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Introduction/purpose: Aerobic exercise training (AET) has been shown to improve mitochondrial bioenergetics and upregulate proteins related to lipid metabolism. However, it remains to be determined if these alterations associated with AET persist when measured in energy balance (EB) in the days after the last bout of training. The purpose of the study was to test the hypothesis that improvements in skeletal muscle mitochondrial function induced by AET observed in previous literature would persist when measured after restoring EB conditions 72 h removed from the last exercise bout., Methods: Participants were 14 premenopausal women (age = 31.2 ± 6.7 yr, BMI = 26.6 ± 5.1 kg·m). The AET program required three monitored training sessions per week for 8-16 wk. Skeletal muscle biopsies were obtained at baseline and after 8-16 wk of AET (≥72 h after the last exercise bout). All food was provided for 72 h before biopsies, and EB was managed 24 h before testing within ±100 kcal of measured energy requirements using a whole-room calorimeter. Mitochondrial oxidative capacity was quantified in permeabilized muscle fibers from the vastus lateralis., Results: We found that AET increased coupled respiration (154%) and uncoupled respiration (90%) rates using a fatty acid substrate (palmitoyl carnitine) (P < 0.05). However, when rates were normalized to complex IV activity (a marker of mitochondrial content), no significant differences were observed. In addition, there were no changes in proteins known to mediate mitochondrial biogenesis or lipid transport and metabolism after AET., Conclusion: Eight to 16 wk of AET improved mitochondrial capacity under fatty acid substrate when assessed in EB, which appears to be due to mitochondrial biogenesis.

Exercise is known to improve insulin sensitivity (SI); however, studies to date have been confounded by negative energy deficits after exercise., Purpose: The primary objective of this study was to assess the effect of 8 to 16 wk of aerobic exercise training on the SI of untrained women under rigorously controlled energy-balanced conditions. The secondary objective was to determine if one acute bout of moderate-intensity continuous (MIC) or high-intensity interval (HII) exercise further affected SI., Methods: Insulin sensitivity was assessed in 28 untrained women at baseline, after 8 to 16 wk of training with no-exercise (NE) before assessment, 22 h after MIC (50% V˙O2peak), and 22 h after HII (84% V˙O2peak) using a hyperinsulinemic-euglycemic clamp. Participants were in a whole-room indirect calorimeter during each condition, and food intake was adjusted to ensure energy balance across 23 h before each clamp., Results: There were no significant differences in acute energy balance between each condition. Results indicated a significant main effect of time, such that SI was higher during the HII condition compared with both baseline and NE (P < 0.05). No significant differences in SI were observed after NE or MIC., Conclusions: Widely reported improvements in SI in response to chronic exercise training may be mediated in part by shifts in energy balance. However, an acute bout of HII exercise may increase SI even in the context of energy balance.

Introduction: Resting energy expenditure (REE) increases after an intense exercise; however, little is known concerning mechanisms., Purpose: The purpose of this study was to determine effects of a single bout of moderate-intensity continuous (MIC) aerobic exercise, or high-intensity interval (HII) exercise on REE under energy balance conditions., Methods: Thirty-three untrained premenopausal women were evaluated at baseline, after 8-16 wk of training, 22 h after either MIC (50% peak V˙O2) or HII (84% peak V˙O2). Participants were in a room calorimeter during and after the exercise challenge. Food intake was adjusted to obtain energy balance across 23 h. REE was measured after 22 h after all conditions. Twenty-three-hour urine norepinephrine concentration and serum creatine kinase activity (CrKact) were obtained. Muscle biopsies were obtained in a subset of 15 participants to examine muscle mitochondrial state 2, 3, and 4 fat oxidation., Results: REE was increased 22 h after MIC (64 ± 119 kcal) and HII (103 ± 137 kcal). Markers of muscle damage (CrKact) increased after HII (9.6 ± 25.5 U·L) and MIC (22.2 ± 22.8 U·L), whereas sympathetic tone (urine norepinephrine) increased after HII (1.1 ± 10.6 ng·mg). Uncoupled phosphorylation (states 2 and 4) fat oxidation were related to REE (r = 0.65 and r = 0.55, respectively); however, neither state 2 nor state 4 fat oxidation increased after MIC or HII. REE was not increased after 8 wk of aerobic training when exercise was restrained for 60 h., Conclusions: Under energy balance conditions, REE increased 22 h after both moderate-intensity and high-intensity exercise. Exercise-induced muscle damage/repair and increased sympathetic tone may contribute to increased REE, whereas uncoupled phosphorylation does not. These results suggest that moderate- to high-intensity exercise may be valuable for increasing energy expenditure for at least 22 h after the exercise.

Purpose: This study aims to determine the effects of aerobic or resistance training on activity-related energy expenditure (AEE; kcal·d(-1)) and physical activity index (activity-related time equivalent (ARTE)) following weight loss. It was hypothesized that weight loss without exercise training would be accompanied by decreases in AEE, ARTE, and nontraining physical activity energy expenditure (nonexercise activity thermogenesis (NEAT)) and that exercise training would prevent decreases in free-living energy expenditure., Methods: One hundred forty premenopausal women had an average weight loss of 25 lb during a diet (800 kcal·d(-1)) of furnished food. One group aerobically trained 3 times per week (40 min·d(-1)), another group resistance-trained 3 times per week (10 exercises/2 sets × 10 repetitions), and the third group did not exercise. Dual-energy x-ray absorptiometry was used to measure body composition, indirect calorimetry was used to measure resting energy expenditure (REE) and walking energy expenditure, and doubly labeled water was used to measure total energy expenditure (TEE). AEE, ARTE, and nontraining physical activity energy expenditure (NEAT) were calculated., Results: TEE, REE, and NEAT all decreased following weight loss for the no-exercise group, but not for aerobic and resistance trainers. Only REE decreased in the two exercise groups. Resistance trainers increased ARTE. HR and oxygen uptake while walking on the flat and up a grade were consistently related to TEE, AEE, NEAT, and ARTE., Conclusions: Exercise training prevents a decrease in energy expenditure, including free-living energy expenditure separate from exercise training, following weight loss. Resistance training increases physical activity, whereas economy/ease of walking is associated with increased TEE, AEE, NEAT, and ARTE.

Purpose: To examine the effects of three different frequencies of combined resistance and aerobic training on total energy expenditure (TEE) and activity-related energy expenditure (AEE) in a group of older adults., Methods: Seventy-two women, 60-74 yr old, were randomly assigned to one of three groups: 1 d · wk(-1) of aerobic training and 1 d · wk(-1) of resistance training (1 + 1), 2 d · wk(-1) of aerobic training and 2 d · wk(-1) resistance training (2 + 2), or 3 d · wk(-1) of aerobic training and 3 d · wk(-1) of resistance training (3 + 3). Body composition (dual-energy x-ray absorptiometry), feeling of fatigue, depression, and vigor (questionnaire), strength (one-repetition maximum), serum cytokines (enzyme-linked immunosorbent assay), maximal oxygen uptake (progressive treadmill test), resting energy expenditure, and TEE were measured before and after 16 wk of training. Aerobic training consisted of 40 min of aerobic exercise at 80% maximum heart rate, and resistance training consisted of two sets of 10 repetitions for 10 different exercises at 80% of one repetition maximum., Results: All groups increased fat-free mass, strength, and aerobic fitness and decreased fat mass. No changes were observed in cytokines or perceptions of fatigue/depression. No time-group interaction was found for any fitness/body composition variable. TEE and AEE increased with the 2 + 2 group but not with the other two groups. Nonexercise training AEE (nonexercise training activity-related thermogenesis) increased significantly in the 2 + 2 group (+200 kcal · d(-1)), group 1 + 1 showed a trend for an increase (+68 kcal · d(-1)), and group 3 + 3 decreased significantly (-150 kcal · d(-1))., Conclusion: Results indicate that 3 + 3 training may inhibit nonexercise training activity-related thermogenesis by being too time consuming and does not induce superior training adaptations to 1 + 1 and 2 + 2 training.