Lipid mobilization from human abdominal, subcutaneous adipose tissue is independent of sex during steady-state exercise

Effects of Abdominal Microcurrent in the Consumption and Proportion of Energy Substrates during Aerobic Exercise: A Pilot Study

Microcurrent therapy can increase lipolytic activity. However, it is unknown if the increased availability of lipids can influence the selection of energy substrates during a single session of aerobic exercise. We aimed to analyze the effect of microcurrent application to the abdominal region in the consumption of lipids and carbohydrates, and respiratory exchange ratio (RER) during a single session of moderate aerobic exercise in young adults. A pilot study was conducted in which participants were allocated to intervention (IG) or placebo (PG) groups. In both groups, 40 min of microcurrent application with two frequencies (25 and 10 Hz) followed by 50 min of moderate-intensity aerobic exercise (45−55% of heart rate reserve) on a cycloergometer were performed. The microcurrent application was performed without intensity in the PG. A portable gas analyzer (K4b2) was used during exercise in both groups. Thirty-eight participants (20.6 ± 1.8 years; 18 in IG and 20 in PG) were enrolled. There were no significant differences in the consumption of substrates or RER between the groups during exercise (p > 0.05). Microcurrent application seems to be insufficient to influence the consumption of energy substrates and RER during a single session of aerobic exercise in young adults.

A 1:1 exercise-to-rest period ratio needed by animals to restore energy sources and replenish anti-oxidative status after exercise

BACKGROUND/OBJECTIVES

Successful recovery of an animal from exercise is essential, especially prior to the next exercise session. This study was conducted to find an effective exercise-to-rest period ratio for the restoration of energy sources and replenishment of anti-oxidative status in tissue after exercise.

MATERIALS/METHODS

Thirty-two rats were assigned to either non-training or training exercise groups for 5 weeks. After that period, the two groups were subdivided into four smaller groups: non-exercise (NE), exercise 0.5 hour and rest 1 hour (ER0.5:1), exercise 1 hour and rest 1 hour (ER1:1), exercise 2 hours and rest 1 hour (ER2:1).

RESULTS

In the training group animals and compared to the NE group, the levels of plasma glucose after the rest period were significantly high in all ER groups but highest in the ER2:1 group. Similarly, the liver glycogen level was highest in the ER2:1 group. The plasma FFA level reached the highest level in the ER2:1 group but was similarly high in the ER0.5:1 group. Liver TG level was unchanged in the ER2:1 and ER1:1 groups but was significantly high in the ER0.5:1 group. Muscle TG levels were decreased in all three ER groups. Plasma protein levels were significantly high in the ER2:1 and ER0.5:1 groups. In both training animal and non-training animals, the liver protein levels did not change significantly between the NE and ER groups, irrespective of the exercise-to-rest ratio. In the training animal group, muscle protein level was significantly low in the ER2:1 and ER0.5:1 groups. The activity levels of superoxide dismutase and catalase, as well as the malondialdehyde concentration, were not significantly different between NE and ER groups, irrespective of the exercise-to-rest period ratio.

CONCLUSIONS

These results indicate that animals provided with a 0.5:1 to 1:1 exercise-to-rest period ratio can restore their muscle energy sources and recover their anti-oxidative defense system.

Determinants of resting lipid oxidation in response to a prior bout of endurance exercise

A single bout of exercise can alter subsequent resting metabolism for many hours and into the next day. However, differences between men and women, effects of nutritional state, and relative effects of resting metabolic rate (RMR) and respiratory exchange ratio (RER) in controlling the increase in lipid oxidation (Lox) after exercise are not yet clear. Effects of aerobic capacity (Vo2 peak) and exercise bout parameters (intensity and volume) also remain to be clearly elucidated as does the time course of changes after exercise. We performed a meta-analysis to assess these potential moderators of the impact of endurance exercise [effect sizes (ESs)] on subsequent Lox at rest (ES = 0.91; 95% CI: 0.69-1.12), on the day of exercise (ES = 1.22; 95% CI: 0.89-1.55), and on the following day (ES = 0.60; 95% CI: 0.35-0.85). ES for the exercise-related increase in resting Lox was significantly greater in men than women in the postabsorptive state but similar in the postprandial state. The ES for depression of RER after exercise was similar between men and women, while the ES for RMR in the postabsorptive state tended to be higher in men than women. Finally, Vo2 peak and exercise energy expenditure (EEE), but not intensity, were predictive of postexercise Lox. The findings indicate importance of EEE and fitness for ability to achieve robust enhancement of Lox after exercise. The results additionally indicate a gender difference in postexercise Lox that is dependent on nutritional state, as the ES for Lox was lower in women only in the postabsorptive state.

Physical activity and exercise in the regulation of human adipose tissue physiology

Physical activity and exercise are key components of energy expenditure and therefore of energy balance. Changes in energy balance alter fat mass. It is therefore reasonable to ask: What are the links between physical activity and adipose tissue function? There are many complexities. Physical activity is a multifaceted behavior of which exercise is just one component. Physical activity influences adipose tissue both acutely and in the longer term. A single bout of exercise stimulates adipose tissue blood flow and fat mobilization, resulting in delivery of fatty acids to skeletal muscles at a rate well-matched to metabolic requirements, except perhaps in vigorous intensity exercise. The stimuli include adrenergic and other circulating factors. There is a period following an exercise bout when fatty acids are directed away from adipose tissue to other tissues such as skeletal muscle, reducing dietary fat storage in adipose. With chronic exercise (training), there are changes in adipose tissue physiology, particularly an enhanced fat mobilization during acute exercise. It is difficult, however, to distinguish chronic "structural" changes from those associated with the last exercise bout. In addition, it is difficult to distinguish between the effects of training per se and negative energy balance. Epidemiological observations support the idea that physically active people have relatively low fat mass, and intervention studies tend to show that exercise training reduces fat mass. A much-discussed effect of exercise versus calorie restriction in preferentially reducing visceral fat is not borne out by meta-analyses. We conclude that, in addition to the regulation of fat mass, physical activity may contribute to metabolic health through beneficial dynamic changes within adipose tissue in response to each activity bout.

Gene by sex interaction for measures of obesity in the framingham heart study

Obesity is an increasingly prevalent and severe health concern with a substantial heritable component and marked sex differences. We sought to determine if the effect of genetic variants also differed by sex by performing a genome-wide association study modeling the effect of genotype-by-sex interaction on obesity phenotypes. Genotype data from individuals in the Framingham Heart Study Offspring cohort were analyzed across five exams. Although no variants showed genome-wide significant gene-by-sex interaction in any individual exam, four polymorphisms displayed a consistent BMI association (P-values .00186 to .00010) across all five exams. These variants were clustered downstream of LYPLAL1, which encodes a lipase/esterase expressed in adipose tissue, a locus previously identified as having sex-specific effects on central obesity. Primary effects in males were in the opposite direction from females and were replicated in Framingham Generation 3. Our data support a sex-influenced association between genetic variation at the LYPLAL1 locus and obesity-related traits.

Effect of a 1-hour single bout of moderate-intensity exercise on fat oxidation kinetics

The present study aimed to examine the effects of a prior 1-hour continuous exercise bout (CONT) at an intensity (Fat(max)) that elicits the maximal fat oxidation (MFO) on the fat oxidation kinetics during a subsequent submaximal incremental test (IncrC). Twenty moderately trained subjects (9 men and 11 women) performed a graded test on a treadmill (Incr), with 3-minute stages and 1-km.h(-1) increments. Fat oxidation was measured using indirect calorimetry and plotted as a function of exercise intensity. A mathematical model (SIN) including 3 independent variables (dilatation, symmetry, and translation) was used to characterize the shape of fat oxidation kinetics and to determine Fat(max) and MFO. On a second visit, the subjects performed CONT at Fat(max) followed by IncrC. After CONT performed at 57% +/- 3% (means +/- SE) maximal oxygen uptake (Vo(2max)), the respiratory exchange ratio during IncrC was lower at every stage compared with Incr (P < .05). Fat(max) (56.4% +/- 2.3% vs 51.5% +/- 2.4% Vo(2max), P = .013), MFO (0.50 +/- 0.03 vs 0.40 +/- 0.03 g.min(-1), P < .001), and fat oxidation rates from 35% to 70% Vo(2max) (P < .05) were significantly greater during IncrC compared with Incr. However, dilatation and translation were not significantly different (P > .05), whereas symmetry tended to be greater in IncrC (P = .096). This study showed that the prior 1-hour continuous moderate-intensity exercise bout increased Fat(max), MFO, and fat oxidation rates over a wide range of intensities during the postexercise incremental test. Moreover, the shape of the postexercise fat oxidation kinetics tended to have a rightward asymmetry.

Basal adipose tissue and hepatic lipid kinetics are not affected by a single exercise bout of moderate duration and intensity in sedentary women

Hypertriacylglycerolaemia is an important risk factor for cardiovascular disease. In men, we have shown that the effects of evening exercise on basal VLDL (very-low-density lipoprotein) metabolism are dose-dependent: a single prolonged bout of aerobic exercise [2 h at 60% of VO(2 peak) (peak oxygen consumption)] reduces fasting plasma TAG [triacylglycerol (triglyceride)] concentrations, via enhanced clearance of VLDL-TAG from the circulation, whereas the same exercise performed for 1 h has no effect on VLDL-TAG metabolism and concentration. We hypothesized that women are more sensitive to the TAG-lowering effect of exercise because they reportedly use more intramuscular TAG as an energy source during exercise, and depletion of muscle TAG stores has been linked to reciprocal changes in skeletal muscle LPL (lipoprotein lipase) activity. To test our hypothesis, we measured basal VLDL-TAG and VLDL-apoB-100 (apolipoprotein B-100), and plasma NEFA [non-esterified fatty acid ('free fatty acid')] kinetics, by using stable isotope-labelled tracer techniques, on the morning after a single session of evening exercise of moderate duration and intensity (1 h at 60% of VO(2 peak)) in eight sedentary pre-menopausal women (age, 28+/-3 years; body mass index, 27+/-2 kg/m(2); body fat, 34+/-3%; values are means+/-S.E.M.). Compared with an equivalent period of evening rest, exercise had no effect on post-absorptive NEFA concentrations and the rate of appearance in plasma, VLDL-TAG and VLDL-apoB-100 concentrations, hepatic VLDL-TAG and VLDL-apoB-100 secretion and plasma clearance rates (all P>0.05). We conclude that, in women, as in men, a single session of exercise of moderate intensity and duration is not sufficient to bring about the alterations in VLDL metabolism that have been linked to post-exercise hypotriacylglycerolaemia.

Adipocyte triglyceride lipase expression in human obesity

We have investigated the gene and protein expression of adipose triglyceride lipase (ATGL) and triglyceride (TG) lipase activity from subcutaneous and visceral adipose tissue of lean and obese subjects. Visceral and subcutaneous adipose tissue was obtained from 16 age-matched lean and obese subjects during abdominal surgery. Tissues were analyzed for mRNA expression of lipolytic enzymes by real-time quantitative PCR. ATGL protein content was assessed by Western blot and TG lipase activity by radiometric assessment. Subcutaneous and visceral adipose tissue of obese subjects had elevated mRNA expression of PNPLA2 (ATGL) and other lipases including PNPLA3, PNPLA4, CES1, and LYPLAL1 (P < 0.05). Surprisingly, ATGL protein expression and TG lipase activity were reduced in subcutaneous adipose tissue of obese subjects. Immunoprecipitation of ATGL reduced total TG lipase activity in adipose lysates by 70% in obese and 83% in lean subjects. No significant differences in the ATGL activator CGI-58 mRNA levels (ABHD5) were associated with obesity. These data demonstrate that ATGL is important for efficient TG lipase activity in humans. They also demonstrate reduced ATGL protein expression and TG lipase activity despite increased mRNA expression of ATGL and other novel lipolytic enzymes in obesity. The lack of correlation between ATGL protein content and in vitro TG lipase activity indicates that small decrements in ATGL protein expression are not responsible for the reduction in TG lipase activity observed here in obesity, and that posttranslational modifications may be important.

Lipolysis and fatty acid metabolism in men and women during the postexercise recovery period

We sought to determine whether lipolysis, fatty acid (FA) mobilization, and plasma FA oxidation would remain elevated for hours following isoenergetic exercise bouts of different intensities. Ten men and eight women received a primed-continuous infusion of [1,1,2,3,3-(2)H(5)]glycerol and continuous infusion of [1-(13)C]palmitate to measure glycerol and plasma FA kinetics. On Day 1 (D1), participants were studied under one of three different conditions, assigned in random order: (1) before, during and 3 h after 90 min of exercise at 45% V(O2)peak (E45), (2) before, during and 3 h after 60 min of exercise at 65% V(O2)peak (E65), and (3) in a time-matched sedentary control trial (C). For each condition, participants were studied by indirect calorimetry the following morning as well (D2). Rate of appearance (Ra) of glycerol (Ra(GL)) increased above C during exercise in men and women (P < 0.05), was higher in E45 than E65 in men (P < 0.05), and was not different between exercise intensities in women. During 3 h of postexercise recovery, Ra(GL) remained significantly elevated in men (P < 0.05), but not women. FA Ra (Ra(FA)) increased during exercise in men and women and was higher in E45 than E65 (P < 0.05), and remained elevated during 3 h of postexercise recovery in both sexes (P < 0.05), but with a greater relative increase in men than women (P < 0.05). Plasma FA oxidation (Rox) increased during exercise with no difference between intensities, and it remained elevated during 3 h of postexercise recovery in both sexes (P < 0.05). Total lipid oxidation (Lox) was elevated in both sexes (P < 0.05), but more in men during 3 h of postexercise recovery on D1 (P < 0.05) and remained elevated on D2 in men (P < 0.05), but not in women. There were no differences between E45 and E65 for postexercise energy substrate turnover or oxidation in men and women as energy expenditure of exercise (EEE) was matched between bouts. We conclude that the impact of exercise upon lipid metabolism persists into recovery, but that women depend more on lipid during exercise whereas, during recovery, lipid metabolism is accentuated to a greater extent in men.

Adipose tissue extracts plasma ammonia after sprint exercise in women and men

This study evaluates a possible contribution of adipose tissue to the elimination of plasma ammonia (NH(3)) after high-intensity sprint exercise. In 14 healthy men and women, repeated blood samples for plasma NH(3) analyses were obtained from brachial artery and from a subcutaneous abdominal vein before and after three repeated 30-s cycle sprints separated by 20 min of recovery. Biopsies from subcutaneous abdominal adipose tissue were obtained and analyzed for glutamine and glutamate content. After exercise, both arterial and abdominal venous plasma NH(3) concentrations were lower in women than in men (P < 0.01 and P < 0.001, respectively). All postexercise measurements showed sex-independent positive arterio-subcutaneous abdominal venous plasma NH(3) concentration differences (a-v(abd)), indicating a net uptake of NH(3) from blood to adipose tissue. However, the fractional extraction (a-v(abd)/a) of NH(3) was higher in women than in men (P < 0.05). The glutamine-to-glutamate ratio in adipose tissue was increased after the second and third bout of sprint exercise (2.2 +/- 0.7 and 1.6 +/- 0.8, respectively) compared with the value at rest (1.2 +/- 0.6), suggesting a reaction of the extracted NH(3) with glutamate resulting in its conversion to glutamine. Adipose tissue may thus play an important physiological role in eliminating plasma NH(3) and thereby reducing the risk of NH(3) intoxication after high-intensity exercise.