Effect of carbohydrate availability on time to exhaustion in exercise performed at two different intensities

Abstract

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 (LT 1 ) and second (LT 2 ) lactate breakpoint for moderate exercise (below LT 2 ) and at 25% of the difference between the maximal load and LT 2 for heavy exercise (above LT 2 ) 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% VO 2max /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 LT 2 , 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 LT 2 , 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 LT 2 . These results suggest that muscle glycogen depletion followed by a period of a low carbohydrate diet impairs high-intensity exercise performance.

Acute high-intensity exercise with low energy expenditure reduced LDL-c and total cholesterol in men

“…We did not find differences between the conditions regarding blood lactate accumulation. In addition, the blood lactate values at exhaustion were similar to those demonstrated in other studies incorporating a similar intensity of exercise (Lima-Silva et al 2009). …”

Prior Exercise Reduces Fast-Start Duration and End-Spurt Magnitude during Cycling Time-Trial

“…, it has previously been demonstrated that performance during high-intensity exercise (80-90% of VO 2 peak; 10-20 min) is impaired if athletes start the test after a muscle glycogen depletion protocol [26,27].…”

“…Furthermore, most studies with CHO availability have focused on investigating its effects on performance during time-to-exhaustion tests [8,14,15,26]. However, time-trials appear to be more reliable and to have a greater external validity compared to constant-workload test until exhaustion [5].…”

Comparison between Preexercise Meals Intake Effect with Different Glycemic Load on Exercise Performance in Female Athletes

“…Glycogen content of muscles decreases during exercise programs and if glycogen depletes, athletes won't be able to continue their exercise plan [2,3]. Several studies report that adherence to a carbohydraterestricted diet can improve athletes' performance, because it can lead to greater fat oxidation and glycogen-sparing effects during exercises [3,4,5].…”

“…Several studies report that adherence to a carbohydraterestricted diet can improve athletes' performance, because it can lead to greater fat oxidation and glycogen-sparing effects during exercises [3,4,5]. However other studies indicated consuming high carbohydrate (CHO) diet before exercise enhances subsequent endurance exercise performance [6] and reduces rating of perceived exertion (RPE), especially in high intensive exercises [2,7]. The concept of the glycemic index (GI) is to classify foods based on their actual postprandial blood glucose or white bread [8].…”