The Effects of Endurance Training Under Low Energy Availability on Muscle Glycogen Contents

Abstract

PURPOSE:Some previous studies demonstrated that acute bout of exercise suppressed appetite and reduced energy intake among athletes. However, the accumulative effects of reduced energy intake during consecutive days of training period remains unclear. The purpose of the present study was to investigate the influences of 3 days of endurance training under low energy availability on muscle glycogen content, endocrine responses and endurance capacity. METHODS:Seven male long distance runners (19.9 ± 0.4 years, 175.6 ± 1.8 cm, 61.4 ± 2.0 kg, 67.5 ± 1.6 ml/kg/min) completed 3 consecutive days of endurance training under low energy availability trial (LEA, 18.9 ± 0.7 kcal/kg FFM/day) and normal energy availability trial (NEA, 52.9 ± 1.9 kcal/kg FFM/day). The order of two trials was randomized with two weeks interval between trials. The experiment consisted of 3 consecutive days of endurance training (days 1-3) and exercise performance test on the following morning (day 4). The endurance training consisted of 75 min of treadmill running at 70% of maximal oxygen uptake (VO2max) in both trials. Muscle glycogen contents, respiratory gas variables, subjective parameters, blood and urinal variables were evaluated in the morning during 3 days of training periods (day 1-day 3) and on the following morning after the training (day 4). As an indication of endurance capacity, time to exhaustion during submaximal running test was determined on day 4. RESULTS:LEA trial showed that body weight, free fat mass and skeletal muscle volume were significantly reduced during training period (P < 0.05). Also, muscle glycogen contents were significantly decreased in LEA (P < 0.001) with significant lower values than those in NEA trial (P < 0.001). Blood glucose, serum free testosterone and insulin like growth factor-1 concentrations were significant lowered with training under LEA (P < 0.05). On the other hand, serum leptin concentration did not change significantly in LEA trial during training period (P > 0.05). Time to exhaustion during submaximal running test evaluated on day 4 was not significantly different between LEA trial (1170 ± 127 s) and NEA trial (1361 ± 196 s, P > 0.05). CONCLUSION:Three consecutive days of endurance training under Low EA reduced muscle glycogen content. However, endurance capacity was not attenuated.