Human performances in sports decline with age in all competitions/disciplines. Since the effects of age are often compounded by disuse, the study of master athletes provides the opportunity to investigate the effects of age per se on the metabolic/biomechanical determinants of performance. For all master age groups, swimming styles and distances, we calculated the metabolic power required to cover the distance (d) in the best performance time as: E' maxR ¼ C d=BTP ¼ C vmax; where C is the energy cost of swimming in young elite swimmers, vmax = d/BTP is the record speed over the distance d, and BTP was obtained form "cross-sectional data" (http://www.fina.org). To establish a record performance, E' maxR must be equal to the maximal available metabolic power (E'maxA). This was calculated assuming a decrease of 1% per year at 40 - 70 years, 2% at 70 - 80 years and 3% at 80 - 90 years (as indicated in the literature) and compared to the E' maxR values, whereas up to about 55 years of age E' maxR ¼ E' maxA; for older subjects E' maxA > E' maxR; the difference increasing linearly by about 0.30% (backstroke), 1.93% (butterfly), 0.92% (front crawl) and 0.37% (breaststroke) per year (average over the 50, 100 and 200 m distances). These data suggest that the energy cost of swimming increases with age. Hence, the decrease in performance in master swimmers is due to both decrease in the metabolic power available (E' maxA) and to an increase in C.