This study investigated the metabolic responses to high glycemic index (HGI) or low glycemic index (LGI) meals consumed during recovery from prolonged exercise. Eight male, trained athletes undertook 2 trials. Following an overnight fast, subjects completed a 90-min run at 70% VO2max. Meals were provided 30 min and 2 h following cessation of exercise. The plasma glucose responses to both meals were greater in the HGI trial compared to the LGI trial (P < 0.05). Following breakfast, there were no differences in the serum insulin concentrations between the trials; however, following lunch, concentrations were higher in the HGI trial compared to the LGI trial (P < 0.05). This suggests that the glycemic index of the carbohydrates consumed during the immediate post-exercise period might not be important as long as sufficient carbohydrate is consumed. The high insulin concentrations following a HGI meal later in the recovery period could facilitate further muscle glycogen resynthesis.
Emma Stevenson, Clyde Williams and Helen Biscoe
Emma Stevenson, Clyde Williams, Gareth McComb and Christopher Oram
This study examined the effects of the glycemic index (GI) of post-exercise carbohydrate (CHO) intake on endurance capacity the following day. Nine active males participated in 2 trials. On day 1, subjects ran for 90 min at 70% VO2max (R1). Thereafter, they were supplied with either a high GI (HGI) or low GI (LGI) CHO diet which provided 8 g CHO/kg body mass (BM). On day 2, after an overnight fast, subjects ran to exhaustion at 70% VO2max (R2). Time to exhaustion during R2 was longer in the LGI trial (108.9 ± 7.4 min) than in the HGI trial (96.9 ± 4.8 min) (P < 0.05). Fat oxidation rates and free fatty acid concentrations were higher in the LGI trial than the HGI trial (P < 0.05). The results suggest that the increased endurance capacity was largely a consequence of the increased fat oxidation following the LGI recovery diet.
Emma Stevenson, Clyde Williams, Maria Nute, Peter Swaile and Monica Tsui
The present study investigated the effect of the glycemic index of an evening meal on responses to a standard high glycemic index (HGI) breakfast the following morning. The metabolic responses to exercise 3 h after breakfast were also investigated. Seven active males completed 2 trials. In each trial, participants were provided with an evening meal on day 1, which was composed of either HGI or LGI (high or low glycemic index) carbohydrates. On day 2, participants were provided with a standard HGI breakfast and then performed a 60 min run at 65% VO2max 3 h later. Plasma glucose and serum insulin concentrations following breakfast were higher in the HGI trial compared to the LGI trial (P < 0.05). During exercise, there were no differences in substrate utilization. The results suggest that consuming a single LGI evening meal can improve glucose tolerance at breakfast but the metabolic responses to subsequent exercise were not affected.
Samuel Erith, Clyde Williams, Emma Stevenson, Siobhan Chamberlain, Pippa Crews and Ian Rushbury
This study examined the effect of high carbohydrate meals with different glycemic indices (GI) on recovery of performance during prolonged intermittent high-intensity shuttle running. Seven male semi-professional soccer players (age 23 ± 2 y, body mass [BM] 73.7 ± 9.0 kg and maximal oxygen uptake 58 ± 1.0 mL · kg−1 · min−1) participated in two trials in a randomized cross-over design. On day 1, the subjects performed 90 min of an intermittent high-intensity shuttle running protocol [Loughborough Intermittent Shuttle Test (LIST)]. They then consumed a mixed high carbohydrate recovery diet (8 g/kg BM) consisting of either high (HGI) (GI: 70) or low (LGI) (GI: 35) GI foods. Twenty-two hours later (day 2) the subjects completed 75 min of the LIST (part A) followed by alternate sprinting and jogging to fatigue (part B). No differences were found between trials in time to fatigue (HGI 25.3 ± 4.0 min vs. LGI 22.9 ± 5.6 min, P = 0.649). Similarly, no differences were found between trials for sprint performance and distance covered during part B of the LIST. In conclusion, the GI of the diet during the 22 h recovery did not affect sprint and endurance performance the following day.
James A. Betts, Emma Stevenson, Clyde Williams, Catrin Sheppard, Edwin Grey and Joe Griffin
Including protein in a carbohydrate solution may accelerate both the rate of glycogen storage and the restoration of exercise capacity following prolonged activity. Two studies were undertaken with nine active men in study A and seven in study B. All participants performed 2 trials, each involving a 90 min run at 70% VO2max followed by a 4 h recovery. During recovery, either a 9.3% carbohydrate solution (CHO) or the same solution plus 1.5% protein (CHO-PRO) was ingested every 30 min in volumes providing either 1.2 g CHO · kg−1 · h−1 (study A) or 0.8 g CHO · kg−1 · h−1 (study B). Exercise capacity was then assessed by run time to exhaustion at 85% VO2max. Ingestion of CHO-PRO elicited greater insulinemic responses than CHO (P ≤ 0.05) but with no differences in run times to exhaustion. Within the context of this experimental design, CHO and CHO-PRO restored running capacity with equal effect.