College of Massage Therapists of British Columbia (CMTBC) Practice Exam

What is an example of a class 3 lever?

1. Towing a car

2. Using scissors

3. Elbow flexion

4. Riding a bicycle

The correct answer is: Elbow flexion

A class 3 lever is characterized by the effort being applied between the fulcrum and the load. In the case of elbow flexion, the fulcrum is the elbow joint, the load is the weight of the forearm and any objects held in the hand, and the effort is applied by the biceps muscle as it contracts to flex the elbow. This specific arrangement is typical of how many muscles work in the body to produce movement, illustrating the principle of mechanical advantage in biomechanics. The other options represent different classes of levers or mechanisms. Towing a car typically utilizes a class 1 lever where the pivot point is between the effort (the force exerted by the vehicle) and the load (the weight of the trailer). Using scissors functions as a class 2 lever because the load (the material being cut) is between the fulcrum (the pivot point of the scissors) and the effort (where the handles are squeezed together). Riding a bicycle involves multiple forces and movements but does not exemplify a class 3 lever in its basic mechanics.