Contributions of muscles to body segment energetics during the squat jump
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Despite the squat jump's intriguing dynamical properties and prevalence in athletics, there is a lack of information regarding the comprehensive functional role of muscles during the squat jump. To increase our understanding of the strategies the human body uses in accelerating joints and contributing energy to body segments, we incorporated experimental data from trained collegiate men and women into musculoskeletal computer simulations. We evaluated the simulations to determine fundamental coordination principles of the squat jump, and the effect of increased loading and gender on muscle strategies employed during the squat jump. Our results revealed that the plantar flexors and vasti were primarily involved in increasing the mechanical energy of the body, while the proximal muscles were primarily involved in redistributing energy throughout the body. The erector spinae muscles extended the lumbar spine, and contributed energy to the torso, while gluteus maximus and hamstrings extended the hip joint, and contributed energy to the pelvis. The vasti extended the knee joint, and contributed energy to the pelvis and torso. Our results suggested that the rectus femoris plays a critical role in converting rotational energy into vertical kinetic energy. Greater barbell loads reduced the rate of lumbar extension, and resulted in increased normalized energy contributions from soleus and vasti to the torso. When comparing the squat jumps between men and women, our results suggested that soleus and vasti are more active in men than women during the body-weight squat jump.