 Efferent motor activity during stepping. During the testing the research participants will be placed on the treadmill in an upright position and suspended in a harness by an overhead cable at the maximum load at which knee buckling and trunk collapse can be avoided i.e. the BWST. All trainers are careful to provide manual assistance only when needed. A trainer positioned behind the research participant will aid in pelvis and trunk stabilization, as well as appropriate weight shifting and hip rotation during the step cycle. The trainer will ensure that the trunk and pelvis are not flexed or hyper-extended during stepping, and that the weight is shifted from the ipsilateral limb to the contralateral limb simultaneous with ipsilateral swing initiation. Research participants will take a break and rest at any time they feel the need to during the session. Joint kinematics, limb load and treadmill speed will be consistently maintained for each phase of the step cycle during these trials. 