Exercise and the treatment of wasting: aging and human immunodeficiency virus infection

A common feature of human immunodeficiency virus (HIV) infection and aging is the loss of skeletal muscle mass. Although the causes of this loss of muscle are multifactorial, there may be some shared characteristics to this loss, and therefore common strategies for its prevention or reversal. For example, loss of muscle mass early in life and early in the progression of HIV infection may result from decreased levels of physical activity. The rapid loss of skeletal muscle mass at the end of life (sometimes referred to as failure to thrive syndrome) and in acquired immunodeficiency syndrome (AIDS) patients may also have common cause: cachexia. However, it also must be pointed out that loss of skeletal muscle mass with advancing age also may result from losses of motor units, decreased rate of skeletal muscle protein synthesis, and impaired regulation of appetite. These factors have not been demonstrated to be consequences of HIV infection. The use of exercise to treat the losses of muscle size, strength, and functional capacity holds great promise. Although the losses of muscle with HIV infection may be more rapid and dramatic than those seen with aging, resistance exercise training can attenuate or arrest this loss. In elderly people, resistance exercise has been demonstrated to result in increased nitrogen balance, muscle mass and strength, functional capacity, energy requirements, and when combined with a protein calorie supplement, increased energy intake. The use of resistance exercise in HIV-infected patients may also provide similar results. This review discusses many of the changes in body composition, physiological function, and metabolism associated with aging and HIV infection. The specific effects of exercise in the elderly and in patients infected with HIV on the treatment of muscle wasting, and its consequences are also discussed.