg, 179.2.0±5.0cm) and 8 females (27±8yr, 60.8±7.2kg, 166.3±5.0cm) before and 1 hr after downhill running [(5x8 min, -12%, 60%V max (females: 7.7±0.9km·h -1 , males: 10.4±0.5km·h -1 )]. Results: Males had higher MVIF values (674.3±59.8N versus 480.6±49.9N, P<0.001) and longer endurance times during 50%MVIF than females (78.7±24.1s versus 57.2±12.6s, P<0.05) before downhill running. After downhill running, MVIF deficits were similar (males: 11.7±7.2%, females: 7.5±7.7%) with no changes in endurance times during 50%MVIF. After the downhill run, there was a trend in females, but not males, of an increased ratio for the root mean square (RMS) values of the VL and VM muscles during MVIF testing by 23% (P=0.054). After the downhill run, females, but not males, lowered during 50%MVIF the change in RMS for VM from 48±32% to 30±31% and for VL from 36±23% to 21±18% (P<0.05). For males, a trend was observed for the change in median frequency in VL during 50%MVIF (P=0.05). After downhill running, females, altered the vastus medialis and vastus lateralis contributions to maximal isometric force production and the activity pattern of these muscles during submaximal isometric fatigue. Conclusion: Acute neuromuscular adaptations after downhill running occur during voluntary isometric contractions of knee extensor muscles in females, but not in males.