Twenty-four-hour metabolic responses to resistance exercise in women

Seven nonobese adult females (40 +/- 8 years) were studied in a room calorimeter on a day that resistance exercise (REX) was performed (4 sets of 10 exercises) and on a nonexercise control day (CON). Twenty-four-hour energy expenditure (EE) on the REX day (mean +/- SD, 2,328 +/- 327 kcal.d(-1)) was greater than CON (2,001 +/- 369 kcal.d(-1), p < 0.001). The net increase in EE during and immediately after (30 minutes) exercise represented 76 +/- 12% of the total increase in 24-hour EE. Twenty four-hour RQ on the REX day (0.86 +/- 0.06) did not differ from CON (0.87 +/- 0.02). Twenty four-hour carbohydrate oxidation was elevated on the REX day, but 24-hour fat and protein oxidation were not different. Thus, in women, the increase in EE due to resistance exercise is largely seen during and immediately after the exercise. The increased energy demand is met by increased carbohydrate oxidation, with no increase in 24-hour fat oxidation.     

Gender-based differences in substrate use during exercise at a self-selected pace

The aim of this study was to investigate gender-based differences in substrate use during exercise at a self-selected pace. Seventeen men and 17 women performed a maximal exercise test and a 20-minute bout of self-paced treadmill walking to determine carbohydrate and fat oxidation rates. Gas exchange measurements were performed throughout the tests, and stoichiometric equations were used to calculate substrate oxidation rates. For each individual, a best-fit polynomial curve was constructed using fat oxidation rate (g·min(-1)) vs. exercise intensity (percentage of maximal oxygen uptake, % VO(2)max). Each individual curve was used to obtain the following variables: maximal fat oxidation (MFO), the peak rate of fat oxidation measured over the entire range of exercise intensities; fat(max), the exercise intensity at which the MFO was observed; and fat(max) zone, range of exercise intensities with fat oxidation rates within 10% of fat oxidation rates at fat(max). Although the MFO was similar between genders, fat(max) was lower in men than in women. Similarly, the "low" and "high" borders of the fat(max) zone were lower in men than in women. During exercise at a self-selected pace, carbohydrate oxidation rates were greater in men than in women, despite no gender-based differences in fat oxidation rates. However, fat oxidation contribution to total energy expenditure (EE) was greater in women than in men, despite no gender-based differences in the exercise intensity. In conclusion, although both genders self-selected a similar exercise intensity, the contribution of fat oxidation to EE is greater in women than in men. Interestingly, both genders self-selected an exercise intensity that falls within the fat(max) zone.     

Changes in 24-h substrate oxidation in older and younger men in response to exercise.

The purpose of this study was to compare 24-h substrate oxidation in older (OM; 60-75 yr, n = 7) and younger (YM; 20-30 yr, n = 7) men studied on sedentary day (Con) and on a day with exercise (Ex; net energy expenditure = 300 kcal). Plasma glucose and free fatty acids were also measured at several time points during the 24-h measurement. Weight was not different in OM and YM (means +/- SD; 84.8 +/- 16.9 vs. 81.4 +/- 10.4 kg, respectively), although percent body fat was slightly higher in OM (25.9 +/- 3.5 vs. 21.9 +/- 9.7%; P = 0.17).Values of 24-h energy expenditure did not differ in OM and YM on the Con (means +/- SE; 2,449 +/- 162 vs. 2,484 +/- 104 kcal/day, respectively) or Ex (2,902 +/- 154 vs. 2,978 +/- 122 kcal/day) days. Under both conditions, 24-h respiratory quotient was significantly lower and fat oxidation significantly higher in OM. Glucose concentrations were not different at any time point, but plasma free fatty acid concentrations were higher in OM, particularly following meals. Thus, under these controlled conditions, 24-h fat oxidation was not reduced and was in fact greater in OM. We speculate that differences in the availability of circulating free fatty acids in the postprandial state contributed to the observed differences in 24-h fat oxidation in OM and YM.     

Effect of resistance exercise on postprandial lipemia.

The purpose of this study was to examine the effect of resistance exercise on postprandial lipemia. Fourteen young men and women participated in each of three treatments: 1) control (Con), 2) resistance exercise (RE), and 3) aerobic exercise (AE) estimated to have an energy expenditure (EE) equal that for RE. Each trial consisted of performing a treatment on day 1 and ingesting a fat-tolerance test meal 16 h later (day 2). Resting metabolic rate and fat oxidation were measured at baseline and at 3 and 6 h postprandial on day 2. Blood was collected at baseline and at 0.5, 1, 2, 3, 4, 5, and 6 h after meal ingestion. RE and AE were similar in EE [1.7 +/- 0.1 vs. 1.6 +/- 0.1 (SE) MJ, respectively], as measured by using the Cosmed K4b(2). Baseline triglycerides (TG) were significantly lower after RE than after Con (19%) and AE (21%). Furthermore, the area under the postprandial response curve for TG, adjusted for baseline differences, was significantly lower after RE than after Con (14%) and AE (18%). Resting fat oxidation was significantly greater after RE than after Con (21%) and AE (28%). These results indicate that resistance exercise lowers baseline and postprandial TG, and increases resting fat oxidation, 16 h after exercise.     

Energy expenditure of elite female runners measured by respiratory chamber and doubly labeled water.

To determine whether female athletes have unusually low energy requirements as suggested by many food intake studies, energy expenditure (EE) and intake were assessed in nine elite distance runners [26 +/- 3 (SD) yr, 53 +/- 4 kg, 12 +/- 3% body fat, and 66 +/- 4 ml.kg-1.min-1 maximal O2 uptake]. Subjects were admitted to a metabolic ward for 40 h during which 24-h sedentary EE was measured in a respiratory chamber. Free-living EE was then assessed by the doubly labeled water method for the next 6 days while the women recorded all food intake, daily body weight, and training mileage (10 +/- 3 miles/day). Energy intakes estimated from free-living EE (2,826 +/- 312 kcal/day) and body weight changes (-84 +/- 71 g/day) averaged 221 +/- 550 kcal/day in excess of those calculated from food records (2,193 +/- 466 kcal/day). The energy cost of training (1,087 +/- 244 kcal/day) was calculated as the difference between free-living EE and 24-h EE in the respiratory chamber (1,681 +/- 84 kcal/day) corrected for the thermic effect of food of the extra energy intake. These data do not support the hypothesis that training as a distance runner results in metabolic adaptations that lower energy requirements in women.     

Effect of a thermogenic beverage on 24-hour energy metabolism in humans

Objective: To test whether consumption of a beverage containing active ingredients will increase 24‐hour energy metabolism in healthy, young, lean individuals. Research Method and Procedures: Thirty‐one male and female subjects consumed 3 × 250‐mL servings of a beverage containing green tea catechins, caffeine, and calcium for 3 days in a single‐center, double‐blind, placebo‐controlled, cross‐over design study. On the 3rd day, 23‐hour energy metabolism, extrapolated to 24‐hour, was measured in a calorimeter chamber. Blood pressure and heart rate were measured, and total day and night urines were analyzed for urea and catecholamine excretion. Results: Twenty‐four‐hour energy expenditure (EE) and 24‐hour fat oxidation were lower in women than in men (p < 0.0001 and p < 0.015, respectively). Although there were no treatment or treatment/gender effects on substrate oxidation, treatment increased 24‐hour EE by 106 ± 31 kcal/24 hours (p = 0.002), equivalent to 4.7 ± 1.6 kcal/h (day; p = 0.005) and 3.3 ± 1.5 kcal/h (night; p = 0.04). No significant differences were observed in hemodynamic parameters. Discussion: The present study provides evidence that consumption of a beverage containing green tea catechins, caffeine, and calcium increases 24‐hour EE by 4.6%, but the contribution of the individual ingredients cannot be distinguished. Although this increase is modest, the results are discussed in relation to proposed public health goals, indicating that such modifications are sufficient to prevent weight gain. When consumed regularly as part of a healthy diet and exercise regime, such a beverage may provide benefits for weight control.     

Low energy availability, not exercise stress, suppresses the diurnal rhythm of leptin in healthy young women

Because the effect of exercise on leptin was not established, we controlled energy intake (I) and exercise energy expenditure (E) to distinguish the independent effects of energy availability (A = I - E) and exercise stress (everything associated with exercise except its energy cost) on the diurnal leptin rhythm in healthy young women. In random order, we set A = 45 and 10 kcal. kg lean body mass(-1) (LBM) x day(-1) for 4 days during the early follicular phase of separate menstrual cycles in sedentary (S, n = 7) and exercising (X, n = 9: E = 30 kcal x kg LBM(-1) x day(-1)) women. Low energy availability suppressed the 24-h mean (P < 10(-6)) and amplitude (P < 10(-5)), whereas exercise stress did not (both P > 0.2). Suppressions of the 24-h mean (-72 +/- 3 vs. -53 +/- 3%, P < 0.001) and amplitude (-85 +/- 3 vs. -58 +/- 6%, P < 0.001) were more extreme in S vs. X than previously reported effects on luteinizing hormone pulsatility and carbohydrate availability. Thus the diurnal rhythm of leptin depends on energy, or carbohydrate, availability, not intake, and exercise has no suppressive effect on the diurnal rhythm of leptin beyond the impact of its energy cost on energy availability.     

Glucose ingestion during exercise blunts exercise-induced gene expression of skeletal muscle fat oxidative genes

Ingestion of carbohydrate during exercise may blunt the stimulation of fat oxidative pathways by raising plasma insulin and glucose concentrations and lowering plasma free fatty acid (FFA) levels, thereby causing a marked shift in substrate oxidation. We investigated the effects of a single 2-h bout of moderate-intensity exercise on the expression of key genes involved in fat and carbohydrate metabolism with or without glucose ingestion in seven healthy untrained men (22.7 +/- 0.6 yr; body mass index: 23.8 +/- 1.0 kg/m(2); maximal O(2) consumption: 3.85 +/- 0.21 l/min). Plasma FFA concentration increased during exercise (P < 0.01) in the fasted state but remained unchanged after glucose ingestion, whereas fat oxidation (indirect calorimetry) was higher in the fasted state vs. glucose feeding (P < 0.05). Except for a significant decrease in the expression of pyruvate dehydrogenase kinase-4 (P < 0.05), glucose ingestion during exercise produced minimal effects on the expression of genes involved in carbohydrate utilization. However, glucose ingestion resulted in a decrease in the expression of genes involved in fatty acid transport and oxidation (CD36, carnitine palmitoyltransferase-1, uncoupling protein 3, and 5'-AMP-activated protein kinase-alpha(2); P < 0.05). In conclusion, glucose ingestion during exercise decreases the expression of genes involved in lipid metabolism rather than increasing genes involved in carbohydrate metabolism.     

Exercise and diet enhance fat oxidation and reduce insulin resistance in older obese adults.

Older, obese, and sedentary individuals are at high risk of developing diabetes and cardiovascular disease. Exercise training improves metabolic anomalies associated with such diseases, but the effects of caloric restriction in addition to exercise in such a high-risk group are not known. Changes in body composition and metabolism during a lifestyle intervention were investigated in 23 older, obese men and women (aged 66 +/- 1 yr, body mass index 33.2 +/- 1.4 kg/m(2)) with impaired glucose tolerance. All volunteers undertook 12 wk of aerobic exercise training [5 days/wk for 60 min at 75% maximal oxygen consumption (Vo(2max))] with either normal caloric intake (eucaloric group, 1,901 +/- 277 kcal/day, n = 12) or a reduced-calorie diet (hypocaloric group, 1,307 +/- 70 kcal/day, n = 11), as dictated by nutritional counseling. Body composition (decreased fat mass; maintained fat-free mass), aerobic fitness (Vo(2max)), leptinemia, insulin sensitivity, and intramyocellular lipid accumulation (IMCL) in skeletal muscle improved in both groups (P < 0.05). Improvements in body composition, leptin, and basal fat oxidation were greater in the hypocaloric group. Following the intervention, there was a correlation between the increase in basal fat oxidation and the decrease in IMCL (r = -0.53, P = 0.04). In addition, basal fat oxidation was associated with circulating leptin after (r = 0.65, P = 0.0007) but not before the intervention (r = 0.05, P = 0.84). In conclusion, these data show that exercise training improves resting substrate oxidation and creates a metabolic milieu that appears to promote lipid utilization in skeletal muscle, thus facilitating a reversal of insulin resistance. We also demonstrate that leptin sensitivity is improved but that such a trend may rely on reducing caloric intake in addition to exercise training.     

Endurance exercise training blunts the deleterious effect of high-fat feeding on whole body efficiency

We recently showed that a week-long, high-fat diet reduced whole body exercise efficiency in sedentary men by >10% (Edwards LM, Murray AJ, Holloway CJ, Carter EE, Kemp GJ, Codreanu I, Brooker H, Tyler DJ, Robbins PA, Clarke K. FASEB J 25: 1088-1096, 2011). To test if a similar dietary regime would blunt whole body efficiency in endurance-trained men and, as a consequence, hinder aerobic exercise performance, 16 endurance-trained men were given a short-term, high-fat (70% kcal from fat) and a moderate carbohydrate (50% kcal from carbohydrate) diet, in random order. Efficiency was assessed during a standardized exercise task on a cycle ergometer, with aerobic performance assessed during a 1-h time trial and mitochondrial function later measured using (31)P-magnetic resonance spectroscopy. The subjects then underwent a 2-wk wash-out period, before the study was repeated with the diets crossed over. Muscle biopsies, for mitochondrial protein analysis, were taken at the start of the study and on the 5th day of each diet. Plasma fatty acids were 60% higher on the high-fat diet compared with moderate carbohydrate diet (P < 0.05). However, there was no change in whole body efficiency and no change in mitochondrial function. Endurance exercise performance was significantly reduced (P < 0.01), most probably due to glycogen depletion. Neither diet led to changes in citrate synthase, ATP synthase, or mitochondrial uncoupling protein 3. We conclude that prior exercise training blunts the deleterious effect of short-term, high-fat feeding on whole body efficiency.     

Lipid oxidation in fit young adults during postexercise recovery.

To evaluate the hypothesis that lipid oxidation predominates in postexercise recovery, we examined healthy men (n = 6; age = 21.2 +/- 0.6 yr) and women (n = 6; age = 22.8 +/- 2.1 yr) during and after two exercise tasks [89 min at 45% and 60 min at 65% of peak rate of oxygen consumption (V(O2 peak))] as well as a time-matched resting control trial (Con). Exercise bouts were matched for energy expenditure. Respiratory exchange ratios (RER) during exercise at 65% V(O2 peak) for both men and women (0.95 +/- 0.01 and 0.93 +/- 0.02) were significantly higher than 45% V(O2 peak) (0.89 +/- 0.01 and 0.86 +/- 0.02) and Con trials (0.86 +/- 0.01 and 0.86 +/- 0.02, respectively). During recovery, for men RER values were 0.78 +/- 0.01 and 0.76 +/- 0.01 after 45% and 65% exercise, respectively. For women, values were 0.79 +/- 0.01 and 0.78 +/- 0.01. These were significantly lower than during both the preexercise resting period and the corresponding no-exercise Con period (0.82 +/- 0.01 and 0.83 +/- 0.01, mean RER for men and women, respectively). Hence, the contribution of lipid oxidation to energy supply increased significantly during recovery compared with preexercise levels, and it was greater after exercise than during the time-matched, no-exercise Con period. It is concluded that, although carbohydrate is the major fuel source during moderate- to high-intensity exercise, 1) there is substantial postexercise lipid oxidation; and 2) lipid oxidation is the same during postexercise recovery whether the relative power output is 45% or 65% of V(O2 peak) when energy expenditure of exercise is matched.     

Determinants of fat oxidation during exercise in healthy men and women: a cross-sectional study.

The aim of the present study was to establish fat oxidation rates over a range of exercise intensities in a large group of healthy men and women. It was hypothesised that exercise intensity is of primary importance to the regulation of fat oxidation and that gender, body composition, physical activity level, and training status are secondary and can explain part of the observed interindividual variation. For this purpose, 300 healthy men and women (157 men and 143 women) performed an incremental exercise test to exhaustion on a treadmill [adapted from a previous protocol (Achten J, Venables MC, and Jeukendrup AE. Metabolism 52: 747-752, 2003)]. Substrate oxidation was determined using indirect calorimetry. For each individual, maximal fat oxidation (MFO) and the intensity at which MFO occurred (Fat(max)) were determined. On average, MFO was 7.8 +/- 0.13 mg.kg fat-free mass (FFM)(-1).min(-1) and occurred at 48.3 +/- 0.9% maximal oxygen uptake (Vo(2 max)), equivalent to 61.5 +/- 0.6% maximal heart rate. MFO (7.4 +/- 0.2 vs. 8.3 +/- 0.2 mg.kg.FFM(-1).min(-1); P < 0.01) and Fat(max) (45 +/- 1 vs. 52 +/- 1% Vo(2 max); P < 0.01) were significantly lower in men compared with women. When corrected for FFM, MFO was predicted by physical activity (self-reported physical activity level), Vo(2 max), and gender (R(2) = 0.12) but not with fat mass. Men compared with women had lower rates of fat oxidation and an earlier shift to using carbohydrate as the dominant fuel. Physical activity, Vo(2 max), and gender explained only 12% of the interindividual variation in MFO during exercise, whereas body fatness was not a predictor. The interindividual variation in fat oxidation remains largely unexplained.     

Effect of training intensity on insulin sensitivity as evaluated by insulin tolerance test

The purpose of this study was to evaluate the role of exercise intensity in the effect of physical training on insulin sensitivity. The insulin tolerance test (ITT) was applied to quantify insulin sensitivity. Eighteen healthy, young, untrained men and women participated in a 4-week, five times per week, 1-h per session bicycle-ergometer training program. Training consisted of 3-min bouts of cycling interspersed with 2 min at a lower exercise intensity. Intensities were 80 and 40% of pretraining maximal power output (W(max)) in the high-intensity (HI) and 40 and 20% W(max) in the low-intensity (LI) group. The insulin sensitivity index (IS(index)) was similar in the HI and LI group before the training intervention [mean (SD) -0.1898 (0.058) and -0.1892 (0.045), respectively]. After training, the IS(index) was -0.2358 (0.051) (P = 0.005 vs pretraining) in the HI group and -0.2050 (0.035) (P = 0. 099 against pretraining) in the LI group. We conclude that improvements in insulin sensitivity are more pronounced with high-intensity training, when exercise frequency and duration are kept similar. We further conclude that the ITT is suitable for use in intervention studies.     

Gender differences in the regulation of amino acid metabolism.

Exercising men, compared with women, have a greater increase in leucine oxidation but not lysine rate of appearance. The cause for this sexual dimorphism is unknown; however, an inhibition of beta-adrenoreceptor activity has previously been shown to mediate amino acid metabolism (Lamont LS, McCullough AJ, and Kalhan SC. Am J Physiol Endocrinol Metab 268: E910-E916, 1995; Lamont LS, Patel DG, and Kalhan SC. J Appl Physiol 67: 221-225, 1989). This study was a gender comparison of leucine and lysine kinetics during a beta-adrenoreceptor blockade (beta1,beta2-blockade) and a placebo control by using a double-blind crossover protocol. Subjects exercised at 50% of their trial-specific maximal O2 consumption (1 h) after 7 days of dietary control. During exercise with beta-blockade, men had an increased nonprotein respiratory exchange ratio (P < 0.001), whereas women had an increased circulation of free fatty acids (P < 0.001). The genders also displayed distinct differences in exercise amino acid kinetics. The men, but not the women, increased leucine oxidation (P < 0.005) and lysine rate of appearance (P < 0.009) when exercising during beta-adrenergic blockade. This study indicates that during beta-blockade, exercising men increase their need for amino acids (and carbohydrate) to fuel energy needs, whereas women increase their mobilization of fat, thereby requiring less alternative fuels such as carbohydrate and amino acids. Gender-specific fuel preferences during exercise are regulated by beta-adrenergic-receptor activity. Substrate availability during exercise appears to modulate the amino acid oxidation differences between genders.     

Effect of exercise training at different intensities on fat metabolism of obese men.

The present study investigated the effect of exercise training at different intensities on fat oxidation in obese men. Twenty-four healthy male obese subjects were randomly divided in either a low- [40% maximal oxygen consumption (VO(2 max))] or high-intensity exercise training program (70% VO(2 max)) for 12 wk, or a non-exercising control group. Before and after the intervention, measurements of fat metabolism at rest and during exercise were performed by using indirect calorimetry, [U-(13)C]palmitate, and [1,2-(13)C]acetate. Furthermore, body composition and maximal aerobic capacity were measured. Total fat oxidation did not change at rest in any group. During exercise, after low-intensity exercise training, fat oxidation was increased by 40% (P < 0.05) because of an increased non-plasma fatty acid oxidation (P < 0.05). High-intensity exercise training did not affect total fat oxidation during exercise. Changes in fat oxidation were not significantly different among groups. It was concluded that low-intensity exercise training in obese subjects seemed to increase fat oxidation during exercise but not at rest. No effect of high-intensity exercise training on fat oxidation could be shown.     

Influences of calorie restriction and age on energy expenditure in the rhesus monkey

Caloric restriction (CR) is known to retard the aging process, and a marker of aging is decreased energy expenditure (EE). To assess longitudinal effects of CR on EE in rhesus monkeys (Macaca mulatta), data from 41 males (M) and 26 females (F) subjected to 9 or 15 yr of CR were studied. EE and body composition of monkeys 11-28 yr of age were measured using indirect calorimetry and dual X-ray absorptiometry. Total EE (24-h EE) was divided into daytime (day EE), nighttime (night EE), and daytime minus nighttime (D - N EE). M calorie-restricted monkeys showed a lower 24-h EE (means +/- SD = 568 +/- 96 kcal/day, P < 0.0001) than controls (C; 630 +/- 129 kcal/day). Calorie-restricted M had a lower night EE (difference = 36 kcal P < 0.0001) compared with C M, but after adjusting for FFM and FM, night EE was not different between calorie-restricted and C males (P = 0.72). The 24-h EE decreased with age (13 kcal decrease/yr, P < 0.0001), but there was no difference between CR and C. Adjusted for FFM and FM, D - N EE decreased with age (9 kcal/yr, P < 0.0001), with no interaction with age (P = 0.72). The F were compared with age-matched M selected from the male cohort. F had a lower 24-h EE (496 +/- 84 kcal/day) than M (636 +/- 139 kcal/day) (P < 0.0001). Adjusting for FFM and FM, night EE was lower in F compared with M (difference = 18 kcal, P = 0.077). Night EE did not differ between calorie-restricted and C younger monkeys after adjusting for FFM and FM. In conclusion, CR did not alter the age-related decrease in EE with CR.     

Gender differences in leucine, but not lysine, kinetics.

There is a controversy in the literature as to the effects of gender on leucine kinetics. Two research groups found that men oxidize more leucine during exercise, whereas another group showed no gender effects. The purpose of our study was to examine the effects of gender on leucine and, for comparison purposes, lysine kinetics. Our subjects (n = 14) were seven matched pairs of men and women selected for their exercise habits and age. After 1 wk of a standardized diet, they exercised at 50% of maximal O(2) uptake for 1 h. There was an effect of exercise in both genders: an increased leucine oxidation and an attenuation in nonoxidative leucine disposal compared with rest (P < 0.05). Furthermore, our study confirms that there are gender differences in leucine, but not lysine, kinetics. Men had a higher rate of leucine oxidation and a lower rate of nonoxidative leucine disposal during exercise (P < 0.05). For women, a larger proportion of their exercise energy needs came from fat; for men, a greater fraction came from carbohydrate (P < 0.05). We conclude that female exercisers rely to a greater extent on fat as an energy source, thereby using less carbohydrate, amino acid, and protein as a fuel source.     

Equal volumes of high and low intensity of eccentric exercise in relation to muscle damage and performance

We examined differences in muscle damage and muscle performance perturbations in relation to the same volumes of high (HI) and low intensity (LI) of eccentric exercise. Untrained young healthy men (n = 12) underwent 2 isokinetic quadriceps eccentric exercise sessions, 1 on each randomly selected leg, separated by a 2-week interval. In the first session subjects performed HI exercise (i.e., 12 sets of 10 maximal voluntary efforts). In the second session, volunteers were subjected to continuous exercise of LI (50% of peak torque) until the total work done was approximately equal to that generated during HI. Muscle damage (serum creatine kinase concentration [CK], delayed onset of muscle soreness, and range of motion) and muscle performance (eccentric [EPT] and isometric peak torque [IPT]) indicators were assessed pre-exercise and 24, 48, 72, and 96 hours postexercise. Compared to baseline data, changes in muscle damage indicators were significantly different (p < 0.05) at almost all postexercise time points in both conditions. However, apart from the significant elevation of CK at 24 hours after HI (p < 0.05), no other significant differences were observed between the 2 exercise conditions (p > 0.05). The main finding in relation to muscle performance was that decrements following HI exercise were significantly greater (p < 0.05) compared to LI. Compared with baseline data, the EPT values following HI and LI exercise were as follows: 24 hours, 72.1% vs. 92%; 48 hours, 81.9% vs. 94.8%; 72 hours, 77.7% vs. 100.6%; 96 hours, 86.8% vs. 107.9%. The corresponding data for IPT were as follows: 24 hours, 86.4% vs. 102.8%; 48 hours, 84.2% vs. 107%; 72 hours, 84.8% vs. 109.2%; 96 hours, 86.8% vs. 114.4%. These results indicate that matching volumes of HI and LI eccentric exercise have similar effects on muscle damage, but HI has a more prominent effect on muscle performance.     

Effects of chronic nitric oxide synthase inhibition on responses to acute exercise in swine.

Nitric oxide (NO) is potentially involved in several responses to acute exercise. We tested the hypotheses that inhibition of NO formation reduces maximal O(2) delivery to muscle, but does not affect O(2) utilization by muscle, therefore lowering maximal O(2) consumption. To test these hypotheses, swine (approximately 30 kg) drank either tap water (Con, n = 25) or water with N(G)-nitro-l-arginine methyl ester (8.0 +/- 0.4 mg x kg(-1) x day(-1) for >or=4 wk; LN, n = 24). Treatment efficacy was reflected by higher mean arterial pressure and lower plasma NO metabolite concentration in LN than Con (both P < 0.05). Swine completed two graded treadmill running tests to maximum. In the first test, O(2) consumption was determined at rest through maximal exercise intensity. O(2) consumption did not differ between groups at rest or at most exercise intensities, including maximum (Con, 40.8 +/- 1.8 ml x min(-1) x kg(-1); LN, 40.4 +/- 2.9; not significant). In the second test, tissue-specific blood flows were determined using the radiolabeled-microsphere technique. At rest, blood flows were lower (P < 0.05) in LN compared with Con for a number of tissues, including kidney, adrenal, lung, and several skeletal muscles. During both submaximal and maximal exercise, however, blood flows were similar between Con and LN for all 16 muscles examined; only blood flows to kidney (Con, 99 +/- 16 ml x min(-1) x 100 g; LN, 55 +/- 15; P < 0.05) and pancreas (Con, 25 +/- 7; LN, 6 +/- 2; P < 0.05) were lower in LN at maximum. Endothelium-dependent, but not -independent, relaxation of renal arterial segments was reduced (P < 0.05) in vitro. These data indicate that exercise-induced increases in muscle blood flows are maintained with chronic inhibition of NO formation and that maximal O(2) consumption is therefore preserved. Redundant vasodilatory pathways and/or upregulation of these pathways may underlie these findings.