Maximal Fat Oxidation Research Articles

Effects of p-Synephrine during Exercise: A Brief Narrative Review.

The p-synephrine is the principal phytochemical found in bitter orange (Citrus aurantium). This substance is widely included in dietary supplements for weight loss/body fat reduction due to its potential benefits of increasing fat oxidation. For years, p-synephrine-containing dietary supplements have been marketed without proper knowledge of their true effectiveness to enhance fat utilization, especially when combined with exercise. However, the effects of p-synephrine on fat oxidation during exercise have been investigated in the last few years. The aim of the current discussion is to summarize the evidence on the effects of p-synephrine intake on fat oxidation and performance during exercise. Previous investigations have demonstrated that the acute intake of p-synephrine does not modify running sprint performance, jumping capacity, or aerobic capacity. However, the acute intake of p-synephrine, in a dose of 2–3 mg/kg of body mass, has been effective to enhance the rate of fat oxidation during incremental and continuous exercise. This effect has been observed in a range of exercise workloads between 30% and 80% of peak oxygen uptake (VO2peak). The p-synephrine has the ability to increase the maximal rate of fat oxidation during exercise of increasing intensity without affecting the workload at which maximal fat oxidation is obtained (Fatmax). The effect of p-synephrine on fat oxidation is normally accompanied by a concomitant reduction of carbohydrate utilization during exercise, without modifying the energy expended during exercise. The shifting in substrate oxidation is obtained without any effect on heart rate during exercise and the prevalence of adverse effects is negligible. Thus, the acute use of p-synephrine, or p-synephrine-containing products, might offer some benefits for those individuals seeking higher fat utilization during exercise at low to moderate intensities. However, more research is still necessary to determine if the effect of p-synephrine on fat oxidation during exercise is maintained with chronic ingestion, in order to ascertain the utility of this substance in conjunction with exercise programs to produce an effective body fat/weight loss reduction.

Caffeine increases maximal fat oxidation during a graded exercise test: is there a diurnal variation?

BackgroundThere is evidence that caffeine increases the maximal fat oxidation rate (MFO) and aerobic capacity, which are known to be lower in the morning than in the afternoon. This paper examines the effect of caffeine intake on the diurnal variation of MFO during a graded exercise test in active men.MethodsUsing a triple-blind, placebo-controlled, crossover experimental design, 15 active caffeine-naïve men (age: 32 ± 7 years) completed a graded exercise test four times at seven-day intervals. The subjects ingested 3 mg/kg of caffeine or a placebo at 8 am in the morning and 5 pm in the afternoon (each subject completed tests under all four conditions in a random order). A graded cycling test was performed. MFO and maximum oxygen uptake (VO2max) were measured by indirect calorimetry, and the intensity of exercise that elicited MFO (Fatmax) calculated.ResultsMFO, Fatmax and VO2max were significantly higher in the afternoon than in the morning (all P < 0.05). Compared to the placebo, caffeine increased mean MFO by 10.7% (0.28 ± 0.10 vs. 0.31 ± 0.09 g/min respectively, P < 0.001) in the morning, and by a mean 29.0% (0.31 ± 0.09 vs. 0.40 ± 0.10 g/min, P < 0.001) in the afternoon. Caffeine also increased mean Fatmax by 11.1% (36.9 ± 14.4 [placebo] vs. 41.0 ± 13.1%, P = 0.005) in the morning, and by 13.1% (42.0 ± 11.6 vs. 47.5 ± 10.8%, P = 0.008) in the afternoon.ConclusionThese findings confirm the previously reported diurnal variation in the whole-body fat oxidation rate during graded exercise in active caffeine-naïve men, and indicate that the acute ingestion of 3 mg/kg of caffeine increases MFO, Fatmax and VO2max independent of the time of day.Trial registrationNCT04320446. Registered 25 March 2020 - Retrospectively registered

A systematic comparison of commonly used stoichiometric equations to estimate fat oxidation during exercise in athletes.

Over the last half-century, different stoichiometric equations for calculating the energy cost of exercise based upon the combustion of mixtures of carbohydrates, fats, and proteins have been proposed and modified. With the means of indirect calorimetry, while measuring oxygen uptake, carbon dioxide production, and urinary urea nitrogen excretion, the contribution of specific substrates to overall energy production can be estimated. However, even with their long history of application, no previous studies have evaluated whether the use of different stoichiometric equations provides similar or distinct maximal fat oxidation rate (MFO) responses and information regarding MFO location (FAT<inf>max</inf>) in male athletes. Twenty healthy male athletes performed graded exercise testing (GXT) cycle ergometry using breath by breath gas analysis to assess fat oxidation and maximal oxygen uptake. Analysis of variance followed by within-equation effects, within-equation factors, and post hoc pairwise comparisons were used to examine within-equation differences. Compared stoichiometric equations demonstrated significant differences in the mean and maximal fat oxidation rates, varying up to nearly 7%. FAT<inf>max</inf> differences, however, were not noticed. Our findings suggest that for within-study designs, the equation used appears to be less important, but when inter-study comparisons are planned, caution is in order due to the presence of inter-equation differences.

Effects of Multi-Ingredient Preworkout Supplementation across a Five-Day Resistance and Endurance Training Microcycle in Middle-Aged Adults.

Preworkout multi-ingredient admixtures are used to maximise exercise performance. The present double-blind, cross-over study compared the acute effects of ingesting a preworkout multi-ingredient (PREW) admixture vs. carbohydrate (CHO) over a week (microcycle) comprising three resistance training (RT) workouts alternated with two 30-min low-intensity endurance sessions (END) on RT volume (kg lifted) and END substrate oxidation. Additionally, postworkout decreases of muscle function and subjective responses were analysed. Following a baseline assessment, fourteen recreationally trained, middle-aged adults (seven females, 48.8 ± 4.7 years old) completed two identical microcycles separated by a two-week washout period while receiving either PREW or CHO (15 min prior to workout). The RT volume, per session (SVOL) and for the entire week (WVOL), was calculated. Fatty acid oxidation (FAO) during 30-min cycling corresponding to their individually determined maximal fat oxidation was measured using expired gasses and indirect calorimetry. Assessments of performance and tensiomyography were conducted within 20 min after each RT. Higher (p = 0.001) SVOL and WVOL along with a larger proportion of FAO (p = 0.05) during the second END workout were determined under the PREW treatment. No other statistically significant differences were observed between conditions. Compared to CHO, a preworkout multi-ingredient appears to increase resistance volume and favour fat oxidation during low-intensity endurance exercises.

Relationships between diet and basal fat oxidation and maximal fat oxidation during exercise in sedentary adults

Background and aimsTo study the relationships between different dietary factors (i.e., energy, macronutrient and fatty acid intake, food group consumption, and dietary pattern) and basal fat oxidation (BFox) and maximal fat oxidation during exercise (MFO) in sedentary adults. Method and resultsA total of 212 (n = 130 women; 32.4 ± 15.1 years) sedentary healthy adults took part in the present study. Information on the different dietary factors examined was gathered through a food frequency questionnaire and three nonconsecutive 24 h recalls. Energy and macronutrient intakes and food consumption were then estimated and dietary patterns calculated. BFox and MFO were measured by indirect calorimetry following standard procedures. Our study shows that dietary fiber intake was positively associated with BFox after taking into consideration the age, sex, and energy intake. A significant positive association between nut consumption and BFox was observed, which became nonsignificant after taking into consideration the age and energy intake. Fat intake and the dietary quality index (DQI), and the DQI for the Mediterranean diet were positively associated with MFO, which was attenuated after taking sex, age, and energy intake into consideration. ConclusionA higher dietary fiber intake and fat intake are associated with higher BFox and MFO, respectively, in sedentary adults. Clinical trialsClinicalTrials.gov, ID: NCT02365129 (https://clinicaltrials.gov/ct2/show/study/NCT02365129) & ID: NCT03334357 (https://clinicaltrials.gov/ct2/show/NCT03334357).

유산소운동 중 최대 지방 산화에 관한 고찰

This study proposed a method for measuring the maximum fat oxidation rate along with a review of maximum fat oxidation (MFO) during aerobic exercise. In addition, we discussed the specific research results that each factor, such as training, sex, and dietary status, promotes or inhibits physiological changes in fat oxidation as determinants of MFO and Fatmax during exercise. As a research method, in order to examine the measurement of fatty acid oxidation and maximum fat oxidation rate during exercise, a literature search was conducted to identify all studies using the Fatmax protocol in the adult population. In the literature, ‘aerobic exercise’, ‘fat oxidation’, ‘maximum fat oxidation’, and ‘Fatmax’ were searched in PubMed and Web of Science databases, Korea Education and Research Information Service (RISS), and 76 studies were included in the review. Exercise intensity, duration, training status, gender and availability of dietary nutrients are all determinants of MFO and Fatmax, all of which affect systemic fat oxidation. In particular, exercise intensity has a significant effect on fat oxidation regardless of training status and dietary effects. Nevertheless, exercise regimens that lead to the ideal adaptation of fat oxidation related to improving exercise effects should be considered.

Chronic Effect of Fatmax Training on Body Weight, Fat Mass, and Cardiorespiratory Fitness in Obese Subjects: A Meta-Analysis of Randomized Clinical Trials.

Exercise training performed at the maximal fat oxidation intensity (FMT) stands out as a potential treatment of overweight and obesity. This work is a meta-analysis of randomized clinical trials of studies about the effect of FMT on fat mass and maximal oxygen consumption using PubMed, SCOPUS, EBSCOhost, and ScienceDirect as databases. Two independent reviewers selected 11 trials from 356 publications identified by the following keywords: fatmax, lipoxmax, maximal fat oxidation, peak of fat oxidation, physical training, physical exercise, body fat (BF), fat mass, overweight, and obesity. The risk of bias was assessed following the Cochrane Guidelines. The pooled mean difference was computed for each outcome with the random-effects model and the inverse-variance method. The meta-analysis was performed with the RevMan software v 5.3, and the heterogeneity across studies by the I2. The statistical significance was accepted at p < 0.05. Results showed that the FMT reduced body weight (MD = −4.30 kg, p < 0.01, I2 = 0%), fat mass (MD = −4.03 kg, p < 0.01, I2 = 0%), and waist circumference (MD = −3.34 cm, p < 0.01). Fat-free mass remains unchanged (MD = 0.08 kg, p = 0.85), but maximal oxygen consumption increased (MD = 2.96 mL∙kg−1∙min−1, p < 0.01, I2 = 0%). We conclude that FMT at short and medium-term (eight to twenty weeks) reduces body weight and BF, increasing cardiovascular fitness in low physical fitness people with obesity.

Substrate oxidation during exercise in taekwondo athletes: impact of aerobic fitness status

The present study aimed to investigate the potential effect of different aerobic fitness levels on substrate oxidation in trained taekwondo athletes. 57 male athletes (age 21.10±7.79 years; VO2max 50.67±6.67 ml/kg/min) with regular weekly taekwondo training and training experience of at least three years completed a graded exercise test to exhaustion on a treadmill. Maximal fat oxidation (MFO), the exercise intensity related to MFO (Fatmax), and carbohydrate (CHO) oxidation rate were measured using indirect calorimetry methods. The athletes then were divided into a low (&lt;50 ml/kg/min, n=18) and high (&gt;50 ml/kg/min, n=39) VO2max group. The average MFO was higher in the high VO2max group than in the low VO2max group (0.46±0.19 vs 0.28±0.11 g/min; P&lt;0.001). Although Fatmax tended toward higher values in the high VO2max group, no difference was observed between the groups (49.15±15.22 vs 42.42±12.37% of VO2max; P=0.18). It was also shown that the high VO2max group had a lower CHO oxidation rate and a higher fat oxidation rate at given exercise intensities. In conclusion, it seems that MFO and substrate oxidation rates in taekwondo athletes can be influenced by aerobic fitness level such that the athletes with higher VO2max appeared to use more fat as a fuel source for energy supply during a given exercise.

Caffeine increases whole-body fat oxidation during 1h of cycling at Fatmax.

The ergogenic effect of caffeine on exercise of maximum intensity has been well established. However, there is controversy regarding the effect of caffeine on shifting substrate oxidation at submaximal exercise. The aim of this study was to investigate the effect of acute caffeine ingestion on whole-body substrate oxidation during 1h of cycling at the intensity that elicits maximal fat oxidation (Fatmax). In a double-blind, randomized, and counterbalanced experiment, 12 healthy participants (VO2max = 50.7 ± 12.1mL/kg/min) performed two acute experimental trials after ingesting either caffeine (3mg/kg) or a placebo (cellulose). The trials consisted of 1h of continuous cycling at Fatmax. Energy expenditure, fat oxidation rate, and carbohydrate oxidation rate were continuously measured by indirect calorimetry. In comparison to the placebo, caffeine increased the amount of fat oxidized during the trial (19.4 ± 7.7 vs 24.7 ± 9.6g, respectively; P = 0.04) and decreased the amount of carbohydrate oxidized (94.6 ± 30.9 vs 73.8 ± 32.4g; P = 0.01) and the mean self-perception of fatigue (Borg scale = 11 ± 2 vs 10 ± 2 arbitrary units; P = 0.05). In contrast, caffeine did not modify total energy expenditure (placebo = 543 ± 175; caffeine = 559 ± 170kcal; P = 0.60) or mean heart rate (125 ± 13 and 127 ± 9 beats/min; P = 0.30) during exercise. Before exercise, caffeine increased systolic and diastolic blood pressure whilst it increased the feelings of nervousness and vigour after exercise (P < 0.05). These results suggest that a moderate dose of caffeine (3mg/kg) increases the amount of fat oxidized during 1h of cycling at Fatmax. Thus, caffeine might be used as an effective strategy to enhance body fat utilization during submaximal exercise. The occurrence of several side effects should be taken into account when using caffeine to reduce body fat in populations with hypertension or high sensitivity to caffeine.

Ultra Trail Performance is Differently Predicted by Endurance Variables in Men and Women.

The study aimed to assess the relationship between peak oxygen uptake, ventilatory thresholds and maximal fat oxidation with ultra trail male and female performance. 47 athletes (29 men and 18 women) completed a cardiopulmonary exercise test between 2 to 4 weeks before a 107-km ultra trail. Body composition was also analyzed using a bioelectrical impedance weight scale. Exploratory correlation analyses showed that peak oxygen uptake (men: r=-0.63, p=0.004; women: r=-0.85, p < 0.001), peak speed (men: r=-0.74, p < 0.001; women: r=-0.69, p=0.009), speed at first (men: r=-0.49, p=0.035; women: r=-0.76, p=0.003) and second (men: r=-0.73, p < 0.001; women: r=-0.76, p=0.003) ventilatory threshold, and maximal fat oxidation (men: r=-0.53, p=0.019; women: r=-0.59, p=0.033) were linked to race time in male and female athletes. Percentage of fat mass (men: r=0.58, p=0.010; women: r=0.62, p= 0.024) and lean body mass (men: r=-0.61, p=0.006; women: r=-0.61, p=0.026) were also associated with performance in both sexes. Subsequent multiple regression analyses revealed that peak speed and maximal fat oxidation together were able to predict 66% of male performance; while peak oxygen uptake was the only statistically significant variable explaining 69% of the variation in women's race time. These results, although exploratory in nature, suggest that ultra trail performance is differently predicted by endurance variables in men and women.

P-Synephrine, the main protoalkaloid of Citrus aurantium, raises fat oxidation during exercise in elite cyclists

The aim of this study was to investigate the acute effects of p-synephrine ingestion on substrate oxidation during exercise in elite cyclists. Fifteen elite cyclists volunteered to participate in a double blind, crossover, randomized and placebo-controlled experimental trial. During two different trials, participants either ingested a placebo (cellulose) or 3 mg/kg of p-synephrine. After 60 min for substances absorption, participants performed an incremental maximal cycle ergometer test until volitional fatigue (25 W/min). Breath-by-breath gas exchange data was continuously recorded during the entire test to estimate energy expenditure, carbohydrate oxidation, and fat oxidation rates by stoichiometric equations. Heart rate was continuously measured by using a heart rate monitor. The ingestion of p-synephrine had no significant effects on energy expenditure (F = 0.71, P = 0.40) or heart rate (F = 0.66, P = 0.43) during exercise. However, there was a main effect of p-synephrine to increase the rate of fat oxidation over the placebo (F = 5.1, P = 0.04) and the rate of fat oxidation was higher with p-synephrine in the following loads: 45 ± 2%, 51 ± 3%, 62 ± 3%, 67 ± 4%, 79 ± 5% and 85 ± 5% of the maximum wattage obtained in the test (all P < 0.05). The ingestion of p-synephrine did not modify the maximal rate of fat oxidation during the ramp test (mean value; 95%CI = 0.91; 0.79–1.03 vs 1.01; 0.91–1.11 g/min, respectively, P = 0.06) nor the exercise intensity at which maximal fat oxidation was achieved (i.e. Fatmax = 49; 48–53 vs 50; 47–51% Wmax, P = 0.52). Acute p-synephrine ingestion moved the fat oxidation-exercise intensity curve upwards during an incremental cycling test without affecting Fatmax.

Effect of ambient temperature on fat oxidation during an incremental cycling exercise test

Aim: The objective of this current research was to compare fat oxidation rates during an incremental cycling exercise test in a temperate vs. hot environment. Methods: Twelve healthy young participants were recruited for a randomised crossover experimental design. Each participant performed a VO2max test in a thermoneutral environment followed by two cycling ramp test trials, one in a temperate environment (18.3°C) and another in a hot environment (36.3°C). The ramp test consisted of 3-min stages of increasing intensity (+10% of VO2max) while gas exchange, heart rate and perceived exertion were measured. Results: During exercise, there was a main effect of the environment temperature on fat oxidation rate (F = 9.35, P = 0.014). The rate of fat oxidation was lower in the heat at 30% VO2max (0.42 ± 0.15 vs.0.37 ± 0.13 g/min; P = 0.042), 60% VO2max (0.37 ± 0.27 vs.0.23 ± 0.23 g/min; P = 0.018) and 70% VO2max (0.22 ± 0.26 vs.0.12 ± 0.26 g/min; P = 0.007). In addition, there was a tendency for a lower maximal fat oxidation rate in the heat (0.55 ± 0.2 vs.0.48 ± 0.2 g/min; P = 0.052) and it occurred at a lower exercise intensity (44 ± 14 vs.38% ± 8% VO2max; P = 0.004). The total amount of fat oxidised was lower in the heat (5.8 ± 2.6 vs 4.6 ± 2.8 g; P = 0.002). The ambient temperature also produced main effects on heart rate (F = 15.18, P = 0.005) and tympanic temperature (F = 25.23, P = 0.001) with no effect on energy expenditure (F = 0.01, P = 0.945). Conclusion: A hot environment notably reduced fat oxidation rates during a ramp exercise test. Exercising in the heat should not be recommended for those individuals seeking to increase fat oxidation during exercise.

Changes in body composition and substrate utilization after a short-term ketogenic diet in endurance-trained males.

Few studies have investigated the short-term effects of a very low carbohydrate ketogenic diet (KD) on body composition and substrate utilization in trained individuals. This study investigated effects on substrate utilization during incremental exercise, and changes in body composition, in response to seven days ad libitum consumption of a KD by athletes from endurance sports. Nine young trained males (age, 21.8 ± 1.9 y; height, 1.83 ± 0.11 m; body mass, 78.4 ± 13.8 kg; body fat, 14.9 ± 3.9%; VO2peak, 54.3 ± 5.9 mL kg-1 min-1) were assessed before (day 0; PRE) and after (day 7; POST) seven days of consuming an ad libitum KD. Following an overnight fast, body composition was measured by dual x-ray absorptiometry, and substrate utilization was measured during an incremental (3 min stages, 35 W increments) exercise test on a cycle ergometer. After KD, Wmax (PRE, 295 ± 30 W; POST, 292 ± 38 W) and VO2peak (PRE, 4.18 ± 0.33 L min-1; POST, 4.10 ± 0.43 L min-1) were unchanged, whereas body mass [-2.4 (-3.2, -1.6) kg; P < 0.001, d = 0.21], fat mass [-0.78 (-1.10, -0.46) kg; P < 0.001, d = 0.22] and fat-free mass (FFM) [-1.82 (-3.12, -0.51) kg; P = 0.013, d = 0.22] all decreased. The respiratory exchange ratio was lower, and rates of fat oxidation were higher, at POST across a range of exercise intensities. Maximal fat oxidation rate was ~1.8-fold higher after KD (PRE, 0.54 ± 0.13 g min-1; POST, 0.95 ± 0.24 g min-1; P < 0.001, d = 2.2). Short-term KD results in loss of both fat mass and FFM, increased rates of fat oxidation and a concomitant reduction in CHO utilization even at moderate-to-high intensities of exercise.

High-fat versus high-carbohydrate diets for optimal higher intensity endurance exercise performance: and the winner is….

High-fat versus high-carbohydrate diets for optimal higher intensity endurance exercise performance: and the winner is….

Maximal fat oxidation capacity is associated with cardiometabolic risk factors in healthy young adults

It is unknown whether resting fat oxidation (RFO), maximal fat oxidation (MFO) and FatMax (intensity at which MFO is reached) are related to cardiometabolic risk (CMR). Thus the aim of this study was to examine the association of RFO, MFO and FatMax with CMR. 81 healthy adults (n = 31 women; 22.72 ± 4.40 years) participated in this cross-sectional study. Glucose and triglycerides were analysed in plasma. Body composition, anthropometry, physical activity, blood pressure (BP) and heart rate measurements were taken. RFO and MFO were determined through indirect calorimetry. Maximal oxygen uptake (VO2max) test was performed until exhaustion after MFO test. The CMR cluster was created from individual CMR factors: waist circumference, body fat percentage, systolic BP, diastolic BP, blood glucose and plasma triglycerides. Groups of high and low MFO and VO2max were created. RFO was not associated with CMR (p < 0.05). FatMax, MFO and VO2max were associated with individual CMR factors as waist circumference (R 2 = 0.144; R 2 = 0.241; R 2 = 0.285; p = 0.001; respectively) and plasma triglycerides (R 2 = 0.111; p = 0.004 and R 2 = 0.130; p = 0.002 and R 2 = 0.093; p = 0.008; respectively) and clustered CMR factors (R 2 = 0.105; p = 0.008 and R 2 = 0.162; p = 0.001 and R 2 = 0.239; p = 0.001; respectively). VO2max was also associated with body fat percentage (R 2 = 0.105; p = 0.003) and diastolic BP (R 2 = 0.083; p = 0.01), even adjusting for sex or age (p < 0.05). Groups with high level of MFO or VO2max obtained lower CMR (p = 0.001), even adjusting for sex or age (p < 0.01). FatMax, MFO and, especially, VO2max are associated with CMR, regardless of age and sex. However, RFO is not associated with CMR.

NIRS-derived skeletal muscle oxidative capacity is correlated with aerobic fitness and independent of sex.

Near-infrared spectroscopy (NIRS) provides a simple and reliable measure of skeletal muscle oxidative capacity; however, its relationship to aerobic fitness and sex are unclear. We hypothesized that NIRS-derived oxidative capacity in the vastus lateralis (VL) and medial gastrocnemius (MG) would be correlated with indices of aerobic fitness and independent of sex. Twenty-six participants (13 males, 13 females) performed ramp- and step-incremental tests to volitional exhaustion on separate days to establish maximal oxygen uptake (V̇o2max), peak power output (PPO), lactate threshold (LT), gas exchange threshold (GET), respiratory compensation point (RCP), and maximal fat oxidation (MFO). Data were normalized to lean body mass to account for sex-based differences in body composition. Exercise tests were preceded by duplicate measurements of NIRS-derived oxidative capacity on the VL and MG muscles (i.e., repeated arterial occlusions following a brief set of muscle contractions). Skeletal muscle oxidative capacity for the VL (means ± SD: 21.9 ± 4.6 s) and MG (22.5 ± 6.1 s) were similar but unrelated (r2 = 0.03, P = 0.39). Skeletal muscle oxidative capacity for the VL, but not the MG (P > 0.05 for all variables), was significantly correlated with V̇o2max (r2 = 0.24; P = 0.01), PPO (r2 = 0.23; P = 0.01), LT (r2 = 0.23; P = 0.01), GET (r2 = 0.23; P = 0.01), and RCP (r2 = 0.27; P = 0.006). MFO was not correlated with VL or MG skeletal muscle oxidative capacity (P > 0.05). Females (54.9 ± 4.5 mL·kg LBM-1·min-1) and males (56.0 ± 6.2 mL·kg LBM-1·min-1), matched for V̇o2max (P = 0.62), had similar NIRS-derived oxidative capacities for VL (20.7 ± 4.4 vs. 23.2 ± 4.6 s; P = 0.18) and MG (24.4 ± 6.8 vs. 20.5 ± 4.8 s; P = 0.10). Overall, NIRS-derived skeletal muscle oxidative capacity in VL is indicative of aerobic fitness and independent of sex in humans.NEW & NOTEWORTHY Near-infrared spectroscopy (NIRS) can be used to measure skeletal muscle oxidative capacity. Here, we demonstrated that NIRS-derived skeletal muscle oxidative capacity of the vastus lateralis was independent of sex, reliable across and within days, and correlated with maximal and submaximal indices of aerobic fitness, including maximal oxygen uptake, lactate threshold, and respiratory compensation point. These findings highlight the utility of NIRS for investigating skeletal muscle oxidative capacity in females and males.

Impact of Acute Eccentric versus Concentric Running on Exercise-Induced Fat Oxidation and Postexercise Physical Activity in Untrained Men

Introduction This study aimed at comparing the rate of exercise-induced fat oxidation and postexercise free-living physical activity after constant-load flat running (FR) and downhill running (DHR) bouts at an intensity that elicited maximal fat oxidation. Methods Participants were 11 healthy untrained men (mean age 25.6 ± 3.3 years; VO2max39.11 ± 8.05 ml/kg/min). The study included four visits. The first two visits determined the intensity of maximal fat oxidation during incremental FR and DHR tests. The second two visits involved constant-load FR or DHR at the intensity that elicited maximal fat oxidation in a counterbalanced order separated by two weeks. Gas exchange analysis was used to measure substrate oxidation during all exercise sessions. Sedentary time and physical activity were measured using ActiGraph triaxial accelerometers for three days including the day of exercise tests (the second day). Results During the incremental exercise tests, fat oxidation was significantly greater during the first stage of FR (P < 0.05) but started to increase during the fourth stage of DHR, although this did not reach significance. Of the 11 participants, 7 had greater fat oxidation during DHR. During continuous constant-load running, fat oxidation was higher during DHR than FR but at only two stages was either significant or borderline significant, and the time/group interaction was not significant. There was no significant effect on sedentary time of time/group interaction (P = 0.769), but there was a significant effect of time (P = 0.005), and there was no significant effect on total physical activity of time/group interaction (P = 0.283) or time (P = 0.602). Conclusion Acute aerobic eccentric exercise at an intensity eliciting maximal fat oxidation enhanced exercise-induced fat oxidation without worsening postexercise free-living physical activity, indicating it could be a useful training modality in weight management programs.

Exercise Duration Affects Maximal Fat Oxidation In Post- Menopausal Women: Implications For Exercise Prescription

The relative exercise intensity at maximal fat oxidation (FATmax, %VO2max) is used for exercise prescription for weight loss and metabolic health. In young men, FATmax is affected by exercise duration, with more prolonged testing protocols leading to higher values. PURPOSE: Since no data exist on post-menopausal women, we determined the effect of exercise duration on FATmax in this population. METHOD: 18 non-obese women (54±4 years; 4±3 years from menopause; 22±3 BMI) performed on a cycle ergometer a ramp test and 30-min steady-state trials at 40, 50, 60, 70 and 80% of the pre-determined VO2max. Based on VO2 and respiratory exchange ratio we calculated and compared (2-way RM ANOVA) absolute fat oxidation (FO, g-1·min-1) across intensities and duration. We compared FATmax derived from ramp (rFATmax), 5 (5FATmax) and 30-min data (30FATmax) (1-way RM ANOVA). We estimated FATmax using exercise duration (1, 5 and 30 min) and rFATmax as explanatory variables. RESULTS: FO was significantly affected by exercise duration, intensity and their interaction (for all p<0.001). Any exercise between 40 and 70% %VO2max, > 30 min, lead to an identical MFO (overall 0.21±0.09 g-1·min-1). 30FATmax occurred at a significantly higher %VO2max (57±10%) than rFATmax and 5FATmax (44±6 and 49±9%, not different). FATmax can be predicted from the linear combination of exercise duration (p<0.001) and rFATmax (p=0.01) as independent explanatory variables (r=0.69, SEE=8.8%). CONCLUSIONS: In post-menopausal women exercises at 40-80%VO2max of longer durations are associated with higher FATmax compared to ramp or short, steady-state sessions. Moreover, any intensity greater than rFATmax will maximize fat oxidation for exercises > 30 min. Finally, the intensity that maximizes fat oxidation can be predicted by exercise duration and rFATmax. This approach offers a valid approach for individualized exercise intensity prescription for weight loss and metabolic health in postmenopausal women.

Correspondence Between Indexes Of Maximal Fat Oxidation From Ramp Vs Steady-state Protocols In Postmenopausal Women

Maximal fat oxidation (MFO, in g-1·min-1) is an index of metabolic flexibility and the relative exercise intensity at MFO (FATmax, as % maximum oxygen consumption (VO2max)) is used for exercise prescription for weight loss and metabolic health. The time-consuming, steady-state protocol required for MFO/FATmax determination hinders the extensive use of these indexes. Alternative, ramp testing has been validated for MFO/FATmax determination in healthy, young males only. PURPOSE: to validate ramp testing for MFO/FATmax measure in post-menopausal women. METHODS: 18 sedentary, postmenopausal women (54±4 years; 4±3 years from menopause; 22±3 BMI) performed on a cycle ergometer: i) a ramp incremental test; ii) steady-state trials at 40, 50, 60, 70 and 80% of the VO2max as determined by the incremental test. We measured VO2, respiratory exchange ratio (R) and heart rate (HR). Based on VO2 and R from the ramp test (breath-by breath data) and steady-state protocol (5th minute of each trial) we measured absolute fat oxidation (FO, in g-1·min-1); then, we determined MFO in absolute units (in g-1·min-1) and the relative intensity corresponding to MFO, i.e. FATmax, that was expressed relative to VO2max and directly determined maximal HR (HRmax). MFO and FATmax from the ramp (rMFO and rFATmax) were compared to the values from the steady-state protocol (ssMFO and ssFATmax) by paired t-Test. RESULTS: The ssMFO was significantly lower than rMFO (0.39±0.13 vs 0.19±0.07 g.min-1 p<0.001). On the contrary, the rFATmax and ssFATmax occurred at an identical %VO2max (45±6 vs 47±7%VO2max p=0.17) and %HRmax (61±6 vs 62±6% HRmax p=0.54). CONCLUSIONS: In agreement with previous studies conducted in young males, our data confirm that only steady-state protocols allow accurate MFO quantification. On the contrary, accurate measures of FATmax can be obtained indifferently from both ramp and steady-state protocols in post-menopausal women. Therefore, ramp testing offers a valid alternative to more time-consuming steady-state protocols for the identification of optimal exercise intensity for weight loss and metabolic health. Time-efficient testing strategies have a high practical value for longitudinal/large-scale evaluation of fat metabolism in postmenopausal women offering the means for individualized exercise prescription.

Low muscle mass impairs fat utilization during light-intensity exercise in Chinese men.

Age-related loss of the muscle mass is linked to obesity and diabetes because the muscle is the major site for fat oxidation which is influenced by exercise. We aimed to explore the association between fat oxidation rates (FORs) and exercise intensity during age-related muscle loss. A total of 224 healthy Chinese men aged 23-92 years were recruited. Fat and lean tissue masses were measured by DXA. The subjects were also tested using graded incremental exercise with an increased intensity of 10 W until maximal fat oxidation rate (Fatmax) was achieved. Real-time contribution (%) of fat to total energy expenditure were determined using indirect calorimetry. We found that appendicular skeletal muscle mass/weight (ASM/Wt) decreased during ageing and positively correlated with FORs during low-intensity exercise. In multiple linear regression models, FORs was positively related with ASM/Wt (β =0.446, P=0.0091) but negatively associated with exercise intensity (β =-0.573, P<0.0001), whereas fat oxidation rate did not show any association with age. Moreover, there was a significantly negative correlation between ASM/Wt and Fatmax. Our findings highlight the importance of muscle mass in fat utilization during low-intensity exercise. A higher exercise intensity indicated by Fatmax is recommended for improving fat oxidation in Chinese men with decreased muscle mass.