Abstract: Current resistance strength-training machines for humans that use structural links and hinges to transfer resistance to muscles constrain the resisted range of motions of the bones of the body's limbs and trunk at their skeletal joints to one rotational degree of freedom. Alternatively, current strength-training cable-and-pulley machines limit biomechanical movements to two rotational axes against vector-resultant resistance. Unconstrained, the humerus, for example, rotates at its shoulder joint in three directions: pitch, yaw, and roll. Similarly, the radius and ulna can rotate at their elbow joint in two directions: pitch and roll.