Biomechanics: Levers

A lever in biomechanics refers to a rigid structure (typically a bone) that rotates around a stationary point called the fulcrum (a joint).
It functions through the interaction of the effort (muscular force) and the resistance (load). Understanding the three types of levers in the body is crucial.

Classifications of Levers

First-class levers: the fulcrum is situated between the effort and the resistance. An example is the nodding of the head, where the neck is the fulcrum, the head is the load, and the muscles at the back of the neck provide the effort.
Second-class levers: the resistance is situated between the fulcrum and the effort. The primary example in the human body is the calf raise, where the ball of the foot is the fulcrum, the body’s weight acts as the resistance, and the calf muscles provide the effort.
Third-class levers: the effort is positioned between the fulcrum and the resistance. The most common class in the human body due to its efficiency in speed and range of motion. An example is the elbow joint during a bicep curl, where the elbow acts as the fulcrum, the weight in the hand is the resistance, and the bicep muscle provides the effort.

Mechanical advantage: The ratio of the effort arm to the resistance arm defines the lever’s mechanical advantage. A mechanical advantage greater than one indicates that less effort is needed to move the resistance.
First-class levers and second-class levers typically provide mechanical advantages and are therefore often associated with strength-related movements.
Third-class levers usually have mechanical disadvantages, but they are efficient for movements that require speed and a wide range of motion.
Familiarity with how levers operate can support in performance improvement in sport and physical activity, and in injury prevention.

The understanding of how levers work can help in optimizing technique and efficiency in sporting movements.
Adjusting the position and alignment of bones and joints changes the lever system’s effectiveness.
Adapting training and conditioning programs according to an understanding of biomechanics and lever systems can lead to improved strength, speed, and mobility, thus enhancing overall performance.
Recognising the function of levers can also contribute to the understanding of injury mechanisms and to the design of safe and effective rehabilitation protocols.