Article

Quantifying Differences in the “Fat Burning” Zone and the Aerobic Zone: Implications For Training

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Abstract

The primary objective of this study was to examine the relationship of the "fat burning" and aerobic zones. Subjects consisted of 36 relatively fit runners (20 male, 16 female) who completed a maximal exercise test to exhaustion on a motor-driven treadmill. The lower and upper limit of the "fat burning" zone was visually assessed by examining each individual graph. Maximal fat oxidation (MFO) was determined to be that point during the test at which fat metabolism in fat calories per minute peaked. The lower limit of the aerobic zone was assessed as 50% of heart rate reserve, whereas the upper limit was set at anaerobic threshold. Although the lower and upper limits of the "fat burning" zone (67.6-87.1% maximal heart rate) were significantly lower (p < 0.05) than their counterparts in the aerobic zone (58.9-76.2%), the considerable overlap of the 2 zones would indicate that training for fat oxidation and training for aerobic fitness are not mutually exclusive and may be accomplished with the same training program. Furthermore, it was determined that this training program could simultaneously meet the requirements of the American College of Sports Medicine for both aerobic fitness and weight control. Maximal fat oxidation occurred at 54.2% maximal oxygen uptake (VO2max). However, the great variability in response between individuals would preclude the prediction of both the "fat burning" zone and MFO, indicating a need for measurement in the laboratory. If laboratory testing is not possible, the practitioner or subject can be reasonably confident MFO lies between 60.2% and 80.0% of the maximal heart rate.

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... Burns et al. (2007) reported that the suppression of appetite during severe exercise was not related to the suppression of total ghrelin. There is some evidence that exercise at higher intensities for longer durations can suppresses acylated ghrelin and appetite 2009). ...
... Currently, little is known about the influence of exercise on acylated ghrelin and acylated ghrelin's relationship with appetite and food intake after exercise. The limited number of studies are in contrast with each other and new studies are certainly needed in this field ( Broom et al., 2007;2009;Kim et al., 2008;King et al., 2010a;2010b;Mackelvie et al., 2007;Marzullo et al., 2008;Unick et al., 2010). ...
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... 2,6,11 previous studies aiming to determine treadmill based correlation, yielded no results, making the existence of a mentioned correlation still not documented. 10,13,14 These studies methodology consisted of using a graded exercise test (GXT) protocol with long stage durations and high inclines while correlating faT max to the lactate threshold (lT). ...
... carey examined the relationship between the "fat burning" and aerobic zones in male athletes using a modified Bruce protocol. 13 he demonstrated how optimal fat burning does occur in the "aerobic zone", yet no correlation was found due to the genetic variability. ...
... carey reported faT max at 55.40% of Vo 2max in female athletes and at 53.20% of Vo 2max in male athletes using a modified Bruce treadmill protocol. 13 Knechtle et al. reported faT max at 55% of Vo 2max in male athletes using a 30 min constant speed treadmill test. 12 achten et al. determined faT max to occur at 62.50% and 65% of Vo 2max in male cyclists using a GXT protocol with 5-and 3-min exercise stages, respectively. ...
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... The latter two misconceptions stem from a poor application of the fatmax and fatmin intensities of exercise presented in the exercise science literature with an additional concern being the mistaken belief that dietary supplements cause greater fat loss (Booth et al. 2000, Carey 2009, Clark 2012, 2019, Croci et al. 2014, Inchiosa 2011). Yet, there are many aspects of lipid metabolism that have nothing to do with these notions. ...
... Given the use of lipids during periods of low carbohydrate concentrations or when ATP demands allow for the preferential use of lipids, one can generate the right conditions to accentuate fat utilization (Carey 2009, Clark 2012, Carta et al 2017, Croci et al. 2014, Kremmyda et al 2011, Peric et al. 2016). This is a common treatment to induce loss of fat mass in those who are overfat and leads to a very interesting question: Where does fat go during weight loss? ...
... These videos are highly accessible and popular and purport to provide "a years' worth of results in 60 days" for those looking to lose weight. 23 contrarily, low intensity workouts, such as walking, have been shown to improve cardiorespiratory endurance 24 and fat burning, 25 which may be another fitness choice used by individuals looking to lose weight. ...
... This intensity was chosen because it is the minimum intensity for eliciting an aerobic training response. 25 prior to all hi and li exercise sessions, participants were given a 100 mm Visual analog Scale (VaS) to assess perceived pain anchored at 0 mm for 'No pain' or 100 mm indicating 'unbearably painful'. ...
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... Seven studies were identified that compared males (N = 439) and females (N = 390) in terms of absolute MFO (g.min −1 ) and/or Fat max (%VO 2max ) (Bircher et al., 2005;Venables et al., 2005;Bogdanis et al., 2008;Carey, 2009;Chenevière et al., 2011;Bagley et al., 2016;Fletcher et al., 2017). In order to quantitatively elucidate sex-mediated effects on these variables, sample sizeweighted means and standard deviations (SD) for males and females were calculated. ...
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The present study investigated the effect of exercise training at different intensities on fat oxidation in obese men. Twenty-four healthy male obese subjects were randomly divided in either a low- [40% maximal oxygen consumption (VO(2 max))] or high-intensity exercise training program (70% VO(2 max)) for 12 wk, or a non-exercising control group. Before and after the intervention, measurements of fat metabolism at rest and during exercise were performed by using indirect calorimetry, [U-(13)C]palmitate, and [1,2-(13)C]acetate. Furthermore, body composition and maximal aerobic capacity were measured. Total fat oxidation did not change at rest in any group. During exercise, after low-intensity exercise training, fat oxidation was increased by 40% (P < 0.05) because of an increased non-plasma fatty acid oxidation (P < 0.05). High-intensity exercise training did not affect total fat oxidation during exercise. Changes in fat oxidation were not significantly different among groups. It was concluded that low-intensity exercise training in obese subjects seemed to increase fat oxidation during exercise but not at rest. No effect of high-intensity exercise training on fat oxidation could be shown.
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Fat oxidation increases from low to moderate exercise intensities and decreases from moderate to high exercise intensities. Recently, a protocol has been developed to determine the exercise intensity, which elicits maximal fat oxidation rates (Fat(max)). The main aim of the present study was to establish the reliability of the estimation of Fat(max) using this protocol (n = 10). An additional aim was to determine Fat(max) in a large group of endurance-trained individuals (n = 55). For the assessment of reliability, subjects performed three graded exercise tests to exhaustion on a cycle ergometer. Tests were performed after an overnight fast and diet and exercise regime on the day before all tests were similar. Fifty-five male subjects performed the graded exercise test on one occasion. The typical error (root mean square error and CV) for Fat(max) and Fat(min) was 0.23 and 0.33 l O(2) x min(-1) and 9.6 and 9.4 % respectively. Maximal fat oxidation rates of 0.52 +/- 0.15 g x min(-1) were reached at 62.5 +/- 9.8 % VO(2)max, while Fat(min) was located at 86.1 +/- 6.8 % VO(2)max. When the subjects were divided in two groups according to their VO(2)max, the large spread in Fat(max) and maximal fat oxidation rates remained present. The CV of the estimation of Fat(max) and Fa(min) is 9.0 - 9.5 %. In the present study the average intensity of maximal fat oxidation was located at 63 % VO(2)max. Even within a homogeneous group of subjects, there was a relatively large inter-individual variation in Fat(max) and the rate of maximal fat oxidation.
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The aim of the present study was to establish fat oxidation rates over a range of exercise intensities in a large group of healthy men and women. It was hypothesised that exercise intensity is of primary importance to the regulation of fat oxidation and that gender, body composition, physical activity level, and training status are secondary and can explain part of the observed interindividual variation. For this purpose, 300 healthy men and women (157 men and 143 women) performed an incremental exercise test to exhaustion on a treadmill [adapted from a previous protocol (Achten J, Venables MC, and Jeukendrup AE. Metabolism 52: 747-752, 2003)]. Substrate oxidation was determined using indirect calorimetry. For each individual, maximal fat oxidation (MFO) and the intensity at which MFO occurred (Fat(max)) were determined. On average, MFO was 7.8 +/- 0.13 mg.kg fat-free mass (FFM)(-1).min(-1) and occurred at 48.3 +/- 0.9% maximal oxygen uptake (Vo(2 max)), equivalent to 61.5 +/- 0.6% maximal heart rate. MFO (7.4 +/- 0.2 vs. 8.3 +/- 0.2 mg.kg.FFM(-1).min(-1); P < 0.01) and Fat(max) (45 +/- 1 vs. 52 +/- 1% Vo(2 max); P < 0.01) were significantly lower in men compared with women. When corrected for FFM, MFO was predicted by physical activity (self-reported physical activity level), Vo(2 max), and gender (R(2) = 0.12) but not with fat mass. Men compared with women had lower rates of fat oxidation and an earlier shift to using carbohydrate as the dominant fuel. Physical activity, Vo(2 max), and gender explained only 12% of the interindividual variation in MFO during exercise, whereas body fatness was not a predictor. The interindividual variation in fat oxidation remains largely unexplained.
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The prevalence of overweight in children and adolescents and obesity in adults in the United States has increased over several decades. To provide current estimates of the prevalence and trends of overweight in children and adolescents and obesity in adults. Analysis of height and weight measurements from 3958 children and adolescents aged 2 to 19 years and 4431 adults aged 20 years or older obtained in 2003-2004 as part of the National Health and Nutrition Examination Survey (NHANES), a nationally representative sample of the US population. Data from the NHANES obtained in 1999-2000 and in 2001-2002 were compared with data from 2003-2004. Estimates of the prevalence of overweight in children and adolescents and obesity in adults. Overweight among children and adolescents was defined as at or above the 95th percentile of the sex-specific body mass index (BMI) for age growth charts. Obesity among adults was defined as a BMI of 30 or higher; extreme obesity was defined as a BMI of 40 or higher. In 2003-2004, 17.1% of US children and adolescents were overweight and 32.2% of adults were obese. Tests for trend were significant for male and female children and adolescents, indicating an increase in the prevalence of overweight in female children and adolescents from 13.8% in 1999-2000 to 16.0% in 2003-2004 and an increase in the prevalence of overweight in male children and adolescents from 14.0% to 18.2%. Among men, the prevalence of obesity increased significantly between 1999-2000 (27.5%) and 2003-2004 (31.1%). Among women, no significant increase in obesity was observed between 1999-2000 (33.4%) and 2003-2004 (33.2%). The prevalence of extreme obesity (body mass index > or =40) in 2003-2004 was 2.8% in men and 6.9% in women. In 2003-2004, significant differences in obesity prevalence remained by race/ethnicity and by age. Approximately 30% of non-Hispanic white adults were obese as were 45.0% of non-Hispanic black adults and 36.8% of Mexican Americans. Among adults aged 20 to 39 years, 28.5% were obese while 36.8% of adults aged 40 to 59 years and 31.0% of those aged 60 years or older were obese in 2003-2004. The prevalence of overweight among children and adolescents and obesity among men increased significantly during the 6-year period from 1999 to 2004; among women, no overall increases in the prevalence of obesity were observed. These estimates were based on a 6-year period and suggest that the increases in body weight are continuing in men and in children and adolescents while they may be leveling off in women.
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To evaluate the contribution of working muscle to whole body lipid oxidation, we examined the effects of exercise intensity and endurance training (9 wk, 5 days/wk, 1 h, 75% Vo(2 peak)) on whole body and leg free fatty acid (FFA) kinetics in eight male subjects (26 +/- 1 yr, means +/- SE). Two pretraining trials [45 and 65% Vo(2 max) (45UT, 65UT)] and two posttraining trials [65% of pretraining Vo(2 peak) (ABT), and 65% of posttraining Vo(2 peak) (RLT)] were performed using [1-(13)C]palmitate infusion and femoral arteriovenous sampling. Training increased Vo(2 peak) by 15% (45.2 +/- 1.2 to 52.0 +/- 1.8 ml.kg(-1).min(-1), P < 0.05). Muscle FFA fractional extraction was lower during exercise (EX) compared with rest regardless of workload or training status ( approximately 20 vs. 48%, P < 0.05). Two-leg net FFA balance increased from net release at rest ( approximately -36 micromol/min) to net uptake during EX for 45UT (179 +/- 75), ABT (236 +/- 63), and RLT (136 +/- 110) (P < 0.05), but not 65UT (51 +/- 127). Leg FFA tracer measured uptake was higher during EX than rest for all trials and greater during posttraining in RLT (716 +/- 173 micromol/min) compared with pretraining (45UT 450 +/- 80, 65UT 461 +/- 72, P < 0.05). Leg muscle lipid oxidation increased with training in ABT (730 +/- 163 micromol/min) vs. 65UT (187 +/- 94, P < 0.05). Leg muscle lipid oxidation represented approximately 62 and 30% of whole body lipid oxidation at lower and higher relative intensities, respectively. In summary, training can increase working muscle tracer measured FFA uptake and lipid oxidation for a given power output, but both before and after training the association between whole body and leg lipid metabolism is reduced as exercise intensity increases.
Article
The purpose of this study was to determine the difference in the relative intensity for peak fat oxidation for cycle ergometer and treadmill exercise. Twenty subjects (8 men and 12 women; age, 26.26 ± 10.36 years; height, 171.18 ± 8.22 cm; mass, 77.25 ± 16.06 kg; percentage of body fat, 22.48 ± 9.04) completed a maximal graded exercise test on a treadmill (V̇O2 peak = 41.36 ± 14.49 ml·kg-1·min-1 as well as a cycle ergometer (V̇O2 peak = 36.45 ± 13.59 49 ml·kg-1·min-1). Subjects also completed submaximal exercise protocols on the cycle (3-minute stage, 30 W increments) and the treadmill (3-minute stage, 0.5 m·h-1 increments). Recordings of V̇O2, respiratory exchange ratio (RER), ratings of perceived exertion, and heart rate were recorded and averaged over the last 30 seconds of each stage. Calculations of total caloric expenditure and fat oxidation were made using the Lusk table. Peak fat oxidation was identified as the stage with the greatest number of fat kilocalories expended (reliability = .60). Relative V̇O2 at the intensity for peak fat oxidation was compared between exercise modes using dependent means t-tests. Significance was set at p < 0.05. Results showed no differences in the relative intensities for peak fat oxidation for treadmill exercise (40.72 ± 14.07% V̇O2 peak) versus cycle exercise (40.94 ± 9.60% V̇O2 peak). RER was significantly higher with the cycle (0.87 ± 0.04) than with the treadmill (0.85 ± 0.04); however, this did not result in any difference in total calories (treadmill = 6.52 ± 3.70, cycle = 5.64 ± 2.15, p = 0.36) or fat calories (treadmill = 3.23 ± 1.54, cycle 2.36 ± 1.31, p = 0.06) expended at peak fat oxidation. The absolute V̇O2 at peak fat utilization was 11% higher with treadmill exercise, but this mirrored differences in V̇O2 peak. We conclude that for both treadmill and cycle exercise, maximal fat calorie expenditure will occur around 40% of V̇O2 peak without significant differences in fat calorie expenditure.
Article
The first aim of this study was to determine the exercise intensity that elicited the highest rate of fat oxidation in sedentary, obese subjects (OB; n=10 men, n=10 women) compared with endurance athletes (AT; n=10 men, n=10 women). The second aim was to investigate the relationship between VO2 at the intensity eliciting the highest rate of fat oxidation and the corresponding VO2 at the lactate threshold. Peak oxygen consumption (VO2peak) was determined in 20 AT and 20 OB using an incremental exercise protocol on a cycle ergometer. Based on their VO2peak values, subjects completed a protocol requiring them to exercise for 20 min at three different workloads (55, 65 and 75% VO2peak), randomly assigned on two separate occasions. The oxidation rates of fat and carbohydrate were measured by indirect calorimetry. The highest rates of fat oxidation were at 75 % VO2peak (AT), and at 65 % VO2peak (OB). The rate of fat oxidation was significantly higher in AT (18.2 ± 6.1) compared with OB women (10.6 ± 4.5 kJ min-1·kg-1) (p < 0.01). There was no significant difference in the rate of fat oxidation for the men (AT 19.7 ± 8.1 vs. OB 17.6 ± 8.2 kJ min-1·kg-1). AT reached LT at a significantly (p < 0.01) higher exercise intensity expressed in VO2peak than obese subjects (AT women 76.4 ± 0.1, men 77.3 ± 0.1 vs. OB women, 49.7 ± 0.1, men 49.5 ± 0.1% VO2peak). A significant correlation was found between VO2 at LT and VO2 (L·min-1) eliciting the maximal rate of fat oxidation in athletes (women; r = 0.67; p = 0.03; men: r = 0.75; p = 0.01) but not in the obese. In summary, we observed higher rates of fat oxidation at higher relative work rates in AT compared with OB. A significant correlation was found between LT and the exercise intensity eliciting a high rate of fat oxidation in AT (r=0.89; p < 0.01) but not in OB. Cardiorespiratory fitness, defined as VO2peak, seems to be important in defining the relationship between a high rate of fat oxidation and LT
Article
The aim of this study was to develop a test protocol to determine the exercise intensity at which fat oxidation rate is maximal (Fat(max)). Eighteen moderately trained cyclists performed a graded exercise test to exhaustion, with 5-min stages and 35-W increments (GE(35/5)). In addition, four to six continuous prolonged exercise tests (CE) at constant work rates, corresponding to the work rates of the GE test, were performed on separate days. The duration of each test was chosen so that all trials would result in an equal energy expenditure. Seven other subjects performed three different GE tests to exhaustion. The test protocols differed in stage duration and in increment size. Fat oxidation was measured using indirect calorimetry. No significant differences were found in Fat(max) determined with the GE(35/5), the average fat oxidation of the CE tests, or fat oxidation measured during the first 5 min of the CE tests (56 +/- 3, 64 +/- 3, 58 +/- 3%VO(2max), respectively). Results of the GE(35/5) protocol were used to construct an exercise intensity versus fat oxidation curve for each individual. Fat(max) was equivalent to 64 +/- 4%VO(2max) and 74 +/- 3%HR(max). The Fat(max) zone (range of intensities with fat oxidation rates within 10% of the peak rate) was located between 55 +/- 3 and 72 +/- 4%VO(2max). The contribution of fat oxidation to energy expenditure became negligible above 89 +/- 3%VO(2max) (92 +/- 1%HR(max)). When stage duration was reduced from 5 to 3 min or when increment size was reduced from 35 to 20 W, no significant differences were found in Fat(max), Fat(min), or the Fat(max) zone. It is concluded that a protocol with 3-min stages and 35-W increments in work rate can be used to determine Fat(max). Fat oxidation rates are high over a large range of intensities; however, at exercise intensities above Fat(max), fat oxidation rates drop markedly.
Article
Skeletal muscle insulin resistance entails dysregulation of both glucose and fatty acid metabolism. This study examined whether a combined intervention of physical activity and weight loss influences fasting rates of fat oxidation and insulin-stimulated glucose disposal. Obese (BMI >30 kg/m(2)) volunteers (9 men and 16 women) without diabetes, aged 39 +/- 4 years, completed 16 weeks of moderate-intensity physical activity combined with caloric reduction. Body composition was determined by dual-energy X-ray absorptiometry and computed tomography. Glucose disposal rates (R(d)) were measured during euglycemic hyperinsulinemia (40 mU x m(-2) x min(-1)), and substrate oxidation was determined via indirect calorimetry. Fat mass and regional fat depots were reduced and VO(2max) improved by 19%, from 38.8 +/- 1.2 to 46.0 +/- 1.0 ml x kg fat-free mass (FFM)(-1) x min(-1) (P < 0.05). Insulin sensitivity improved 49 +/- 10% (6.70 +/- 0.40 to 9.51 +/- 0.51 mg x min(-1) x kg FFM(-1); P < 0.05). Rates of fat oxidation following an overnight fast increased (1.16 +/- 0.06 to 1.36 +/- 0.05 mg x min(-1) x kg FFM(-1); P < 0.05), and the proportion of energy derived from fat increased from 38 to 52%. The strongest predictor of the improved insulin sensitivity was enhanced fasting rates of fat oxidation, accounting for 52% of the variance. In conclusion, exercise combined with weight loss enhances postabsorptive fat oxidation, which appears to be a key aspect of the improvement in insulin sensitivity in obesity.
Article
The aim of the present study was to examine the effect of ingesting 75 g of glucose 45 min before the start of a graded exercise test to exhaustion on the determination of the intensity that elicits maximal fat oxidation (Fatmax). Eleven moderately trained individuals (VO2max: 58.9 +/- 1.0 ml x kg(-1) x min(-1); mean +/- sx), who had fasted overnight, performed two graded exercise tests to exhaustion, one 45 min after ingesting a placebo drink and one 45 min after ingesting 75 g of carbohydrate in the form of glucose. The tests started at 95 W and the workload was increased by 35 W every 3 min. Gas exchange measures and heart rate were recorded throughout exercise. Fat oxidation rates were calculated using stoichiometric equations. Blood samples were collected at rest and at the end of each stage of the test. Maximal fat oxidation rates decreased from 0.46 +/- 0.06 to 0.33 +/- 0.06 g min(-1) when carbohydrate was ingested before the start of exercise (P < 0.01). There was also a decrease in the intensity which elicited maximal fat oxidation (60.1 +/- 1.9% vs 52.0+3.4% VO2max) after carbohydrate ingestion (P < 0.05). Maximal power output was higher in the carbohydrate than in the placebo trial (346 +/- 12 vs 332 +/- 12 W) (P < 0.05). In conclusion, the ingestion of 75 g of carbohydrate 45 min before the onset of exercise decreased Fatmax by 14%, while the maximal rate of fat oxidation decreased by 28%.
Article
Increasing exercise intensities will induce an increase in glycolytic flux. High glycolytic activity is associated with reduced fat oxidation rates and increased accumulation of lactate. Both lactate and hydrogen ions have been shown to be directly related to the decreased fat oxidation rates. The aim of the present study was to determine whether the exercise intensity at which maximal fat oxidation rates occur coincides with the intensity at which lactate starts to accumulate in plasma. Thirty-three moderately trained endurance athletes performed a graded exercise test to exhaustion on a cycle-ergometer with 35 W increments every three minutes. Expired gas analysis was performed throughout the test and stoichiometric equations were used to calculate fat oxidation rates. The intensity which elicited maximal fat oxidation (Fat (max)) and the intensity at which fat oxidation rates became negligible (Fat (min)) were determined. Blood samples for lactate analysis were collected at the end of each stage of the graded exercise test. The intensity at which lactate concentration increased above baseline (LIAB) and the lactate threshold (LT-D) were determined (D-max method). Fat (max) was located at 63 +/- 9 % V.O (2)max and LIAB at 61 +/- 5 % V.O (2)max and there appeared to be no statistical difference between the two intensities. Fat (max) and LIAB were significantly correlated. Fat (min) and LT-D were also significantly correlated but were located at different intensities (82 +/- 7 and 87 +/- 9 % V.O (2)max respectively). The data of the present study showed that accumulation of lactate in plasma is strongly correlated to the reduction seen in fatty acid oxidation with increasing exercise intensities. The first rise of lactate concentration occurred at the same intensity as the intensity which elicited maximal fat oxidation rates.
Article
Measures of substrate oxidation have traditionally been calculated from indirect calorimetry measurements using stoichiometric equations. Although this has proven to be a solid technique and it has become one of the standard techniques to measure whole body substrate metabolism, there are also several limitations that have to be considered. When indirect calorimetry is used during exercise most of the assumptions on which the method is based hold true although changes in the size of the bicarbonate pool at higher exercise intensities may invalidate the calculations of carbohydrate and fat oxidation. Most of the existing equations are based on stoichiometric equations of glucose oxidation and the oxidation of a triacylglycerol that is representative of human adipose tissue. However, in many exercise conditions, glycogen and not glucose is the predominant carbohydrate substrate. Therefore we propose slightly modified equations for the calculation of carbohydrate and fat oxidation for use during low to high intensity exercise. Studies that investigated fat oxidation over a wide range of intensities and that determined the exercise intensity at which fat oxidation is maximal have provided useful insights in the variation in fat oxidation between individuals and in the factors that affect fat oxidation. Fat oxidation during exercise can be influenced by exercise intensity and duration, diet, exercise training, exercise mode and gender. Although a number of important factors regulating fat oxidation have been identified, it is apparent that a considerable degree of inter-subject variability in substrate utilization persists and cannot be explained by the aforementioned factors. Future research should investigate the causes of the large inter-individual differences in fat metabolism between individuals and their links with various disease states.
Article
During whole-body exercise, peak fat oxidation occurs at a moderate intensity. This study investigated whole-body peak fat oxidation in untrained and trained subjects, and the presence of a relation between skeletal muscle oxidative enzyme activity and whole-body peak fat oxidation. Healthy male subjects were recruited and categorized into an untrained (N=8, VO2max 3.5±0.1 L/min) and a trained (N=8, VO2max 4.6±0.2 L/min) group. Subjects performed a graded exercise test commencing at 60 W for 8 min followed by 35 W increments every 3 min. On a separate day, muscle biopsies were obtained from vastus lateralis and a 3 h bicycle exercise test was performed at 58% of VO2max. Whole-body fat oxidation was calculated during prolonged and graded exercise from the respiratory exchange ratio using standard indirect calorimetry equations. Based on the graded exercise test, whole-body peak fat oxidation was determined. The body composition was determined by DEXA. Whole-body peak fat oxidation (250±25 and 462±33 mg/min) was higher (P<0.05) and occurred at a higher (P<0.05) relative workload (43.5±1.8% and 49.9±1.2% VO2max) in trained compared with untrained subjects, respectively. Muscle citrate synthase activity and β-hydroxy-acyl-CoA-dehydrogenase activity were higher (49% and 35%, respectively, P<0.05) in trained compared with untrained subjects. Both lean body mass and maximal oxygen uptake were significantly correlated to whole-body peak fat oxidation (r2=0.57, P<0.001), but leg muscle oxidative capacity was not correlated to whole-body peak fat oxidation. In conclusion, whole-body peak fat oxidation occurred at a higher relative exercise load in trained compared with untrained subjects. Whole-body peak fat oxidation was not significantly related to leg muscle oxidative capacity, but was related to lean body mass and maximal oxygen uptake. This may suggest that leg muscle oxidative activity is not the main determinant of whole-body peak fat oxidation.
Article
The aim of the present study was to examine the differences in fat oxidation between endurance trained (ET) and untrained (UT) women. Eight ET and nine UT women performed a progressive cycle ergometer test until exhaustion. The rate of fat oxidation was similar at low work rates (<or=90 W) but was 80-200% higher in ET subjects at 120-180 W. When related to relative exercise intensity, the fat oxidation was similar in the low-intensity domain (<or=40% VO2max), but higher in the ET subjects both at moderate intensities (45-60% VO2max; +22% vs. UT) and at high intensities (65-80% VO2max; +35% vs. UT). There was no difference in the maximal fat oxidation rates between the trained and untrained women. The relative exercise intensity that elicited the highest rate of fat oxidation (Fatmax) was 56+/-3% and 53+/-2% VO2max in ET and UT women, respectively (NS). In biopsies from m. vastus lateralis, the activity of the enzymes citrate synthase, beta-hydroxy acyl CoA dehydrogenase (HAD), and hormone sensitive lipase was higher in the ET subjects. The HAD activity correlated significantly with fat oxidation at moderate and high intensities. We conclude that the ET women had a higher fat oxidation at moderate- and high-exercise intensities both at same relative and at absolute intensity compared with the UT women. The HAD activity and fat oxidation rates were highly correlated indicating that training-induced adaptation in muscle fat oxidative capacity is an important factor for enhanced fat oxidation. Interestingly, maximal fat oxidation occurred at the same exercise intensity.
Determining the precision of the Medgraphics VO2000 when measuring_VO2,_VCO2, and VE
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Bayard, A and Dengel, D. Determining the precision of the Medgraphics VO2000 when measuring_VO2,_VCO2, and VE. Med Sci Sports Exerc 30: 122–124, 1998
General principles of exercise prescription In: ACSM's Guidelines for Exercise Testing and Prescription
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American College of Sports Medicine. General principles of exercise prescription. In: ACSM's Guidelines for Exercise Testing and Prescription. Philadelphia, PA: Lippincott Williams and Wilkins, 2006. pp. 133–148.
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Ogden, C, Carroll, M, Curtin, L, McDowell, M, Tabak, C, and Flegal, K. Prevalence of overweight and obesity in the United States, 1999-2004. JAMA 295: 1549–1555, 2006.