This study attempted to investigate on ten male subjects the intensity of muscular activity during the execution of various physical fitness exercises. Each subject executed thirteen exercises of different types which were selected because of their popularity in physical fitness programs. The various exercises involved muscles of the shoulder, elbow, knee and hip joints as well as abdominal and back muscles. The electrical activity of four muscles for each joint or muscular area was investigated by surface electromyography. The statistical analysis showed that the various exercises solicitated the participation of the same muscles at a given joint or muscular area. However, the intensity of solicitation, varied significantly between the various exercises. The results imply that the selection of various exercises should be carefully considered by physical fitness instructors.