Gender Differences in Leg Stiffness and Stiffness Recruitment Strategy During Two-Legged Hopping

Abstract

The authors compared leg stiffness (K VERT ), muscle activation, and joint movement patterns between 11 men and 10 women during hopping. Physically active and healthy men and women performed continuous 2-legged hopping at their preferred rate and at 3.0 Hz. Compared with men, women demonstrated decreased K VERT ; however, after the authors normalized for body mass, gender differences in K VERT were eliminated. In comparison with men, women also demonstrated increased quadriceps and soleus activity, as well as greater quadriceps-to-hamstrings coactivation ratios. There were no significant gender differences for joint movement patterns (p > .05). The relationship between the observed gender differences in muscle recruitment and the increased risk of anterior cruciate ligament injury in women requires further study. KeywordsACL; quadriceps; coactivation; hop; jump Females' anterior cruciate ligament (ACL) injury rates are 2.0 to 9.7 times greater than are males' ACL injury rates

Altered neuromuscular control of leg stiffness following soccer-specific exercise

“…The use of a preferred frequency is similar to other studies in adults (Hobara et al 2007;Padua et al 2005) and children (Oliver and Smith 2010). Participants were instructed to hop with hands placed on the hips and with an upright torso.…”

“…Participants were required to perform two-legged hopping at their freely chosen preferred frequency on a force plate to measure leg stiffness, with hopping trials performed immediately before and after participants completed a 42 min soccer-specific intermittent exercise test on a non-motorised treadmill. Two legged hopping has been described as a highly controlled and well documented functional task (Padua et al 2005) and enables movement representative of the spring-mass model. During hopping trials muscle activity was monitored around the ankle and knee using bipolar surface electromyography.…”

“…Double-integration of the force-time data allowed calculation of CoM displacement during ground contact, leg stiffness was then calculated as peak ground reaction force (GRF) divided by peak CoM discplacment (Farley and Morgenroth, 1999). Spring-like behaviour was confirmed where the relationship between CoM displacement and GRF were r > 0.8 (Padua et al 2005). The moment of ground contact was taken to have occurred when force data became >10 N, and take-off occurred when force data became < 10 N (Voigt et al 1998).…”

“…Activity during each period was normalised by expressing activity as a percentage of the total muscle activity during the entire ground contact period (Oliver and Smith 2010;Lloyd et al 2012). Co-contraction indices were calculated around the ankle (TA:SOL) and the knee (BF:VL) with the amount of antagonist activity divided by the amount of agonist (extensor muscle) activity during the 60-ms immediately proceeding ground contact (Padua et al 2005).…”

“…Leg stiffness describes the multi-joint response of the lower limbs to generate force and resist deformation during rebounding activities (Komi 2000;Padua et al 2005). Increased leg stiffness is suggested to enhance rate of force development, locomotor kinematics and energy storage and utilisation (Brughelli and Cronin 2008), providing performance benefits of increased force output, movement speed and running economy (Butler et al 2003;Wilson and Flanagan 2008).…”