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James A. Betts
James A. Betts
James A. Betts
James A. Betts
Rebecca J. Toone and James A. Betts
This study was designed to compare the effects of energy-matched carbohydrate (CHO) and carbohydrate-protein (CHO-PRO) supplements on cycling time-trial performance. Twelve competitive male cyclists and triathletes each completed 2 trials in a randomized and counterbalanced order that were separated by 5–10 d and applied in a double-blind manner. Participants performed a 45-min variable-intensity exercise protocol on a cycle ergometer while ingesting either a 9% CHO solution or a mixture of 6.8% CHO plus 2.2% protein in volumes providing 22 kJ/kg body mass. Participants were then asked to cycle 6 km in the shortest time possible. Blood glucose and lactate concentrations were measured every 15 min during exercise, along with measures of substrate oxidation via indirect calorimetry, heart rate, and ratings of perceived exertion. Mean time to complete the 6-km time trial was 433 ± 21 s in CHO trials and 438 ± 22 s in CHO-PRO trials, which represents a 0.94% (CI: 0.01, 1.86) decrement in performance with the inclusion of protein (p = .048). However, no other variable measured in this study was significantly different between trials. Reducing the quantity of CHO included in a supplement and replacing it with protein may not represent an effective nutritional strategy when the supplement is ingested during exercise. This may reflect the central ergogenic influence of exogenous CHO during such activity.
Professor James A. Betts
Edward A. Gray, Thomas A. Green, James A. Betts, and Javier T. Gonzalez
During short-term recovery, postexercise glucose–fructose coingestion can accelerate total glycogen repletion and augment recovery of running capacity. It is unknown if this advantage translates to cycling, or to a longer (e.g., overnight) recovery. Using two experiments, the present research investigated if postexercise glucose–fructose coingestion augments exercise capacity following 4-hr (short experiment; n = 8) and 15-hr (overnight experiment; n = 8) recoveries from exhaustive exercise in trained cyclists, compared with isocaloric glucose alone. In each experiment, a glycogen depleting exercise protocol was followed by a 4-hr recovery, with ingestion of 1.5 or 1.2 g·kg−1·hr−1 carbohydrate in the short experiment (double blind) and the overnight experiment (single blind), respectively. Treatments were provided in a randomized order using a crossover design. Four or fifteen hours after the glycogen depletion protocol, participants cycled to exhaustion at 70% W max or 65% W max in the short experiment and the overnight experiment, respectively. In both experiments there was no difference in substrate oxidation or blood glucose and lactate concentrations between treatments during the exercise capacity test (trial effect, p > .05). Nevertheless, cycling capacity was greater in glucose + fructose versus glucose only in the short experiment (28.0 ± 8.4 vs. 22.8 ± 7.3 min, d = 0.65, p = .039) and the overnight experiment (35.9 ± 10.7 vs. 30.6 ± 9.2 min, d = 0.53, p = .026). This is the first study to demonstrate that postexercise glucose–fructose coingestion enhances cycling capacity following short-term (4 hr) and overnight (15 hr) recovery durations. Therefore, if multistage endurance athletes are ingesting glucose for rapid postexercise recovery then fructose containing carbohydrates may be advisable.
Abdullah F. Alghannam, Dawid Jedrzejewski, James Bilzon, Dylan Thompson, Kostas Tsintzas, and James A. Betts
We examined whether carbohydrate-protein ingestion influences muscle glycogen metabolism during short-term recovery from exhaustive treadmill running and subsequent exercise. Six endurance-trained individuals underwent two trials in a randomized double-blind design, each involving an initial run-to-exhaustion at 70% VO2max (Run-1) followed by 4-h recovery (REC) and subsequent run-to-exhaustion at 70% VO2max (Run-2). Carbohydrate-protein (CHO-P; 0.8 g carbohydrate·kg body mass [BM-1]·h-1 plus 0.4 g protein·kg BM-1·h-1) or isocaloric carbohydrate (CHO; 1.2 g carbohydrate·kg BM-1·h-1) beverages were ingested at 30-min intervals during recovery. Muscle biopsies were taken upon cessation of Run-1, postrecovery and fatigue in Run-2. Time-to-exhaustion in Run-1 was similar with CHO and CHO-P (81 ± 17 and 84 ± 19 min, respectively). Muscle glycogen concentrations were similar between treatments after Run-1 (99 ± 3 mmol·kg dry mass [dm-1]). During REC, muscle glycogen concentrations increased to 252 ± 45 mmol·kg dm-1 in CHO and 266 ± 30 mmol·kg dm-1 in CHO-P (p = .44). Muscle glycogen degradation during Run-2 was similar between trials (3.3 ± 1.4 versus 3.5 ± 1.9 mmol·kg dm-1·min-1 in CHO and CHO-P, respectively) and no differences were observed at the respective points of exhaustion (93 ± 21 versus 100 ± 11 mmol·kg dm-1; CHO and CHO-P, respectively). Similarly, time-to-exhaustion was not different between treatments in Run-2 (51 ± 13 and 49 ± 15 min in CHO and CHO-P, respectively). Carbohydrate-protein ingestion equally accelerates muscle glycogen resynthesis during short-term recovery from exhaustive running as when 1.2 g carbohydrate·kg BM-1·h-1 are ingested. The addition of protein did not alter muscle glycogen utilization or time to fatigue during repeated exhaustive running.
James A. Betts, Keith A. Stokes, Rebecca J. Toone, and Clyde Williams
Endocrine responses to repeated exercise have barely been investigated, and no data are available regarding the mediating influence of nutrition. On 3 occasions, participants ran for 90 min at 70% VO2max (R1) before a second exhaustive treadmill run at the same intensity (R2; 91.6 ± 17.9 min). During the intervening 4-hr recovery, participants ingested either 0.8 g sucrose · kg−1 · hr−1 with 0.3 g · kg−1 · hr−1 whey-protein isolate (CHO-PRO), 0.8 g sucrose · kg−1 · hr−1 (CHO), or 1.1 g sucrose · kg−1 · hr−1 (CHO-CHO). The latter 2 solutions therefore matched the former for carbohydrate or for available energy, respectively. Serum growth-hormone concentrations increased from 2 ± 1 μg/L to 17 ± 8 μg/L during R1 considered across all treatments (M ± SD; p ≤ .01). Concentrations were similar immediately after R2 irrespective of whether CHO or CHO-CHO was ingested (19 ± 4 μg/L and 19 ± 5 μg/L, respectively), whereas ingestion of CHO-PRO produced an augmented response (31 ± 4 μg/L; p ≤ .05). Growth-hormone-binding protein concentrations were unaffected by R1 but increased similarly across all treatments during R2 (from 414 ± 202 pmol/L to 577 ± 167 pmol/L; p ≤ .01), as was the case for plasma total testosterone (from 9.3 ± 3.3 nmol/L to 14.7 ± 4.6 nmol/L; p ≤ .01). There was an overall treatment effect for serum cortisol (p ≤ .05), with no specific differences at any given time point but lower concentrations immediately after R2 with CHO-PRO (608 ± 133 nmol/L) than with CHO (796 ± 278 nmol/L) or CHO-CHO (838 ± 134 nmol/L). Ingesting carbohydrate with added whey-protein isolate during short-term recovery from 90 min of treadmill running increases the growth-hormone response to a second exhaustive exercise bout of similar duration.
Gregg Afman, Richard M. Garside, Neal Dinan, Nicholas Gant, James A. Betts, and Clyde Williams
Current recommendations for nutritional interventions in basketball are largely extrapolated from laboratory-based studies that are not sport-specific. We therefore adapted and validated a basketball simulation test relative to competitive basketball games using well-trained basketball players (n = 10), then employed this test to evaluate the effects of two common preexercise nutritional interventions on basketball-specific physical and skilled performance. Specifically, in a randomized and counterbalanced order, participants ingested solutions providing either 75 g carbohydrate (sucrose) 45 min before exercise (Study A; n = 10) or 2 × 0.2 g·kg−1 sodium bicarbonate (NaHCO3) 90 and 20 min before exercise (Study B; n = 7), each relative to appropriate placebos (H2O and 2 × 0.14 g·kg−1 NaCl, respectively). Heart rate, sweat rate, pedometer count, and perceived exertion did not systematically differ between the 60-min basketball simulation test and competitive basketball, with a strong positive correlation in heart rate response (r = .9, p < .001). Preexercise carbohydrate ingestion resulted in marked hypoglycemia (< 3.5 mmol·l−1) throughout the first quarter, coincident with impaired sprinting (+0.08 ± 0.05 second; p = .01) and layup shooting performance (8.5/11 versus 10.3/11 baskets; p < .01). However, ingestion of either carbohydrate or sodium bicarbonate before exercise offset fatigue such that sprinting performance was maintained into the final quarter relative to placebo (Study A: –0.07 ± 0.04 second; p < .01 and Study B: -0.08 ± 0.05 second; p = .02), although neither translated into improved skilled (layup shooting) performance. This basketball simulation test provides a valid reflection of physiological demands in competitive basketball and is sufficiently sensitive to detect meaningful changes in physical and skilled performance. While there are benefits of preexercise carbohydrate or sodium bicarbonate ingestion, these should be balanced against potential negative side effects.