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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.

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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.

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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.

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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

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Iñigo Mujika

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

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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

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Alan J. McCubbin, Anyi Zhu, Stephanie K. Gaskell and Ricardo J.S. Costa

et al., 2019a ) were recorded every 15 min during SS. Capillary blood glucose concentration was measured before and every 30 min during SS (Accu-Chek Performa; Roche Diagnostics, Indianapolis, IN). Total nonprotein carbohydrate and fat oxidation was measured every 30 min using breath

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Trent Stellingwerff, James P. Morton and Louise M. Burke

glucose, provides an effective and dominant fuel source for performance across a wide variety of events in athletics ( Hawley & Leckey, 2015 ). Indeed, it has been known for nearly a century that 100% CHO produces ∼5.5% more ATP per liter of oxygen consumed than compared with 100% fat oxidation ( Krogh

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Edward A. Gray, Thomas A. Green, James A. Betts and Javier T. Gonzalez

). Differences in gastrointestinal discomfort, blood glucose, lactate and rates of carbohydrate, and fat oxidation were assessed between treatments and across time using a two-way repeated-measures analysis of variance. Following a significant interaction, Bonferroni post hoc tests were used to locate

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efforts. Alleged performance benefits are attributed to optimized fat oxidation. However, recent data demonstrates that a low carb, high fat diet (LCHF) leads to an impaired performance and less efficient energy metabolism in elite endurance athletes. The aim of the study was to analyze the alteration of