The term body composition refers to the percentage of body weight that is fat (% body fat) compared with total lean mass. Its measurement is based on the assumption that body weight can be divided into lean body weight and fat weight. Levels of subcutaneous body fat levels in the upper body (waist measurement) and lower body (hip measurement) are distributed differently by sex, age, body type, and activity level.
Proper muscle balance, in which agonist and antagonist muscle pairs maintain appropriate ratios of strength, flexibility, and length to one another, is important for avoiding musculoskeletal injury. To move body segments, the muscles opposite those performing the movement (antagonist muscles) must lengthen sufficiently. Tight muscles, tendons, and ligaments limit lengthening of the antagonist muscles and thus reduce the range of movement of body segments.