How do you account for the motion of your arms and legs ?

Explanation

The concept of torque accounts for the motion of our arms and legs.
For example, when we bend our arm at the elbow, our forearm rotates about the elbow, which acts as fulcrum. The biceps produce the torque. Muscles, exert forces when they shorten and the tendons carry these forces to the required location.
When we hold a metal block in our hand of the bent arm, the force of gravity on the block tends to straigten our arm by exerting a torque. To keep our arm bent, our biceps must produce an equal torque in the opposite direction. Obviously, the force exerted by the biceps, which is closer to the hinge (elbow) must be greater than the force of gravity on the block, which is farther from the elbow.