Skeletal muscle mass and muscular function in master swimmers is related to training distance.

It is unknown whether or not the daily swim training distances of master swimmers (MS) affect the observed changes in skeletal muscle mass (SM) and physical function commonly associated with the aging process. Twenty-two male MS aged 52-82 years were divided into two groups based upon training distance: High MS (>3000 meters swim/session and 4.1 times/week; n=11) and moderate MS (1500-2800 meters swim/session and 3.4 times/week; n=11). Eleven age- and body mass index-matched older (aged 56-80 years) men served as controls (AMC). Subjects who performed resistance training were excluded in this study. Muscle thickness (MTH) was measured by ultrasound at nine sites on the anterior/posterior aspects of the body (forearm, upper arm, trunk, thigh, and lower leg), and from this, total and segmental SM mass values were estimated. Thigh MTH (anterior:posterior mid-thigh, A50:P50) ratio was calculated to assess the site-specific thigh muscle loss. Straight and zigzag walking performance and maximum knee extension/flexion strength were also measured. Arm SM was greater for high MS and moderate MS than for AMC. Total SM index was higher for high MS than for moderate MS and AMC. A50:P50 ratio was greater for high MS than for AMC. Absolute and relative knee extension strength, but not flexion strength, was greater in high MS than in AMC. The A50:P50 ratio inversely correlated (p<0.05) with zigzag walking time, whereas relative knee extension strength positively correlated (p<0.05) with both straight and zigzag walking performance. Training distance in older MS may be an important factor for maintaining muscle mass and function in the aging process.