Exercise treatment to counteract protein wasting of chronic diseases.

PURPOSE OF REVIEW: The objective is to summarize the findings from recent (June 2001-2002) studies that have examined the potential benefits of exercise training for the treatment of wasting associated with sarcopenia, cancer, chronic renal insufficiency, rheumatoid arthritis, osteoarthritis and HIV. In many clinical conditions, protein wasting and unintentional weight loss are predictors of morbidity and mortality. The pathogenesis of protein wasting in these conditions can be different, but the fundamental mechanism is an imbalance between muscle protein synthetic and proteolytic processes. The muscle proteins most affected and the precise alterations in their synthetic and proteolytic rates that occur in each cachectic condition are still under investigation.

RECENT FINDINGS: Regular exercise, or sometimes just a modest increase in physical activity, can mitigate muscle protein wasting. Aerobic exercise training primarily alters mitochondrial and cytosolic proteins (enzyme activities), while progressive resistance exercise training predominantly increases contractile protein mass. Previous studies indicate that resistance exercise acutely increases the muscle protein synthetic rate more than muscle proteolysis such that the muscle amino acid balance is increased for up to 2 days after exercise. Progressive resistance exercise training increases muscle protein synthesis and muscle mass, but attenuates the increment in proteolysis that results from a single bout of resistance exercise. The cellular mechanisms that produce these adaptations are not entirely clear.

SUMMARY: In general, patients with wasting conditions who can and will comply with a proper exercise program gain muscle protein mass, strength and endurance, and, in some cases, are more capable of performing the activities of daily living.