MUSCLE BIOPSY AS A TOOL IN THE STUDY OF AGING

The needle biopsy procedure provides a minimally invasive means of obt aining small samples of skeletal muscle from human volunteers, Such sa mples can be used to examine a variety of structural and functional ch aracteristics of muscle, including fiber type and size, capillarizatio n, enzymatic capacities, energy substrate or protein/mRNA concentratio ns, metabolic responses, and contractile properties. In conjunction wi th other methods, biopsy sampling can also be used to estimate total m uscle mass and fiber number, and to determine rates of protein synthes is and degradation. Optimal handling and storage conditions vary widel y, but in general, most of the above measurements can be made using fr ozen tissue, so that samples can be stored almost indefinitely. The pr ocedure is also safe and generally wed-tolerated, making it possible t o perform longitudinal studies of the same person. The biopsy techniqu e is therefore well suited for examining the underlying physiological mechanisms responsible for muscle wasting in the elderly, as well as f or assessing the effects of nutritional, hormonal, and/or lifestyle (e .g., exercise) interventions intended to combat this problem. Although sample size limitations have been largely overcome; by the developmen t of microtechniques, more information is needed an how to minimize th e variability introduced by studying only a small fraction of the whol e muscle. Studies are also required to determine whether it is suffici ent to biopsy only one muscle (and if so, which is optimal), or whethe r there are differential effects of aging in various muscle groups tha t would preclude extrapolating from one muscle to all muscles in the b ody. Despite the latter limitations, the biopsy technique has been and will continue to be an important tool in the study of the effects of aging on human skeletal muscle.