The time of ingestion of a carbohydrate supplement on muscle glycogen storage postexercise was examined. Twelve male cyclists exercised continuously for 70 min on a cycle ergometer at 68% VO2max, interrupted by six 2-min intervals at 88% VO2max, on two separate occasions. A 25% carbohydrate solution (2 g/kg body wt) was ingested immediately postexercise (P-EX) or 2 h postexercise (2P-EX). Muscle biopsies were taken from the vastus lateralis at 0, 2, and 4 h postexercise. Blood samples were obtained from an antecubital vein before and during exercise and at specific times after exercise. Muscle glycogen immediately postexercise was not significantly different for the P-EX and 2P-EX treatments. During the first 2 h postexercise, the rate of muscle glycogen storage was 7.7 mumol.g wet wt-1.h-1 for the P-EX treatment, but only 2.5 mumol.g wet wt-1.h-1 for the 2P-EX treatment. During the second 2 h of recovery, the rate of glycogen storage slowed to 4.3 mumol.g wet wt-1.h-1 during treatment P-EX but increased to 4.1 mumol.g wet wt-1.h-1 during treatment 2P-EX. This rate, however, was still 45% slower (P less than 0.05) than that for the P-EX treatment during the first 2 h of recovery. This slower rate of glycogen storage occurred despite significantly elevated plasma glucose and insulin levels. The results suggest that delaying the ingestion of a carbohydrate supplement post-exercise will result in a reduced rate of muscle glycogen storage.
Six men were studied to determine the interrelationships among blood supply, motor unit (MU) activity and lactate concentrations during intermittent isometric contractions of the hand grip muscles. The subjects performed repeated contractions at 20% of maximal voluntary contraction (MVC) for 2 s followed by 2-s rest for 4 min with either unhindered blood circulation or arterial occlusion given between the 1st and 2nd min. The simultaneously recorded intramuscular MU spikes and surface electromyogram (EMG) data indicated that mean MU spike amplitude, firing frequency and the parameters of surface EMG power spectra (mean power frequency and root mean square amplitude) remained constant during the experiment with unhindered circulation, providing no electrophysiological signs of muscle fatigue. Significant increases in mean MU spike amplitude and frequency were, however, evident during the contractions with arterial occlusion. Similar patterns of significant changes in the surface EMG spectra parameters and venous lactate concentration were also observed, while the integrated force-time curves remained constant. These data would suggest that the metabolic state of the active muscles may have played an important role in the regulation of MU recruitment and rate coding patterns during exercise.
Although the group average for PAR-PAEE agreed with DLW-PAEE, there were differences in the methods among the subjects. PAEE determined by Tritrac, CSA, and Yamax significantly underestimate free-living PAEE in women.
This study examined the effect of three exercise-diet regimens on muscle glycogen supercompensation and subsequent performance during a 20.9-km run. A diet containing 15% carbohydrate (CHO,L), 50% CHO (M), or 70% (CHO (H) was arranged in three trials as follows: trial A = 3 days L, 3 days H; trial B = 3 days M, 3 days H; trial C = 6 days M. For each trial a 5-day depletion-taper exercise sequence was conducted on the treadmill at 73% VO2 max. The runs were 90, 40, 40, 20, and 20 min, respectively. A day of rest preceded the 20.9-km performance run. Muscle biopsies were obtained from the gastrocnemius on days 4 and 7 (both prior to and after the performance run). Trials A, B, and C elevated muscle glycogen to 207, 203, and 159 mmol glucosyl units/kg wet tissue (mmG), respectively. The performance run in both trials A and B utilized significantly more glycogen than in trial C: 5.0 and 5.1 mmG/km vs. 3.1 mmG/km. There were, however, no differences in either performance run times or post-performance run glycogen levels between the trials. These data demonstrate that (1) muscle glycogen can be elevated to high levels with a moderate exercise-diet regimen; (2) initial muscle glycogen levels influence the amount subsequently utilized during exercise; (3) carbohydrate loading is of no benefit to performance for trained runners during a 20.9-km run.
This study examined the effects of no carbohydrate (PP), preexercise carbohydrate feeding (CP), carbohydrate feedings during exercise (PC), and the combination of carbohydrate feedings before and during exercise (CC) on the metabolic responses during exercise and on exercise performance. Nine well-trained cyclists exercised at 70% of maximal O2 uptake until exhaustion. Blood glucose peaked 30 min after the preexercise carbohydrate feeding and at the start of exercise was 25% below the prefeeding concentration (4.76 mM). At exhaustion, glucose had declined to 3.8 (PP), 4.0 (CP), 4.6 (PC), and 5.0 mM (CC). Insulin was 300% above basal (7 microU/ml) at the start of exercise for CC and CP and returned to baseline by 120 min of exercise. When carbohydrates were consumed, the rate of carbohydrate oxidation was significantly higher throughout exercise than during PP. Total work produced during exercise was 19-46% (P less than 0.05) higher when carbohydrates were consumed. Time to exhaustion was 44% (CC), 32% (PC), and 18% (CP) greater than PP (201 min; P less than 0.05). Performance was improved by ingestion of carbohydrates before and/or during exercise; performance was further improved by their combination. This is probably the result of enhanced carbohydrate oxidation, especially during the later stages of exercise.
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