A knee prosthesis comprises an agonist-antagonist arrangement of two series-elastic actuators in parallel, including a knee joint, flexion and extension actuators connected to the joint in parallel with a leg member, and a controller for independently energizing the actuators to control the movement of the knee joint and leg. 6 to 10 and a content of isotactic pentads, measured by 13C NMR on the fraction insoluble in xylene at 25\xb0 C. Each cooling hole includes in downstream serial cooling flow relationship, a curved inlet, a constant area and constant width metering section, and a spanwise diverging section leading into the trailing edge cooling slot, and a spanwise height substantially greater than a hole width through the cooling hole.