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Introduction: Liver fat (LF) and visceral adipose tissue (VAT) content decreases with training, however, this has mainly been investigated in sedentary obese or healthy participants. The aim of this study was to investigate the effects of repeated prolonged exercise on LF and VAT content in well‐trained older men and to compare baseline LF and VAT content to recreationally active older men. Method: A group of five well‐trained older men were tested before and after cycling a total distance of 2558 km in 16 consecutive days. VAT content and body composition was measured using DXA before a bicycle ergometer test was performed to determine maximal fat oxidation (MFO), maximal oxygen consumption (VO2max$$ {\mathrm{VO}}_{2_{\mathrm{max}}} $$), and the relative intensity at which MFO occurred (Fatmax). LF content was measured on a separate day using MRI. For comparison of baseline values, a control group of eight healthy age‐ and BMI‐matched recreationally active men were recruited. Results: The well‐trained older men had lower VAT (p = 0.02), and a tendency toward lower LF content (p = 0.06) compared with the control group. The intervention resulted in decreased LF content (p = 0.02), but VAT, fat mass, and lean mass remained unchanged. VO2max$$ {\mathrm{VO}}_{2_{\mathrm{max}}} $$, MFO, and Fatmax were not affected by the intervention. Conclusion: The study found that repeated prolonged exercise reduced LF content, but VAT and VO2max$$ {\mathrm{VO}}_{2_{\mathrm{max}}} $$ remained unchanged. Aerobic capacity was aligned with lower LF and VAT in older active men. [ABSTRACT FROM AUTHOR]

Introduction: In men, whole body peak fat oxidation (PFO) determined by a graded exercise test is closely tied to plasma free fatty acid (FFA) availability. Men and women exhibit divergent metabolic responses to fasting and exercise, and it remains unknown how the combined fasting and exercise affect substrate utilization in women. We aimed to investigate this, hypothesizing that increased plasma FFA concentrations in women caused by fasting and repeated exercise will increase PFO during exercise. Then, that PFO would be higher in women compared with men (data from a previous study). Methods: On two separate days, 11 young endurance-trained women were investigated, either after an overnight fast (Fast) or 3.5 h after a standardized meal (Fed). On each day, a validated graded exercise protocol (GXT), used to establish PFO by indirect calorimetry, was performed four times separated by 3.5 h of bed rest both in the fasted (Fast) or fed (Fed) state. Results: Peak fat oxidation increased in the fasted state from 11 ± 3 (after an overnight fast, Fast 1) to 16 ± 3 (mean ± SD) mg/min/kg lean body mass (LBM) (after ~22 h fast, Fast 4), and this was highly associated with plasma FFA concentrations, which increased from 404 ± 203 (Fast 1) to 865 ± 210 μmol/L (Fast 4). No increase in PFO was found during the fed condition with repeated exercise. Compared with trained men from a former identical study, we found no sex differences in relative PFO (mg/min/kg LBM) between men and women, in spite of significant differences in plasma FFA concentrations during exercise after fasting. Conclusion: Peak fat oxidation increased with fasting and repeated exercise in trained women, but the relative PFO was similar in young trained men and women, despite major differences in plasma lipid concentrations during graded exercise. [ABSTRACT FROM AUTHOR]

An attenuated ability to appropriately oxidize fat (metabolic inflexibility) has been associated with the development of obesity and type 2 diabetes. Previous studies have found that regular exercise training increases the body's ability to oxidize fat during exercise, but also shown that fat oxidation at the same relative and absolute exercise intensity is lower in old compared with young adults. Based on these studies we investigated the effect of training status on the whole-body peak fat oxidation rate (PFO) during exercise in young and middle-aged trained and untrained men. We hypothesized that aging was associated with decreased PFO, but regular exercise training could counteract this decline. 36 healthy non-overweight young and middle-aged men were recruited into a four groups: young (27 [24–30] yrs, (Mean [95% CI])) untrained (⩒O2peak: 47 [44–49] ml/min/kg), young (28 [26–30] yrs) trained (⩒O2peak: 64 [62–67] ml/min/kg), middle-aged (55 [53–57] yrs) untrained (⩒O2peak: 37 [32–42] ml/min/kg) and middle-aged (54 [51–57] yrs) trained (⩒O2peak: 55 [51–58] ml/min/kg). PFO was measured by indirect calorimetry while subjects performed a validated incremental exercise protocol on a cycle ergometer. Whole-body peak fat oxidation rate was higher in the young trained compared to young untrained subjects (0.70 [0.65–0.75] vs.0.45 [0.36–0.54] g/min, post-hoc: p < 0.001); however, this training effect was attenuated in middle-aged trained and untrained subjects (0.44 [0.38–0.50] vs. 0.41 [0.35–0.47] g/min, post-hoc: p = 0.83, respectively). In summary, these findings suggest that the training induced effects on whole-body fat oxidation found in young men may be attenuated in middle-aged men. [ABSTRACT FROM AUTHOR]

Peak fat oxidation rate (PFO) and the intensity that elicits PFO (Fatmax) are commonly determined by a validated graded exercise test (GE) on a cycling ergometer with indirect calorimetry. However, for upper body exercise fat oxidation rates are not well elucidated and no protocol has been validated. Thus, our aim was to test validity and inter‐method reliability for determination of PFO and Fatmax in trained men using a GE protocol applying double poling on a ski‐ergometer. PFO and Fatmax were assessed during two identical GE tests (GE1 and GE2) and validated against separated short continuous exercise bouts (SCE) at 35%, 50%, and 65% of V̇O2peak on the ski‐ergometer in 10 endurance‐trained men (V̇O2peak: 65.1 ± 1.0 mL·min−1·kg−1, mean ± SEM). Between GE tests no differences were found in PFO (GE1: 0.42 ± 0.03; GE2: 0.45 ± 0.03 g·min−1, P = .256) or Fatmax (GE1: 41 ± 2%; GE2: 43 ± 3% of V̇O2peak, P = .457) and the intra‐individual coefficient of variation (CV) was 8 ± 2% and 11 ± 2% for PFO and Fatmax, respectively. Between GE and SCE tests, PFO (GEavg: 0.44 ± 0.03; SCE; 0.47 ± 0.06 g·min−1, P = .510) was not different, whereas a difference in Fatmax (GEavg: 42 ± 2%; SCE: 52 ± 4% of V̇O2peak, P = .030) was observed with a CV of 17 ± 4% and 15 ± 4% for PFO and Fatmax, respectively. In conclusion, GE has a high day‐to‐day reliability in determination of PFO and Fatmax in trained men, whereas it is unclear if PFO and Fatmax determined by GE reflect continuous exercise in general. [ABSTRACT FROM AUTHOR]

The aim of the present study was to investigate the relationship between maximal fat oxidation rate (MFO) measured during a progressive exercise test on a cycle ergometer and ultra-endurance performance. 61 male ironman athletes (age: 35 ± 1 yrs. [23-47 yrs.], with a BMI of 23.6 ± 0.3 kg/m² [20.0-30.1 kg/ m²], a body fat percentage of 16.7 ± 0.7 % [8.4-30.7 %] and a VO2peak of 58.7 ± 0.7 ml/min/kg [43.9-72.5 ml/m in/kg] SEM [Range]) were tested in the laboratory between 25 and 4 days prior to the ultra-endurance event, 2016 Ironman Copenhagen. Simple bivariate analyses revealed significant negative correlations between race time and MFO (r² = 0.12, p < 0.005) and VO2peak (r² = 0.45, p < 0.0001) and a positive correlation between race time and body fat percentage (r² = 0.27, p < 0.0001). MFO and VO2peak were not correlated. When the significant variables from the bivariate regression analyses were entered into the multiple regression models, VO2peak and MFO together explained 50 % of the variation observed in race time among the 61 Ironman athletes (adj R² = 0.50, p < 0.001). These results suggests that maximal fat oxidation rate exert an independent influence on ultra-endurance performance (> 9 h). Furthermore, we demonstrate that 50 % of the variation in Ironman triathlon race time can be explained by peak oxygen uptake and maximal fat oxidation. [ABSTRACT FROM AUTHOR]