Relation to muscle typesEdit
An individual's physical strength is determined by two factors, their genetic inheritance of muscle fiber types and their degree and type of strength training they may undertake. Individuals with a high proportion of type I slow twitch fibers will be relatively weaker than a similar individual with a high proportion of Muscle type II fast twitch fibers, but would have a greater inherent capacity for physical endurance. The genetic inheritance of muscle fiber type sets the outermost boundaries of physical strength possible (barring the use of enhancing agents such as testosterone), though the unique position within this envelope is determined by training. Individual muscle fiber ratios can be determined through a muscle biopsy. Other considerations are the ability to recruit muscle fibers for a particular activity, joint angles, and the length of each limb. For a given cross-section, shorter limbs are able to lift more weight. The ability to gain muscle also varies person to person based upon genes dictating the amounts of hormones secreted, adequate nutrients in the diet, sex, and the health and age of the person.