Heredity and changes in body composition and adipose tissue metabolism after short-term exercise-training

The purpose of the experiment was to investigate the genotype dependency of body composition and adipose tissue metabolism following short-term exercise-training. Six pairs of male, sedentary monozygotic twins took part in a 22 day ergocycle training program at 58% VO2max, with a mean exercise duration of 116 min x day-1. Body weight, fat mass, percent body fat and VO2max, were evaluated before and after the training program. From a suprailiac region fat biopsy, the following adipose tissue metabolic variables were evaluated: fat cell diameter, basal and epinephrine stimulated lipolysis, basal and insulin stimulated lipogenesis from glucose and heparin releasable lipoprotein lipase activity. The exercise-training program increased (p less than 0.01) VO2max and decreased (p less than 0.01) body weight, fat mass and percent body fat. Variation in response within twin pairs was not significantly different than response between pairs in the aforementioned variables. However, a significant within pair resemblance (p less than 0.01) for changes in fat free mass was observed. Adipose tissue metabolic indicators exhibited a large interindividual variation in response to exercise-training. Significant within twin pair resemblance was observed only for basal lipogenesis. Moreover, the non significant within twin pair resemblance for changes in body fat and adipose tissue metabolic indicators suggests that heredity is not a major factor influencing changes in body fat and adipose tissue indicators to short-term training resulting in negative energy balance. Changes in fat free mass were, however, closely coupled to the genotype.     

Peripheral effects of endurance training in young and old subjects

The effects of 12 wk of endurance training at 70% peak O2 consumption (VO2) were studied in 10 elderly (65.1 +/- 2.9 yr) and 10 young (23.6 +/- 1.8 yr) healthy men and women. Training had no effect on weight or body composition in either group. The elderly had more adipose tissue and less muscle mass than the young. Initial peak VO2 was lower in the elderly, but the absolute increase of 5.5-6.0 ml.kg-1.min-1 after training was similar for both groups. Muscle biopsies taken at rest showed that, before training, muscle glycogen stores were 61% higher in the young. Before training, glycogen utilization per joule during submaximal exercise was higher in the elderly. Glycogen stores and muscle O2 consumption increased significantly in response to training in the elderly only. After training, the proportion of energy derived from whole body carbohydrate oxidation during submaximal exercise declined in the young only. The absolute changes that training produced in peak VO2 were similar in both age groups, but the 128% increase in muscle oxidative capacity was greater in the elderly, suggesting that peripheral factors play an important role in the response of the elderly to endurance exercise.     

Increases in submaximal cycling efficiency mediated by altitude acclimatization.

To investigate the hypothesis that respiratory gas exchange and, in particular, the O(2) consumption (VO(2)) response to exercise is altered after a 21-day expedition to 6,194 m, five male climbers (age 28.2 +/- 2 yr; weight 76.9 +/- 4.3 kg; means +/- SE) performed a progressive and prolonged two-step cycle test both before and 3-4 days after return to sea level. During both exercise tests, a depression (P < 0.05) in VO(2) (l/min) and an increase (P < 0.05) in minute ventilation (VE BTPS; l/min) and respiratory exchange ratio were observed after the expedition. These changes occurred in the absence of changes in CO(2) production (l/min). During steady-state submaximal exercise, net efficiency, calculated from the rates of the mechanical power output to the energy expended (VO(2)) above that measured at rest, increased (P < 0.05) from 25.9 +/- 1.6 to 31. 3 +/- 1.3% at the lighter power output and from 24.4 +/- 1.3 to 29.5 +/- 1.5% at the heavy power output. These changes were accompanied by a 4.5% reduction (P < 0.05) in peak VO(2) (3.99 +/- 0.17 vs. 3.81 +/- 0.18 l/min). After the expedition, an increase (P < 0.05) in hemoglobin concentration (15.0 +/- 0.49 vs. 15.8 +/- 0.41 g/100 ml) was found. It is concluded that, because resting VO(2) was unchanged, net efficiency is enhanced during submaximal exercise after a mountaineering expedition when the exercise is performed soon after return to sea level conditions.     

Endurance training in older men and women II. Blood lactate response to submaximal exercise

Seven men and four women (age 63 +/- 2 yr, mean +/- SD, range 61-67 yr) participated in a 12-mo endurance training program to determine the effects of low-intensity (LI) and high-intensity (HI) training on the blood lactate response to submaximal exercise in older individuals. Maximal oxygen uptake (VO2max), blood lactate, O2 uptake (VO2), heart rate (HR), ventilation (VE), and respiratory exchange ratio (R) during three submaximal exercise bouts (65-90% VO2max) were determined before training, after 6 mo of LI training, and after an additional 6 mo of HI training. VO2max (ml X kg-1 X min-1) was increased 12% after LI training (P less than 0.05), while HI training induced a further increase of 18% (P less than 0.01). Lactate, HR, VE, and R were significantly lower (P less than 0.05) at the same absolute work rates after LI training, while HI training induced further but smaller reductions in these parameters (P greater than 0.05). In general, at the same relative work rates (ie., % of VO2max) after training, lactate was lower or unchanged, HR and R were unchanged, and VO2 and VE were higher. These findings indicate that LI training in older individuals results in adaptations in the response to submaximal exercise that are similar to those observed in younger populations and that additional higher intensity training results in further but less-marked changes.     

Short-Term Overfeeding Increases Circulating Adiponectin Independent of Obesity Status

Background

Adiponectin is an adipose tissue derived hormone which strengthens insulin sensitivity. However, there is little data available regarding the influence of a positive energy challenge (PEC) on circulating adiponectin and the role of obesity status on this response.

Objective

The purpose of this study was to investigate how circulating adiponectin will respond to a short-term PEC and whether or not this response will differ among normal-weight(NW), overweight(OW) and obese(OB).

Design

We examined adiponectin among 64 young men (19-29 yr) before and after a 7-day overfeeding (70% above normal energy requirements). The relationship between adiponectin and obesity related phenotypes including; weight, percent body fat (%BF), percent trunk fat (%TF), percent android fat (%AF), body mass index (BMI), total cholesterol, HDLc, LDLc, glucose, insulin, homeostatic model assessment insulin resistance (HOMA-IR) and β-cell function (HOMA-β) were analyzed before and after overfeeding.

Results

Analysis of variance (ANOVA) and partial correlations were used to compute the effect of overfeeding on adiponectin and its association with adiposity measurements, respectively. Circulating Adiponectin levels significantly increased after the 7-day overfeeding in all three adiposity groups. Moreover, adiponectin at baseline was not significantly different among NW, OW and OB subjects defined by either %BF or BMI. Baseline adiponectin was negatively correlated with weight and BMI for the entire cohort and %TF, glucose, insulin and HOMA-IR in OB. However, after controlling for insulin resistance the correlation of adiponectin with weight, BMI and %TF were nullified.

Conclusion

Our study provides evidence that the protective response of adiponectin is preserved during a PEC regardless of adiposity. Baseline adiponectin level is not directly associated with obesity status and weight gain in response to short-term overfeeding. However, the significant increase of adiponectin in response to overfeeding indicates the physiological potential for adiponectin to attenuate insulin resistance during the development of obesity.     

Early onset of pulmonary gas exchange disturbance during progressive exercise in healthy active men.

Some recent studies of competitive athletes have shown exercise-induced hypoxemia to begin in submaximal exercise. We examined the role of ventilatory factors in the submaximal exercise gas exchange disturbance (GED) of healthy men involved in regular work-related exercise but not in competitive activities. From the 38 national mountain rescue workers evaluated (36 +/- 1 yr), 14 were classified as GED and were compared with 14 subjects matched for age, height, weight, and maximal oxygen uptake (VO2 max; 3.61 +/- 0.12 l/min) and showing a normal response (N). Mean arterial PO2 was already lower than N (P = 0.05) at 40% VO2 max and continued to fall until VO2 max (GED: 80.2 +/- 1.6 vs. N: 91.7 +/- 1.3 Torr). A parallel upward shift in the alveolar-arterial oxygen difference vs. %VO2 max relationship was observed in GED compared with N from the onset throughout the incremental protocol. At submaximal intensities, ideal alveolar PO2, tidal volume, respiratory frequency, and dead space-to-tidal volume ratio were identical between groups. As per the higher arterial PCO2 of GED at VO2 max, subjects with an exaggerated submaximal alveolar-arterial oxygen difference also showed a relative maximal hypoventilation. Results thus suggest the existence of a common denominator that contributes to the GED of submaximal exercise and affects the maximal ventilatory response.     

Intermittent hypoxia increases ventilation and Sa(O2) during hypoxic exercise and hypoxic chemosensitivity.

The purpose of this study was 1) to test the hypothesis that ventilation and arterial oxygen saturation (Sa(O2)) during acute hypoxia may increase during intermittent hypoxia and remain elevated for a week without hypoxic exposure and 2) to clarify whether the changes in ventilation and Sa(O2) during hypoxic exercise are correlated with the change in hypoxic chemosensitivity. Six subjects were exposed to a simulated altitude of 4,500 m altitude for 7 days (1 h/day). Oxygen uptake (VO2), expired minute ventilation (VE), and Sa(O2) were measured during maximal and submaximal exercise at 432 Torr before (Pre), after intermittent hypoxia (Post), and again after a week at sea level (De). Hypoxic ventilatory response (HVR) was also determined. At both Post and De, significant increases from Pre were found in HVR at rest and in ventilatory equivalent for O2 (VE/VO2) and Sa(O2) during submaximal exercise. There were significant correlations among the changes in HVR at rest and in VE/VO2 and Sa(O2) during hypoxic exercise during intermittent hypoxia. We conclude that 1 wk of daily exposure to 1 h of hypoxia significantly improved oxygenation in exercise during subsequent acute hypoxic exposures up to 1 wk after the conditioning, presumably caused by the enhanced hypoxic ventilatory chemosensitivity.     

The Response to Exercise with Constant Energy Intake in Identical Twins

Seven pairs of young adult male identical twins completed a negative energy balance protocol during which they exercised on cycle ergometers twice a day, 9 out of 10 days, over a period of 93 days while being kept on a constant daily energy and nutrient intake. The total energy deficit caused by exercise above the estimated energy cost of body weight maintenance reached 244 ± 9.8 MJ (Mean ± SEM). Baseline energy intake was estimated over a period of 17 days preceding the negative energy balance protocol. Mean body weight loss was 5.0 kg (SEM = 0.6) (p <0.001) and it was entirely accounted for by the loss of fat mass (p <0.001). Fat-free mass was unchanged. Body energy losses reached 191 MJ (SEM = 24) (p <0.001) which represented about 78% of the estimated energy deficit. Subcutaneous fat loss was slightly more pronounced on the trunk than on the limbs as estimated from skinfolds, circumferences, and computed tomography (CT). The reduction in CT-assessed abdominal visceral fat was quite striking, from 81 cm² (SEM = 5) to 52 cm² (SEM = 6) (p <0.001). At the same submaximal power output level, subjects oxidized more lipids than carbohydrates after the program as indicated by the changes in the respiratory exchange ratio (p <0.05). Intrapair resemblance was observed for the changes in body weight (p <0.05), fat mass (P <0.01), percent fat (p <0.01), body energy content (p <0.01), sum of 10 skinfolds (p <0.01), abdominal visceral fat (p <0.01), fasting plasma triglycerides (p <0.05) and cholesterol (p <0.05), maximal oxygen uptake (p <0.05), and respiratory exchange ratio during submaximal work (p <0.01). We conclude that even though there were large individual differences in response to the negative energy balance and exercise protocol, subjects with the same genotype were more alike in responses than subjects with different genotypes particularly for body fat, body energy, and abdominal visceral fat changes. High lipid oxidizers and low lipid oxidizers during sub-maximal exercise were also seen despite the fact that all subjects had experienced the same exercise and nutritional conditions for about three months.     

Metabolic Effects of Mental Stress during Over- and Underfeeding in Healthy Women

Objective: To assess the short-term consequences of carbohydrate or fat overfeeding or of food restriction on the metabolic effects of mental stress in healthy lean women. Research Methods and Procedures: The effects of a sympathetic activation elicited by mental stress were evaluated in a group of healthy women after standardized isocaloric feeding (ISO) or after a 3-day overfeeding with 40% excess calories as either carbohydrate overfeeding (CHO OF) or fat overfeeding (FAT OF). Oxygen consumption rate (VO ₂) was measured as an index of energy expenditure, and subcutaneous glycerol concentrations were monitored with microdialysis. The same measurements were performed in another group of healthy women after ISO and after a 3-day period of underfeeding with a protein sparing modified fast (UF). Results: In all conditions, mental stress significantly increased heart rate, blood pressure, plasma norepinephrine and epinephrine concentrations, and VO ₂, and produced a nonsignificant increase in subcutaneous glycerol concentrations. CHO OF and FAT OF did not alter the effects of mental stress on VO ₂ and subcutaneous glycerol concentrations. In contrast, UF increased basal VO ₂ but significantly reduced its stimulation by mental stress. UF also enhanced the increase in subcutaneous glycerol concentrations during mental stress. Discussion: UF reduces the stimulation of energy expenditure and enhances lipolysis during sympathetic activation. These adaptations may be involved in mobilization of endogenous fat while limiting weight loss. In contrast, short-term overfeeding fails to alter the sympathetic control of energy expenditure and lipolysis.     

Dynamic exercise training in foxhounds. I. Oxygen consumption and hemodynamic responses

Ten foxhounds were studied during maximal and submaximal exercise on a motor-driven treadmill before and after 8-12 wk of training. Training consisted of working at 80% of maximal heart rate 1 h/day, 5 days/wk. Maximal O2 consumption (VO2max) increased 28% from 113.7 +/- 5.5 to 146.1 +/- 5.4 ml O2 X min-1 X kg-1, pre- to posttraining. This increase in VO2max was due primarily to a 27% increase in maximal cardiac output, since maximal arteriovenous O2 difference increased only 4% above pretraining values. Mean arterial pressure during maximal exercise did not change from pre- to posttraining, with the result that calculated systemic vascular resistance (SVR) decreased 20%. There were no training-induced changes in O2 consumption, cardiac output, arteriovenous O2 difference, mean arterial pressure, or SVR at any level of submaximal exercise. However, if post- and pretraining values are compared, heart rate was lower and stroke volume was greater at any level of submaximal exercise. Venous lactate concentrations during a given level of submaximal exercise were significantly lower during posttraining compared with pretraining, but venous lactate concentrations during maximal exercise did not change as a result of exercise training. These results indicate that a program of endurance training will produce a significant increase in VO2max in the foxhound. This increase in VO2max is similar to that reported previously for humans and rats but is derived primarily from central (stroke volume) changes rather than a combination of central and peripheral (O2 extraction) changes.     

Cardiovascular responses of 70- to 79-yr-old men and women to exercise training

This study determined the effects of endurance or resistance exercise training on maximal O2 consumption (VO2max) and the cardiovascular responses to exercise of 70- to 79-yr-old men and women. Healthy untrained subjects were randomly assigned to a control group (n = 12) or to an endurance (n = 16) or resistance training group (n = 19). Training consisted of three sessions per week for 26 wk. Resistance training consisted of one set of 8-12 repetitions on 10 Nautilus machines. Endurance training consisted of 40 min at 50-70% VO2max and at 75-85% VO2max for the first and last 13 wk of training, respectively. The endurance training group increased its VO2max by 16% during the first 13 wk of training and by a total of 22% after 26 wk of training; this group also increased its maximal O2 pulse, systolic blood pressure, and ventilation, and decreased its heart rate and perceived exertion during submaximal exercise. The resistance training group did not elicit significant changes in VO2max or in other maximal or submaximal cardiovascular responses despite eliciting 9 and 18% increases in lower and upper body strength, respectively. Thus healthy men and women in their 70s can respond to prolonged endurance exercise training with adaptations similar to those of younger individuals. Resistance training in older individuals has no effect on cardiovascular responses to submaximal or maximal treadmill exercise.     

Cardiopulmonary responses to exercise in obese girls and young women.

A study of exercise performance was carried out in 17 obese girls and young adults. During submaximal steady-state bicycle exercise oxygen intake (Vo2) for a given work output (W) was raised in obese subjects but minute ventilation at a fixed carbon dioxide output, gas exchange, blood gases, and cardiac output at a given VO2 were similar to the values previously found for normals. In obese subjects high levels of VO2 for fixed W were also obtained on the treadmill but when these were standardized for body weight (unlike the bicycle test) it was shown that the obese girls and women exercised within the normal (expected) range of aerobic energy expenditure. During maximal performance the absolute VO2 max was the same in obese and nonobese subjects but for a given body weight, lean body mass, and leg muscle (plus) bone volume, VO2max was reduced by 23.8, 16.3, and 24.5% respectively, in the former group. It was concluded that obesity though having minimal affect on responses to submaximal exercise is nevertheless associated with a marked reduction in physiological performance at or near maximal effort.     

Effect of endurance exercise training on ventilatory function in older individuals

To evaluate the effect of endurance training on ventilatory function in older individuals, 1) 14 master athletes (MA) [age 63 +/- 2 yr (mean +/- SD); maximum O2 uptake (VO2max) 52.1 +/- 7.9 ml . kg-1 . min-1] were compared with 14 healthy male sedentary controls (CON) (age 63 +/- 3 yr; VO2max of 27.6 +/- 3.4 ml . kg-1 . min-1), and 2) 11 sedentary healthy men and women, age 63 +/- 2 yr, were reevaluated after 12 mo of endurance training that increased their VO2max 25%. MA had a significantly lower ventilatory response to submaximal exercise at the same O2 uptake (VE/VO2) and greater maximal voluntary ventilation (MVV), maximal exercise ventilation (VEmax), and ratio of VEmax to MVV than CON. Except for MVV, all of these parameters improved significantly in the previously sedentary subjects in response to training. Hypercapnic ventilatory response (HCVR) at rest and the ventilatory equivalent for CO2 (VE/VCO2) during submaximal exercise were similar for MA and CON and unaffected by training. We conclude that the increase in VE/VO2 during submaximal exercise observed with aging can be reversed by endurance training, and that after training, previously sedentary older individuals breathe at the same percentage of MVV during maximal exercise as highly trained athletes of similar age.     

Relationships between body dimensions and resting and working oxygen consumption in boys aged 11 to 18 years

The relationships between VO2 at rest, VO2max and VO2 during submaximal work on a treadmill with body weight, height and lean body mass assessed by densitometry were analyzed annually in 39 boys aged 11 to 18 years. Interindividual differences in VO2 at rest and VO2max during growth depended in the first place on interindividual differences in lean body mass, to a lesser extent on differences in body weight and least on differences in height. Intersubject differences in VO2 during submaximal work were primarily conditioned by differences in body weight, due to the fact that, at a given running speed, energy output depends on body weight. The differences in submaximal VO2 depended to a lesser extent on differences in lean body mass and least on differences in height. The relationships between VO2 increments and increases in body dimensions were somewhat different in 90 boys between the ages of 11 and 15 years: VO2max increments were determined primarily by changes in body weight and height, changes in lean body mass being of secondary importance. Increases in submaximal VO2 were influenced decisively by increments in body weight, followed by increments in lean body mass and least by increments in height. In the equation y = a.xb expressing the relationship of VO2max to body weight and height, the values of b at the ages of 14 and 15 years were 0.87 and 0.88 in relation to body weight, 2.63 and 2.72 in relation to height. These values are significantly higher than the theoretical values of 0.67 for body weight and 2.00 for height. Similar significant differences from these theoretical values were found for all values between the ages of 11 and 15 years.     

The effect of oral supplementation with L-carnitine on maximum and submaximum exercise capacity

Two trials were conducted to investigate the effects of L-carnitine supplementation upon maximum and submaximum exercise capacity. Two groups of healthy, untrained subjects were studied in double-blind cross-over trails. Oral supplementation of 2 g per day L-carnitine was used for 2 weeks in the first trial and the same dose but for 4 weeks in the second trial. Maximum and submaximum exercise capacity were assessed during a continuous progressive cycle ergometer exercise test performed at 70 rpm. In trial 1, plasma concentrations of lactate and beta-hydroxybutyrate were measured pre- and post-exercise. In trial 2, pre- and post-exercise plasma lactate were measured. The results of treatment with L-carnitine demonstrated no significant changes in maximum oxygen uptake (VO2max) or in maximum heart rate. In trial 1, there was a small improvement in submaximal performance as evidenced by a decrease in the heart-rate response to a work-load requiring 50% of VO2max. The more extensive trial 2 did not reproduce the significant result obtained in trial 1, that is, there was no significant decrease in heart rate at any given submaximal exercise intensity, under carnitine-supplemented conditions. Plasma metabolic concentrations were unchanged following L-carnitine, in both trials. It is concluded, that in contrast to other reports, carnitine supplementation may be of little benefit to exercise performance since the observed effects were small and inconsistent.     

Muscle morphological and biochemical adaptations to training in obese Zucker rats

The purposes of the present study were to characterize the histochemical and enzymatic profiles of various hindlimb skeletal muscles, as well as to determine maximal O2 consumption (VO2max) and respiratory exchange ratios (R) during steady-state exercise in the obese Zucker rat. The changes that occurred in these parameters in response to a 6-wk training program were then assessed. Obese rats were randomly assigned to a sedentary or training group. Lean littermates served as a second control. Training consisted of treadmill running at 18 m/min up an 8% grade, 1.5 h/day, 5 day/wk for 6 wk. During week 6, VO2max and R during a steady-state run (74% max) were determined. After 2 days of inactivity, hindlimb muscles were excised, stained for fiber type and capillaries, and assayed for hexokinase, citrate synthase, cytochrome oxidase, and beta-hydroxyacetyl-CoA dehydrogenase. The obese sedentary rats demonstrated greater oxidative enzyme activities per gram of muscle tissue than their lean littermates, greater R values during submaximal exercise of the same relative intensity, and greater absolute VO2max values. Training resulted in a 20-56% increase in oxidative enzymes, a 10% increase in VO2max, and an increase in capillary density in the soleus and plantaris. There was no alteration in R values during exercise at 74% VO2max or in fiber type composition in response to exercise training. Results suggest that the muscle of the obese Zucker rat manifests a greater oxidative capacity than the muscle of its lean littermates. The apparent inability of the obese rat to increase its use of fat during submaximal exercise of the same relative intensity in response to training remains to be elucidated.     

Day-to-day changes in oxygen uptake kinetics at the onset of exercise during strenuous endurance training.

The aim of this study was to assess the effect of strenuous endurance training on day-to-day changes in oxygen uptake (VO2) on-kinetics (time constant) at the onset of exercise. Four healthy men participated in strenuous training for 30 min.day-1, 6 days.week-1 for 3 weeks. The VO2 was measured breath-by-breath every day except Sunday at exercise intensities corresponding to the lactate threshold (LT) and the onset of blood lactate accumulation (OBLA) which were obtained before training. Furthermore, an incremental exercise test was performed to determine LT, OBLA and maximal oxygen uptake (VO2max) before and after the training period and every weekend. The 30-min heavy endurance training was performed on a cycle ergometer 5 days.week-1 for 3 weeks. Another six men served as the control group. After training, significant reductions of the VO2 time constant for exercise at the pretraining LT exercise intensity (P less than 0.05) and at OBLA exercise intensity (P less than 0.01) were observed, whereas the VO2 time constants in the control group did not change significantly. A high correlation between the decrease in the VO2 time constant and training day was observed in exercise at the pretraining LT exercise intensity (r = -0.76; P less than 0.001) as well as in the OBLA exercise intensity (r = -0.91; P less than 0.001). A significant reduction in the blood lactate concentration during submaximal exercise and in the heart rate on-kinetics was observed in the training group.(ABSTRACT TRUNCATED AT 250 WORDS)     

Metabolic response of endurance athletes to training with added load

Endurance athletes were divided into experimental (n = 12) and control (n = 12) groups to investigate the effects of extra-load training on energy metabolism during exercise. A vest weighing 9%-10% body weight was worn every day from morning to evening for 4 weeks including every (n = 6) or every other (n = 6) training session. After 4 weeks the control group had a lower blood lactate concentration during submaximal running, whereas the experimental group had significantly higher blood lactate and oxygen uptake (p less than 0.01--p less than 0.05), and a lower 2 mmol lactate threshold (p less than 0.05) and an increased blood lactate concentration after a short running test to exhaustion (p less than 0.05). Those experimental subjects (n = 6) who used the added load during every training session had a lower 2 mmol lactate threshold, improved running time to exhaustion, improved vertical velocity when running up stairs and an increased VO2 during submaximal running after the added load increased anaerobic metabolism in the leg muscle during submaximal and maximal exercise. An increased recruitment and adaptation of the fast twitch muscle fibres is suggested as the principal explanation for the observed changes.     

Reduced submaximal leg blood flow after high-intensity aerobic training.

This study evaluated the hypothesis that active muscle blood flow is lower during exercise at a given submaximal power output after aerobic conditioning as a result of unchanged cardiac output and blunted splanchnic vasoconstriction. Eight untrained subjects (4 men, 4 women, 23-31 yr) performed high-intensity aerobic training for 9-12 wk. Leg blood flow (femoral vein thermodilution), splanchnic blood flow (indocyanine green clearance), cardiac output (acetylene rebreathing), whole body O(2) uptake (VO(2)), and arterial-venous blood gases were measured before and after training at identical submaximal power outputs (70 and 140 W; upright 2-leg cycling). Training increased (P < 0.05) peak VO(2) (12-36%) but did not significantly change submaximal VO(2) or cardiac output. Leg blood flow during both submaximal power outputs averaged 18% lower after training (P = 0.001; n = 7), but these reductions were not correlated with changes in splanchnic vasoconstriction. Submaximal leg VO(2) was also lower after training. These findings support the hypothesis that aerobic training reduces active muscle blood flow at a given submaximal power output. However, changes in leg and splanchnic blood flow resulting from high-intensity training may not be causally linked.