Training will consist of unilateral and bilateral leg presses (Total Gym GTS, San Diego CA), which will primarily target the quadriceps followed by the hip extensors and plantarflexors. Target load will be 40% to 80% of 1-repetition maximum (1RM) with progression toward 80%. Each participant will perform 3 to 5 sub-maximal efforts followed by 6 sets of 5 maximum-effort repetitions at the predetermined percentage of 1RM for each leg separately. Following the unilateral leg presses, 6 sets of 5 repetitions of bilateral leg presses will be performed at the predetermined percentage of 1RM. To minimize fatigue, 1-2 minutes of rest will be given between sets.

The therapy includes: activities of adequate intensity that promote gait adaptation and gait speed sustainment, exploratory activities that enhance the somatosensory experience through rich/novel movement, and optimally challenging activities that emphasize planning and problem solving that requires altering the leg kinematics to meet the environmental and task constraints. This includes a 15-minutes of sustaining and adapting gait speed while walking along a 40-meter hallway. Participants will alter their gait through exploratory movements. During the following 20 minutes participants will perform discrete problem solving activities including: waling backward sand stair negotiation.

The child will walk on the treadmill for 35-minutes, while the body weight is supported with an overhead system at 30 percent of the child's body weight, reducing every other week by 10 percent until no support is provided during the final 2 weeks. Treadmill speed will be set at 90% of the child's over ground walking speed, gradually increasing each session. Speed adjustments depend on the child's ability to control their steps and achieve: activities that promote symmetry of the leg kinematics, activities that promote maintaining an upright lower limb posture and clearing the tow during the swing, and activities that promote pushing off with ankle at terminal stance.

Physical therapy will be implemented three times a week with subjects over an eight week span. Each physical therapy session will last 40-minutes and will be conducted by a licensed physical therapist.

To assess the activity of the motor cortices, the child will produce an isometric knee extension force to match a target that is between 5-30% of his/her maximum voluntary force. The children will be instructed to perform the target matching task as rapidly and as accurately as possible. The MEG experiment will involve the child performing ~120 isometric target matching trials.

To assess the activity of the somatosensory cortices, a tactile stimulation will be applied to the bottom of the foot at the first metatarsal using a small airbladder. For each child, 120 paired-pulse trials will be collected using an inter-stimulus interval of 500 ms, and an inter-pair interval that randomly varied between 4.5 and 4.8 s.

The childs 10-meter preferred and fast-as-possible walking speeds will be evaluated. The children will complete three trials at each speed, and the mean of the respective trials will be the key metric. During these tests, the child will walk across a GaitRITE digital mat (CIR Systems, Sparta, NJ) that will quantify the walking speed, step length, step width and cadence.

The child's walking endurance will be assessed by asking them to walk as far as possible for a one-minute time period. Cones will be placed at the ends of a 40-m hallway and the child will be asked to walk back and forth during the time period. During the walk the child will wear a heart-rate monitor and wireless accelerometers that are positioned on the lower back and feet. The heart-rate monitor will be used as an indirect measure of the child's physical fitness, while the accelerometers will be used assess the child's dynamic balance.

The resting state activity of the brain will also be collected. This will involve the child sitting quietly with his/her eyes closed for 5 minutes.