Lima-Silva A E, De-Oliveira F R, Nakamura F Y, Gevaerd M S
Laboratório de Aptidão Física, Desempenho e Saúde, Universidade Federal de Alagoas, Maceió, AL, Brasil.
Braz J Med Biol Res. 2009 May;42(5):404-12. doi: 10.1590/s0100-879x2009000500002.
This study examined the effects of pre-exercise carbohydrate availability on the time to exhaustion for moderate and heavy exercise. Seven men participated in a randomized order in two diet and exercise regimens each lasting 3 days with a 1-week interval for washout. The tests were performed at 50% of the difference between the first (LT1) and second (LT2) lactate breakpoint for moderate exercise (below LT2) and at 25% of the difference between the maximal load and LT2 for heavy exercise (above LT2) until exhaustion. Forty-eight hours before each experimental session, subjects performed a 90-min cycling exercise followed by 5-min rest periods and a subsequent 1-min cycling bout at 125% VO2max/1-min rest periods until exhaustion to deplete muscle glycogen. A diet providing 10% (CHO(low)) or 65% (CHO(mod)) energy as carbohydrates was consumed for 2 days until the day of the experimental test. In the exercise below LT2, time to exhaustion did not differ between the CHO(mod) and the CHO(low) diets (57.22 +/- 24.24 vs 57.16 +/- 25.24 min). In the exercise above LT2, time to exhaustion decreased significantly from 23.16 +/- 8.76 min on the CHO(mod) diet to 18.30 +/- 5.86 min on the CHO(low) diet (P < 0.05). The rate of carbohydrate oxidation, respiratory exchange ratio and blood lactate concentration were reduced for CHO(low) only during exercise above LT2. These results suggest that muscle glycogen depletion followed by a period of a low carbohydrate diet impairs high-intensity exercise performance.
本研究考察了运动前碳水化合物可利用性对中等强度和高强度运动至疲劳时间的影响。七名男性以随机顺序参与两种饮食和运动方案,每种方案持续3天,间隔1周进行洗脱期。测试在中等强度运动(低于LT2)时,在第一次(LT1)和第二次(LT2)乳酸拐点差值的50%强度下进行;在高强度运动(高于LT2)时,在最大负荷与LT2差值的25%强度下进行,直至疲劳。在每次实验前48小时,受试者先进行90分钟的骑行运动,随后休息5分钟,接着以125%VO2max进行1分钟骑行运动/休息1分钟,直至疲劳,以耗尽肌肉糖原。在实验测试当天前2天,受试者食用提供10%(CHO(低))或65%(CHO(中))能量来自碳水化合物的饮食。在低于LT2的运动中,CHO(中)组和CHO(低)组的疲劳时间无差异(57.22±24.24分钟 vs 57.16±25.24分钟)。在高于LT2的运动中,疲劳时间从CHO(中)组的23.16±8.76分钟显著降至CHO(低)组的18.30±5.86分钟(P<0.05)。仅在高于LT2的运动中,CHO(低)组的碳水化合物氧化率、呼吸交换率和血乳酸浓度降低。这些结果表明,肌肉糖原耗尽后再经历一段低碳水化合物饮食期会损害高强度运动表现。