Search Results

You are looking at 41 - 50 of 88 items for :

  • "fat oxidation" x
  • Physical Education and Coaching x
Clear All
Restricted access

José Moncada-Jiménez, Eric P. Plaisance, Michael L. Mestek, Lance Ratcliff, Felipe Araya-Ramírez, James K. Taylor, Peter W. Grandjean and Luis F. AragónVargas

Purpose:

This study investigated the effects of short-term dietary changes on metabolism and duathlon performance.

Methods:

Eleven men underwent a high-fat (HF; >65% fat from energy) or a high-carbohydrate (CHO; HC) diet (>60% CHO from energy). Energy intake was individualized, and commercially available foods were prepared and packaged for each participant 48 hr before they completed a laboratory-based duathlon (5-km run, 30 km cycling, and 10-km run). Blood samples were obtained before, immediately after, and 1 and 2 hr after the duathlon for determination of glucose, insulin, and glucagon. Oxygen consumption, ratings of perceived exertion (RPE), and respiratory-exchange ratio were assessed, and fat and CHO oxidation were estimated before, during, and after the duathlon.

Results:

Dietary records indicated a significant difference in fat content ingested before the duathlons (p < .05). Time to complete the duathlon did not differ between the HC- and the HF-diet trials. CHO-oxidation rate was higher during the HC-diet trial than during the HF-diet trial (p = .006). Fat-oxidation rates were higher in the HF-diet trial than in the HC-diet trial (p = .001). No differences in RPE were found between dietary trials. Blood glucose concentration was higher immediately after the duathlon in the HC-diet trial than in the HF-diet trial and remained higher 1 and 2 hr after the duathlon (p < .05).

Conclusion:

Duathlon performance was not altered by short-term changes in dietary fat or CHO composition despite higher blood glucose concentrations under the HC condition.

Restricted access

Stephen H.S Wong, Oi Won Chan, Ya Jun Chen, Heng Long Hu, Ching Wan Lam and Pak Kwong Chung

Purpose:

This study examined the effect of consuming carbohydrate- (CHO) electrolyte solution on running performance after different-glycemic-index (GI) meals.

Methods:

Nine men completed 3 trials in a randomized counterbalanced order, with trials separated by at least 7 days. Two hours before the run after an overnight fast, each participant consumed a high-GI (GI = 83) or low-GI (GI = 36) CHO meal or low-energy sugar-free Jell-O (GI = 0, control). The 2 isocaloric GI meals provided 1.5 g available CHO/kg body mass. During each trial, 2 ml/kg body mass of a 6.6% CHO-electrolyte solution was provided immediately before exercise and every 2.5 km after the start of running. Each trial consisted of a 21-km performance run on a level treadmill. The participants were required to run at 70% VO2max during the first 5 km of the run. They then completed the remaining 16 km as fast as possible.

Results:

There was no difference in the time to complete the 21-km run (high-GI vs. low-GI vs. control: 91.1 ± 2.0 vs. 91.8 ± 2.2 vs. 92.9 ± 2.0 min, n.s.). There were no differences in total CHO and fat oxidation throughout the trials, despite differences in preexercise blood glucose, serum insulin, and serum free-fatty-acid concentrations.

Conclusion:

When a CHO-electrolyte solution is consumed during a 21-km run, the GI of the preexercise CHO meal makes no difference in running performance.

Restricted access

Carolyn M. Donaldson, Tracy L. Perry and Meredith C. Rose

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.

Restricted access

Jie Kang, Robert J. Robertson, Bart G. Denys, Sergio G. DaSilva, Paul Visich, Richard R. Suminski, Alan C. Utter, Fredric L. Goss and Kenneth F. Metz

This investigation determined whether carbohydrate ingestion during prolonged moderate-intensity exercise enhanced endurance performance when the exercise was preceded by carbohydrate supercompensation. Seven male trained cyclists performed two trials at an initial power output corresponding to 71 ± 1 % of their peak oxygen consumption. During the trials, subjects ingested either a 6% glucose/sucrose (C) solution or an equal volume of artificially flavored and sweetened placebo (P) every 20 min throughout exercise. Both C and P were preceded by a 6-day carbohydrate supercompensation procedure in which subjects undertook a depletion-taper exercise sequence in conjunction with a moderate- and high-carbohydrate diet regimen. Statistical analysis of time to exhaustion, plasma glucose concentration, carbohydrate oxidation rate, fat oxidation rate, and plasma glycerol concentration indicated that in spite of a carbohydrate supercompensation procedure administered prior to exercise, carbohydrate ingestion during exercise can exert an additional ergogenic effect by preventing a decline in blood glucose levels and maintaining carbohydrate oxidation during the later stages of moderate-intensity exercise.

Restricted access

Llion A. Roberts, Kris Beattie, Graeme L. Close and James P. Morton

Purpose:

To test the hypothesis that antioxidants can attenuate high-intensity interval training–induced improvements in exercise performance.

Methods:

Two groups of recreationally active males performed a high-intensity interval running protocol, four times per week for 4 wk. Group 1 (n = 8) consumed 1 g of vitamin C daily throughout the training period, whereas Group 2 (n = 7) consumed a visually identical placebo. Pre- and posttraining, subjects were assessed for VO2max, 10 km time trial, running economy at 12 km/h and distance run on the YoYo intermittent recovery tests level 1 and 2 (YoYoIRT1/2). Subjects also performed a 60 min run before and after training at a running velocity of 65% of pretraining VO2max so as to assess training-induced changes in substrate oxidation rates.

Results:

Training improved (P < .0005) VO2max, 10 km time trial, running economy, YoYoIRT1 and YoYoIRT2 in both groups, although there was no difference (P = .31, 0.29, 0.24, 0.76 and 0.59) between groups in the magnitude of training-induced improvements in any of the aforementioned parameters. Similarly, training also decreased (P < .0005) mean carbohydrate and increased mean fat oxidation rates during submaximal exercise in both groups, although no differences (P = .98 and 0.94) existed between training conditions.

Conclusions:

Daily oral consumption of 1 g of vitamin C during a 4 wk high-intensity interval training period does not impair training-induced improvements in the exercise performance of recreationally active males.

Restricted access

Laura J.S. Moore, Adrian W. Midgley, Gemma Thomas, Shane Thurlow and Lars R. McNaughton

Purpose:

The aim of this work was to determine whether the consumption of pre-exercise high– or low–glycemic index (GI) meals has a beneficial effect on time trial performance.

Methods:

Eight male cyclists were provided with either a high-GI or low-GI meal, providing 1 g·kg−1 body mass of carbohydrate, 45 min before performing a 40-km time trial on a Velotron cyclePro.

Results:

Time trial performance was significantly improved in the low-GI trial (92.5 ± 5.2 min) compared with the high-GI trial (95.6 ± 6.0 min) (P = .009). Blood glucose concentrations at the point of exhaustion were significantly higher in the low-GI trial (5.2± 0.6 mmol·L−1) compared with the high-GI trial (4.7 ± 0.7 mmol·L−1) (P = .001). There was no significant difference in estimated carbohydrate oxidation data between the low-GI (2.51 ± 1.74 g·min−1) and high-GI (2.18 ± 1.53 g·min−1) meals (P = .195). No significant difference in estimated fat oxidation was observed between the low-GI (0.15 ± 0.15 g·min−1) and high-GI (0.29 ± 0.18 g·min−1) diets (P = .83).

Conclusions:

The improvement in time trial performance for the low-GI trial may be associated with an increased availability of glucose to the working muscles, contributing additional carbohydrate for oxidation and possibly sparing limited muscle and liver glycogen stores.

Restricted access

Ching-Lin Wu and Clyde Williams

This study investigated the effects of ingesting a low (LGI) or high (HGI) glyce-mic index carbohydrate (CHO) meal 3 h prior to exercise on endurance running capacity. Eight male recreational runners undertook two trials (LGI or HGI) which were randomized and separated by 7 d. After an overnight fast (12 h) the subjects ingested either a LGI or HGI meal 3 h prior to running at 70% VO2max until exhaustion. The meals contained 2 g/kg body mass CHO and were isocaloric and iso-macronutrient with calculated GI values 77 and 37 for the HGI and LGI respectively. The run times for the LGI and HGI trials were 108.8 ± 4.1 min and 101.4 ± 5.2 min respectively (P = 0.038). Fat oxidation rates were higher during exercise after the LGI meal than after the HGI meal (P < 0.05). In summary, ingestion of a LGI meal 3 h before exercise resulted in a greater endurance capacity than after the ingestion of a HGI meal.

Restricted access

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.

Restricted access

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.

Restricted access

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.