 Experimental materials. We will acquire lower extremity trunk muscles surface EMG activity kinematics bilaterally during all experimental conditions. We will also use fine-wire EMG to acquire activity from the illio-psoas, extensor hallicus longus, extensor digitorum longus other deep muscles muscle. We will also record individual limb loading level of BWS during standing stepping conditions. We may acquire continuous blood pressure with a finger cuff, breathing rate using an elastic band place loosely around their chest temperature with 1-3 small sensors taped over their skin above below their injury level. 