Hypogonadism in men is associated with decreased physical performance. This phenomenon depends on significantly measurable adverse traits in body composition, namely increased body fat content and reduced muscle mass. Physical abilities in hy-pogonadal men are further hampered by lower oxygen supply due to decreased hemoglobin concentrations and by poor glucose utilization. In addition, dysthymia and lack of necessary aggressiveness contribute to further deterioration of physical features. T substitution can improve lipid and insulin metabolism, resulting in changes of body composition, such as decreasing fat depots. Growth of muscle fibers can also be observed. Stabilization of the musculo-skeletal system by increased bone density will further contribute to increased physical fitness, reflected by increased strength and endurance. Treatment outcome is strongly influenced by age and training. The issues reviewed strongly support T treatment of hypogonadal men accompanied by regular monitoring.