Fat storage in athletes : the metabolic and hormonal responses to swimming and running exercise

• Main Author: Flynn, Michael Gerald
• Other Authors: Costill, David L.
• Format: Others
• Published: 2011
• Subjects: Fat.; Swimming > Physiological aspects.; Running > Physiological aspects.
• Online Access: http://cardinalscholar.bsu.edu/handle/handle/176197; http://liblink.bsu.edu/uhtbin/catkey/516210

Despite similar rates of energy expenditure during training, competitive swimmers have been shown to store significantly greater amounts of body fat than competitive runners. In an attempt to explain these discrepancies, male collegiate swimmers (n=8) and runners (n=8) were monitored during 45 min of swimming and running, respectively (75% V02 max), and during two hours of recovery. In addition, a group of male competitive triathletes (n=6) were similarly monitored during and after both swimming and running exercise.Blood samples were obtained after 15 min rest prior to exercise and at 0, 15, 30, 60 and 120 min of recovery and were analyzed for glucose, lactate, glycerol, free fatty acids, insulin, glucagons, norepinephrine (NE) and epinephrine (E). Respiratory gases were collected at 15 min intervals during exercise and at 15, 30, 45, 60, 90 and 120 min of recovery. Heart rate and mean body temperature were recorded at 10 min intervals throughout recovery. There were no differences in post-exercise oxygen consumption or heart rate while the RER suggested increased fat oxidation after exercise for the swimmers and the swimming triathletes. The mean body temperature and mean skin temperatures were significantly lower throughout 120 min of recovery for the swimmers compared to the runners. The triathletes demonstrated a similar tendency but these differences were not significant. The serum glucose levels were significantly greater (P<0.05) immediately post-exercise for the runners compared to the swimmers (6.71 +0.29 and 4.97 +0.19 mmol•1-1, respectively). Blood glucose values were also significantly greater immediately post-run for the triathletes (6.40 +0.26 and 4.87 ±0.18 mmol-l-1 for running and swimming, respectively). Blood glucose values remained elevated for runners and the running triathletes up to 30 min of recovery. Free fatty acids were similar after the run and the swim, but glycerols were increased immediately after running in the runners (P<0.05) and the triathletes (P<0.05). Differences in blood glucose levels or fat release were not explained by differences in NE, E or cortisol. The glucagon-to-insulin (G:I) ratio was significantly increased after exercise in the swimmers and the swimming triathletes. This, combined with a reduced RER after the swimming trials, suggests that the reduced glucose levels were due to reduced hepatic glycogen stores. The results of this study suggest that there were differences in substrate utilization during running and swimming exercise of the same intensity. These differences were not explained by NE, E or cortisol; however, the increased G:T ratio suggests increased carbohydrate use during exercise in the swimmers. Finally, body fat differences between runners and swimmers were not explained by differences in post-exercise energy expenditure or fat oxidation.