The aim of this review is to provide an up-to-date summary of the evidence surrounding glycemic index (GI) and endurance performance. Athletes are commonly instructed to consume low-GI (LGI) carbohydrate (CHO) before exercise, but this recommendation appears to be based on the results of only a few studies, whereas others have found that the GI of CHO ingested before exercise has no impact on performance. Only 1 study was designed to directly investigate the impact of the GI of CHO ingested during exercise on endurance performance. Although the results indicate that GI is not as important as consuming CHO itself, more research in this area is clearly needed. Initial research investigating the impact of GI on postexercise recovery indicated consuming high-GI (HGI) CHO increased muscle glycogen resynthesis. However, recent studies indicate an interaction between LGI CHO and fat oxidation, which may play a role in enhancing performance in subsequent exercise. Despite the fact that the relationship between GI and sporting performance has been a topic of research for more than 15 yr, there is no consensus on whether consuming CHO of differing GI improves endurance performance. Until further well-designed research is carried out, athletes are encouraged to follow standard recommendations for CHO consumption and let practical issues and individual experience dictate the use of HGI or LGI meals and supplements before, during, and after exercise.
Carolyn M. Donaldson, Tracy L. Perry and Meredith C. Rose
Keisuke Ueda, Yutaka Nakamura, Makoto Yamaguchi, Takeshi Mori, Masayuki Uchida and Satoshi Fujita
Although there have been many investigations of the beneficial effects of both exercise and amino acids (AAs), little is known about their combined effects on the single-dose ingestion of AAs for lipid metabolism during exercise. We hypothesize that taking a specific combination of AAs implicated in glucagon secretion during exercise may increase fat metabolism. We recently developed a new mixture, d–AA mixture (D-mix), that contains arginine, alanine, and phenylalanine to investigate fat oxidation. In a double-blind, placebo-controlled crossover study, 10 healthy male volunteers were randomized to ingest either D-mix (3 g/dose) or placebo. Subjects in each condition subsequently performed a physical task that included workload trials on a cycle ergometer at 50% of maximal oxygen consumption for 1 hr. After oral intake of D-mix, maximum serum concentrations of glycerol (9.32 ± 6.29 mg/L and 5.22 ± 2.22 mg/L, respectively; p = .028), free fatty acid level (0.77 ± 0.26 mEq/L and 0.63 ± 0.28 mEq/L, respectively; p = .022), and acetoacetic acid levels (37.9 ± 17.7 μmol/L and 30.3 ± 13.9 μmol/L, respectively; p = .040) were significantly higher than in the placebo groups. The area under the curve for glucagon during recovery was numerically higher than placebo (6.61 ± 1.33 μg/L • min and 6.06 ± 1.23 μg/L • min, respectively; p = .099). These results suggest that preexercise ingestion of D-mix may stimulate fat metabolism. Combined with exercise, the administration of AA mixtures could prove to be a useful nutritional strategy to maximize fat metabolism.
Jesse Fleming, Matthew J. Sharman, Neva G. Avery, Dawn M. Love, Ana L. Gómez, Timothy P. Scheett, William J. Kraemer and Jeff S. Volek
The effects of adaptation to a high-fat diet on endurance performance are equivocal, and there is little data regarding the effects on high-intensity exercise performance. This study examined the effects of a high-fat/moderate protein diet on submaximal, maximal, and supramaximal performance. Twenty non-highly trained men were assigned to either a high-fat/moderate-protein (HFMP; 61% fat) diet (n = 12) or a control (C; 25% fat) group (n = 8). A maximal oxygen consumption test, two 30-s Wingate anaerobic tests, and a 45-min timed ride were performed before and after 6 weeks of diet and training. Body mass decreased significantly (–2.2 kg; p ≤ .05) in HFMP subjects. Maximal oxygen consumption significantly decreased in the HFMP group (3.5 ± 0.14 to 3.27 ± 0.09 L · min−1) but was unaffected when corrected for body mass. Perceived exertion was significantly higher during this test in the HFMP group. Main time effects indicated that peak and mean power decreased significantly during bout 1 of the Wingate sprints in the HFMP (–10 and –20%, respectively) group but not the C (–8 and –16%, respectively) group. Only peak power was lower during bout 1 in the HFMP group when corrected for body mass. Despite significantly reduced RER values in the HFMP group during the 45-min cycling bout, work output was significantly decreased (–18%). Adaptation to a 6-week HFMP diet in non-highly trained men resulted in increased fat oxidation during exercise and small decrements in peak power output and endurance performance. These deleterious effects on exercise performance may be accounted for in part by a reduction in body mass and/or increased ratings of perceived exertion.
Jens Bangsbo, Fedon Marcello Iaia and Peter Krustrup
The physical demands in soccer have been studied intensively, and the aim of the present review is to provide an overview of metabolic changes during a game and their relation to the development of fatigue. Heart-rate and body-temperature measurements suggest that for elite soccer players the average oxygen uptake during a match is around 70% of maximum oxygen uptake (VO2 max). A top-class player has 150 to 250 brief intense actions during a game, indicating that the rates of creatine-phosphate (CP) utilization and glycolysis are frequently high during a game, which is supported by findings of reduced muscle CP levels and several-fold increases in blood and muscle lactate concentrations. Likewise, muscle pH is lowered and muscle inosine monophosphate (IMP) elevated during a soccer game. Fatigue appears to occur temporarily during a game, but it is not likely to be caused by elevated muscle lactate, lowered muscle pH, or change in muscle-energy status. It is unclear what causes the transient reduced ability of players to perform maximally. Muscle glycogen is reduced by 40% to 90% during a game and is probably the most important substrate for energy production, and fatigue toward the end of a game might be related to depletion of glycogen in some muscle fibers. Blood glucose and catecholamines are elevated and insulin lowered during a game. The blood free-fatty-acid levels increase progressively during a game, probably reflecting an increasing fat oxidation compensating for the lowering of muscle glycogen. Thus, elite soccer players have high aerobic requirements throughout a game and extensive anaerobic demands during periods of a match leading to major metabolic changes, which might contribute to the observed development of fatigue during and toward the end of a game.
Estelle V. Lambert, Julia H. Goedecke, Charl van Zyl, Kim Murphy, John A. Hawley, Steven C. Dennis and Timothy D. Noakes
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 (V̇O2peak), 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.
Brian D. Roy, Katherine Luttmer, Michael J. Bosman and Mark A. Tarnopolsky
The purpose of this investigation was to determine the influence of post-exercise macronutrient intake on weight loss, protein metabolism, and endurance exercise performance during a period of increased training volume. Ten healthy young female endurance athletes performed 4 60-min bouts of cycle ergometry at ~65% of V̇O2peak on 4 days (day 1, 3, 4, and 6) during 2 separate 1-week periods. On day 7. participants performed a ride to exhaustion at ~75% of V̇O2peak. One of the 7-day periods served as a control condition, where a placebo beverage was consumed following the exercise bouts on days 1, 3, 4, and 6 (CON). During the other 7-day protocol (POST), participants consumed a predefined formula beverage with added carbohydrate following the exercise bouts on days 1. 3,4, and 6. Energy intake and macronutrient proportions were the same between the 2 trials; the only difference was the timing at which the macronutrients were consumed. Calculated fat oxidation was greater during exercise on day 6 during POST as compared to CON (p < .05). Glucose and insulin concentrations were significantly higher (p < .05) following exercise during POST as compared to CON. There was a trend (p = .06) for nitrogen balance to be greater on days 5 and 6 with POST as compared to CON. Time to exhaustion during exercise on day 7 was longer during POST as compared to CON (p < .05). POST resulted in a maintenance of body weight during the 7-day protocol, while there was a significant (p < .05) reduction with CON. It was concluded that post-exercise macronutrient intake following endurance exercise can attenuate reductions in body weight and improve nitrogen balance during 7 days of increased energy expenditure. Importantly, post-exercise supplementation improved time to exhaustion during a subsequent bout of endurance exercise.
Michael C. Riddell, Sara L. Partington, Nicole Stupka, David Armstrong, C. Rennie and Mark A. Tarnopolsky
Compared to males, females oxidize proportionately more fat and less carbohydrate during endurance exercise performed in the fasted state. This study was designed to test the hypothesis that there may also be gender differences in exogenous carbohydrate (CHOexo) oxidation during exercise. Healthy, young males (n = 7) and females (n = 7) each completed 2 exercise trials (90 min cycle ergometry at 60% VO2peak), 1 week apart. Females were eumenorrheic and were tested in the midfollicular phase of their menstrual cycle. Subjects drank intermittently either 8% CHOexo (1 g glucose · kg · h−1) enriched with U-13C glucose or an artificially sweetened placebo during the trial. Whole-body substrate oxidation was determined from RER, urinary urea excretion, and the ratio of 13C:12C in expired gas during the final 60 min of exercise. During the placebo trial, fat oxidation was higher in females than in males (0.42 · 0.07 vs. 0.32 · 0.09 g · min−1 · kg LBM–1 × 10–2) at 30 min of exercise (p < .05). When averaged over the final 60 min of exercise, the relative proportions of fat, total carbohydrate, and protein were similar between groups. During CHOexo ingestion, both the ratio of 13C:12C in expired gas (p < .05) and the proportion of energy derived from CHOexo relative to LBM (p < .05) were higher in females compared to males at 75- and 90-min exercise. When averaged over the final 60 min of exercise, the percentage of CHOexo to the total energy contribution tended to be higher in females (14.3 · 1.2%) than in males (11.2 · 1.2%; p = .09). The reduction in endogenous CHO oxidation with CHOexo intake was also greater in females (12.9 · 3.1%) than in males (5.1 · 2.0%; p = .05). Compared to males, females may oxidize a greater relative proportion of CHOexo during endurance exercise which, in turn, may spare more endogenous fuel. Based on these observations, ingested carbohydrate may be a particularly beneficial source of fuel during endurance exercise for females.
Andrés Pérez, Domingo J. Ramos-Campo, Cristian Marín-Pagan, Francisco J. Martínez-Noguera, Linda H. Chung and Pedro E. Alcaraz
Interestingly, POL has shown to improve VO 2 peak, anaerobic threshold, aerobic efficiency, time to exhaustion during an incremental test, 14 finishing time in 10-km races, 13 and running economy in ultrarunners. 9 In addition, fat metabolism has a key role in endurance events. 15 The maximal fat oxidation
intake may induce gastrointestinal (GI) distress during long-distance races ( Jeukendrup et al., 2005 ; Pfeiffer et al., 2012 ). Given these potential limitations, it has been suggested that strategies that enhance fat oxidation could be beneficial for performance in ultra-endurance events ( Volek et
count during walking and running in the laboratory setting. Effects of Daily and Intermittent Intake of New Zealand Blackcurrant Extract on Whole-Body Fat Oxidation During Moderate Intensity Exercise in Males MA Şahin 1,2 P Bilgiç 2 , S Montanari 1 , MET Willems 1 1 Institute of Sport, University of