| The purpose of this investigation was to examine how kinetic and electromyographic variables are affected in males and females when performing landing tasks and the extent to which leg muscle volume and body fat percentage explain these sex differences. Fifteen males (age = 25.0 +/- 4.1 yrs, height = 180.9 +/- 6.6 cm, weight = 84.2 +/- 15.5 kg) and 15 females (age = 24.0 +/- 3.7 yrs, height = 166.1 +/- 8.4 cm, weight = 57.8 +/- 8.9 kg) participated in this study. Hip, knee and ankle moments and tibial anterior shear force were determined by the inverse dynamics approach using the Vicon Motion Analysis System (Oxford Metrics, Oxford, England) upon single leg landing from a 40 cm height. Muscular preactivity onset, preactivity mean amplitude and post-landing mean amplitude were determined using the MA - 300-16 EMG System (Motion Lab Systems, Inc., Baton Rouge, LA). Analysis of kinematic data revealed that females experience 30% greater tibial anterior shear forces and 37% greater lower extremity internal extension moments when compared to males. Leg muscle volume was a significant predictor of knee kinematics, explaining 51--57% of the variance for anterior tibial shear force and 37--41% of the variance for internal knee extension moment. Analysis of electromyographic data revealed that prior to landing, females activate their quadriceps 42% greater than males, and their gastrocnemius 49% less than males. Leg muscle volume was inversely related to rectus femoris (r = -.426) and medial hamstring (r = -.376) muscle preactivity amplitude, and positively correlated with lateral gastrocnemius (r = .377) preactivity amplitude. These findings suggest that, when performing a single leg landing task from a height of 40 cm, females utilize general motor programs that place greater emphasis on the knee extensor mechanism, resulting in joint forces that have the potential to increase strain on the anterior cruciate ligament. While leg muscle volume may in part explain sex differences in neuromuscular and biomechanical function, more research is needed to explain the effects of body composition on lower extremity motor control strategies, and the potential for altering these strategies through specific training interventions. |
