Fat Storage in Athletes: Metabolic and Hormonal Responses to Swimming and Running

Abstract

Despite similar rates of energy expenditure during training, it has been suggested that swimmers store greater amounts of body fat than runners. To investigate these discrepancies, eight male swimmers (S) and runners (R) were monitored during 45 min of swimming or running (75% V̇O₂max), respectively, and six triathletes were monitored during swimming (ST) and running (RT). Each group was also monitored during two hours of recovery. Venous blood samples were obtained before exercise, immediately after exercise (0 min) and at 15, 30, 60 and 120 min of recovery. These samples were analyzed for glucose, lactate, glycerol, free fatty acids (FFA), insulin, glucagon, norepinephrine (NE) and epinephrine (E). Expired gases and heart rates (HR) were obtained during exercise and also during recovery. The caloric cost of recovery was similar, but the RER results suggested increased fat oxidation during recovery for the S and the ST. Serum glucose was greater (P < 0.05) immediately after exercise for R (6.71±0.29 mmol/l) and RT (6.40±0.26) compared to the S (4.97±0.19) and ST (4.87±0.18), and was significantly elevated for the initial 30 min of recovery. FFA were similar throughout the recovery period; however, blood glycerol was greater immediately after exercise (0 min) for R compared to S (NS) and was significantly elevated after exercise (0 min) for RT compared to ST. Differences in blood glucose or fat release were not explained by differences in NE or E; however, the glucacon-to-insulin ratio was significantly greater after exercise in the S and ST compared to the R and RT. The results suggest that there may be differences in substrate utilization during running and swimming exercise of the same intensity. During recovery, however, neither post-exercise energy expenditure nor fat oxidation favored increased fat storage in swimmers.

Key words

Swimming - running - body compostion - metabolic/hormonal response - recovery