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Ulrika Andersson-Hall, Stefan Pettersson, Fredrik Edin, Anders Pedersen, Daniel Malmodin and Klavs Madsen

In order to maximize the adaptive response to endurance training among athletes and/or to promote healthy living in the general population, there has recently been interest in ways to increase the capacity of fat oxidation during exercise. As glycogen stores are limited, a higher reliance on fat

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Mark Elisabeth Theodorus Willems, Mehmet Akif Şahin and Matthew David Cook

reported health benefits of regular intake of green tea such as a reduced risk for some cancers ( Guo et al., 2017 ) and cardiovascular and ischemic-related diseases ( Pang et al., 2016 ). Green tea has also been implicated in body weight management ( Janssens et al., 2016 ) by promoting fat oxidation

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Francisco J. Amaro-Gahete, Lucas Jurado-Fasoli, Alejandro R. Triviño, Guillermo Sanchez-Delgado, Alejandro De-la-O, Jørn W. Helge and Jonatan R. Ruiz

energy storage is effectively unlimited during prolonged exercise. 3 Therefore, the capacity to adapt fuel oxidation to fuel availability (known as metabolic flexibility) is a key determinant of endurance sport performance. 4 Therefore, the maximal fat oxidation (MFO) capacity during a graded exercise

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Amy Warren, Erin J. Howden, Andrew D. Williams, James W. Fell and Nathan A. Johnson

Postexercise fat oxidation may be important for exercise prescription aimed at optimizing fat loss. The authors examined the effects of exercise intensity, duration, and modality on postexercise oxygen consumption (VO2) and substrate selection/respiratory-exchange ratio (RER) in healthy individuals. Three experiments (n = 7 for each) compared (a) short- (SD) vs. long-duration (LD) ergometer cycling exercise (30 min vs. 90 min) matched for intensity, (b) low- (LI) vs. high-intensity (HI) cycling (50% vs. 85% of VO2max) matched for energy expenditure, and (c) continuous (CON) vs. interval (INT) cycling matched for energy expenditure and mean intensity. All experiments were administered by crossover design. Altering exercise duration did not affect postexercise VO2 or RER kinetics (p > .05). However, RER was lower and fat oxidation was higher during the postexercise period in LD vs. SD (p < .05). HI vs. LI resulted in a significant increase in total postexercise energy expenditure and fat oxidation (p < .01). Altering exercise modality (CON vs. INT) did not affect postexercise VO2, RER, or fat oxidation (p > .05). These results demonstrate that postexercise energy expenditure and fat oxidation can be augmented by increasing exercise intensity, but these benefits cannot be exploited by undertaking interval exercise (1:2-min work:recovery ratio) when total energy expenditure, duration, and mean intensity remain unchanged. In spite of the apparent benefit of these strategies, the amount of fat oxidized after exercise may be inconsequential compared with that oxidized during the exercise bout.

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Benoit Capostagno and Andrew Bosch

This study examined the differences in fat and carbohydrate oxidation during running and cycling at the same relative exercise intensities, with intensity determined in a number of ways. Specifically, exercise intensity was expressed as a percentage of maximum workload (WLmax), maximum oxygen uptake (%VO2max), and maximum heart rate (%HRmax) and as rating of perceived exertion (RPE). Ten male triathletes performed maximal running and cycling trials and subsequently exercised at 60%, 65%, 70%, 75%, and 80% of their WLmax. VO2, HR, RPE, and plasma lactate concentrations were measured during all submaximal trials. Fat and carbohydrate oxidation were calculated from VO2 and VCO2 data. A 2-way ANOVA for repeated measures was used to determine any statistically significant differences between exercise modes. Fat oxidation was shown to be significantly higher in running than in cycling at the same relative intensities expressed as either %WLmax or %VO2max. Neither were there any significant differences in VO2max and HRmax between the 2 exercise modes, nor in submaximal VO2 or RPE between the exercise modes at the same %WLmax. However, heart rate and plasma lactate concentrations were significantly higher when cycling at 60% and 65% and 65–80%WLmax, respectively. In conclusion, fat oxidation is significantly higher during running than during cycling at the same relative intensity expressed as either %WLmax or %VO2max.

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Julia Zakrzewski and Keith Tolfrey

Consensus on the exercise protocol used to measure Fatmax (exercise intensity corresponding to maximum fat oxidation (MFO)) in children has not been reached. The present study compared Fatmax estimated using the 3 min incremental cycling protocol (3-INC) and a protocol consisting of several 10 min constant work rate exercise bouts (10-CWR) in 26 prepubertal children. Group Fatmax values were the same for 3-INC and 10-CWR (55% VO2peak) and 95% limits of agreement (LoA) were ± 7% VO2peak. Group MFO values were similar between protocols, although 95% LoA were -94 to 113 mg·min−1. While 3-INC provides a valid estimation of Fatmax compared with 10-CWR, caution should be exercised when estimating MFO in prepubertal children.

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Sara Dean, Andrea Braakhuis and Carl Paton

Researchers have long been investigating strategies that can increase athletes’ ability to oxidize fatty acids and spare carbohydrate, thus potentially improving endurance capacity. Green-tea extract (epigallocatechin-3-gallate; EGCG) has been shown to improve endurance capacity in mice. If a green-tea extract can stimulate fat oxidation and as a result spare glycogen stores, then athletes may benefit through improved endurance performance. Eight male cyclists completed a study incorporating a 3-way crossover, randomized, placebo-controlled, double-blinded, diet-controlled research design. All participants received 3 different treatments (placebo 270 mg, EGCG 270 mg, and placebo 270 mg + caffeine 3 mg/kg) over a 6-day period and 1 hr before exercise testing. Each participant completed 3 exercise trials consisting of 60 min of cycling at 60% maximum oxygen uptake (VO2max) immediately followed by a self-paced 40-km cycling time trial. The study found little benefit in consuming green-tea extract on fat oxidation or cycling performance, unlike caffeine, which did benefit cycling performance. The physiological responses observed during submaximal cycling after caffeine ingestion were similar to those reported previously, including an increase in heart rate (EGCG 147 ± 17, caffeine 146 ± 19, and placebo 144 ± 15 beats/min), glucose at the 40-min exercise time point (placebo 5.0 ± 0.8, EGCG 5.4 ± 1.0, and caffeine 5.8 ± 1.0 mmol/L), and resting plasma free fatty acids and no change in the amount of carbohydrate and fat being oxidized. Therefore, it was concluded that green-tea extract offers no additional benefit to cyclists over and above those achieved by using caffeine.

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Tanja Oosthuyse, Matthew Carstens and Aletta M.E. Millen

Certain commercial carbohydrate replacement products include slowly absorbed carbohydrates such as isomaltulose. Few studies have investigated the metabolic effects of ingesting isomaltulose during exercise and none have evaluated exercise performance and gastrointestinal comfort. Nine male cyclists participated postprandially during three trials of 2-h steady-state (S-S) exercise (60% W max) followed by a 16 km time trial (TT) while ingesting 63 g∙h-1 of either, 0.8:1 fructose: maltodextrin (F:M) or isomaltulose (ISO) or placebo-flavored water (PL). Data were analyzed by magnitude-based inferences. During S-S exercise, ISO and PL similarly increased plasma nonesterified fatty acid (NEFA) concentration (mean change ISO versus F:M: 0.18, 90%CI ± 0.21 mmol∙L-1, 88% likelihood) and fat oxidation (10, 90%CI ± 9 g, 89% likelihood) while decreasing carbohydrate oxidation (-36, 90%CI ± 30.2 g, 91% likelihood) compared with F:M, despite equal elevations in blood glucose concentration with ISO and F:M. Rating of stomach cramps and bloating increased progressively with ISO (rating: 0-90 min S-S, weak; 120 min S-S, moderate; TT, strong) compared with F:M and PL (0-120 min S-S and TT, very weak). TT performance was substantially slower with ISO (mean change: 1.5, 90%CI ± 1.4 min, 94% likely harmful) compared with F:M. The metabolic response of ISO ingestion during moderate exercise to increase NEFA availability and fat oxidation despite elevating blood glucose concentration is anomalous for a carbohydrate supplement. However, ingesting isomaltulose at a continuous high frequency to meet the recommended carbohydrate replacement dose, results in severe gastrointestinal symptoms during prolonged or high intensity exercise and negatively affects exercise performance compared with fructose-maltodextrin supplementation.

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Ricardo J.S. Costa, Beat Knechtle, Mark Tarnopolsky and Martin D. Hoffman

evidence from sport nutrition professionals suggests a growing number of elite and amateur ultramarathon runners are purposely attempting, with or without professional guidance, adherence to low-carbohydrate high-fat (LCHF) or ketogenic diets, aiming to enhance maximal and relative fat oxidation capacity

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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.