Sarcopenia--mechanisms and treatments.

BACKGROUND: Sarcopenia is a consequence of aging. This atrophic event is responsible for decrease in strength and associated functional deficits seen in the aging adult. PURPOSE: This paper reviews: (1) the mechanisms contributing to sarcopenia, (2) the impact of age-related changes in muscle composition on 3 processes integral to muscle function, (3) the efficacy of pharmaceuticals and over-the-counter nutritional supplements in the management of sarcopenia, (4) experimental use of pharmaceutical regulation of myostatin to increase muscle mass and strength in animal models, and (5) efficacy of resistance training as a means of maintaining or recovering muscle mass and strength. METHODS: PubMed was searched for relevant research articles using the following descriptors: sarcopenia, aging, muscle mass, muscle performance, muscle strength, myostatin, testosterone, growth hormone, dehydroepiandrosterone, hormone replacement, nutrition, resistance training, and endurance training. RESULTS: Sarcopenia is mediated by multiple mechanisms, including alpha-motor neuron death, altered hormone concentrations, increased inflammation, and altered nutritional status. Age-related changes within muscle likely affect processes integral to muscle function. These changes negatively influence muscle performance directly or by contributing to sarcopenia. Pharmaceutical or supplement interventions to treat sarcopenia have not proved encouraging to date, either lacking or providing limited efficacy, along with the potential for negative health consequences. In contrast, resistance training has proven safe and highly effective for increasing muscle mass and strength in aging adults. CONCLUSION: Sarcopenia is a multifactorial consequence of aging that will affect many adults. Resistance training is the most effective and safe intervention to attenuate or recover some of the loss of muscle mass and strength that accompanies aging.

Comparison of maximum tolerated muscle torques produced by 2 pulse durations.

BACKGROUND: Neuromuscular electrical stimulation (NMES) is an effective therapeutic technique for strengthening weak muscles. A positive dose-response relationship exists between the elicited muscle forces during training and strength (force-generating capacity) gains. Patient discomfort limits NMES muscle forces, potentially compromising efficacy. OBJECTIVE: The purpose of this study was to compare the NMES muscle torques produced by stimulation trains consisting of 2 different pulse durations. DESIGN: During a single testing session, the 2 pulse duration conditions (50 and 200 microseconds) were tested on the opposite lower extremities of the participants. METHODS: The study participants were 10 adults without remarkable medical histories. The maximum tolerated isometric knee extensor torque was the primary dependent variable. The peak currents and phase charges that produced the maximally tolerated torques, as well as the sensory, motor, and pain thresholds for the 2 pulse conditions, were compared. RESULTS: The 200-microsecond pulse duration condition resulted in participants tolerating significantly greater muscle torques; it was associated with significantly greater phase charges but significantly lower peak currents. LIMITATIONS: This study only compared muscle torques in response to stimulation trains consisting of pulses with short (50-microsecond) or medium (200-microsecond) durations and did not examine long ( approximately 400- to 600-microsecond) durations. Furthermore, the result of this study may not apply to NMES that uses stimulation patterns other than monophasic, square-wave pulsed current. CONCLUSIONS: It has been suggested that short pulse durations are most appropriate for NMES because they are less likely to recruit nociceptors. The results of this study, however, support the use of a medium pulse duration rather than a short pulse duration when the goal is to produce a maximum torque response from a muscle. These observations may be related to the currents and phase charges for the pain thresholds for the 2 pulse duration conditions.