Fig. 4. Individual and summed joint torque (A) and power (B) curves during the stance phases of ramp descent (broken lines) and ascent (solid lines) walking, averaged across all subjects. Positive torques are extensors and positive powers are energy generation. Summed torques were similar in shape and magnitude and showed that both gaits were produced by net extensor torques across all joints. Hip and ankle extensor torques were larger in ascent vs descent, whereas knee extensor torque was larger in descent. Summed powers in ramp descent and ascent were nearly entirely negative and positive, respectively. The individual joint powers, however, showed that muscles crossing each joint contributed both negative and positive power and work to both movements. Negative power occurred primarily at the knee and then ankle joints in descent whereas positive power occurred primarily at the ankle and hip joints in ascent. Ramp descent had a 15% shorter stance phase, partially leading to reduced area under the joint power curves and reduced muscle work compared to ramp ascent.