ABSTRACT
Muscle mass, strength, and power contribute to athletic performance of extraordinary levels. In the general aging population, high levels of muscular fitness prolong the ability to perform activities of daily living and are related to high levels of physical and psychological well-being. The increase in muscle mass with age due to fiber hypertrophy is fairly linear from young childhood until puberty, with small but consistent advantages in boys. The sex difference enlarges during and after puberty, driven primarily by the differences in sex steroids. Muscle strength is subdivided into static or isometric strength, dynamic concentric contractions, dynamic eccentric contractions, muscle power, and muscular endurance. Isokinetic tests aim to measure the ability of contracting muscle to generate force at a preset speed of contraction – though only over a limited range of motion during shorting or lengthening of the muscle. Covariation and uniqueness of multiple types of muscle contraction and strength tests have been explored in multivariate genetic and environmental models.
