Effects of exercise intensity on 24-h energy expenditure and substrate oxidation

Intense interval exercise induces greater changes in post-exercise metabolism compared to submaximal exercise in middle-aged adults

INTRODUCTION

High-intensity interval training (HIIT) and sprint interval training (SIT) consistently elevate post-exercise metabolism compared to moderate-intensity continuous training (MICT) in young adults (18-25 years), however few studies have investigated this in middle-aged adults.

PURPOSE

To assess the effect of exercise intensity on post-exercise metabolism following submaximal, near-maximal, and supramaximal exercise protocols in middle-aged adults.

METHODS

12 participants (8 females; age: 44 ± 10 years; V ˙ O2max: 35.73 ± 9.97 mL·kg-1 min-1) had their oxygen consumption ( V ˙ O2) measured during and for 2 h following 4 experimental sessions: (1) no-exercise control (CTRL); (2) MICT exercise (30 min at 65% V ˙ O2max); (3) HIIT exercise (10 × 1 min at 90% maximum heart rate with 1 min rest); and (4) modified-SIT exercise (8 × 15 s "all-out" efforts with 2 min rest). Between session differences for V ˙ O2 and fat oxidation were compared.

RESULTS

O2 consumed post-exercise was elevated during the 1st h and 2nd h following HIIT (15.9 ± 2.6, 14.7 ± 2.3 L; P < 0.036, d > 0.98) and modified-SIT exercise (16.9 ± 3.3, 15.30 ± 3.4 L; P < 0.041, d > 0.96) compared to CTRL (13.3 ± 1.9, 12.0 ± 2.5 L) while modified-SIT was also elevated vs HIIT in the 1st h (P < 0.041, d > 0.96). Total post-exercise O2 consumption was elevated following all exercise sessions (MICT: 27.7 ± 4.1, HIIT: 30.6 ± 4.8, SIT: 32.2 ± 6.6 L; P < 0.027, d > 1.03) compared to CTRL (24.9 ± 4.1 L). Modified-SIT exercise increased fat oxidation (0.103 ± 0.019 g min-1) compared to all sessions post-exercise (CTRL: 0.059 ± 0.025, MICT: 0.075 ± 0.022, HIIT: 0.081 ± 0.021 g·min-1; P < 0.007, d > 1.30) and HIIT exercise increased compared to CTRL (P = 0.046, d = 0.87).

CONCLUSION

Exercise intensity has an important effect on post-exercise metabolism in middle-aged adults.

Exercise Timing Matters for Glycogen Metabolism and Accumulated Fat Oxidation over 24 h

Due to increasingly diverse lifestyles, exercise timings vary between individuals: before breakfast, in the afternoon, or in the evening. The endocrine and autonomic nervous systems, which are associated with metabolic responses to exercise, show diurnal variations. Moreover, physiological responses to exercise differ depending on the timing of the exercise. The postabsorptive state is associated with greater fat oxidation during exercise compared to the postprandial state. The increase in energy expenditure persists during the post-exercise period, known as "Excess Post-exercise Oxygen Consumption". A 24 h evaluation of accumulated energy expenditure and substrate oxidation is required to discuss the role of exercise in weight control. Using a whole-room indirect calorimeter, researchers revealed that exercise performed during the postabsorptive state, but not during the postprandial state, increased accumulated fat oxidation over 24 h. The time course of the carbohydrate pool, as estimated by indirect calorimetry, suggests that glycogen depletion after postabsorptive exercise underlies an increase in accumulated fat oxidation over 24 h. Subsequent studies using ¹³C magnetic resonance spectroscopy confirmed that the variations in muscle and liver glycogen caused by postabsorptive or postprandial exercise were consistent with indirect calorimetry data. These findings suggest that postabsorptive exercise alone effectively increases 24 h fat oxidation.

Metabolic adaptation after combined resistance and aerobic exercise training in older women

OBJECTIVE

This study investigated whether combined aerobic and resistance training in older women leads to metabolic adaptation.

METHODS

A total of 80 women (64 White individuals; BMI: 30.0 [4.4] kg/m² ; age: 64.8 [3.5] years) followed 32 weeks of aerobic and resistance training. Body weight/composition (dual-energy X-ray absorptiometry) and resting metabolic rate (RMR; indirect calorimetry) were measured at baseline, week 16, and week 32. Metabolic adaptation was defined as significantly lower measured versus predicted RMR. A regression model to predict metabolic adaptation was developed that included race, age, baseline fat-free mass, RMR and respiratory quotient, and changes in net submaximal oxygen consumption after different tasks.

RESULTS

There was significant metabolic adaptation at week 16 (-59 [136] kcal/d, p = 0.002), following a 640-kcal/wk energy loss (-0.7 [2.6] kg of weight loss). In 53 women with complete data, metabolic adaptation was seen both at week 16 (-64 [129] kcal/d, p = 0.001) and at week 32 (-94 [127] kcal/d, p < 0.001). Metabolic adaptation at week 16 was predicted by race, age, baseline fat-free mass, RMR and respiratory quotient, and change in net oxygen consumption of walking (R² adjusted = 0.90, p < 0.001). Similar results were seen at week 32.

CONCLUSIONS

In older women with overweight and obesity, a minimal energy deficit induced by aerobic and resistance exercise is associated with metabolic adaptation at the level of RMR.

A Comparison of Substrate Utilization Profiles During Maximal and Submaximal Exercise Tests in Athletes

Background

Exercise is primarily sustained by energy derived from lipids (plasma free fatty acids and intramuscular triglycerides), and glucose (plasma glucose and muscle glycogen). Substrate utilization is the pattern by which these fuel sources are used during activity. There are many factors that influence substrate utilization. We aim to delineate the effect of exercise intensity and body composition on substrate utilization.

Objective

The objective of our study was to discern the differences in substrate utilization profiles during a maximal and submaximal graded exercise test, and to determine the extent to which body composition influences substrate utilization during the exercise tests.

Methods

A total of 27 male athletes, 32.5 ± 11 years of age, were recruited for this study. Body composition was analyzed using a bioelectrical impedance analyzer. Maximal and submaximal exercise tests were performed on a treadmill. A novel graded submaximal treadmill protocol was used for the submaximal test.

Results

Average percent body fat (PBF) was 15.8 ± 5%. Average maximal oxygen consumption (VO₂max) was 47.6 ± 9 mL/kg/min, while the average exercise intensity (percent VO₂max) at which participants were shifting to glucose predominance for energy during the maximal and submaximal tests were 76 ± 8.3% and 58.4 ± 21.1%, respectively. A paired-samples t-test was conducted to compare percent VO₂max at crossover point in maximal and submaximal graded exercise tests. There was a significant difference in percent VO₂max at the crossover point for maximal (76 ± 8.3%) and submaximal (58 ± 21.1%) tests (t = 4.752, p = 0.001). A linear regression was performed to elucidate the interaction between exercise intensity at the crossover point and body composition during a maximal and submaximal graded exercise test. There was a significant effect of PBF on percent VO₂max at crossover point during the maximal graded exercise test [F(1,24) = 9.10, P = 0.006] with an R² of 0.245. However, there was no significant effect of PBF on percent VO₂max at crossover point during the submaximal graded exercise test (P > 0.05).

Conclusion

Substrate utilization, represented by the crossover point, is dependent on the rate of increase in exercise intensity. At maximal efforts, the crossover to carbohydrates from fats as the predominant fuel source occurs at a significantly later stage of percent VO₂max than at submaximal efforts. Furthermore, body composition represented by PBF is a significant predictor of substrate utilization during maximal efforts. Athletes with a relatively higher PBF are more likely to have increased lipid oxidation during high intensity exercises than those with a lower body fat percentage.

Magnitude and duration of excess of post-exercise oxygen consumption between high-intensity interval and moderate-intensity continuous exercise: A systematic review

The present systematic review examined the effect of exercise intensity (high-intensity interval exercise [HIIE] vs. moderate-intensity continuous exercise [MICE] vs. sprint interval exercise [SIE]) on excess post-exercise oxygen consumption (EPOC). Twenty-two studies were included in the final evaluation. The retrieved investigations were split into studies that analysed short-duration (until 3 h) and long-duration (more than 3 h) EPOC. Studies that subtracted the baseline energy expenditure (EE) were analysed separately from those that did not. Most short-duration evaluations that subtracted baseline EE reported higher EPOC for HIIE (average of ~136 kJ) compared with MICE (average of ~101 kJ) and higher values for SIE (average of ~241 kJ) compared with MICE (average of ~151 kJ). The long-duration evaluations resulted in greater EPOC for HIIE (average of ~289 kJ) compared with MICE (average of ~159 kJ), while no studies comparing SIE versus MICE provided appropriate values. EE from EPOC seems to be greater following HIIE and SIE compared with MICE, and long-duration evaluations seem to present higher values than short-duration evaluations. Additionally, more standardized methodologies are needed in order to determine the effective EPOC time following these protocols.

Exercise Effects on Mitochondrial Function and Lipid Metabolism during Energy Balance

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.

Comparative Effectiveness of High-Intensity Interval Training and Moderate-Intensity Continuous Training for Cardiometabolic Risk Factors and Cardiorespiratory Fitness in Childhood Obesity: A Meta-Analysis of Randomized Controlled Trials

Purpose: The main objective of this meta-analysis was to compare the effectiveness of high-intensity interval training (HIIT) and of moderate-intensity continuous training (MICT) on cardiometabolic health in childhood obesity and determine whether HIIT is a superior form of training in managing obese children's metabolic health.

Methods: Relevant studies published in PubMed, Web of Science, Embase, the Cochrane Library, EBSCO, and CNKI were searched, restricted to those published from inception to 1 October 2019. Only randomized controlled trials (RCTs) depicting the effect of HIIT on childhood obesity were included.

Results: Nine RCTs involving 309 participants were included in the meta-analysis. Among the 309 participants, 158 subjects were randomized for HIIT, while the others were randomized for MICT. Significant differences were observed in the body weight (mean difference [MD] = −5.45 kg, p = 0.001), body mass index (BMI; MD = −1.661 kg/m², p = 0.0001), systolic blood pressure (SBP; MD = −3.994 mmHg, p = 0.003), and diastolic blood pressure (DBP; MD = −3.087 mmHg, p = 0.0001) in the HIIT group relative to the baseline values. Similar effects were found in the MICT group, as depicted by the significantly decreased values for body weight (MD = −4.604 kg, p = 0.0001), BMI (MD = −2.366 kg/m², p = 0.0001), SBP (MD = −3.089 mmHg, p = 0.019), and DBP (MD = −3.087 mmHg, p = 0.0001). However, no significant differences were observed in the changes in body weight, BMI, SBP, or DBP between the HIIT and MICT groups. Furthermore, our studies showed that both HIIT and MICT could significantly improve VO_2peak (HIIT, MD = 4.17 ml/kg/min, 95% CI: 3.191 to 5.163, p = 0.0001; MICT, MD = 1.704 ml/kg/min, 95% CI: 0.279 to 3.130, p = 0.019). HIIT also showed more positive effects on VO_2peak (SMD = 0.468, 95% CI: 0.040 to 0.897, p = 0.006) than MICT.

Conclusion: HIIT positively affects the cardiometabolic risk factors in childhood obesity. Similar positive effects on body composition and blood pressure were established. Moreover, HIIT can improve cardiorespiratory fitness more significantly than MICT. These findings indicate that HIIT may be an alternative and effective training method for managing childhood obesity.

PROSPERO Registration Number: CRD42018111308.

Mechanistic and methodological perspectives on the impact of intense interval training on post-exercise metabolism

The post-exercise recovery period is associated with an elevated metabolism known as excess post-exercise oxygen consumption (EPOC). The relationship between exercise duration and EPOC magnitude is thought to be linear whereas the relationship between EPOC magnitude and exercise intensity is thought to be exponential. Accordingly, near-maximal and supramaximal protocols such as high-intensity interval training (HIIT) and sprint interval training (SIT) protocols have been hypothesized to produce greater EPOC magnitudes than submaximal moderate-intensity continuous training (MICT). This review updates previous reviews by focusing on the impact of HIIT and SIT on EPOC. Research to date suggests small differences in EPOC post-HIIT compared to MICT in the immediate (<1 hour) recovery period, but greater EPOC values post-HIIT when examined over 24 hours. Conversely, differences in EPOC post-SIT are more pronounced, as SIT tends to produce a larger EPOC vs MICT at all time points. We discuss potential mechanisms that may drive the EPOC response to interval training (eg, glycogen resynthesis, mitochondrial uncoupling, and protein turnover among others) and also consider the role of EPOC as one of the potential contributors to fat loss following HIIT/SIT interventions. Lastly, we highlight a number of methodological shortcomings related to the measurement of EPOC following HIIT and SIT.

Relationship between V̇o2peak, cycle economy, and mitochondrial respiration in untrained/trained

Aerobic capacity is negatively related to locomotion economy. The purpose of this paper is to determine what effect aerobic exercise training has on the relationship between net cycling oxygen uptake (inverse of economy) and aerobic capacity [peak oxygen uptake (V̇o_2peak)], as well as what role mitochondrial coupled and uncoupled respiration may play in whole body aerobic capacity and cycling economy. Cycling net oxygen uptake and V̇o_2peak were evaluated on 31 premenopausal women before exercise training (baseline) and after 8-16 wk of aerobic training. Muscle tissue was collected from 15 subjects at baseline and post-training. Mitochondrial respiration assays were performed using high-resolution respirometry. Pre- (r = 0.46, P < 0.01) and postexercise training (r = 0.62, P < 0.01) V̇o_2peak and cycling net oxygen uptake were related. In addition, uncoupled and coupled fat respiration were related both at baseline (r = 0.62, P < 0.01) and post-training (r = 0.89, P < 01). Post-training coupled (r = 0.74, P < 0.01) and uncoupled carbohydrate respiration (r = 0.52, P < 05) were related to cycle net oxygen uptake. In addition, correlations between V̇o_2peak and cycle net oxygen uptake persist both at baseline and after training, even after adjusting for submaximal cycle respiratory quotient (an index of fat oxidation). These results suggest that the negative relationship between locomotion economy and aerobic capacity is increased following exercise training. In addition, it is proposed that at least one of the primary factors influencing this relationship has its foundation within the mitochondria. Strong relationships between coupled and uncoupled respiration appear to be contributing factors for this relationship.NEW & NOTEWORTHY The negative relationship between cycle economy and aerobic capacity is increased following exercise training. The strong relationship between coupled and uncoupled respiration, especially after training, appears to be contributing to this negative relationship between aerobic capacity and cycling economy, suggesting that mitochondrial economy is not increased following aerobic exercise training. These results are suggestive that training programs designed to improve locomotion economy should focus on changing biomechanics.

Effects of Exercise With and Without Energy Replacement on Substrate Utilization in the Fasting State

Objective: The present study aimed to examine the interactive effect of exercise and energy balance on energy expenditure and substrate utilization.Method: Seven men and 7 women underwent three 2-day experimental protocols in a random order. Each protocol consisted of no exercise (NE), exercise only (EO), or exercise with a matched energy replacement (ER) on day 1 followed by metabolic testing that occurred after a 12-hour overnight fasting on day 2. Both EO and ER involved treadmill running at 60% maximal oxygen uptake (VO₂max) that induced an energy expenditure of ∼ 500 kcal. The replacement meal used in ER contained ∼ 500 kcal made up of 45% carbohydrate, 30% fat, and 25% protein. During metabolic testing, oxygen uptake (VO₂), heart rate (HR), respiratory exchange ratio (RER), and rates of carbohydrate (COX) and fat oxidation (FOX) were determined in three successive 15-minute periods including rest and exercise at 50% and 70% VO₂max.Results: No differences in VO₂ and HR were found at rest among NE, EO, and ER. However, RER was lower in EO than NE (0.840 ± 0.014 vs 0.889 ± 0.012, p < 0.05), COX (g·min^-1) was lower in ER than NE (0.144 ± 0.016 vs 0.197 ± 0.019, p < 0.05), and FOX (g·min^-1) was higher in EO or ER than NE (0.054 ± 0.010 or 0.057 ± 0.009 vs 0.034 ± 0.007, p < 0.05). No treatment effects were observed for all variables at either intensity.Conclusions: This study demonstrates that an exercise of moderate intensity can increase resting fat oxidation even when the exercise-induced energy expenditure is balanced by energy intake. This finding suggests that muscle action is vital in augmenting fat utilization.

Sarcopenia and Its Implications for Metabolic Health

Sarcopenia not only affects the ability to lead an active lifestyle but also contributes to increased obesity, reduced quality of life, osteoporosis, and metabolic health, in part due to reduced locomotion economy and ease. On the other hand, increased obesity, decreased quality of life, and reduced metabolic health also contribute to sarcopenia. The purpose of this mini-review is to discuss the implications sarcopenia has for the development of obesity and comorbidities that occur with aging.

Effects of High-Intensity Interval Training vs. Sprint Interval Training on Anthropometric Measures and Cardiorespiratory Fitness in Healthy Young Women

Purpose: To compare the effects of 8 weeks of two types of interval training, Sprint Interval Training (SIT) and High-Intensity Interval Training (HIIT), on anthropometric measures and cardiorespiratory fitness in healthy young women.

Methods: A randomized clinical trial in which 49 young active women [age, 30.4 ± 6.1 years; body mass index, 24.8 ± 3.1 kg.m⁻²; peak oxygen consumption (VO₂peak), 34.9±7.5 mL.kg⁻¹.min⁻¹] were randomly allocated into a SIT or HIIT group. The SIT group performed four bouts of 30 s all-out cycling efforts interspersed with 4 min of recovery (passive or light cycling with no load). The HIIT group performed four bouts of 4-min efforts at 90–95% of peak heart rate (HRpeak) interspersed with 3 min of active recovery at 50–60% of HRpeak. At baseline and after 8 weeks of intervention, waist circumference, skinfolds (triceps, subscapular, suprailiac, abdominal, and thigh), body mass and BMI were measured by standard procedures and cardiorespiratory fitness was assessed by cardiorespiratory graded exertion test on an electromagnetically braked cycle ergometer.

Results: The HIIT and SIT groups improved, respectively, 14.5 ± 22.9% (P < 0.001) and 16.9 ± 23.4% (P < 0.001) in VO₂peak after intervention, with no significant difference between groups. Sum of skinfolds reduced 15.8 ± 7.9 and 22.2 ± 6.4 from baseline (P < 0.001) for HIIT and SIT groups, respectively, with greater reduction for SIT compared to HIIT (P < 0.05). There were statistically significant decreases in waist circumference (P < 0.001) for the HIIT (−3.1 ± 1.1%) and SIT (−3.3 ± 1.8%) groups, with no significant difference between groups. Only SIT showed significant reductions in body weight and BMI (p < 0.05).

Conclusions: Eight weeks of HIIT and SIT resulted in improvements in anthropometric measures and cardiorespiratory fitness, even in the absence of changes in dietary intake. In addition, the SIT protocol induced greater reductions than the HIIT protocol in the sum of skinfolds. Both protocols appear to be time-efficient interventions, since the HIIT and SIT protocols took 33 and 23 min (16 and 2 min of effective training) per session, respectively.

High-Intensity Intermittent Exercise Increases Fat Oxidation Rate and Reduces Postprandial Triglyceride Concentrations

(1) Background: This study investigated the effect of acute barehanded whole body high-intensity intermittent exercise (HIIE) and moderate intensity and continuous exercise (MICE) at the same quantity of energy expenditure on postprandial triglyceride (TG) concentrations. (2) Methods: Nine healthy males completed three trials (HIIE, MICE and control (CON)) in a random order separated by at least 14 days. After each intervention, the participants rested for 12 h and consumed a high-fat test meal on the next day. The blood samples and respiratory exchange ratio were observed in the fasted state and for 4 h after consuming the test meal. (3) Results: The HIIE had a significantly higher area under the curve of postprandial fat oxidation rate than MICE (p = 0.027) and CON (p = 0.035) and exhibited significantly lower postprandial TG concentration than the MICE and CON at 2 and 4 h after the test meal. Moreover, the HIIE displayed a higher postprandial TG concentration area under the curve than MICE (p = 0.013) and CON (p = 0.048). (4) Conclusions: The present study concluded that acute barehanded whole body HIIE could significantly lower postprandial TG concentrations. It possibly can induce a rise in the postprandial fat oxidation rate.

Why intensity is not a bad word: Optimizing health status at any age

Age-related declines in health and function make locomotion increasingly difficult leading to reductions in non-exercise activity thermogenesis (NEAT), skeletal muscle size and strength, and increased adiposity. Exercise is an important strategy to attenuate loss of function through the life cycle. Despite claims to the contrary, high-intensity exercise is important for the prevention of obesity and sarcopenia with advancing age. Therefore, the purpose of this mini-review is to present literature supporting the contention that low volume, high-intensity aerobic and/or resistance training can slow sarcopenia, sustain ease of movement, stimulate NEAT, and attenuate the accretion of fat mass.

Potential Causes of Elevated REE after High-Intensity Exercise

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.

Exercise before breakfast increases 24-h fat oxidation in female subjects

Background

Exercise performed in a postprandial state does not increase 24-h fat oxidation of male and female subjects. Conversely, it has been shown in male subjects that exercise performed in a postabsorptive state increases 24-h fat oxidation compared with that in sedentary control and that with exercise trials performed after breakfast, lunch, or dinner. There is a paucity of study evaluating the effect of exercise performed in a postabsorptive state in female subjects.

Method

Nine young female subjects participated in indirect calorimetry measurement over 24-h using a room-size metabolic chamber in which subjects remained sedentary or performed 60 min exercise before breakfast at 50% of V˙O2max. Exercise was accompanied by an increase in energy intake to ensure that subjects were in a similar state of energy balance over 24 h for the two trials.

Findings

Compared with the sedentary condition, exercise performed before breakfast increased 24-h fat oxidation (519 ± 37 vs. 400 ± 41 kcal/day). Time courses of relative energy balance differed between trials with transient negative energy balance observed before breakfast. The lowest values of relative energy balance observed during the 24-h calorimetry, i.e., transient energy deficit, were greater in exercise trials than in sedentary trials. The transient deficit in carbohydrate balance was also observed before breakfast, and magnitude of the deficit was greater in exercise trial compared to that of sedentary trial.

Interpretation

Under energy-balanced conditions, exercise performed in a post-absorptive state increases 24-h fat oxidation in female subjects. The effect of exercise performed before breakfast can be attributed to nutritional state: a transient deficit in energy and carbohydrate at the end of exercise.

Similar metabolic response to lower- versus upper-body interval exercise or endurance exercise

PURPOSE

To compare energy use and substrate partitioning arising from repeated lower- versus upper-body sprints, or endurance exercise, across a 24-h period.

METHODS

Twelve untrained males (24±4 y) completed three trials in randomized order: (1) repeated sprints (five 30-s Wingate, 4.5-min recovery) on a cycle ergometer (SIT_Legs); (2) 50-min continuous cycling at 65% V̇O₂max (END); (3) repeated sprints on an arm-crank ergometer (SIT_Arms). Respiratory gas exchange was assessed before and during exercise, and at eight points across 22h of recovery.

RESULTS

Metabolic rate was elevated to greater extent in the first 8h after SIT_Legs than SIT_Arms (by 0.8±1.1kJ/min, p=0.03), and tended to be greater than END (by 0.7±1.3kJ/min, p=0.08). Total 24-h energy use (exercise+recovery) was equivalent between SIT_Legs and END (p = 0.55), and SIT_Legs and SIT_Arms (p=0.13), but 24-h fat use was higher with SIT_Legs than END (by 26±38g, p=0.04) and SIT_Arms (by 27±43g, p=0.05), whereas carbohydrate use was higher with SIT_Arms than SIT_Legs (by 32±51g, p=0.05). Plasma volume-corrected post-exercise and fasting glucose and lipid concentrations were unchanged.

CONCLUSION

Despite much lower energy use during five sprints than 50-min continuous exercise, 24-h energy use was not reliably different. However, (i) fat metabolism was greater after sprints, and (ii) carbohydrate metabolism was greater in the hours after sprints with arms than legs, while 24-h energy usage was comparable. Thus, sprints using arms or legs may be an important adjunct exercise mode for metabolic health.

5'-AMP activated protein kinase α2 controls substrate metabolism during post-exercise recovery via regulation of pyruvate dehydrogenase kinase 4

It is well known that exercise has a major impact on substrate metabolism for many hours after exercise. However, the regulatory mechanisms increasing lipid oxidation and facilitating glycogen resynthesis in the post-exercise period are unknown. To address this, substrate oxidation was measured after prolonged exercise and during the following 6 h post-exercise in 5´-AMP activated protein kinase (AMPK) α2 and α1 knock-out (KO) and wild-type (WT) mice with free access to food. Substrate oxidation was similar during exercise at the same relative intensity between genotypes. During post-exercise recovery, a lower lipid oxidation (P < 0.05) and higher glucose oxidation were observed in AMPKα2 KO (respiratory exchange ratio (RER) = 0.84 ± 0.02) than in WT and AMPKα1 KO (average RER = 0.80 ± 0.01) without genotype differences in muscle malonyl-CoA or free-carnitine concentrations. A similar increase in muscle pyruvate dehydrogenase kinase 4 (PDK4) mRNA expression in WT and AMPKα2 KO was observed following exercise, which is consistent with AMPKα2 deficiency not affecting the exercise-induced activation of the PDK4 transcriptional regulators HDAC4 and SIRT1. Interestingly, PDK4 protein content increased (63%, P < 0.001) in WT but remained unchanged in AMPKα2 KO. In accordance with the lack of increase in PDK4 protein content, lower (P < 0.01) inhibitory pyruvate dehydrogenase (PDH)-E1α Ser(293) phosphorylation was observed in AMPKα2 KO muscle compared to WT. These findings indicate that AMPKα2 regulates muscle metabolism post-exercise through inhibition of the PDH complex and hence glucose oxidation, subsequently creating conditions for increased fatty acid oxidation.

Exercise Training and Energy Expenditure following Weight Loss

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.

Sex differences in the effects of 12 weeks sprint interval training on body fat mass and the rates of fatty acid oxidation and VO2max during exercise

BACKGROUND

The purpose of this study was to examine whether very short duration, very high intensity sprint interval training (SIT) leads to loss of body fat mass in association with improvements to VO2max and fatty acid oxidation, and to assess the extent of sex dimorphism in these physiological responses.

METHODS

A total of 24 men and 17 women (mean (SEM) age: 39 (±2) years; body mass index 24.6 (0.6)) completed measurements of the maximal rate of oxygen uptake (VO2max) and fatty acid oxidation (FATmax). Body fat and lean mass were measured by dual emission x-ray absorptiometry, and fasting blood lipid, glucose and insulin profiles were assessed before and after training. SIT consisted of 4×20 s sprints on a cycle ergometer at approximately 175% VO2max, three times per week for 12 weeks.

RESULTS

Fat mass decreased by 1.0 kg, although men lost statistically significantly more fat than women both when expressed in Kg and as % body fat. VO2max increased by around 9%, but women improved VO2max significantly more than men. FATmax improved by around 13%, but fasting plasma glucose, insulin, total triglyceride, total cholesterol and high-density lipoprotein (HDL) did not change after training, while low-density lipoprotein decreased by 8% (p=0.028) and the HDL:Total Cholesterol ratio improved by 6%. There were no sex differences in these metabolic responses to training.

CONCLUSIONS

These results show lower body fat %, and higher rates of fatty acid oxidation and VO2max after 12 weeks of training for just 4 min per week. Notably, women improved VO2max more than men, while men lost more fat than women.

Strong influence of dietary intake and physical activity on body fatness in elderly Japanese men: age-associated loss of polygenic resistance against obesity

Genome-wide association studies identified single nucleotide polymorphisms (SNPs) associated with body mass index (BMI) in middle-aged populations; however, it is unclear whether these SNPs are associated with body fatness in elderly people. We examined the association between genetic risk score (GRS) from BMI-associated SNPs and body fatness in elderly Japanese men. We also examined the contribution of GRS, dietary macronutrient intake, and physical activity to body fatness by different age groups. GRS was calculated from 10 BMI-associated SNPs in 84 middle-aged (30-64 years) and 97 elderly (65-79 years) Japanese men; subjects were divided into low, middle, and high GRS groups. Dietary macronutrient intake was assessed using a questionnaire, and physical activity was evaluated using both a questionnaire and an accelerometer. The middle-aged individuals with a high GRS had greater BMI; waist circumference; and total abdominal fat, visceral fat, and subcutaneous fat areas than the middle-aged individuals with low GRS, whereas the indicators were not different between the GRS groups in elderly individuals. Multiple linear regression analysis showed that GRS was the strongest predictor of BMI, total abdominal fat, and visceral fat in the middle-aged group, whereas fat, alcohol, and protein intakes or vigorous-intensity physical activity were more strongly associated with these indicators than was GRS in the elderly group. These results suggest that GRS from BMI-associated SNPs is not predictive of body fatness in elderly Japanese men. The stronger contribution of dietary macronutrient intake and physical activity to body fatness may attenuate the genetic predisposition in elderly men.

Adding sprints to continuous exercise at the intensity that maximises fat oxidation: implications for acute energy balance and enjoyment

The objective was to examine the effect of adding sprints to continuous exercise at the intensity that maximises fat oxidation (Fat(max)) on energy expenditure, substrate oxidation, enjoyment and post-exercise energy intake in boys. Nine overweight and nine normal weight boys (8-12 years) attended the laboratory on three mornings. First, body anthropometrics, peak aerobic capacity and Fat(max) were assessed. On the remaining two sessions, resting metabolic rate was determined before participants completed 30 min of either continuous cycling at Fat(max) (MOD) or sprint interval exercise consisting of continuous cycling at Fat(max) interspersed with four-second maximal sprints every two minutes (SI). Energy expenditure and substrate oxidation were measured during exercise and for 30 min post-exercise, while participants completed a modified Physical Activity Enjoyment Scale (PACES). This was followed by a buffet-like breakfast to measure post-exercise energy intake. Fat oxidation rate was similar between groups and protocols (P>0.05). Both groups expended more energy with SI compared to MOD, resulting from increased carbohydrate oxidation (P<0.05), which was not compensated by increased energy intake. Participants indicated that they preferred SI more than MOD, although there was no significant difference in PACES score between the protocols (P>0.05). In summary, the addition of short sprints to continuous exercise at Fat(max) increased energy expenditure without compromising fat oxidation or stimulating increased post-exercise energy intake. The boys preferred SI and did not perceive it to be any harder than MOD, indicating that sprint interval exercise should be considered in exercise prescription for this population.

A 45-minute vigorous exercise bout increases metabolic rate for 14 hours

INTRODUCTION

The magnitude and duration of the elevation in resting energy expenditure after vigorous exercise have not been measured in a metabolic chamber. This study investigated the effects of inserting a 45-min vigorous cycling bout into the daily schedule versus a controlled resting day on 24-h energy expenditure in a metabolic chamber.

METHODS

Ten male subjects (age = 22-33 yr) completed two separate 24-h chamber visits (one rest and one exercise day), and energy balance was maintained for each visit condition. On the exercise day, subjects completed 45 min of cycling at 57% Wmax (mean ± SD = 72.8% ± 5.8% VO(2)max) starting at 11:00 a.m. Activities of daily living were tightly controlled to ensure uniformity on both rest and exercise days. The area under the energy expenditure curve for exercise and rest days was calculated using the trapezoid rule in the EXPAND procedure in the SAS and then contrasted.

RESULTS

The 45-min exercise bout resulted in a net energy expenditure of 519 ± 60.9 kcal (P < 0.001). For 14 h after exercise, energy expenditure was increased 190 ± 71.4 kcal compared with the rest day (P < 0.001).

CONCLUSIONS

In young male subjects, vigorous exercise for 45 min resulted in a significant elevation in postexercise energy expenditure that persisted for 14 h. The 190 kcal expended after exercise above resting levels represented an additional 37% to the net energy expended during the 45-min cycling bout. The magnitude and duration of increased energy expenditure after a 45-min bout of vigorous exercise may have implications for weight loss and management.

Consumo de oxigênio de recuperação em resposta a duas sessões de treinamento de força com diferentes intensidades

O objetivo do presente estudo foi comparar o comportamento do consumo de oxigênio (VO2) em resposta a uma sessão de treinamento de força (TF) com objetivo em hipertrofia muscular (HP) com uma sessão com objetivo em resistência muscular localizada (RML). Nove indivíduos do sexo masculino (23,1 ± 2,1 anos) foram recrutados para este estudo. A força muscular dinâmica foi mensurada através do teste de 1RM. O VO2 foi coletado durante o repouso e 10 minutos de recuperação com um analisador de gases (CPX/D). As sessões foram compostas por um exercício de membros superiores (supino) e um de membros inferiores (agachamento), e compreenderam a execução de três séries de 6-8 repetições máximas (RM) a 80% de 1RM para HP e 15-20 RM a 55% de 1RM para RML. Foram analisados os dados de VO2 pós-exercício (EPOC), gasto energético (GE) de recuperação e constante de tempo de VO2 (CT). Foi observado que ambas sessões provocaram comportamento significativamente elevado de VO2 durante os 10min de recuperação em relação aos valores de repouso. Não houve diferenças significativas entre os valores de EPOC (litros) para HP (2,21 ± 0,54) e RML (2,60 ± 0,44), GE (kcal) para HP (10,36 ± 2,53) e RML (12,18 ± 2,04) e CT (segundos) para HP (56 ± 7) e RML (57 ± 6) (p > 0,05). Esses resultados demonstraram que uma sessão de TF com objetivo em RML é capaz de causar distúrbios metabólicos semelhantes àqueles provocados por uma sessão de HP, mesmo que seja em menor intensidade relativa a carga máxima.

Exercise improves fat metabolism in muscle but does not increase 24-h fat oxidation

Despite decades of research into the effects of exercise on fat metabolism, there is still no clear understanding of how exercise helps to regulate fat mass. Although exercise improves the capacity of muscle to oxidize fat, our studies suggest that moderate duration exercise (< or =1 h) has little impact on 24-h fat oxidation.

Resistance training conserves fat-free mass and resting energy expenditure following weight loss

OBJECTIVE

To determine what effect diet-induced approximately 12 kg weight loss in combination with exercise training has on body composition and resting energy expenditure (REE) in premenopausal African-American (AA) and European-American (EA) women.

METHODS AND PROCEDURES

This study was a longitudinal, randomized weight loss clinical intervention, with either aerobic (AT), resistance (RT), or no exercise training (NT). Forty-eight AA and forty-six EA premenopausal overweight (BMI between 27 and 30) women underwent weight loss to a BMI<25. Body composition (densitometry), REE (indirect calorimetry), maximal oxygen uptake (VO2max), and muscular strength (isometric elbow flexion) were evaluated when subjects were in energy balance.

RESULTS

AA women lost less fat-free mass (FFM, P<or=0.05) (47.0+/-4.6 to 46.9+/-5.0 kg) than EA women (46.4+/-4.9 to 45.2+/-4.6 kg). Regardless of race, RT maintained FFM (P<or=0.05) following weight loss (46.9+/-5.2 to 47.2+/-5.0 kg) whereas AT (45.4+/-4.2 to 44.4+/-4.1 kg) and NT (47.9+/-4.7 to 46.4+/-5.1 kg) decreased FFM (P<or=0.05). Both AT and NT decreased in REE with weight loss but RT did not. Significant time by group interactions (all P<or=0.05) for strength indicated that RT maintained strength and AT did not.

DISCUSSION

AA women lost less FFM than EA women during equivalent weight losses. However, following weight loss in both AA and EA, RT conserved FFM, REE, and strength fitness when compared to women who AT or did not train.

Excess post-exercise oxygen consumption in untrained men following exercise of equal energy expenditure: comparisons of upper and lower body exercise

AIM

This study assessed excess post-exercise oxygen consumption (EPOC) following continuous 200- kcal bouts of upper body exercise (UBE) and lower body exercise (LBE).

METHODS

Ten untrained men (age: 25.7 +/- 5.83 years; arm VO(2peak): 2.2 +/- 0.25 l/min; 21.5 +/- 4.35 ml/kg/min; leg VO(2peak): 3.1 +/- 0.38 l/min; 30.7 +/- 7.79 ml/kg/min) exercised at 60% mode-specific VO(2) peak using either an arm crank or a leg cycle protocol (counterbalanced order with 48 h between). Baseline VO(2) was monitored for 30 min. EPOC was measured until baseline was re-established.

RESULTS

EPOC magnitude and duration were significantly greater (p < 0.05) following LBE (2.93 +/- 1.4 l/min; 16.5 +/- 7.4 min) compared with UBE (1.89 +/- 0.7 l/min; 11.5 +/- 6.1 min).

CONCLUSIONS

Results indicate that leg exercise elicited a greater EPOC magnitude and duration compared with arm exercise of the same relative intensity and energy expenditure.

The Influence of Calcium Consumption on Weight and Fat Following 9 Months of Exercise in Men and Women

BACKGROUND

There is some evidence that calcium consumption improves weight loss during energy restriction but the effects of calcium consumption in conjunction with chronic exercise are unknown.

OBJECTIVE

The purpose of the study was to determine the degree to which calcium consumption influences weight and fat weight change as a result of 9 months of verified supervised exercise in the absence of energy restriction.

METHODS

Participants were 50 previously sedentary, overweight and moderately obese men (n=20) and women (n=30). Exercise of moderate intensity was performed for 45 min/d, 5 d/wk, under supervision. Diet intake was ad libitum and was measured for energy, macronutrient and micronutrient composition at baseline, 4 and 9 months by use of observer recorded weighed plate waste and multiple-pass 24-h dietary recall procedures.

RESULTS

Average calcium consumption was 987 +/- 389 mg/day for men and 786 +/- 276 mg/day for women. Weight change over the 9 months was -4.6 +/- 4.6 kg for men and 0.2 +/- 3.3 kg for women. Calcium consumption was associated with weight change (r =-0.47, p<0.05) in men. The calcium to protein ratio was associated with weight change (r=0.56) and fat weight change (r=-0.53) in men. There was no observed association between calcium and weight or fat weight change in women.

CONCLUSION

Weight and fat weight loss as a result of nine months of moderate intensity exercise may be improved by increased calcium consumption in men but was not observed in women.

Increased resting energy expenditure after 40 minutes of aerobic but not resistance exercise

OBJECTIVE

Resting energy expenditure (REE) is increased 24 hours after high-intensity aerobic exercise lasting 60 minutes, whereas results have been inconsistent after resistance training and aerobic exercise of shorter duration. The objective of the study was to compare the effects of 40 minutes of high-intensity aerobic vs. resistance exercise on REE 19 to 67 hours after exercise.

RESEARCH METHODS AND PROCEDURES

REE was compared 19, 43, and 67 hours after 40 minutes of aerobic training (AT; 80% maximum heart rate) or resistance training (RT; 10 repetitions at 80% maximum strength, two sets and eight exercises). Twenty-three black and 22 white women were randomly assigned to AT, RT, or no training (controls). Exercisers trained 25 weeks. REE was measured after a 12-hour fast.

RESULTS

There was a significant time x group interaction for REE when adjusted for fat-free mass and fat mass, with post hoc tests revealing that the 50-kcal difference between 19 and 43 hours (1310 +/- 196 to 1260 +/- 161 kcal) and the 34-kcal difference between 19 and 67 hours (1310 +/- 196 to 1276 +/- 168 kcal) were significant for AT. No other differences were found, including RT (19 hours, 1256 +/- 160; 43 hours, 1251 +/- 160; 67 hours, 1268 +/- 188 kcal). Urine norepinephrine increased with training only in AT. After adjusting for fat-free mass, REE Delta between 19 and both 43 and 67 hours was significantly related to urine norepinephrine (r = 0.76, p < 0.01 and 0.68, p < 0.03, respectively).

DISCUSSION

Consistent with findings on longer duration AT, these results show that 40 minutes of AT elevates REE for 19 hours in trained black and white women. This elevation did not occur with 40 minutes of RT. Results suggest that differences are, in part, due to increased sympathetic tone.

Excess post-exercise oxygen consumption in untrained males: effects of intermittent durations of arm ergometry

The purpose of this study was to investigate excess post-exercise oxygen consumption (EPOC) following a continuous 30 min bout of upper-body exercise (UBE) compared with 3 consecutive 10 min bouts of UBE. Ten male subjects (age (mean +/- standard deviation), 25.7 +/- 5.83 years; arm VO(2) (peak), 2.2 +/- 0.25 L x min(-1), on separate days (48 h between trials) and in counterbalanced order, performed a continuous 30 min bout of arm exercise at 60% of arm VO2 peak and 3 separate 10 min bouts of arm exercise at 60% of arm VO(2) (peak). Subjects reported to the laboratory rested and after a 12 h fast. Each test was preceded by a 30 min baseline test to determine resting metabolic rate. Post-exercise VO2 was continuously monitored until baseline was re-established. Results showed that the combined magnitude of the EPOCs from the intermittent exercise sessions was significantly (p > .05) greater (4.47 +/- 1.58 L O2) than that elicited from the continuous exercise session (1.54 +/- 1.25 L O2). These data indicate that separating a continuous 30 min arm exercise into 3 equal 10 min arm exercises will elicit a small but significantly higher EPOC, and thus result in greater post-exercise energy expenditure. This could be beneficial for those unable to perform lower-body exercise (LBE), or for those with limited exercise capacities.

Substrate oxidation differences between high- and low-intensity exercise are compensated over 24 hours in obese men

OBJECTIVE

Exercise has been proposed as a tool for the prevention of obesity. Apart from an effect on energy expenditure, in particular low-intensity (LI) exercise might also influence substrate metabolism in favour of fat oxidation. It is however unclear what is the most beneficial exercise regime for obese people. We therefore studied the effect of either high-intensity (HI) or LI exercise on 24 h energy expenditure (24 h EE) and substrate metabolism.

METHODS

Eight healthy obese male volunteers (age: 38+/-1 y, BMI: 31+/-1 kg/m(2), W(max): 235+/-16 W) stayed in the respiration chamber for two nights and the day in-between. In the chamber they cycled either at a HI (three times 30 min in a interval protocol (2.5 min 80/50% W(max))) or LI (three times 60 min continuously at 38% W(max)) protocol with an equicaloric energy expenditure. In the chamber subjects were fed in energy balance (37/48/15% of energy as fat/carbohydrate/protein).

RESULTS

The 24 h EE was not significantly different between protocols. In both protocols, sleeping metabolic rate (SMR) was elevated after the exercise (average+6.7%). The 24 h respiratory quotient (24 h RQ) was not different between protocols. During exercise, RQ was higher in the HI compared to the LI protocol (0.93 vs 0.91 resp., P<0.05), whereas in the postexercise period RQ tended to be lower in the HI compared to the LI protocol (P=0.06).

CONCLUSION

24 h EE is not differently affected by HI or LI exercise in obese men. Similarly, the differences in HI and LI exercise, RQ are compensated postexercise leading to similar substrate oxidation patterns over 24 h independently of the level of exercise intensity.

Larger mass of high-metabolic-rate organs does not explain higher resting energy expenditure in children

BACKGROUND

Children have a high resting energy expenditure (REE) relative to their body weight. The decline in REE during growth may be due to changes in body composition or to changes in the metabolic rate of individual organs and tissues.

OBJECTIVES

The goals were to quantify body-composition components in children at the organ-tissue level in vivo and to determine whether the observed masses 1) account for the elevated REE in children and 2) account, when combined with specific organ-tissue metabolic constants, for children's REE.

DESIGN

This was a cross-sectional evaluation of 15 children (aged 9.3 +/- 1.7 y) and 13 young adults (aged 26.0 +/- 1.8 y) with body mass indexes (in kg/m(2)) < 30. Magnetic resonance imaging-derived in vivo measures of brain, liver, kidney, heart, skeletal muscle, and adipose tissue were acquired. REE was measured by indirect calorimetry (REE(m)). Previously published organ-tissue metabolic rate constants were used to calculate whole-body REE (REE(c)).

RESULTS

The proportion of adipose-tissue-free mass as liver (3.7 +/- 0.5% compared with 3.1 +/- 0.5%; P < 0.01) and brain (6.2 +/- 1.2% compared with 3.3 +/- 0.9%; P < 0.001) was significantly greater in children than in young adults. The addition of brain and liver mass significantly improved the model but did not eliminate the role of age. REE(c) with published metabolic coefficients underestimated REE(m) (REE(c) = 3869 +/- 615 kJ/d; REE(m) = 5119 +/- 769 kJ/d; P < 0.001) in children.

CONCLUSION

The decline in REE during growth is likely due to both a decrease in the proportion of some of the more metabolically active organs and tissues and changes in the metabolic rate of individual organs and tissues.

Effects of resistance exercise bouts of different intensities but equal work on EPOC

PURPOSE

To compare the effect of low- and high-intensity resistance exercise of equal work output, on exercise and excess postexercise oxygen consumption (EPOC).

METHODS

Fourteen female subjects performed a no-exercise baseline control (CN), and nine exercises for two sets of 15 repetitions at 45% of their 8-RM during one session (LO) and two sets of 8 repetitions at 85% of their 8-RM during another session (HI). Measures for all three sessions included: heart rate (HR) and blood lactate (La) preexercise, immediately postexercise and 20 min, 60 min, and 120 min postexercise; and ventilation volume (VE), oxygen consumption (VO(2)), and respiratory exchange ratio (RER) during exercise and at intervals 0-20 min, 45-60 min, and 105-120 min postexercise.

RESULTS

Exercise .VO(2) was not significantly different between HI and LO, but VE, [La], and HR were significantly greater for HI compared with LO. Exercise RER for HI (1.07 +/- 0.03 and LO (1.05 +/- 0.02) were significantly higher than CN (0.86 +/- 0.02), but there were no differences among conditions postexercise. EPOC was greater for HI compared with low at 0-20 min (HI,1.72 +/- 0.70 LO(2); LO, 0.9 +/- 0.65, LO(2)), 45-60 min (HI, 0.35 +/- 0.25 LO(2); LO, 0.14 +/- 0.19 LO2), and 105-120 min (HI, 0.22 +/- 0.22 LO(2); LO, 0.05 +/- 0.11, LO(2)).

CONCLUSION

These data indicate that for resistance exercise bouts with an equated work volume, high-intensity exercise (85% 8-RM) will produce similar exercise oxygen consumption, with a greater EPOC magnitude and volume than low-intensity exercise (45% 8-RM).

Skeletal muscle energetics assessed by (31)P-NMR in prepubertal girls with a familial predisposition to obesity

OBJECTIVE

To determine whether skeletal muscle energetics, measured by in vivo (31)P-nuclear magnetic resonance spectroscopy during plantar flexion exercise, differ between multiethnic, prepubertal girls with or without a predisposition to obesity.

DESIGN

Cross-sectional study.

SUBJECTS

Girls (mean age and body fat+/-s.d.=8.6+/-0.3 y and 22.6+/-4.2%) were recruited according to parental leanness or obesity defined as follows: LN (n=22), two lean parents, LNOB (n=18), one lean and one obese parent; and OB (n=15), two obese parents.

MEASUREMENTS

A 3 min, rest-exercise-recovery plantar flexion protocol was completed. Work was calculated from the force data. Spectra were analyzed for inorganic intracellular phosphate (P(i)), phosphocreatine (PCr), P(i)/PCr (ratio of the low and high energy phosphates indicating the bioenergetic state of the cell), intracellular pH, and adenosine triphosphate (ATP). Magnetic resonance imaging was used to determine calf muscle volume.

RESULTS

BMI was lower in the girls in the LN group (15.9+/-1.5 kg/m(2)) compared to the OB group (16.7+/-1.3 kg/m(2)) of girls (P<0.05), with no difference with the LNOB group (16.7+/-1.9 kg/m(2)). Adjusted for muscle volume and cumulative work, no differences in P(i), PCr, P(i)/PCr, pH, or ATP were observed among the LN, LNOB and OB groups at rest, the end of exercise, and after 60 and 300 s of recovery. From rest to the end of exercise, P(i) and P(i)/PCr (mean+/-s.d.: 0.2+/-0.1 vs 1.5+/-1.0) increased, whereas PCr and pH (7.04+/-0.06 vs 6.95+/-0.10) decreased (all P<0.001). By 60 s of recovery, P(i) and P(i)/PCr decreased, whereas PCr and pH increased (all P<0.001).

CONCLUSIONS

Skeletal muscle energetics, specifically P(i)/PCr and pH measured during plantar flexion exercise, do not differ between prepubertal girls with or without a familial predisposition to obesity.

Absolute versus relative intensity of physical activity in a dose-response context

PURPOSE

To examine the importance of relative versus absolute intensities of physical activity in the context of population health.

METHODS

A standard computer-search of the literature was supplemented by review of extensive personal files.

RESULTS

Consensus reports (Category D Evidence) have commonly recommended moderate rather than hard physical activity in the context of population health. Much of the available literature provides Category C Evidence. It has often confounded issues of relative intensity with absolute intensity or total weekly dose of exercise. In terms of cardiovascular health, there is some evidence for a threshold intensity of effort, perhaps as high as 6 METs, in addition to a minimum volume of physical activity. Decreases in blood pressure and prevention of stroke seem best achieved by moderate rather than high relative intensities of physical activity. Many aspects of metabolic health depend on the total volume of activity; moderate relative intensities of effort are more effective in mobilizing body fat, but harder relative intensities may help to increase energy expenditures postexercise. Hard relative intensities seem needed to augment bone density, but this may reflect an associated increase in volume of activity. Hard relative intensities of exercise induce a transient immunosuppression. The optimal intensity of effort, relative or absolute, for protection against various types of cancer remains unresolved. Acute effects of exercise on mood state also require further study; long-term benefits seem associated with a moderate rather than a hard relative intensity of effort.

CONCLUSIONS

The importance of relative versus absolute intensity of effort depends on the desired health outcome, and many issues remain to be resolved. Progress will depend on more precise epidemiological methods of assessing energy expenditures and studies that equate total energy expenditures between differing relative intensities. There is a need to focus on gains in quality-adjusted life expectancy.

Muscle metabolic economy is inversely related to exercise intensity and type II myofiber distribution

It is not known what causes the well-established inverse relationship between whole-body exercise economy and exercise intensity. The purpose of this study was to: (1) evaluate muscle exercise economy at 45%, 70%, and maximum isometric strength using 31P magnetic resonance spectroscopy (31P-MRS); and (2) determine the relationship between percent type II muscle fiber cross-section, whole-body exercise economy, and muscle exercise economy. Subjects included 32 premenopausal women. Muscle exercise economy was significantly different across the three exercise intensities (28.1 +/- 10.4, 24.8 +/- 8.2, and 20.2 +/- 7.5 N/cm2. mmol/L adenosine triphosphate [ATP] for the 45%, 70%, and maximum intensities, respectively). Percent type II muscle area was significantly related to whole-body metabolic economy during activities of daily living (r = -0.68) and 31P-MRS muscle metabolic economy during isometric plantar flexion (r = -0.53). These data suggest that skeletal muscle becomes less economical as force production increases, and that these decreases in metabolic economy may be related to increased dependence on inefficient type II muscle.

Age-related decrease in resting energy expenditure in sedentary white women: effects of regional differences in lean and fat mass

BACKGROUND

Lean mass and resting energy expenditure (REE) decrease with age. However, it is unknown whether age-related changes in regional lean and fat mass are responsible for the age-related decrease in REE.

OBJECTIVE

Our objective was to determine how regional lean and fat mass vary with age and whether age is independently related to REE after adjustment for regional fat and lean mass.

DESIGN

The study was a cross-sectional evaluation of 58 white women aged 23-77 y. Regional and whole-body lean and fat mass were measured by dual-energy X-ray absorptiometry, subcutaneous abdominal tissue (SAT) and intraabdominal adipose tissue (IAF) by computed tomography, and REE by ventilated-canopy indirect calorimetry.

RESULTS

Independent of other significant correlates, age was significantly and independently associated with greater IAF (beta = 0.49) and less leg lean mass (beta = -0.35). IAF (r = -0.28) and IAF:SAT (r = -0.31) correlated negatively with REE. REE was negatively associated with greater age (beta = -0.42), independent of changes in lean and fat mass in different parts of the body. By contrast, trunk lean (beta = 0.27) and leg fat (beta = 0.27) mass were associated with greater REE independent of age and other body-composition variables.

CONCLUSIONS

These results suggest that trunk lean mass (presumably primarily organ tissue) is relatively resistant to age-related changes in body composition, whereas muscle mass, especially leg muscle, tends to be lost. These data also suggest that the age-related decreases in REE are not fully explained by changes in body composition.

Reduced whole-body fat oxidation in women and in the elderly

OBJECTIVE

To test the hypothesis that the increase in fat mass observed with aging might be related to a decrease in whole-body fat oxidation.

SUBJECTS AND MEASUREMENTS

Forty volunteers had measurements of sleeping and 24 h substrate oxidation in calorimetric chambers, body composition with the (18)O dilution technique, VO(2)max, and fiber composition analysis from a biopsy of vastus lateralis. They were divided into 10 young women, 10 young men, 10 elderly women and 10 elderly men.

RESULTS

Sleeping fat oxidation and 24 h fat oxidation were lower in women than in men and in elderly than in young participants. Sleeping fat oxidation was correlated to fat-free mass and energy balance (multivariate analysis). Twenty four hour fat oxidation was correlated to total energy expenditure and energy balance (multivariate analysis). After adjustment for differences in these factors, sleeping and 24 h fat oxidation were no longer different between age and sex groups. None of the parameters of macronutrient metabolism was correlated with muscle fiber composition.

CONCLUSION

Our data suggest that fat oxidation is lower in elderly subjects. This difference could favour fat mass gain if fat intake is not adequately reduced. Differences in fat-free mass and in total energy expenditure appear to participate in the reduction in fat oxidation. International Journal of Obesity (2001) 25, 39-44

The role of high-fat diets and physical activity in the regulation of body weight

The prevalence of obesity is increasing in westernized societies. In the USA the age-adjusted prevalence of BMI > 30 kg/m2 increased between 1960 and 1994 from 13% to 23% for people over 20 years of age. This increase in the prevalence of obesity has been attributed to an increased fat intake and a decreased physical activity. However, the role of the impact of the level of dietary fat intake on human obesity has been challenged. High-fat diets, due to their high energy density, stimulate voluntary energy intake. An increased fat intake does not stimulate its own oxidation but the fat is stored in the human body. When diet composition is isoenergetically switched from low to high fat, fat oxidation only slowly increases, resulting in positive fat balances on the short term. Together with a diminished fat oxidation capacity in pre-obese subjects, high-fat diets can therefore be considered to be fattening. Another environmental factor which could explain the increasing prevalence of obesity is a decrease in physical activity. The percentage of body fat is negatively associated with physical activity and exercise has pronounced effects on energy expenditure and substrate oxidation. High-intensity exercise, due to a lowering of glycogen stores, can lead to a rapid increase in fat oxidation, which could compensate for the consumption of high-fat diets in westernized societies. Although the consumption of high-fat diets and low physical activity will easily lead to the development of obesity, there is still considerable inter-individual variability in body composition in individuals on similar diets. This can be attributed to the genetic background, and some candidate genes have been discovered recently. Both leptin and uncoupling protein have been suggested to play a role in the prevention of diet-induced obesity. Indeed, leptin levels are increased on a high-fat diet but this effect can be attributed to the increased fat mass observed on the high-fat diet. No effect of a high-fat diet per se on leptin levels is observed. Uncoupling proteins are increased by high-fat diets in rats but no data are available in human subjects yet. In conclusion, the increased intake of dietary fat and a decreasing physical activity level are the most important environmental factors explaining the increased prevalence of obesity in westernized societies.

Postexercise macronutrient oxidation: a factor dependent on postexercise macronutrient intake

BACKGROUND

It has been widely shown that exercise increases postexercise fat oxidation and energy expenditure.

OBJECTIVE

The aim of this study was to investigate the effect of exercise on postexercise substrate oxidation and energy expenditure when the exercise-induced expenditure of energy and macronutrients oxidized is compensated by an equivalent intake immediately after exercise.

DESIGN

Twenty-four-hour energy expenditure (24EE) and macronutrient oxidation of 8 young men were measured in a whole-body indirect calorimeter under the 2 following, randomly assigned conditions: 1) a control session of sedentary activities in the calorimeter for 61 h and 2) a similar session preceded by 60 min of exercise at 50% of maximal oxygen consumption. Immediately after exercising, subjects ingested a milk shake containing the same amount of energy (above resting metabolic rate) expended during exercise and with a food quotient corresponding to the mean exercise respiratory quotient. 24EE and substrate oxidation were compared between conditions on a day-to-day basis (days 1, 2, and 3) and for the 61-h observation period.

RESULTS

There was no difference in 24EE between the 2 conditions. Moreover, the composition of the postexercise fuel mix oxidized, as reflected by the respiratory quotient, was strictly the same under the 2 conditions.

CONCLUSION

Voluntary postexercise compensations in energy and macronutrient intakes play a major role in the ability of exercise to alter postexercise substrate utilization.

Postexercise recovery of skeletal muscle malonyl-CoA, acetyl-CoA carboxylase, and AMP-activated protein kinase

Previous studies have demonstrated that oxygen consumption and fat oxidation remain elevated in the postexercise period. The purpose of this study was to determine whether malonyl-CoA, an inhibitor of fatty acid oxidation, remains depressed in muscle after exercise. Rats were sprinted for 5 min (40 m/min, 5% grade) or run for 30 min (21 m/min, 15% grade). Red quadriceps malonyl-CoA returned to resting values by 90 min postexercise in the sprinting rats and remained significantly lower at least 90 min postexercise in the 30-min exercise group. AMP-activated protein kinase activity remained significantly elevated (P < 0.05) for 10 min after exercise in both groups. The most rapid rate of glycogen repletion was in the first 30 min postexercise. The respiratory exchange ratio decreased from a nonexercise value of 0.87 +/- 0.01 to an average 0.82 +/- 0.01 during the 90-min period after 30 min of exercise. Thus muscle malonyl-CoA remains depressed and fat oxidation is elevated for relatively prolonged periods after a single bout of exercise. This may allow fat oxidation to contribute more to muscle energy requirements, thus leaving more glucose for replenishment of muscle glycogen.

The etiology of obesity: relative contribution of metabolic factors, diet, and physical activity

Three major factors modulate body weight: metabolic factors, diet, and physical activity, each influenced by genetic traits. Despite recent advances in these areas, the prevalence of obesity in Westernized societies has increased. In contrast to monogenic animal models and rare human genetic syndromes, predisposition to common forms of obesity is probably influenced by numerous susceptibility genes, accounting for variations in energy requirements, fuel utilization, muscle metabolic characteristics, and taste preferences. Although recent increases in obesity prevalence cannot be explained by changes in the gene pool, previously "silent" genetic variants may now play important permissive roles in modern societies. Available data suggest that variations in resting energy expenditure, thermic effect of food, and fuel utilization exist but, by themselves, are unlikely to explain the onset of obesity. Regarding diet, the best available trend survey data indicate that fat and energy intake have fallen, in this and other Westernized countries. Diverging trends of decreasing energy intake and increasing body weight suggest that reduced physical activity may be the most important current factor explaining the rising prevalence of obesity. Subsistence in modern societies requires extreme adaptations in previously useful energy-conserving diet and exercise behaviors. Recognizing the difficulties in sustaining energy-restricted diets in the presence of fast foods and social feasts, the current trend toward increasing body weight is not likely to be reversed solely through recommendations for further reductions in energy intake. In all likelihood, activity levels will have to increase in response to an environment engineered to be more physically demanding.

Fat balance and ageing: results from the Québec Family Study

The aim of the present study was to evaluate changes in participation in physical activity and in fat and alcohol intake associated with ageing. This issue was examined in adults (n 207) who were tested between 1978 and 1982 and re-tested 12 years later. These adults were 42.3 (SD 4.9) years of age at baseline. Their children (n 122) were tested over the same follow-up period. They were, on average, 12.5 (SD 1.9) years at entry into the study. A decrease in the proportion of daily energy intake as fat and an increase in participation in vigorous physical activities were observed over the 12-year period in both groups. The proportion of dietary energy as alcohol remained stable in adults whereas it increased markedly in children. Correlation analyses between baseline and follow-up levels were significant for dietary fat and alcohol intake in adults. In children, the levels of these variables in the growing years did not predict the levels attained 12 years later. Even though the adults displayed changes in fat balance generally following current public health recommendations, a substantial increase in skinfold thicknesses was observed in these subjects during follow-up. This observation suggests that there is a strong effect of age-related factors on fat balance.