ArticleLiterature Review

Measurement of Substrate Oxidation During Exercise by Means of Gas Exchange Measurements

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Abstract

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.

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... Carbohydrate utilization is estimated using indirect calorimetry, but this method is not valid during high-intensity intermittent exercise because of shifting acid-base balance and excess (non-oxidative) CO 2 excretion through hyperpnea [4]. Changes in muscle glycogen are often used to estimate carbohydrate utilization, but this requires an invasive muscle biopsy with medical supervision and does not provide information on whole-body carbohydrate use. ...
... by the workload in the last completed stage plus the workload relative to the time spent in the last incomplete stage [power of completed stage + (30 × (seconds at uncompleted stage/60)], and V O 2max and peak fat oxidation were recorded as the highest 15-s value from a moving average, calculated using the equation of Jeukendrup and Wallis [4] and a 1-s interpolation of breath-by-breath data. ...
... This is because the energy yield from carbohydrate varies depending on the source, with a range from 3.719 kcal/g of glucose to 4.187 kcal/g of glycogen [29]. The equations of Jeukendrup and Wallis [4] vary based on exercise intensity, assuming 50% of the carbohydrate oxidation is derived from plasma glucose and 50% from muscle glycogen during low-intensity exercise (40-50% V O 2max ), and 20% from glucose and 80% from muscle glycogen at moderate-to-high intensity exercise (50-75% V O 2max ). This results in carbohydrate oxidation yielding 3.95 kcal/g of carbohydrate during low-intensity exercise, and 4.07 kcal/g of carbohydrate during moderateto-high intensity exercise [4]. ...
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Background Sports nutrition guidelines recommend carbohydrate (CHO) intake be individualized to the athlete and modulated according to changes in training load. However, there are limited methods to assess CHO utilization during training sessions. Objectives We aimed to (1) quantify bivariate relationships between both CHO and overall energy expenditure (EE) during exercise and commonly used, non-invasive measures of training load across sessions of varying duration and intensity and (2) build and evaluate prediction models to estimate CHO utilization and EE with the same training load measures and easily quantified individual factors. Methods This study was undertaken in two parts: a primary study, where participants performed four different laboratory-based cycle training sessions, and a validation study where different participants performed a single laboratory-based training session using one of three exercise modalities (cycling, running, or kayaking). The primary study included 15 cyclists (five female; maximal oxygen consumption [V˙V˙\dot{V}O2max], 51.9 ± 7.2 mL/kg/min), the validation study included 21 cyclists (seven female; V˙V˙\dot{V}O2max 53.5 ± 11.0 mL/kg/min), 20 runners (six female; V˙V˙\dot{V}O2max 57.5 ± 7.2 mL/kg/min), and 18 kayakers (five female; V˙V˙\dot{V}O2max 45.6 ± 4.8 mL/kg/min). Training sessions were quantified using six training load metrics: two using heart rate, three using power, and one using perceived exertion. Carbohydrate use and EE were determined separately for aerobic (gas exchange) and anaerobic (net lactate accumulation, body mass, and O2 lactate equivalent method) energy systems and summed. Repeated-measures correlations were used to examine relationships between training load and both CHO utilization and EE. General estimating equations were used to model CHO utilization and EE, using training load alongside measures of fitness and sex. Models were built in the primary study and tested in the validation study. Model performance is reported as the coefficient of determination (R²) and mean absolute error, with measures of calibration used for model evaluation and for sport-specific model re-calibration. Results Very-large to near-perfect within-subject correlations (r = 0.76–0.96) were evident between all training load metrics and both CHO utilization and EE. In the primary study, all models explained a large amount of variance (R² = 0.77–0.96) and displayed good accuracy (mean absolute error; CHO = 16–21 g [10–14%], EE = 53–82 kcal [7–11%]). In the validation study, the mean absolute error ranged from 16–50 g [15–45%] for CHO models to 53–182 kcal [9–31%] for EE models. The calibrated mean absolute error ranged from 9–20 g [8–18%] for CHO models to 36–72 kcal [6–12%] for EE models. Conclusions At the individual level, there are strong linear relationships between all measures of training load and both CHO utilization and EE during cycling. When combined with other measures of fitness, EE and CHO utilization during cycling can be estimated accurately. These models can be applied in running and kayaking when used with a calibration adjustment.
... Carbohydrate utilization is estimated using indirect calorimetry, but this method is not valid during high-intensity intermittent exercise due to shifting acid-base balance and excess (nonoxidative) CO2 excretion through hyperpnea [4]. Changes in muscle glycogen are often used to estimate carbohydrate utilization, but this requires an invasive muscle biopsy with medical supervision and does not provide information on whole-body carbohydrate use. ...
... This is because the energy yield from carbohydrate varies depending on the source, ranging from 3.719 kcal per gram of glucose to 4.187 kcal per gram of glycogen [29]. The equations of Jeukendrup and Wallis [4] vary based on exercise intensity, assuming 50% of the carbohydrate oxidation is derived from plasma glucose and 50% from muscle glycogen during low intensity exercise (40-50% Vd O2max), and 20% from glucose and 80% from muscle glycogen at moderate to high intensity exercise (50-75% Vd O2max). This results in carbohydrate oxidation yielding 3.95 kcal per gram of carbohydrate during low intensity exercise, and 4.07 kcal per gram of carbohydrate during moderate to high intensity exercise [4]. ...
... The equations of Jeukendrup and Wallis [4] vary based on exercise intensity, assuming 50% of the carbohydrate oxidation is derived from plasma glucose and 50% from muscle glycogen during low intensity exercise (40-50% Vd O2max), and 20% from glucose and 80% from muscle glycogen at moderate to high intensity exercise (50-75% Vd O2max). This results in carbohydrate oxidation yielding 3.95 kcal per gram of carbohydrate during low intensity exercise, and 4.07 kcal per gram of carbohydrate during moderate to high intensity exercise [4]. It has also been recommended that resting analyses should assume 100% glucose oxidation [4]. ...
... Our MFO values ranging from 0.13 -0.16 g/min are substantially lower than those reported from other exercise modalities including cycling (1) and treadmill running (27), which is attributed to the small muscle mass inherent with ACE. They are also lower than values (~0.20 g/min) shown in trained men with SCI completing progressive ACE (19). Nevertheless, they are markedly higher than values (0.06 g/min) reported for able-bodied adults (18), despite these individuals having higher VO2peak (27 mL/kg/min) than our sample. ...
... Yet in this study, exercise was completed after a 3 -4 h fast, which should elicit lower estimates of FOx compared to an overnight fast (22). Moreover, different stoichiometric equations were used (19), which may elicit different estimates of FOx and CHOOx across studies. ...
... However, this approach may lead to a substantially longer exercise bout which may be unpleasant for nonathletic adults. Second, we used the Frayn equations (11) to estimate substrate metabolism, so our data do not apply to studies in which alternate equations are used (19). Third, due to known differences in substrate metabolism between trained and untrained muscle (14), our results acquired in individuals unfamiliar with ACE do not apply to individuals who regularly complete ACE and/or endurance training of the upper-body, as performed by swimmers, boxers, etc. Fourth, the sample was small and heterogeneous in sex, body mass, and VO2peak, which may alter interpretation of our results. ...
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Arm cycling ergometry (ACE) leads to a lower maximal oxygen uptake (VO2max) than cycling which is related to a smaller active muscle mass. This study compared estimates of fat and carbohydrate oxidation (FOx and CHOOx) between progressive exercise protocols varying in stage duration in an attempt to create a standard exercise protocol for determining substrate metabolism using ACE. Four men and seven women (age = 24 ± 9 yr) unfamiliar with ACE completed incremental exercise to determine peak power output and VO2peak. During two subsequent sessions completed after an overnight fast, they completed progressive ACE using 3- or 5-min stages during which FOx, CHOOx, and blood lactate concentration (BLa) were measured. Results showed no difference (p > 0.05) in FOx, CHOOx, or BLa across stage duration, and there was no difference in maximal fat oxidation (0.16 ± 0.08 vs. 0.13 ± 0.07 g/min, p = 0.07). However, respiratory exchange ratio in response to the 3 min stage duration was significantly lower than the 5 min duration (0.83 ± 0.05 vs. 0.86 ± 0.03, p = 0.04, Cohen’s d = 0.76). Results suggest that a 3-min stage duration is preferred to assess substrate metabolism during upper-body exercise in healthy adults.
... As described above, cardiopulmonary data were measured continuously during the performance trial to determine HR, V̇O 2 , V̇CO 2 , respiratory exchange rate (RER), minute ventilation (V̇E), respiratory frequency (f R ), and tidal volume (V T ). Absolute rates of carbohydrate and fat oxidation were calculated using previously published equations [39]. Total energy expenditure was calculated by multiplying the absolute rates of substrate oxidation by the energy density of each substrate (4.07 kcal/g carbohydrate, 9.75 kcal/g lipid) [39]. ...
... Absolute rates of carbohydrate and fat oxidation were calculated using previously published equations [39]. Total energy expenditure was calculated by multiplying the absolute rates of substrate oxidation by the energy density of each substrate (4.07 kcal/g carbohydrate, 9.75 kcal/g lipid) [39]. For analysis, values were averaged from 10 to 30 min of the heavy bout. ...
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Epidemiological evidence suggests low‐frequency physical activity provides health benefits, but the physiological impacts of weekly training frequency are understudied. We investigated whether “Weekend Warrior” (WW) training was inferior to traditional, high‐frequency (HF) training for improving maximal oxygen uptake (V̇O2max). The secondary aim was to assess integrative physiological adaptations to each protocol. Twenty‐eight sedentary‐to‐recreationally‐active adults aged 18–45 years (14 males and 14 females) were randomized to perform 8‐weeks of HF or WW training on a cycle ergometer (either four or two sessions weekly, respectively), consisting of continuous and interval exercise, with intensity and volume matched between groups. WW training was not inferior to HF training for improving V̇O2max (mean ± standard deviation; WW: 43.5 ± 6.5 vs. 47.8 ± 6.4 mL/kg/min; HF: 42.3 ± 6.2 vs. 47.3 ± 6.7; main effect of training, p < 0.001). Severe domain cycling time‐to‐task‐failure also increased in both groups (WW: 3.7 ± 1.6 vs. 8.6 ± 3.2 min; HF: 3.5 ± 0.9 vs. 7.7 ± 2.8; main effect of training: p < 0.001). Frequency did not affect improvements in hemoglobin mass (WW: 771 ± 203 vs. 790 ± 189 g; HF: 754 ± 185 vs. 765 ± 202; main effect of training: p = 0.043) or skeletal muscle oxidative capacity (WW: 0.034 ± 0.008 vs. 0.045 ± 0.015 s⁻¹; HF: 0.036 ± 0.011 vs. 0.041 ± 0.010; main effect of training: p = 0.002), nor did it influence improvements in cardiorespiratory, substrate oxidation, voluntary muscle contractile, and perceptual responses to submaximal exercise (interaction effect: p > 0.05 for all outcomes). Eight weeks of training improved V̇O2max and a wide range of physiological outcomes with no difference between training frequencies, suggesting that the distribution of weekly exercise volume has a limited effect during short‐term training. Trial Registration: This trial was registered at ClinicalTrials.gov identifier: NCT05908578
... After confirmation of their suitability for the main study, participants were asked whether they would be interested in participating in the present exercise sub-study. Interested individuals then performed a graded exercise test to volitional exhaustion on a workload-controlled cycle ergometer (Corival, Lode©, Groningen, The Netherlands) as previously described [19,20]. The results were used to determine the individualized workload (watts) required to complete the moderate-intensity (~60% VȮ2peak) exercise sessions incorporated in each of the exercise study's experimental visits. ...
... After confirmation of their suitability for the main study, participants were asked whether they would be interested in participating in the present exercise sub-study. Interested individuals then performed a graded exercise test to volitional exhaustion on a workload-controlled cycle ergometer (Corival, Lode©, Groningen, The Netherlands) as previously described [19,20]. The results were used to determine the individualized workload (watts) required to complete the moderate-intensity (~60%VO 2peak ) exercise sessions incorporated in each of the exercise study's experimental visits. ...
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Objectives: This article compares metabolic, pancreatic, and gut-derived hormone responses to isomaltulose ingestion, before versus during submaximal sustained exercise, in adults with type 1 diabetes (T1D) using automated insulin delivery systems. Methods: In a randomized, cross-over trial, eight participants with T1D being treated with automated insulin pumps (five females, age: 47 ± 16 years, BMI: 27.5 ± 3.8 kg·m², diabetes duration: 23 ± 11 years, HbA1c: 8.3 ± 0.9 [67.5 ± 9.5]% [mmol/mol]) attended the laboratory on two separate occasions and consumed an isocaloric amount of isomaltulose as either (1) a single serving (0.75g CHO·kg⁻¹ BM) with a 25% reduction in bolus insulin 90 min before 45 min of cycling (PEC) or (2) three separate isocaloric servings (0.25g CHO·kg⁻¹ BM each) without bolus insulin during exercise (DEC). Plasma glucose (PG), gut incretins (GLP-1 and GIP), pancreatic glucagon, exogenous insulin, and whole-body fuel oxidation rates were determined. Data were treated via a two-way repeated measures ANOVA, with p ≤ 0.05 accepted as significant. Results: PG concentrations throughout exercise were higher and less variable with DEC compared to PEC. The exercise-induced change in PG was directionally divergent between trials (PEC: ∆ − 3.2 ± 1.2 mmol/L vs. DEC: ∆ + 1.7 ± 1.5 mmol/L, p < 0.001), changing at a rate of −0.07 ± 0.03 mmol/L/min with PEC and +0.04 ± 0.03 mmol/L/min with DEC (p < 0.001 between conditions). Throughout the exercise period, GLP-1, GIP, glucagon, and total insulin concentrations were lower with DEC (all p ≤ 0.02). The oxidation rates of carbohydrates were lower (p = 0.009) and of lipids were greater (p = 0.014) with DEC compared to PEC. Conclusions: The consumption of smaller servings of isomaltulose during, rather than as a single isocaloric serving before, submaximal sustained exercise provided (i) a better glycemic protective effect, (ii) a lesser push on pancreatic and gut-mediated glucoregulatory hormones, and (iii) a lower reliance on whole-body carbohydrate oxidation. Such information serves to remind us of the potential importance of nutrition for modulating the metabolic fate of an acute bout of exercise and may help inform best practice guidelines for exercise management in the T1D-sphere.
... Furthermore, males demonstrated an~22% greater O 2 pulse than females, which, as absolute VO 2 was similar between sexes, reflects their lower heart rate and higher capacity for oxygen utilisation in the additional~10 kg (~20%) of lean mass. As a result of their higher relative exercise intensity, females demonstrated a higher RER, indicating an increased reliance upon carbohydrates during these occupational tasks [57]. These differences in relative intensity and macronutrient utilisation between males and females need to be taken into consideration during both training and operations that impose load carriage tasks beyond that reflective of the PES. ...
... Thirdly, nutritional strategies could be developed to support training and occupational task performance. The metabolic data in the current study demonstrated that with heavier loads and faster walking speeds, females have a greater reliance on carbohydrate oxidation as a result of the greater exercise intensity [57]. Considering that load carriage tasks are typically prolonged, these data suggest that a greater emphasis should be placed on maintaining carbohydrate stores in female personnel to ensure that they are able to complete any high-intensity, mission-critical tasks following the more challenging load carriage marches. ...
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This study aimed to investigate the physiological, perceptual, and biomechanical differences between male and female soldiers across several military-relevant load and walking speed combinations. Eleven female and twelve male soldiers completed twelve 12 min walking trials at varying speeds (3.5 km·h−1, 5.5 km·h−1, 6.5 km·h−1) and with varying external loads (7.2 kg, 23.2 kg, 35.2 kg). Physiological (indirect calorimetry, heart rate), perceptual (perceived exertion), and biomechanical (spatiotemporal, kinematic, kinetic) outcomes were measured throughout each trial. Females had a lower aerobic capacity and lower body strength than males, which resulted in them working at a greater exercise intensity (%VO2peak and heart rate) but with a lower oxygen pulse. Females demonstrated higher breathing frequency and perceived exertion with specific loads. At selected loads and speeds, frontal and sagittal pelvis, hip, and knee motions and forces were greater for females. Females consistently displayed greater relative stride length and step width. In conclusion, this study demonstrates the importance of tailored interventions, periodisation, and nutritional strategies for female military personnel, given their higher relative work rate and increased injury risk during load carriage tasks. Understanding these differences is crucial for preparing female soldiers for the physical demands of military service.
... To calculate EC, updated nonprotein respiratory quotient equations (20) were used to estimate substrate utilization (g·min −1 ). The energy derived from each substrate was calculated by multiplying fat and carbohydrate utilization by 9.75 and 4.07 kcal, respectively (26). Absolute EC was calculated as the sum of the energy derived from fat and carbohydrate expressed as kcal·kg −1 ·km −1 . ...
... The fractional differences between the changes in OC and EC can be explained by the surprisingly small changes in RER during the run, decreasing from 0.92 to 0.91 between 15 and 30 min, and remaining constant thereafter until 90 min. This indicates a slightly higher reliance on fat oxidation, which requires around 10% more oxygen to yield a given amount of energy (26), and larger differences between EC and OC would be expected to occur when substrate utilization changes more profoundly. Indeed, a study by Kyrolainen et al. (10) measured changes in oxygen (mL·kg −1 ·min −1 ) and energy uptake (J·kg −1 ·min −1 ) before and after a marathon, and reported a bigger difference in RE deterioration between measures (OC +16% vs EC +14%) than the current results, due to a larger RER change (0.82 pre vs 0.75 post). ...
Article
Introduction Running economy (RE) deteriorates during prolonged running, although the effect of measuring energy cost (EC) or oxygen cost (OC) on the magnitude of these changes has not been investigated. Similarly, it is unknown if runners’ performance level may influence the deterioration of RE during prolonged running. The aims of this study were to compare changes in EC and OC measurements of RE during a prolonged run in a large cohort of well-trained male runners, and to compare changes between runners of high and low performance standard. Methods Forty-four male runners (maximal oxygen uptake ( V̇ O 2 max) 62.4 ml·kg ⁻¹ ·min ⁻¹ ; 10 km time 35:50 ± 4:40 mm:ss) completed an incremental test determining lactate threshold 1 (LT1) and V̇ O 2 max, and on a separate occasion, a 90 min run at LT1. Respiratory gases were collected at 15 min intervals. Subsequently, sub-groups of high- (HP, 10 km 31:20 ± 01:00 mm:ss) and low-performing (LP, 10 km 41:50 ± 01:20 mm:ss) runners were compared. Results RE deterioration was only fractionally larger when expressed as OC than EC (0.1% greater from 30-90 min; p < 0.001), perhaps due to the small change in RER (-0.01) in this study. For the HP group increases were lower than LP after 90 min in both EC (+2.3 vs +4.3%; p < 0.01) and OC (+2.4 vs +4.5%; p < 0.01). Similarly, at standardized distances, changes were lower for HP vs LP e.g. at 16.7 km +1.0 vs +3.2% for EC (p < 0.01), and + 1.2 vs +3.4% for OC (p < 0.001). Conclusions The deterioration of RE was dependent on athlete’s performance level, with HP runners displaying superior RE durability. The use of EC or OC had only a fractional influence on RE durability, although this may gain importance with larger shifts in substrate metabolism.
... This VȮ 2 was converted to power output by linear regression of the VȮ 2 vs. power output relationship, using the last minute of VȮ 2 data from each 3-min stage. The last minute of expired gas data in each 3-min stage was also used to quantify wholebody rates of carbohydrate and fat oxidation using standard equations (Eq. 1) (Jeukendrup and Wallis 2005). The highest observed rate of whole-body fat oxidation was identified as the peak fat oxidation rate (PFO) . ...
... The PRE and POST trials began with a 5-min warm-up at 100 W. Following warm-up, participants cycled for 150 min at 90% of their estimated VT 1 power output in the POST but not PRE trial, with expired gases collected for 4 min every 15 min. Expired gases were used to quantify rates of wholebody rates of energy expenditure, carbohydrate oxidation, and fat oxidation during the 150-min preload using standard equations (Jeukendrup and Wallis 2005). In POST, participants consumed 150 mL of water every 15 min in a solution made with electrolyte mix (LMNT) containing 125 mg Na + , 25 mg K + , and 7.5 mg Mg 2+ during the first 120 min of the 150-min preload. ...
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Purpose Power output at the moderate-to-heavy-intensity transition decreases during prolonged exercise, and resilience to this has been termed ‘durability’. The purpose of this study was to assess the relationship between durability and the effect of prolonged exercise on severe-intensity performance, and explore intramuscular correlates of durability. Methods On separate days, 13 well-trained cyclists and triathletes (V̇O2peak, 57.3 ± 4.8 mL kg⁻¹ min⁻¹; training volume, 12 ± 2.1 h week⁻¹) undertook an incremental test and 5-min time trial (TT) to determine power output at the first ventilatory threshold (VT1) and severe-intensity performance, with and without 150-min of prior moderate-intensity cycling. A single resting vastus lateralis microbiopsy was obtained. Results Prolonged exercise reduced power output at VT1 (211 ± 40 vs. 198 ± 39 W, ∆ -13 ± 16 W, ∆ -6 ± 7%, P = 0.013) and 5-min TT performance (333 ± 75 vs. 302 ± 63 W, ∆ -31 ± 41 W, ∆ -9 ± 10%, P = 0.017). The reduction in 5-min TT performance was significantly associated with durability of VT1 (rs = 0.719, P = 0.007). Durability of VT1 was not related to vastus lateralis carnosine content, citrate synthase activity, or complex I activity (P > 0.05). Conclusion These data provide the first direct support that durability of the moderate-to-heavy-intensity transition is an important performance parameter, as more durable athletes exhibited smaller reductions in 5-min TT performance following prolonged exercise. We did not find relationships between durability and vastus lateralis carnosine content, citrate synthase activity, or complex I activity.
... To calculate substrate oxidation under steady-state conditions, the data of the last 30 s of the 2.50 m·s −1 stage were used (n = 14). The following equations, according to Jeukendrup and Wallis (2005), for moderate-to-high-intensity exercise were used in order to calculate CHO and fat oxidation; Eqs 2, 3 were modified in order to convert g·min −1 into J·s −1 : ...
... Total energy expenditure was estimated as the sum of CHO and fat oxidation, whereas the contribution of protein oxidation was neglected (Jeukendrup and Wallis, 2005). ...
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The usage of the oral contraceptive pill is widespread among athletes of various levels. However, there is limited knowledge on how the intake of the pill alters the submaximal and maximal endurance parameters between the oral contraceptive phases. Therefore, the aim of this study was to examine potential differences between the pill intake and withdrawal phase on endurance-related parameters in first-division handball players. In total, 15 female team handball players performed two graded exercise tests until volitional exhaustion on a motorized treadmill. Tests were performed during the pill intake (days 16–17) and withdrawal phase (day 2–3). Throughout the test, respiratory gases were measured breath-by-breath, and the heart rate was measured continuously. Before and after the graded exercise test, blood samples were obtained in order to assess the blood lactate concentration. Before each test, venous blood samples were taken to determine endogenous sex hormone levels. Ventilatory parameters ( V ˙ O2, V ˙ CO2, and V ˙ E, and respiratory equivalents for V ˙ O2 and V ˙ CO2) were measured, and the oxidation of fat and carbohydrates was calculated. A paired-sample t-test was used to assess differences between the two time points, and the significance was accepted as p < 0.050. Significant differences with lower values during the consumption phase were found for absolute (mean difference ± SD: 88 ± 131 mL∙min⁻¹; p = 0.021) and relative V ˙ O2peak (mean difference ± SD: 1 ± 2 mL∙min⁻¹∙kg⁻¹; p = 0.012). Higher values during the consumption phase were found for submaximal respiratory equivalents for V ˙ O2 (mean difference ± SD: −1.1 ± 1.7; p = 0.028) and V ˙ CO2 (mean difference ± SD: −0.9 ± 1.5; p = 0.032). No differences were found for all other parameters, including differences for endogenous sex hormones (p > 0.050). The results of the current study suggest only marginal and physiologically insignificant differences in endurance-related parameters between oral contraceptive phases.
... Assessment of the first ventilatory threshold using ventilatory equivalents has excellent reliability (3.5%) (Pallares et al. 2016). The last minute of expired gas data in each 3-min stage was also used to quantify whole-body fat oxidation rates and gross efficiency (GE) using standard stoichiometric equations (Jeukendrup and Wallis 2005;Hopker et al. 2009) (Eq. 1). ...
... 'Time 0' for calculating time-to-task failure was the beginning of the warm-up before the first incremental step test. Expired gases were collected throughout all incremental tests, and the V O 2 and V CO 2 in the last minute of each of the six 4-min stages was used to calculate the respiratory exchange ratio (RER), and rates of fat and carbohydrate oxidation using stoichiometric equations (Eq. 1) (Jeukendrup and Wallis 2005). During each 30 min bout at 90% of estimated VT 1 , participants consumed 600 mL of water in a solution made with an electrolyte mix (Science in Sport GO Hydro). ...
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Purpose The aims of this study were to: (i) describe the time course of the decrease in power output at the moderate-to-heavy intensity transition during prolonged exercise; (ii) investigate the association between durability of the moderate-to-heavy intensity transition and exercise capacity; and (iii) explore physiological correlates of durability of the moderate-to-heavy intensity transition. Methods Twelve trained cyclists (age: 40 ± 8 y, V˙V˙\dot{\text{V}}O2peak: 52.3 ± 5.2 mL·min⁻¹·kg⁻¹) performed an exhaustive cycling protocol involving alternating incremental exercise tests to determine power output at the moderate-to-heavy intensity transition via the first ventilatory threshold (VT1), and 30-min bouts at 90% of the power output at the previously estimated VT1 in the rested state. The individual time course of VT1 was modelled using linear and second-order polynomial functions, and time to a 5% decrease in VT1 (Δ5%VT1) was estimated using the best-fitting model. Results Power output at VT1 decreased according to a second-order polynomial function in 11 of 12 participants. Time-to-task failure (234 ± 66 min) was correlated with Δ5%VT1 (139 ± 78 min, rs = 0.676, p = 0.016), and these were strongly correlated with absolute and relative rates of fat oxidation at specific exercise intensities measured during the incremental test performed in the rested state. Conclusions These data: (i) identify a non-linear time course of decreases in the moderate-to-heavy intensity transition during prolonged exercise; (ii) support the importance of durability of the moderate-to-heavy intensity transition in prolonged exercise capacity; and (iii) suggest durability of the moderate-to-heavy intensity transition is related to fat oxidation rates.
... The energy expenditure (EE) and respiratory exchange ratio (RER) were determined through the evaluation of oxygen consumption (VO 2 ) and carbon dioxide production (VCO 2 ). Additionally, established formulas from the literature were applied to estimate carbohydrate and lipid oxidation [52,53]. Notably, protein oxidation could not be directly assessed from respiratory exchanges, as the oxidation of proteins is incomplete due to urinary nitrogen waste [52,54]. ...
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The chemotherapeutic agent doxorubicin (DOX) leads to the loss of skeletal muscle and adipose tissue mass, contributing to cancer cachexia. Experimental research on the molecular mechanisms of long-term DOX treatment is modest, and its effect on both skeletal muscle and adipose tissue has not been studied in an integrative manner. Dexrazoxane (DEXRA) is used to prevent DOX-induced cancer-therapy-related cardiovascular dysfunction (CTRCD), but its impact on skeletal muscle and adipose tissue remains elusive. Therefore, this study aimed to investigate the long-term effects of DOX on adipose tissue and skeletal muscle metabolism, and evaluate whether DEXRA can mitigate these effects. To this end, 10-week-old male C57BL6/J mice (n = 32) were divided into four groups: (1) DOX, (2) DOX-DEXRA combined, (3) DEXRA and (4) control. DOX (4 mg/kg weekly) and DEXRA (40 mg/kg weekly) were administered intraperitoneally over 6 weeks. Indirect calorimetry was used to assess metabolic parameters, followed by a molecular analysis and histological evaluation of skeletal muscle and adipose tissue. DOX treatment led to significant white adipose tissue (WAT) loss (74%) and moderate skeletal muscle loss (Gastrocnemius (GAS): 10%), along with decreased basal activity (53%) and energy expenditure (27%). A trend toward a reduced type IIa fiber cross-sectional area and a fast-to-slow fiber type switch in the Soleus muscle was observed. The WAT of DOX-treated mice displayed reduced Pparg (p < 0.0001), Cd36 (p < 0.0001) and Glut4 (p < 0.05) mRNA expression—markers of fat and glucose metabolism—compared to controls. In contrast, the GAS of DOX-treated mice showed increased Cd36 (p < 0.05) and Glut4 (p < 0.01), together with elevated Pdk4 (p < 0.001) mRNA expression—suggesting reduced carbohydrate oxidation—compared to controls. Additionally, DOX increased Murf1 (p < 0.05) and Atrogin1 (p < 0.05) mRNA expression—markers of protein degradation—compared to controls. In both the WAT and GAS of DOX-treated mice, Ppard mRNA expression remained unchanged. Overall, DEXRA failed to prevent these DOX-induced changes. Collectively, our results suggest that DOX induced varying degrees of wasting in adipose tissue and skeletal muscle, driven by distinct mechanisms. While DEXRA protected against DOX-induced CTRCD, it did not counteract its adverse effects on skeletal muscle and adipose tissue.
... Equations from Jeukendrup and Wallis (17) were used to determine rates of energy expenditure, fat oxidation (FAT ox ) and carbohydrate oxidation (CHO ox ). Oxygen uptake kinetics was evaluated by means of a monoexponential function using nonlinear regression, similar to Ingham et al (5). ...
Article
Purpose To examine the physiological, power-duration, nutritional intake and training characteristics of the recent lightweight (- 75 kg) 50+, 60+ and 70 + yr world champion indoor rowers. Methods Laboratory assessments, undertaken over 2 visits, examined body composition, pulmonary function, blood lactate/ventilatory landmarks, efficiency, fat/carbohydrate oxidation, primary component time-constant to steady-state [𝜏pc]) and peak oxygen consumption (V̇O2peak). Training, performance and nutritional intake were also reported. Results The athletes’ world championship 2000 m times were 06:34.8, 06:44.0 and 07:15.2, respectively. Their training distribution could be considered pyramidal, with ≈65% in the moderate domain, ≈30% in heavy/severe domains and ≈5% in the extreme domain (rowing ≈67 km.week-1). The athletes demonstrated highly-developed attributes such as fat free mass (FFM; [63.4 to 68.1 kg]), forced vital capacity (4.9 to 5.5 L), 𝜏PC; [13.8 to 17.4 s]), peak power output (550 to 797 W), V̇O2peak (56.2 to 44.7 mL.kg.min-1) and critical power (217 to 288 W). Comparisons with young Olympic champion rowers suggest that age-related 2000 m performance mean power declines of -21.6 to -41.4% in world champions ≈25-, 35-, and 45-years older may be predominantly driven by 'central' factors (e.g., V̇O2peak, critical power; -18.1 to -43.8%). In contrast, 'peripheral' factors (e.g., gross efficiency, τPC; +6.1 to -25.1%) seem to display notable preservation despite ageing, aligning closely with values seen in young Olympic champions. Conclusions These results challenge conventional perspectives of age-related physiological capacities and decline trajectories. They also suggest that, commensurate with adequate training and nutritional provision, various physiologic systems can exhibit remarkable adaptability and sustain exceptionally high function during ageing. Finally, large differences among the athletes’ power-duration and physiological characteristics imply that achieving world-class rowing performance can be predicated by diverse cardiovascular, metabolic and neuromuscular attributes.
... Deadspace ventilation was calculated as the difference between V E and V A (Stickland et al., 2013;West & Luks, 2020). Carbohydrate (CHO) and fat oxidation (g·min −1 ) were calculated via application of stoichiochemical equations to VO 2 and VCO 2 on the assumption that protein oxidation is negligible during exercise (Jeukendrup & Wallis, 2005). ...
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To assess the impact of thoracic load carriage on the physiological response to exercise in hypoxia. Healthy males (n = 12) completed 3 trials consisting of 45 min walking in the following conditions: (1) unloaded normoxia (UN; FIO2:20.93%); (2) unloaded hypoxia (UH; FIO2:~13.0%); and (3) loaded hypoxia (LH; 29.5 kg; FIO2:~13.0%). Intensity was matched for absolute VO2 (2.0 ± 0.2 L·min⁻¹) across conditions and relative VO2 (64.0 ± 2.6 %VO2max) across hypoxic conditions. With LH versus UH, there were increases in breathing frequency (5–11 breaths·min⁻¹; p < 0.05) and decreases in tidal volume (10%–18%; p < 0.05) throughout exercise due to reductions in end inspiratory lung volumes (p < 0.05). Consequently, deadspace (11%–23%; p < 0.05) and minute ventilation (7%–11%; p < 0.05) were increased starting at 20 and 30 min, respectively. In addition, LH increased perceived exertion/dyspnea and induced inspiratory (~12%; p < 0.05 vs. UN) and expiratory (~10%; p < 0.05 vs. pre‐exercise) respiratory muscle fatigue. Expiratory flow limitation was present in 50% of subjects during LH. Cardiac output and muscle oxygenation were maintained during LH despite reduced stroke volume (6%–8%; p < 0.05). Finally, cerebral oxygenated/total hemoglobin were elevated in the LH condition versus UH starting at 15 min (p < 0.05). Thoracic load carriage increases physiological strain and interferes with the compensatory response to hypoxic exposure.
... For Visits 3 and 4, participants exercised at an individualized speed to elicit 50% VO 2 max, with measurement of heart rate (Polar H7, Polar Electro Oy) and expired gases (Cortex Metalyzer 3B, Biophysik GmbH) and with analysis every 5 min by averaging the last 60 s of each 5-min section. Stoichiometric equations were used to calculate carbohydrate and FATOX (Jeukendrup & Wallis, 2005). Rating of perceived exertion (Borg 6-20) was recorded every 15 min. ...
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New Zealand black currant extract (NZBC) has been shown to increase fat oxidation during exercise and decrease the postexercise blood pressure in men and women. The change in fat oxidation by NZBC has also been shown to be correlated to body composition in men and women. There has never been a comparison of sex responses within the same study. Twenty-two participants (11 men and 11 women, age: 29 ± 8 years, maximal oxygen uptake: 44 ± 9 ml·kg ⁻¹ ·min ⁻¹ , body fat: 18% ± 6%) had resting blood pressure measured for 2 hr (no exercise). In a double-blind, placebo-controlled (PLA), randomized crossover design, participants completed 1 hr of treadmill exercise at 50% maximal oxygen uptake with expired gas measurement, followed by 2-hr resting blood pressure measurement with 7 days of NZBC or PLA. Average fat oxidation was different between the conditions (NZBC: 0.27 ± 0.11 g/min, PLA: 0.21 ± 0.12 g/min, p < .001), but the response between men and women was not different. When combined, there was no relationship ( p > .05) between body fat percentage and change in fat oxidation ( r = −.079), with men also demonstrating no relationship ( r = −.069), although women did demonstrate a relationship ( r = .691, p < .05). In the 2-hr rest, systolic pressure delta change was larger with NZBC than PLA (no exercise vs. NZBC: −5.5 ± 5.4 mmHg vs. no exercise vs. PLA: −2.9 ± 5.1 mmHg, p < .001) but was not different between men and women. A 7-day intake of NZBC extract increases fat oxidation during moderate-intensity exercise and decreases postexercise blood pressure in men and women. The magnitude of change in fat oxidation in women is correlated to body fat percentage.
... This lack of difference, likely due to metabolic requirements for mixed fuelling, is reflected in minimal differences in the pooled-analysis and no effect in the meta-analysis. At high intensities (75-99%), exercise involves mixed substrate utilisation with a greater contribution of glucose utilisation, but once again RER may be higher in the follicular phase which may indicate an earlier reliance on anaerobic metabolism due to the likelihood of reaching an RER of 1 earlier [58] and a more pronounced shift towards reliance on carbohydrates reflected by greater RER values [59]. These findings at low and high intensities contradict the effect evidenced in meta-analyses, where it appeared that there were no differences in RER or that RER was lower in the follicular phase than the luteal phase. ...
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Background: Oestradiol has been implicated as a factor in substrate utilisation in male and mouse studies but the effect of acute changes during the menstrual cycle is yet to be fully understood. Objective: To determine the role of oestradiol in respiratory exchange ratio (RER) during exercise at various intensities. Methods: This systematic review was conducted and reported in accordance with the Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) statement. From inception to November 2023, four online databases (Cochrane, SPORTDiscus, MEDline and Web of Science) were searched for relevant articles. Studies that reported a resting oestradiol measurement in naturally menstruating women with exercise at a percentage of maximal aerobic capacity (%V˙O2max) were included. Mean and standard deviation for oestradiol, RER and exercise intensity were extracted and study quality assessed using a modified Downs and Black checklist. Risk of bias was assessed using I2 measure of heterogeneity and Egger’s regression test, assessment of bias from methodological quality was identified by sensitivity analysis. Eligible datasets were extracted for pairwise comparisons within a meta-analysis and correlation between change in oestradiol and change in RER. Data were also pooled to produce a mean and standard deviation for RER for menstrual stage and for low and high oestradiol groups. Results: Twenty-four articles were identified, over 50% were identified as high quality. Sixteen articles included datasets eligible for meta-analysis. Eleven articles utilised a submaximal constant-load exercise intensity, finding a standardised mean difference of − 0.09 ([CI: −0.35–0.17], p = 0.5) suggesting no effect of menstrual phase on constant-load exercise RER. In six articles using incremental exercise tests to exhaustion, a standardised mean difference of 0.60 ([CI 0.00–1.19], p = 0.05) was identified towards a higher maximal RER attained in follicular compared to luteal phase. There was no correlation (R = −0.26, p = 0.2) between change in oestradiol and change in RER between phases. All 24 articles, totalling 650 participants, were included in pooled analysis. When grouped by menstrual cycle phase or when grouped by oestradiol levels, RER was higher in the follicular phase than the luteal phase at low and high constant load exercise intensities. Discussion: Findings from the pooled-analysis and meta-analysis suggest that there may be menstrual cycle phase differences in RER that are intensity dependent. These differences may be related to sex hormone levels, but this was not supported by evidence of correlation between differences in RER and differences in oestradiol. At present, it remains best practice to assess performance in the same menstrual cycle phase if seeking to assess change from baseline.
... By using the following Equations (1) and (2) substrate oxidation rates were calculated assuming a negligible protein oxidation. 33,34 Carbohydrate Oxidation g min u u . . ...
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Background Although a palaeolithic diet promotes healthier food choices that aid in weight management and reduce cardiovascular risks, its effectiveness in endurance sports is still debated due to its typically low carbohydrate content. Objective This study examined the impact of a 6-week palaeolithic diet (PD-G) versus a mixed diet (MD-G), both paired with Sprint interval training (SIT), on various metabolic and performance-related parameters. Methods Body composition, time trial (TT) performance (covered distance during a 60-minute run on a 400-metre track) and changes in metabolic (respiratory exchange ratio [RER], substrate oxidation rates) and performance-related (time at ventilatory threshold [VT] and respiratory compensation point [RCP], maximum oxygen uptake (V̇O2max) and time to exhaustion [TTE]) parameters during a ramp incremental running test were assessed in 14 male endurance athletes. Additionally, Gastrointestinal Quality of Life index (GLQI) and perceptual responses to the diets [visual analogue scale (VAS)] were measured. Results After 6 weeks, both groups improved in TTE and distance covered in the 60-minute TT, without significant group differences. In the PD-G body weight, fat mass and systolic and diastolic blood pressure decreased. At rest, RER and carbohydrate oxidation significantly decreased in the PD-G, with a tendency towards significance during exercise, while changes in fat oxidation rates were not statistically significant at rest and throughout the exercise test; in contrast, the MD-G exhibited smaller changes across these parameters. Conclusion In this investigation, a palaeolithic diet in combination with SIT appeared to have positive effects on fat mass, blood pressure and substrate utilization under resting conditions in a group of male endurance athletes. However, based on the current findings for performance metrics, a palaeolithic diet cannot be recommended unreservedly for healthy endurance athletes.
... Running vampire bats exhibited a RER of 0.8-0.9, which remained consistent across all treadmill speeds (t = 0.82, p = 0.42; figure 2a). An RER of 0.8-0.9 can reflect a mixture of lipid and carbohydrate use, but may also indicate protein oxidation (for a review, see [17]). Although the RER remained consistent, we found that VCO 2 and VO 2 were significantly affected by exercise intensity (VCO 2 : t = 20.39, ...
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In most mammals, running is fuelled by oxidization of endogenous carbohydrates and lipids while amino acids contribute little (< 5–10%). Common vampire bats (Desmodus rotundus), however, specialize on a unique, protein-rich blood diet. Therefore, we hypothesized that (i) vampire bats would rapidly begin utilizing dietary amino acids to support running metabolism, and (ii) that relative reliance on essential and non-essential amino acids would be similar. We fed bats cow’s blood enriched either with isotopically labelled glycine (non-essential amino acid) or leucine (essential amino acid). Bats were exercised at speeds of 10, 20 and 30 m min⁻¹ on a respirometry treadmill, allowing us to assess metabolic rate (i.e. O2 consumption and CO2 production) and track the oxidation of labelled amino acids in exhaled CO2. Vampire bats oxidized amino acids as their primary fuel as indicated by a respiratory exchange ratio (RER = ratio of CO2 production to O2 consumption rates) of approximately 0.8–0.9 at all speeds, with the labelled meal accounting for as much as 60% of oxidized fuels at peak usage. Similar oxidation rates indicated bats did not discriminate between essential and non-essential amino acid use. These findings reiterate how strongly metabolism can be shaped by a specialized diet.
... Distinct parameters of cardiorespiratory fitness and metabolic flexibility will also be determined by a maximal stress test exercise test on one treadmill (Quinton TM55, WA, USA) or cycle ergometer (Monark Exercise AB, Vansbro, Sweden), as described in Table 2. Gas exchange and heart rate (Polar H10, Polar ® Electro OY, Kempele, Finland) will be recorded throughout the exercise tests, while the rate of perceived exertion will be registered at the end of each stage using the modified Borg scale with a 0-10 rating. The average VO 2 and VCO 2 values of the last 2 min of each stage before RER ≥ 1.0 will be used to calculate fat and carbohydrate oxidation using the stoichiometric equations of Jeukendrup and Wallis [19]. The maximum rate of fat oxidation and its corresponding intensity during exercise will be determined by mathematical modeling of fat oxidation kinetics, plotted against oxygen consumption (% VO 2 max) [20]. ...
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Background: Exercise is an essential pillar for human health, as it contributes to physical, mental, and emotional well-being. Well-recognized international organizations, such as the World Health Organization, advocate for integrating exercise into healthy lifestyles, recognizing its importance in disease prevention and improving quality of life. However, despite the consensus on its value, there is no universal agreement on specific prescriptions for vulnerable groups, highlighting the need for personalized approaches that consider the unique characteristics and needs of everyone. Emerging studies have demonstrated that exercise training performed at the intensity that elicits maximal fat oxidation improves insulin sensitivity, cardiorespiratory fitness, and body composition in patients with obesity, making it a highly effective strategy for long-term weight management and metabolic health in this specific population. Methods: The present study protocol settles the basis for a 16-week randomized clinical trial based on exercise prescription at the maximal fat oxidation rate combined with resistance training in young individuals with overweight and obesity. Expected Results: This study will elucidate how FatMax, with or without resistance exercises, can enhance metabolic flexibility, increase fat oxidation, and improve body composition, evaluating changes in biochemical parameters (cholesterol, glucose, triglycerides, and inflammatory markers), metabolic biomarkers (determination of fat and carbohydrate utilization rates during rest and exercise), and epigenetic indicators (focusing on microRNAs associated with adipogenesis, inflammation, and fat metabolism). ClinicalTrials.gov identification number: NCT06553482 (FatMax Training on Metabolic and Epigenetic Parameters).
... Additionally, VO 2 , percentage of VO 2max (%VO 2max ), HR, percentage of HR max (%HR max ), power output (PO), and PO normalized to FFM (PO/FFM) were determined at the intensity corresponding to MFO. Energy expenditure normalized to FFM (EE/FFM) was determined from FATox/FFM and CHox/FFM (Jeukendrup and Wallis 2005). EE/FFM (cal/min/FFM) = FATox/FFM · 9.75 +CHox/FFM · 4.07 · 1000 ...
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The first aim was to explore the difference in metabolic flexibility between sexes in response to changing exercise intensity under control conditions. The second aim was to evaluate metabolic flexibility between sexes in response to exercise intensity adding two different metabolically challenging stimuli (glycogen depletion and heat). Eleven males (22 ± 3 years, 176.2 ± 4 cm, 68.4 ± 4.9 kg, and 60.2 ± 4.1 mL/kg FFM/min) and nine females (22 ± 2 years, 166.7 ± 4.5 cm, 61.9 ± 2.9 kg, and 64.2 ± 5.6 mL/kg FFM/min) performed a maximal incremental exercise test (30 W every 3 min) on a cycle ergometer under three conditions: control (24 h high-carbohydrate diet followed by the incremental test), glycogen depletion (glycogen-depletion protocol followed by 24 h low-carbohydrate diet and then the incremental test), and heat (24 h high-carbohydrate diet followed by 30 min passive heating and then the incremental test in heat). In the last minute of each step, lactate was analysed, fat (FATox/FFM) and carbohydrate oxidation (CHox/FFM), and energy expenditure (EE/FFM) normalized to fat-free mass (FFM) was estimated by indirect calorimetry. Females presented a greater FATox/FFM as exercise intensity increases across conditions (control, glycogen depletion, and heat) (p = 0.006). In contrast, CHox/FFM was not significantly different between sexes at any specific intensity across conditions (p > 0.05). Consequently, EE/FFM was higher in females throughout the different intensities across conditions (p = 0.002). Finally, lactate concentration was not different between sexes at the same intensities across conditions (p = 0.87). In conclusion, females present a greater metabolic flexibility, due to the higher FATox/FFM throughout the different intensities, regardless of whether the test is performed in conditions emphasizing the oxidative pathway (glycogen depletion) or the glycolytic pathway (heat). Clinical trials: NCT05703100
... For estimating energy expenditure and substrate utilisation during the 75-min run at 70% VO 2 peak, a 3-min breath sample was obtained every 15 min by indirect calorimetry utilising a metabolic cart (Vyntus, Vyaire Medical, IL, US). The values were calculated utilising the equations of Jeukendrup & Wallis (Jeukendrup & Wallis, 2005). For the analysis, exercise energy expenditure was not considered within the energy expenditure data. ...
... However, as the main difference between experimental conditions is CIT, this limitation only apply when comparing BRG or CIT + BRG vs. the PLAG. Regarding substrate oxidation, we estimated FATOx and CHOOx using equations derived for moderate to high-intensity exercise (i.e., 50-75% VO 2max ), as proposed by Jeukendrup and Wallis (Jeukendrup & Wallis 2005). While this range aligns with most moderate exercise protocols, the exercise intensity during our performance test may have exceeded this recommended range. ...
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Purpose Citrulline (CIT) and beetroot extract (BR) supplements positively impacts exercise performance in elite rowers. However, its influence on metabolic outcomes such as whole-body volumes of oxygen consumption (VO2) and carbon dioxide production (VCO2), substrate oxidation, energy expenditure (EE), and gross efficiency remains unknown. We studied the effects of 1 week of daily co-supplementation of 3.5 g BR (500 mg NO3⁻) plus 6 g CIT on VO2 and VCO2 kinetics, substrate utilization, EE, and gross efficiency in elite male rowers compared to a placebo and to a BR supplementation. Methods Twenty elite rowers participated in this randomized, double-blind, placebo-controlled crossover trial completing 1 week of supplementation in each group of study: Placebo (PLAG); BRG; and BR-CITG. Efficiency (70% VO2max) and performance (incremental maximal) tests were performed, and gas-exchange data were collected via indirect calorimetry. Results Analysis of covariance (ANCOVA) showed no mean between-condition differences on respiratory exchange ratio (RER), EE, and gross efficiency in the efficiency test (all P > 0.06), and in the performance test (all P > 0.28). Moreover, in both tests no interaction Time × Supplement effects were observed for VO2, VCO2, RER, EE, substrate oxidation, and, gross efficiency (all P > 0.12). Conclusion After 1 week, no effects on energy metabolism and substrate utilization were observed after the daily co-ingestion of BR extract plus CIT supplement, therefore longer (> 7 days) and higher doses of supplementation might be needed to influence metabolism.
... To determine 13 C enrichment of expired CO 2 , breath samples were collected in 12-ml exetainers (Labco Ltd.), filled in duplicate by 10-s exhalation. Whole-body substrate oxidation was calculated fromVO 2 andVCO 2 according to stochiometric equations (Frayn, 1983;Jeukendrup & Wallis, 2005). The 13 C/ 12 C ratio of expired CO 2 was determined by continuous flow isotope ratio mass spectrometry (Iso-Analytical) and the enrichment expressed as δ per mil difference between the 13 C/ 12 C ratio of the sample and a known standard. ...
Article
There is little evidence that body size alters exogenous glucose oxidation rates during exercise. This study assessed whether larger people oxidize more exogenous glucose during exercise than smaller people. Fifteen cyclists were allocated into two groups based on body mass (SMALL, <70 kg body mass, n = 9, two females) or (LARGE, >70 kg body mass, n = 6) matched for lactate threshold (SMALL: 2.3 ± 0.4 W/kg, LARGE: 2.3 ± 0.3 W/kg). SMALL completed 120 min of cycling at 95% of lactate threshold 1 . LARGE completed two trials in a random order, one at 95% of lactate threshold 1 (thereby exercising at the same relative intensity [RELATIVE]) and one at an absolute intensity matched to SMALL (ABSOLUTE). In all trials, cyclists ingested 90 g/hr of ¹³ C-enriched glucose. Total exogenous glucose oxidation was (mean ± SD ) 33 ± 8 g/hr in SMALL versus 45 ± 13 g/hr in LARGE-RELATIVE (mean difference: 13 g/hr, 95% confidence interval [2, 24] g/hr, p = .03). Large positive correlations were observed for measures of exogenous carbohydrate oxidation versus body size (body mass, height, and body surface area; e.g., body surface area vs. peak exogenous glucose oxidation, r = .85, 95% confidence interval [.51, .95], p < .01). When larger athletes reduced the intensity from RELATIVE to ABSOLUTE, total exogenous glucose oxidation was 39 ± 7 g/hr ( p = .43 vs. LARGE-RELATIVE). In conclusion, the capacity for exogenous glucose oxidation is, on average, higher in larger athletes than smaller athletes during exercise. The extent to which this is due to higher absolute exercise intensity requires further research, but body size may be a consideration in tailoring sports nutrition guidelines for carbohydrate intake during exercise.
... Recovery from a cycling test of this duration (i.e. approximately 105 minutes) benefits from tart cherry juice supplementation [13] and this duration of cycling is adequate to cause low- [17]. After the time trial, muscle soreness, MVC, and force output at low and high stimulation frequencies were again determined. ...
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Tart cherries have low glycemic index, antioxidant and anti-inflammatory properties, and therefore may benefit performance and recovery from exercise. We determined the effects of consuming tart cherry juice versus a high-glycemic index sports drink on cycling performance, substrate oxidation, and recovery of low-frequency fatigue. Using a randomized, counter-balanced cross-over design, with one-month washout, 12 recreational cyclists (8 males and 4 females; 35±16y; VO2peak 38.2±7.4 ml/kg/min) consumed cherry juice or sports drink twice a day (300mL/d) for 4d before and 2d after exercise. On the exercise day, beverages (providing 1g/kg carbohydrate) were consumed 45min before 90min of cycling at 65%VO2peak, followed by a 10km time trial. Blood glucose, lactate, carbohydrate and fat oxidation, respiratory exchange ratio (RER), O2 cost of cycling, and rating of perceived exertion (RPE) were measured during the initial 90min of cycling. Muscle soreness, maximal voluntary contraction (MVC) and low-frequency fatigue were determined at baseline and after the time trial on the exercise day, and 30min after beverage consumption 24 and 48h later. There were no differences for time trial performance (17±3min cherry juice vs. 17±2min sports drink, p = 0.27) or any other measures between drink conditions. There were time main effects (p<0.05) for isometric MVC (decreasing) and low-frequency fatigue (increasing; i.e. decreased force at low relative to high stimulation frequencies), changing significantly from baseline to post-exercise and then returning to baseline at 24h post-exercise. Tart cherry juice was not effective for improving performance, substrate oxidation during exercise, and recovery from exercise, compared to a high-glycemic index sports drink.
... The gross oxygen cost of cycling (mL min −1 kg −1 ) was calculated during the final minute of each increment. Additionally, the gross caloric unit cost of cycling (kcal min −1 kg −1 ) was obtained according to previous recommendations [12]. Capillary blood samples (20 μL) were collected from the earlobe, inserted into reaction capsules containing a haemolyzing agent, and then analysed using a Biosen analyser (Biosen S-Line, EKF Diagnostics, Barleben, Germany). ...
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Objectives Cycling economy is associated with muscle strength in athletes. However, the relationship between strength capacity (i.e. maximal and explosive strength) and cycling economy in previously untrained but healthy individuals remains unclear. Therefore, this study aimed to assess the associations between cycling economy and strength performance in a population of recreationally active but untrained healthy individuals. Methods A total of 155 recreationally active individuals (95 males and 60 females) were included. Strength capacity was assessed through an incremental one-repetition maximum test, from which the one-repetition maximum, mean propulsive velocity, and mean propulsive power were derived as strength indices. Cycling economy was assessed using a step protocol on a cycle ergometer and gross oxygen cost and caloric unit cost were determined at submaximal intensities. Results Marginal R² ranged between 0.013 and 0.062 for the gross oxygen cost and between 0.022 and 0.103 for the gross caloric unit cost, respectively. Greater cycling economy is related to higher strength levels. However, the relationship is relatively weak, explaining only 1.3–6.2 % of the variance in gross oxygen cost and 2.2–10.3 % of the variance in gross caloric unit cost. Conclusions Greater cycling economy in recreationally active males and females is related to higher strength levels (i.e. one-repetition maximum, mean propulsive velocity, mean propulsive power).
... To estimate energy expenditure (EE), fat oxidation and gross efficiency, the following equations for moderate to highintensity exercise (50%-75% VO 2max ) were used, assuming a negligible contribution of protein oxidation for all calculations [30]: ...
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Fatigue resistance is vital for success in elite road cycling, as repeated, intense efforts challenge the athletes' ability to sustain peak performance throughout prolonged races. The present study combined recurrent performance testing and physiological measures during 6 h simulated racing with laboratory testing to investigate factors influencing fatigue resistance. Twelve male national elite cyclists (25 ± 3 years; 76 ± 6 kg and VO2max of 5.2 ± 0.5 L/min) completed incremental power and maximal fat oxidation tests. Subsequently, they underwent field testing with physiological measures and fatigue responses evaluated through peak sprint power and 5 km time trial (TT) testing after 0, 2, 4, and 6 h of exercise. Peak power declined from 1362 ± 176 W in first sprint to 1271 ± 152 W after 2 h (p < 0.01) and then stabilized. In contrast, TT mean power gradually declined from 412 ± 38 W in the first TT to 384 ± 41 W in the final trial, with individual losses ranging from 2% to 14% and moderately correlated (r² = 0.45) to accumulated exercise time above lactate threshold. High carbohydrate intake (~90 g/h) maintained blood glucose levels, but post‐TT [lactate] decreased from 15.1 ± 2 mM to 7.1 ± 2.3 mM, while fat oxidation increased from 0.7 ± 0.3 g/min at 0 h to 1.1 ± 0.1 g/min after 6 h. The study identifies fatigue patterns in national elite cyclists. Peak sprint power stabilized after an initial impairment from 0 to 2 h, while TT power gradually declined over the 6 h simulated race, with increased differentiation in fatigue responses among athletes.
... After this period, participants performed a warm-up consisting of 10 min at 30% VO 2 max. After the warmup, the ramp exercise test was initiated, with increments of 10% VO 2 max every 3 min until the RER was > 1.00 [36]. All participants completed had obtained peak values of fat oxidation rate at 70% VO 2 max and the analysis of exercise intensity in this study ranged then from 30 to 70% VO 2 max. ...
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Purpose The aim of this study was to determine the influence of the CYP1A2 c.-163 A > C (rs762551) polymorphism on the effect of oral caffeine intake on fat oxidation during exercise. Methods Using a pilot randomized, double-blind, crossover, placebo-controlled trial, 32 young and healthy individuals (women = 14, men = 18) performed an incremental test on a cycle ergometer with 3-min stages at workloads from 30 to 70% of maximal oxygen uptake (VO2max). Participants performed this test after the ingestion of (a) placebo; (b) 3 mg/kg of caffeine; (c) 6 mg/kg of caffeine. Fat oxidation rate during exercise was measured by indirect calorimetry. The influence of the CYP1A2 c.-163 A > C polymorphism in the effect of caffeine on fat oxidation rates during exercise was established with a three-way ANOVA (substance × genotype × intensity). Results Eight participants were genotyped as AA, 18 participants were CA heterozygotes, and 6 participants were CC. There was a main effect of substance (F = 3.348, p = 0.050) on fat oxidation rates during exercise with no genotype effect (F = 0.158, p = 0.959). The post hoc analysis revealed that, in comparison to the placebo, 3 and 6 mg/kg of caffeine increased fat oxidation at 40–50% VO2max in AA (all p < 0.050) and 50–60% VO2max in CA and CC participants (all p < 0.050). Conclusion Oral intake of 3 and 6 mg/kg of caffeine increased fat oxidation rate during aerobic exercise in individuals with AA, CA and CC genotypes. This suggests that the effect of caffeine to enhance fat oxidation during exercise is not influenced by the CYP1A2 c.-163 A > C polymorphism. Trial registration The study was registered on clinicaltrials.gov with ID: NCT05975489.
... Breath-by-breath data were inspected in 30-second windows to discard aberrant breaths (±2 standard deviations away from the local mean) due to e.g., talking, coughing, swallowing. For every stage completed under lactate threshold, the measured _ VO 2 and _ VCO 2 were used to estimate aerobic energy expenditure using the Jeukendrup and Wallis equation for substrate oxidation during exercise (Jeukendrup & Wallis, 2005). The average value over the last minute of each sub-lactate threshold stage was calculated, normalised by body mass and expressed as the aerobic energy expenditure per minute per kg (kcal/min/kg) i.e., running economy (Beck et al., 2018). ...
... Respiratory gases were monitored for 2, 3 min periods, starting at 30 min and 57 min. Carbohydrate and fat oxidation rates were calculated using equations (Jeukendrup and Wallis 2005) based on the last minute of each collection. ...
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Purpose Chewing duration can affect food particle size, gastric processing, and postprandial glycemia, but these effects have not been investigated with exercise. This study examined how the chewing duration of a food bar impacts glycemic and metabolic responses, gastrointestinal (GI) symptoms, psychological affect, and performance during endurance running. Methods This randomized, unblinded, crossover study had 15 males (35.2 ± 7.4 years, VO2peak: 56.1 ± 5.2 ml/kg/min) attend three laboratory visits. Visit 1 required a VO2peak test, 10 min familiarization run at 60% VO2peak, and familiarization time-to-exhaustion (TTE) test (10 min at 90% VO2peak, followed by TTE at 100% VO2peak). Visits 2 and 3 consisted of a 60 min run at 60% VO2peak, followed by TTE testing. Participants were fed 45 g of a bar (180 kcal, 4 g fat, 33 g carbohydrate, 3 g protein, 1 g fiber) in 9 g servings 30 min before running, and 27 g of bar in 9 g servings at three timepoints during the 60 min run. Participants consumed the servings in 20 (20CHEW) or 40 (40CHEW) masticatory cycles, at 1 chew/second. Outcomes included blood glucose, substrate use, GI symptoms, perceived exertion (RPE), overall feeling, and TTE. Results Post-prandial blood glucose, GI symptoms, and RPE increased over time, but there were no significant between-condition or condition-by-time effects. TTE showed no significant between-condition effect (20CHEW: 288 ± 133 s; 40CHEW: 335 ± 299 s; p = 0.240). Overall feeling demonstrated a time-by-condition effect (p = 0.006), suggesting possible better maintenance over time with 40CHEW. Conclusion Cumulatively, the results suggest that extended chewing minimally impacts physiology, perceptions, and performance during 60 min moderate-intensity running.
... Some breath analysis systems have already been developed for space applications. Specifically, NASA's PUMA (Fig. 3a) is a wearable device [126] based on indirect calorimetry to quantify fatty acid and carbohydrate oxidation rates [127]. More specifically, the device featured a breathing mask to collect breath and measure the expiratory gas flow rate [11]. ...
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Humanity endeavors to resume crewed missions to the Moon and prepares for the exploration of Mars. These missions will require sustained human presence in space for longer periods than ever before. Space exposes astronauts to demanding conditions, including microgravity, radiation, rapid light-dark cycles, and hazardous chemicals. Gas sensors will be pivotal in preserving astronaut health by providing critical health data (e.g., through breath analysis) and space-resolved environmental information. Here, we explore the recent progress of gas sensors to meet the key needs of space exploration. First, the fundamental sensing principles of electrochemical, chemoresistive, mass-sensitive, and optical sensors are briefly introduced. Then, we connect space-related health challenges with suitable breath markers and sensor solutions, encompassing areas like gut microbiome, muscle activity, cardiovascular health, hepatic and renal function, and circadian rhythm. Finally, environmental exposure guidelines and suitable sensor innovations for distributed air quality monitoring in space vehicles and habitats are presented.
... During exercise, VȮ 2 , VĊO 2 , and HR were measured six times at approximately 0, 20, 40, 60, 70, and 80 min. Energy expenditure, carbohydrate, and fat oxidation rates were calculated from VȮ 2 (L/ min) and VĊO 2 (L/min) during the 90-min exercise bout as described by Jeukendrup and Wallis (2005;Péronnet & Massicotte, 1991): ...
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This study investigated the effects of EPO on hemoglobin (Hgb) and hematocrit (Hct), time trial (TT) performance, substrate oxidation, and skeletal muscle phenotype throughout 28 days of strenuous exercise. Eight males completed this longitudinal controlled exercise and feeding study using EPO (50 IU/kg body mass) 3×/week for 28 days. Hgb, Hct, and TT performance were assessed PRE and on Days 7, 14, 21, and 27 of EPO. Rested/fasted muscle obtained PRE and POST EPO were analyzed for gene expression, protein signaling, fiber type, and capillarization. Substrate oxidation and glucose turnover were assessed during 90‐min of treadmill load carriage (LC; 30% body mass; 55 ± 5% V̇O2peak) exercise using indirect calorimetry, and 6‐6‐[²H2]‐glucose PRE and POST. Hgb and Hct increased, and TT performance improved on Days 21 and 27 compared to PRE (p < 0.05). Energy expenditure, fat oxidation, and metabolic clearance rate during LC increased (p < 0.05) from PRE to POST. Myofiber type, protein markers of mitochondrial biogenesis, and capillarization were unchanged PRE to POST. Transcriptional regulation of mitochondrial activity and fat metabolism increased from PRE to POST (p < 0.05). These data indicate EPO administration during 28 days of strenuous exercise can enhance aerobic performance through improved oxygen carrying capacity, whole‐body and skeletal muscle fat metabolism.
... Fatmax stages were then determined as the stage closest to the peak of the curve. Oxidation rates of CHO and fat were calculated as previously described 11 . ...
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Introduction: We investigated the reliability of a novel Fatmax protocol on a treadmill, and if exercising at Fatmax in the cold would increase fat oxidation and energy expenditure.Methods: On separate days, five participants performed two identical Fatmax tests. They then exercised at Fatmax, in cold (~0°C) and thermoneutral (~22°C) environments for 30 min.Results: Excellent reliability (ICC >.9) was found for the Fatmax protocol, and a non- significant increase in fat utilization was observed during cold exercise at Fatmax. Conclusions: Our novel Fatmax protocol on a treadmill is reliable and its impact on fat utilization in the cold should be further studied.
... Substrate oxidation during the 1 h treadmill run was calculated with the proposed equations from Jeukendrup and Wallis [25] for exercise with moderate intensity (50% . VO 2max ) to high intensity (75% . ...
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Four weeks before competition in the 2023 Marathon des Sables, a 6-stage, ~250 km running event in the Sahara Desert, we examined the effects of a 7-day intake of New Zealand blackcurrant extract (210 mg anthocyanins per day) on 1 h treadmill running-induced physiological and metabolic responses in the heat (~34 °C, relative humidity: ~30%) in non-acclimatized amateur female and male athletes (age: 23, 38 yrs, BMI: 24.2, 28.4 kg·m−2, body fat%: 29.2, 18.8%, V˙O2max: 50.1, 52.1 mL·kg−1·min−1). During the 1 h run at 50%V˙O2max (speed female: 7.3, male: 7.5 km·h−1), indirect calorimetry was used, and heart rate was recorded at 15 min intervals with core temperature monitoring (0.05 Hz). The 1 h runs took place 3 h after a light breakfast and 2 h after intake of the final dose of New Zealand blackcurrant extract with water allowed ad libitum during the run. The New Zealand blackcurrant extract had no effects on the female athlete. The respiratory exchange ratio (RER) of the female athlete in the non-supplement control condition was 0.77 ± 0.01, indicating an existing ~77% contribution of fat oxidation to the energy requirements. In the male athlete, during 1 h of running, fat oxidation was higher by 21% (p < 0.01), carbohydrate oxidation was 31% lower (p = 0.05), RER was 0.03 units lower (p = 0.04), and core temperature was 0.4 °C lower (p < 0.01) with no differences for heart rate, minute ventilation, oxygen uptake, and carbon dioxide production for the New Zealand blackcurrant condition compared to the non-supplement control condition. Seven-day intake of New Zealand blackcurrant extract (210 mg anthocyanins per day) provided beneficial physiological and metabolic responses during exertional heat stress by 1 h of indoor (~34 °C) treadmill running in a male Marathon des Sables athlete 4 weeks before competition. Future work is required to address whether New Zealand blackcurrant provides a nutritional ergogenic effect for Marathon des Sables athletes during long-duration running in the heat combined with personalized nutrition.
... Participants were then instructed to begin the experimental trial and were required to maintain a cadence of 80 rev/min at an intensity equivalent to thermoneutral GET until volitional exhaustion. Total carbohydrate and fat oxidation rates (g/min) were calculated using equations suggested for moderate-to-high intensity exercise but less than approximately 75% of V O 2max (Jeukendrup and Wallis 2005), with the assumption of negligible protein oxidation. The participants were informed to abstain from consuming fluid until the end of the test. ...
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Purpose Caffeine is a commonly used ergogenic aid for endurance events; however, its efficacy and safety have been questioned in hot environmental conditions. The aim of this study was to investigate the effects of acute caffeine supplementation on cycling time to exhaustion and thermoregulation in the heat. Methods In a double-blind, randomised, cross-over trial, 12 healthy caffeine-habituated and unacclimatised males cycled to exhaustion in the heat (35 °C, 40% RH) at an intensity associated with the thermoneutral gas exchange threshold, on two separate occasions, 60 min after ingesting caffeine (5 mg/kg) or placebo (5 mg/kg). Results There was no effect of caffeine supplementation on cycling time to exhaustion (TTE) (caffeine; 28.5 ± 8.3 min vs. placebo; 29.9 ± 8.8 min, P = 0.251). Caffeine increased pulmonary oxygen uptake by 7.4% (P = 0.003), heat production by 7.9% (P = 0.004), whole-body sweat rate (WBSR) by 21% (P = 0.008), evaporative heat transfer by 16.5% (P = 0.006) and decreased estimated skin blood flow by 14.1% (P < 0.001) compared to placebo. Core temperature was higher by 0.6% (P = 0.013) but thermal comfort decreased by − 18.3% (P = 0.040), in the caffeine condition, with no changes in rate of perceived exertion (P > 0.05). Conclusion The greater heat production and storage, as indicated by a sustained increase in core temperature, corroborate previous research showing a thermogenic effect of caffeine ingestion. When exercising at the pre-determined gas exchange threshold in the heat, 5 mg/kg of caffeine did not provide a performance benefit and increased the thermal strain of participants.
... This was multiplied by the time in minutes and converted to kJ by multiplying kcal by 4.184. Fat and carbohydrate oxidation rates were calculated using the equations from Jeukendrup and Wallis (2005). Data from the first 30 minutes postexercise was used to assess excess postexercise oxygen consumption (Burt et al., 2014), which was calculated by subtracting pre-exercise VO 2 from postexercise VO 2 (Binzen et al., 2001). ...
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Background: Manipulation of macronutrient intake and exercise can alter overall energy consumption and potentially body composition. Aim: The purpose of this study was to manipulate the macronutrient content of breakfast before exercise to investigate the impact on exercise energy expenditure and postexercise energy intake (EI). Methods: Twelve active men were recruited, 11 finished the study protocol (age: 28 ± 9 years; VO 2 max: 56 ± 5 ml·kg ⁻¹ ·min ⁻¹ ). In a randomized crossover design, each participant completed 4 trials, 3 consisting of a specific breakfast (protein, PRO; carbohydrate, CHO; noncaloric; NON-CAL) followed in 1 h by a 45 minutes moderate intensity treadmill exercise protocol. The fourth trial consisted of breakfast and no exercise (CON). An ad-libitum lunch and food for the rest of the day were provided and assessed for EI. Measures included resting metabolic rate pre- and postbreakfast along with oxygen uptake (VO 2 ) during and after exercise, along with hunger scales, and blood measures of glucose, insulin and plasma-PYY prebreakfast, pre-exercise, postexercise, and 60 minutes postexercise. Results: Fat oxidation was highest during exercise in the NON-CAL (0.57 g·min ⁻¹ ) trial with similar levels of fat oxidation between PRO (0.50 g·min ⁻¹ ) and CHO trials (0.48 g·min ⁻¹ ). Hunger was not affected by PRO intake or exercise, nor was appetite hormones and glucose. EI at lunch and dinner was not significantly different between trials. Conclusion: Pre-exercise PRO intake did not modify fat oxidation during exercise, did not lead to a larger VO 2 versus CHO, nor did it attenuate EI postexercise.
... The rate of oxygen consumption (VȮ 2 ) and carbon dioxide (VĊO 2 ) production were measured continuously and computed at 5-second intervals throughout the running trials. VȮ 2 and VĊO 2 were subsequently used to determine substrate utilization using nonprotein equations, 32 with energy cost being determined as the sum of fat and carbohydrate use. The energy cost was then expressed as J•kg 0.75 •m −1 (i.e., allometrically scaled) to better account for differences in body mass in heterogeneous samples as opposed to linear scaling. ...
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Background Prior studies investigated selected discrete sagittal‐plane outcomes (e.g., peak knee flexion) in relation to running economy, hereby discarding the potential relevance of running technique parameters during noninvestigated phases of the gait cycle and in other movement planes. Purpose Investigate which components of running technique distinguish groups of runners with better and poorer economy and higher and lower weekly running distance using an artificial neural network (ANN) approach with layer‐wise relevance propagation. Methods Forty‐one participants (22 males and 19 females) ran at 2.78 m∙s⁻¹ while three‐dimensional kinematics and gas exchange data were collected. Two groups were created that differed in running economy or weekly training distance. The three‐dimensional kinematic data were used as input to an ANN to predict group allocations. Layer‐wise relevance propagation was used to determine the relevance of three‐dimensional kinematics for group classification. Results The ANN classified runners in the correct economy or distance group with accuracies of up to 62% and 71%, respectively. Knee, hip, and ankle flexion were most relevant to both classifications. Runners with poorer running economy showed higher knee flexion during swing, more hip flexion during early stance, and more ankle extension after toe‐off. Runners with higher running distance showed less trunk rotation during swing. Conclusion The ANN accuracy was moderate when predicting whether runners had better, or poorer running economy, or had a higher or lower weekly training distance based on their running technique. The kinematic components that contributed the most to the classification may nevertheless inform future research and training.
... Finally, 10 min post-exercise, participants completed an exercise enjoyment questionnaire (Kendzierski & DeCarlo, 1991). Gas exchange data were averaged over the final 5 min of each collection period, with rates of carbohydrate and fat oxidation calculated using published stoichiometric equations for exercise (Jeukendrup & Wallis, 2005). ...
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Data suggest cannabis users have similar or lower levels of blood lipids compared to nonusers. However, the extent to which cannabis users experience postprandial lipemia is not known. Eleven cannabis users and 11 nonusers completed either rest or 1 h of exercise at their ventilatory threshold the evening before a meal tolerance test (MTT). Substrate oxidation, blood pressure, and capillary blood were obtained before and every 30–60 min post‐meal for 3 h. Linear mixed models were utilized to examine differences in variables between groups, conditions, across time, and their interactions. Exercise led to increased fat oxidation post‐MTT ( p < 0.05), with cannabis users exhibiting higher AUC compared to the control trial ( p < 0.05). Exercise also caused significantly lower levels of triglycerides ( p < 0.05). Metabolic flexibility was improved in cannabis users in the exercise trial only ( p < 0.05). No effect of group, trial, or interactions were detected for other variables of interest (all p > 0.05). This study indicated that prior exercise improves lipid metabolism in cannabis users and nonusers after a high‐fat meal test. Cannabis users appear sensitive to the effects of exercise. Future studies should incorporate additional meals and variables related to cardiovascular health and metabolism.
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This study assessed the correlation between fat and carbohydrate oxidation dynamics in professional football players (body fat: 15.5 ± 1.0%; VO2max: 56.5 ± 1.2 ml kg−1 min−1), exploring its association to physical fitness and self-reported macronutrient intake. A graded exercise test was performed on a treadmill for the assessment of nutrient oxidation rates via indirect calorimetry. Then fat oxidation kinetics was fitted through the sine mathematical model for determining maximal fat oxidation (MFO) and its corresponding exercise intensity (FATmax). The symmetry, dilatation and translation of the curve were also computed. Carbohydrate oxidation kinetics was modelled through a third-degree polynomial regression and its area under the curve (AUCcarbs) was computed for each individual. Body composition was examined through bioelectrical impedance and macronutrient intake was determined by the 24 h recall method. The AUCcarbs was inversely related to the FATmax (r = −0.69, p < 0.01), the exercise intensity at which fat oxidation became negligible (r = −0.87, p < 0.01), and the dilatation of the fat oxidation kinetics (r = −0.51, p < 0.05). Furthermore, only body fat percentage turned to be positively correlated to MFO (r = 0.49, p < 0.05), whereas cardiorespiratory fitness was inversely related to the dilatation of the fat oxidation curve (r = −0.51, p < 0.05). The self-reported macronutrient intake was not related to fuel oxidation during the exercise. In conclusion, nutrient oxidation is associated with physical fitness but not self-reported macronutrient intake in professional football players. The impact of long-term nutritional interventions on footballer’s metabolism warrants further investigation.
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Women may be challenged to maintain thermoregulation due to hormonal changes associated with the menstrual cycle. The purpose of this study was to assess the effect of the menstrual cycle phase on core temperature, hydration status, and perceived exertion while exercising under uncompensable heat gain. Eleven eumenorrheic women (24.4±1.1 yrs, 65.7±2.4 kg, 22.7±1.5% body fat) walked for two 180-minute trials in a heat chamber (35ºC and 30% relative humidity) during early-follicular (EF) and mid-luteal (ML) phases. Subjects completed three intervals of 50 minutes of exercise at 50% VO2max. Physiological strain index (PSI), core temperature (TC), perceived heat (PH), and rating of perceived exertion (RPE) were measured throughout both trials. Nude body weight (NBW) and blood samples were collected pre- and post-trial. Blood samples were analyzed for hematocrit (Hct), hemoglobin (Hb), serum estrogen, progesterone, and aldosterone. NBW showed a main effect of time (p=0.002, ηp2=0.62). Aldosterone showed main effect of time (p=0.004, ηp2=0.59) and phase (p=0.014, ηp2=0.47), peaking post exercise in both EF and ML (527.6.1±89.0 pg·mL-1 vs 827.4±129.5 pg·mL-1 respectively, p=0.014). Estradiol and progesterone showed main effects of phase (p=0.007, ηp2=0.53; p=0.045, ηp2=0.30) but not time (p=0.68, p=0.32). TC showed main effect of time (p<0.001, ηp2=0.89) and phase, peaking at 170 min (EF: 37.8±0.1ºC vs. ML: 38.0±0.1 ºC, p=0.032, ηp2=0.38). Main effect of time was seen for PSI (p=0.002, ηp2=0.88), PH (p=0.004, ηp2=0.66), and RPE (p=0.026, ηp2=0.80). Sweat rate, Hct, Hb, and percent dehydration were not different between the phases. In conclusion, subjects demonstrated elevated Tc and basal aldosterone in ML corresponding with elevations in estrogen and progesterone. Aldosterone significantly increased following exercise in the heat but remained elevated in ML. These results indicate that elevated Tc during ML is maintained during exercise in the heat despite similar perceived heat and effort between phases.
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Sports drinks are specialised formulations used by athletes to enhance performance and accelerate recovery. The main component of these drinks is water, but they also contain carbohydrates, electrolytes, proteins and sometimes vitamins. These substances maintain fluid balance, replenish energy stores and prevent dehydration from leading to a decrease in performance. There are three main categories of sports drinks: isotonic, hypotonic and hypertonic, which cater to different needs depending on intensity and duration. Energy drinks are different from sports drinks. They usually contain caffeine, sugar and sometimes other stimulating ingredients. These drinks are consumed to increase mental alertness and provide temporary energy, but do not support recovery after exercise. While proper use of sports drinks can improve exercise performance, excessive consumption can lead to stomach upsets, weight gain or other health problems. This review highlights that sports drinks, when used appropriately, make an important contribution to optimise athletic performance and recovery. Consuming sports drinks at the right time and in the right amount is beneficial for the overall health and success of athletes.
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Paradigma, bilim insanlarının dünyaya bakış açısını şekillendirmek amacıyla kullanılmakta olan görüş demektir. Çok yönlü bir nitelik barındıran paradigma, yaklaşım ve modelleri çevreleyen ve araştırmacı bireyin olay ve olgularla alakalı durumdaki bakış açısını yahut dünya görüşünü ifade etmesine paradigma denmektedir. Bundan dolayı bilimsel konular üzerinde gerçekleştirilen her türlü araştırmada paradigmalar etken niteliktedir. Ayrıca araştırmacı bireyin kendi felsefi düşüncesine göre nicel, nitel yahut karma paradigmalardan birinden yararlanılabilir. Sporda Yeni Paradigmalar isimli kitabımız, spor bilimlerindeki akademik çalışmaları bir araya getirerek multidisipliner bir yaklaşımla hazırlanmıştır. Spor bilimleri alanındaki yenilikçi çalışmalara yer verilerek hazırlanan kitapta yedi bölüm bulunmaktadır. Bu bölümlerde teknolojik yeniliklerin ve yeni yaklaşımların oluşturulması hedeflenmiştir. Ayrıca Spor eğitiminden ve spor yönetimine kadar farklı bölümler mevcuttur. Alandaki yenilikçi çalışmaların literatüre katkı sağlaması amaçlanmaktadır.
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Purpose To determine the effect of carbohydrate ingestion during prolonged exercise on durability of the moderate-to-heavy-intensity transition and severe-intensity performance. Methods Twelve trained cyclists and triathletes (10 males, 2 females; V˙O2\dot{V}{\text{O}}_{2}peak, 59 ± 5 mL kg⁻¹ min⁻¹; training volume, 14 ± 5 h week⁻¹) performed an incremental test and 5-min time trial (TT) without prior exercise (PRE), and after 150 min of moderate-intensity cycling, with (POSTCHO) and without (POSTCON) carbohydrate ingestion. Results Power output at the first ventilatory threshold (VT1) was lower in POSTCHO (225 ± 36 W, ∆ -3 ± 2%, P = 0.027, n = 11) and POSTCON (216 ± 35 W, ∆ -6 ± 4%, P = 0.001, n = 12) than PRE (229 ± 37 W, n = 12), and lower in POSTCON than POSTCHO (∆ -7 ± 9 W, ∆ -3 ± 4%, P = 0.019). Mean power output in the 5-min TT was lower in POSTCHO (351 ± 53 W, ∆ -4 ± 3%, P = 0.025) and POSTCON (328 ± 63 W, ∆ -10 ± 10%, P = 0.027) than PRE (363 ± 55 W), but POSTCHO and POSTCON were not significantly different (∆ 25 ± 37 W, ∆ 9 ± 13%, P = 0.186). Blood glucose concentration was maintained in POSTCHO, and was significantly lower at the 120 and 150-min timepoint in POSTCON (P < 0.05). Conclusion These data suggest that durability of the moderate-to-heavy-intensity transition is improved with carbohydrate ingestion. This has implications for training programming and load monitoring.
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Background Carbohydrate restriction can alter substrate utilization and potentially impair endurance performance in female athletes. Caffeine intake may mitigate this performance decrements. Objectives The aim of this study was to test the hypothesis that maximal fat oxidation (MFO) rate would be enhanced in the carbohydrate (CHO) restricted state in trained females. Additionally, the impact of caffeine intake before exercise under conditions of low CHO availability was examined on time-trial performance. Methods By using a randomized, double-blinded, placebo-controlled, crossover design, 17 female endurance athletes completed 3 experimental blocks. Each block consisted of high-intensity-interval–training (HIT) in the evening, followed by a fat oxidation test to measure MFO rate and a 20-min time trial (20TT) performance the next morning. The females received standardized, isoenergetic diets with different timing of CHO intake: No CHO between exercise sessions without (FASTED) or with 300 mg caffeine (4.1–4.9 mg/kg body mass) (FASTED+CAFF) before morning exercise tests or CHO ingestion after HIT (FED). Results MFO rate was higher in FASTED+CAFF (0.57 ± 0.04 g/min) than that in FED (0.50 ± 0.04 g/min, P = 0.039) but not different from FASTED condition. Power output performed during the 20TT was higher after FASTED+CAFF (189 ± 9 W) than that after FASTED (+6.9%, P = 0.022) and FED (+4.2%, P = 0.054). Conclusions CHO restriction during recovery from HIT enhances MFO rate during subsequent exercise compared with the condition where CHOs were consumed during the recovery period, but the effect was only significant when CHO restriction was combined with caffeine supplementation before the MFO test. In addition, caffeine ingestion before exercise in the CHO-restricted state compensates for the decreased work capacity associated with the CHO-restricted state.
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Relative to exercise in a thermoneutral environment, there is only limited evidence demonstrating that a low glycaemic index (LGI) pre-exercise meal can enhance endurance exercise performance in a hot-humid (HH) condition. Also, previous studies predominantly utilised Western-based and single food items, with minimal focus on Asian-based mixed meals. This study aimed to investigate the impact of pre-exercise LGI and high glycaemic index (HGI) rice-based mixed meals on endurance performance among acclimatised trained athletes in HH condition (32 °C, 65% relative humidity). Twelve native-born endurance-trained male runners (age 22.0 ± 5.8 years; peak oxygen consumption (V̇O2peak) 64.2 ± 5.5 mL kg⁻¹ min⁻¹) completed two trials consisting of 45 min steady-state (SS) run at 70% V̇O2peak followed by 10 km performance run (TT10km). Three hours before exercise, participants consumed an isocaloric rice-based mixed meals containing either LGI (GI value = 47) or HGI (GI value = 80), providing 1.3 g of carbohydrate (CHO) per kg of body mass. Participants ran faster during TT10 km after consuming the LGI meal compared to the HGI meal (LGI: 55.18 ± 1.22 vs. HGI: 57.03 ± 2.25 min, p = 0.010). End rectal temperature did not significantly differ between trials (LGI: 39.16 ± 0.74 vs. HGI: 38.95 ± 0.46 °C, p = 0.352). Fat oxidation was higher during the SS run in the LGI compared to the HGI trial (LGI: 0.19 ± 0.05 vs. HGI: 0.13 ± 0.19 g min⁻¹, p = 0.001). This study demonstrated that, relative to HGI, consuming a pre-exercise LGI rice-based mixed meal enhanced endurance performance in HH environment among acclimatised trained male athletes.
Article
Restricted sugar and ketogenic diets can alter energy balance/metabolism, but decreased energy intake may be compensated by reduced expenditure. In healthy adults, randomization to restricting free sugars or overall carbohydrates (ketogenic diet) for 12 weeks reduces fat mass without changing energy expenditure versus control. Free-sugar restriction minimally affects metabolism or gut microbiome but decreases low-density lipoprotein cholesterol (LDL-C). In contrast, a ketogenic diet decreases glucose tolerance, increases skeletal muscle PDK4, and reduces AMPK and GLUT4 levels. By week 4, the ketogenic diet reduces fasting glucose and increases apolipoprotein B, C-reactive protein, and postprandial glycerol concentrations. However, despite sustained ketosis, these effects are no longer apparent by week 12, when gut microbial beta diversity is altered, possibly reflective of longer-term adjustments to the ketogenic diet and/or energy balance. These data demonstrate that restricting free sugars or overall carbohydrates reduces energy intake without altering physical activity, but with divergent effects on glucose tolerance, lipoprotein profiles, and gut microbiome.
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O presente estudo tem como tema principal os treinos em Zona 1 e seu impacto nas variáveis fisiológicas e desempenho na corrida. O objetivo geral da pesquisa é avaliar, por meio de uma revisão bibliográfica criteriosa e abrangente, o efeito dos treinos realizados nessa zona específica de intensidade no desempenho atlético, com foco na modalidade corrida. A questão norteadora desta investigação é: "Como os treinos em zona 1 podem impactar nas variáveis fisiológicas e no desempenho na corrida?". Através dela, busca-se elucidar a relação entre a intensidade do treino, as respostas fisiológicas do corpo humano e o consequente desempenho nas competições de corrida. A metodologia utilizada para responder a essa questão consiste em uma revisão bibliográfica abrangente, que envolve a análise crítica de estudos anteriores relacionados ao tema. Foram coletados artigos científicos em bancos de dados confiáveis, livros especializados na área de Fisiologia do Exercício e documentos oficiais de organizações esportivas que tratam do tema. Espera-se que este estudo contribua para a compreensão mais detalhada sobre como os treinos em zona 1 afetam as variáveis fisiológicas dos atletas e influenciam seu desempenho na corrida. Esses resultados podem auxiliar técnicos e atletas na elaboração de estratégias eficazes para melhorar o rendimento nas competições. A partir disso, este trabalho se torna relevante por trazer novas perspectivas e contribuições para o campo de estudo da Fisiologia do Exercício, especificamente em relação ao treinamento para corrida. Além disso, os achados desta pesquisa podem servir como base para futuros estudos sobre o tema.
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Context How pre-exercise meal composition influences metabolic and health responses to exercise later in the day is currently unclear. Objective Examine the effects of substituting carbohydrate for protein at lunch on subsequent exercise metabolism, appetite, and energy intake. Methods Twelve healthy males completed three trials in randomized, counterbalanced order. Following a standardized breakfast (779 ± 66 kcal; ∼08:15), participants consumed a lunch (1186 ± 140 kcal; ∼13:15) containing either 0.2 g·kg-1 carbohydrate and ∼2 g·kg-1 protein (LO-CARB), 2 g·kg-1 carbohydrate and ∼0.4 g·kg-1 protein (HI-CARB), or fasted (FAST). Participants later cycled at ∼60% V̇O2peak for 1 h (∼16:15) and post-exercise ad-libitum energy intake was measured (∼18:30). Substrate oxidation, subjective appetite, and plasma concentrations of glucose, insulin, non-esterified fatty acids (NEFA), peptide YY (PYY), glucagon-like peptide-1 (GLP-1), and acylated ghrelin (AG) were measured for 5 h post-lunch. Results Fat oxidation was greater during FAST (+11.66 ± 6.63 g) and LO-CARB (+8.00 ± 3.83 g) than HI-CARB (p < 0.001), with FAST greater than LO-CARB (+3.67 ± 5.07 g; p < 0.05). NEFA were lowest in HI-CARB and highest in FAST, with insulin demonstrating the inverse response (all p < 0.01). PYY and GLP-1 demonstrated a stepwise pattern, with LO-CARB greatest and FAST lowest (all p < 0.01). AG was lower during HI-CARB and LO-CARB versus FAST (p < 0.01). Energy intake in LO-CARB was lower than FAST (-383 ± 233 kcal; p < 0.001) and HI-CARB (-313 ± 284 kcal; p < 0.001). Conclusion Substituting carbohydrate for protein in a pre-exercise lunch increased fat oxidation, suppressed subjective and hormonal appetite, and reduced post-exercise energy intake.
Article
Purpose: To assess (1) whether and how a higher maximal lactate steady state (MLSS) at higher cycling cadence (RPM) comes along with higher absolute and/or fractional carbohydrate combustion (CHOMLSS), respectively, and (2) whether there is an interrelation between potential RPM-dependent MLSS effects and the maximally achievable RPM (RPMMAX). Methods: Twelve healthy males performed incremental load tests to determine peak power, peak oxygen uptake, and 30-minute MLSS tests at 50 and 100 per minute, respectively, to assess RPM-dependent MLSS, corresponding power output, CHOMLSS responses, and 6-second sprints to measure RPMMAX. Results: Peak power, peak carbon dioxide production, and power output at MLSS were lower (P = .000, ω2 = 0.922; P = .044, ω2 > 0.275; and P = .016, ω2 = 0.373) at 100 per minute than at 50 per minute. With 6.0 (1.5) versus 3.8 (1.2) mmol·L-1, MLSS was higher (P = .000, ω2 = 0.771) at 100 per minute than at 50 per minute. No corresponding RPM-dependent differences were found in oxygen uptake at MLSS, carbon dioxide production at MLSS, respiratory exchange ratio at MLSS, CHOMLSS, or fraction of oxygen uptake used for CHO at MLSS, respectively. There was no correlation between the RPM-dependent difference in MLSS and RPMMAX. Conclusions: The present study extends the previous finding of a consistently higher MLSS at higher RPM by indicating (1) that at fully established MLSS conditions, respiration and CHOMLSS management do not differ significantly between 100 per minute and 50 per minute, and (2) that linear correlation models did not identify linear interdependencies between RPM-dependent MLSS conditions and RPMMAX.
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It has been recognized that facilitation of fat metabolism is important for both performance and the health-related aspects of exercise. Although several studies have described the relationship between exercise intensity and fat oxidation, few studies have studied this relationship over a wide range of intensities. In absolute terms, carbohydrate oxidation will increase proportionally with exercise intensity, whereas the rate of fat oxidation will initially increase but will decrease again at high exercise intensities. Here we have defined the exercise intensity at which maximal fat oxidation is observed as Fatmax. This exercise intensity may have importance for weight loss programs, health-related exercise programs, and endurance training. Future research should focus on developing an exercise test with which Fatmax can be accurately determined. Further research should investigate the efficacy of training at Fatmax in a variety of conditions. Key Points: • It has been recognized that facilitation of fat metabolism is important for both performance and the health-related aspects of exercise. • In absolute terms, carbohydrate oxidation will increase proportionally with exercise intensity, whereas the rate of fat oxidation will initially increase but will decrease again at high exercise intensities. • Here we have defined the exercise intensity at which maximal fat oxidation is observed as Fatmax. • Fatmax may have importance for weight loss programs, health-related exercise programs, and endurance training. Introduction Much of the emphasis of exercise programs for obese patients, and endurance training for athletes, is on cardiovascular and respiratory benefits, and increasing the oxidative capacity of skeletal muscle (3, 11). Fat metabolism, however, is an area that has received less attention, even though its importance has been recognized for both performance and the health-related aspects of exercise (14–17, 25).
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We examined the effects of exercise intensity and a 10-wk cycle ergometer training program [5 days/wk, 1 h, 75% peak oxygen consumption (VO2 peak)] on plasma free fatty acid (FFA) flux, total fat oxidation, and whole body lipolysis in healthy male subjects (n = 10; age = 25.6 +/- 1.0 yr). Two pretraining trials (45 and 65% of VO2 peak) and two posttraining trials (same absolute workload, 65% of old VO2 peak; and same relative workload, 65% of new VO2 peak) were performed by using an infusion of [1-13C]palmitate and [1,1,2,3, 3-2H]glycerol. An additional nine subjects (age 25.4 +/- 0.8 yr) were treated similarly but were infused with [1,1,2,3,3-2H]glycerol and not [1-13C]palmitate. Subjects were studied postabsorptive for 90 min of rest and 1 h of cycling exercise. After training, subjects increased VO2 peak by 9.4 +/- 1.4%. Pretraining, plasma FFA kinetics were inversely related to exercise intensity with rates of appearance (Ra) and disappearance (Rd) being significantly higher at 45 than at 65% VO2 peak (Ra: 8.14 +/- 1.28 vs. 6.64 +/- 0.46, Rd: 8. 03 +/- 1.28 vs. 6.42 +/- 0.41 mol. kg-1. min-1) (P </= 0.05). After training, when measured at the same absolute and relative intensities, FFA Ra increased to 8.84 +/- 1.1, 8.44 +/- 1.1 and Rd to 8.82 +/- 1.1, 8.35 +/- 1.1 mol. kg-1. min-1, respectively (P </= 0.05). Total fat oxidation determined from respiratory exchange ratio was elevated during exercise compared with rest, but did not differ among the four conditions. Glycerol Ra was elevated during exercise compared with rest but did not demonstrate significant intensity or training effects during exercise. Thus, in young men, plasma FFA flux is increased during exercise after endurance training, but total fat oxidation and whole-body lipolysis are unaffected when measured at the same absolute or relative exercise intensities.
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