Final answer:
The forces exerted by our limbs are smaller than those produced by our muscles because of the lever principle, where muscles attach near joints creating a mechanical disadvantage that requires greater internal forces to effectively move the limbs.
Step-by-step explanation:
Understanding Muscle Forces and Limb Movements
The forces exerted by our limbs on the external world are generally much smaller than the forces produced by our muscles due to the lever principle. Muscles attach to bones close to joints through tendons, resulting in a mechanical advantage that is often less than one. This implies that muscles must exert larger forces to overcome the mechanical disadvantage and move the limb effectively. When looking at the musculoskeletal system as a simple machine, the input force—generated by the muscle—is significantly greater than the output force—the force exerted by the limb on the outside world.
Lever Principle's Role in Muscle Force
The lever principle explains how forces are distributed within the body. The location of the muscle and tendon attachment near the joint operates as a fulcrum, with the muscle force acting as the effort and the resistance being the weight of the limb or any external resistance. Considering that our muscles often engage very close to joints, the distance from the fulcrum to the point of muscle attachment (effort arm) is much shorter compared to the distance to where the limb applies the external force (load arm). Consequently, to move the load, muscles must apply a force that is significantly greater than the force the limb exerts externally.
The lever system in the body showcases how biomechanics allows for efficient movement despite the apparently disproportionate internal muscle forces compared to external forces exerted by the limbs.