Search Results

Consumption of low glycemic index (GI) foods before submaximal endurance exercise may be beneficial to performance. To test whether this may also be true for high intensity exercise. 10 trained cyclists began an incremental exercise test to exhaustion 65 min after consuming equal carbohydrate portions of glucose (HGI), pasta (LGI), and a noncarbohydrate control (PL). Time to fatigue did not differ significantly (p = 0.05) between treatments. Plasma glucose concentration was significantly lower after LGI vs. HGI from 15 to 45 min of rest postprandial. During exercise, plasma glucose concentration was significantly lower after HGI vs. LGI from 200 W until exhaustion. Plasma lactate concentration following HGI was significantly higher than PL from 30 min of rest postprandial through to the end of the 200-W workload. Plasma lactate concentration following LGI was significantly lower than after HGI from 45 min of rest postprandial through to the end of the 100-W workload. At higher exercise intensities, there was no significant difference in plasma lactate levels between treatments. These findings suggest that a high GI carbohydrate meal (1 g/kg body wt) 65 min prior to exercise decreases plasma glucose and increases plasma lactate levels compared to a low GI meal, but not enough to be detrimental to incremental exercise performance.

The purpose of this study was to determine if pre-exercise glucose ingestion would improve distance swimming performance. Additionally, pre-exercise glucose was provided at 2 different feeding intervals to investigate the affects of the timing of administration. Ten male triathletes ( $\overline{\text{X}}\pm SD$ : age, 29.5 ± 5.0 years; V̇O_2peak, 48.8 ± 3.2 ml · kg’¹ · min’) swam 4000 m on 3 occasions following the consumption of either a 10% glucose solution 5 min prior to exercise (G⁵), a 10% glucose solution 35 min prior to exercise (G³⁵), or a similar volume of placebo (PL). Despite a significant difference (p < ,01) in blood glucose concentration prior to exercise ( $\overline{\text{X}}\pm SD$ in mmol · L ’: G" 8.4 ± 1.1 vs. G⁵ 5.2 ± 0.5 or PL 5.3 ± 0.4), no significant differences were observed in total time ( $\overline{\text{X}}\pm SD$ in minutes: G* 70.7 ± 7.6, G^s 70.1 ± 7.6. PL 71.9 ± 8.4). post-exercise blood glucose ( $\overline{\text{X}}\pm SD$ inmmol · L⁻¹: G³⁵ 5.1 ± 1.1, G⁵ 5.1 ± 0.9, PL 5.3 ± 0.4), and average heart rate ( $\overline{\text{X}}\pm SD$ in bpnv.G" 155.8±10.8, G⁵ 153.6±12.6. PL 152.0± 12.5; p > .05). While not reaching statistical significance, glucose feedings did result in improved individual performance times, ranging from 24 s to 5 min in 8 of the 10 subjects compared to the placebo. These results were found despite significant differences in blood glucose between trials immediately prior to exercise.

The current case study intended to measure blood glucose fluctuation in 2 marathon runners during a 100-km race using a continuous glucose-monitoring system (CGMS) and investigate the relationship between glucose profile and change in running speed. Two experienced ultramarathon runners participated in this study. A CGMS glucose sensor was inserted into the subcutaneous abdominal tissue at 35 h before the 100-km race, and the glucose profile was monitored continuously until the end of the race. Race pace and energy intake during the race were recorded. Participants finished the race in 6h:51min:17s (runner A) and 8h:56min:04s (runner B), and the race-pace decrement ratios were 17.6% for runner A and 27.2% for runner B. The average relative intensity throughout the 100-km race was 89.9% ± 5.8% lactate threshold (LT) in runner A and 78.4% ± 8.6% LT in runner B. The total amount of carbohydrate intake during the race was 249 g and 366 g in runners A and B, respectively. Despite lower carbohydrate intake, runner A maintained a normal glucose level throughout the race, while runner B rapidly decreased blood glucose and became hypoglycemic after the 80-km point. These results suggest that elite ultramarathon runners may have the ability to prevent a large decrement in blood glucose level regardless of the amount of energy intake during the race to maintain higher relative running intensity.

We examined the effects of a high-fat diet (HFD-CHO) versus a habitual diet, prior to carbohydrate (CHO)-loading on fuel metabolism and cycling time-trial (TT) performance. Five endurance-trained cyclists participated in two 14-day randomized cross-over trials during which subjects consumed either a HFD (>65% MJ from fat) or their habitual diet (CTL) (30 ± 5% MJ from fat) for 10 day, before ingesting a high-CHO diet (CHO-loading, CHO > 70% MJ) for 3 days. Trials consisted of a 150-min cycle at 70% of peak oxygen uptake (V̇O_2peak), followed immediately by a 20-km TT. One hour before each trial, cyclists ingested 400 ml of a 3.44% medium-chain triacylglycerol (MCT) solution, and during the trial, ingested 600 ml/hour of a 10% 14C-glucose + 3.44% MCT solution. The dietary treatments did not alter the subjects’ weight, body fat, or lipid profile. There were also no changes in circulating glucose, lactate, free fatty acid (FFA), and β-hydroxybutyrate concentrations during exercise. However, mean serum glycerol concentrations were significantly higher (p < .01) in the HFD-CHO trial. The HFD-CHO diet increased total fat oxidation and reduced total CHO oxidation but did not alter plasma glucose oxidation during exercise. By contrast, the estimated rates of muscle glycogen and lactate oxidation were lower after the HFD-CHO diet. The HFD-CHO treatment was also associated with improved TT times (29.5 ± 2.9 min vs. 30.9 ± 3.4 min for HFD-CHO and CTL-CHO, p < .05). High-fat feeding for 10 days prior to CHO-loading was associated with an increased reliance on fat, a decreased reliance on muscle glycogen, and improved time trial performance after prolonged exercise.