Effects of training on glucose metabolism of gluconeogenesis-inhibited short-term-fasted rats

To evaluate the effects of endurance training on gluconeogenesis and blood glucose homeostasis, trained as well as untrained short-term-fasted rats were injected with mercaptopicolinic acid (MPA), a gluconeogenic inhibitor, or the injection vehicle. Glucose kinetics were assessed by primed-continuous venous infusion of [U-14C]- and [6-3H]glucose at rest and during submaximal exercise at 13.4 m/min on level grade. Arterial blood was sampled for the determination of blood glucose and lactate concentrations and specific activities. In resting untrained sham-injected rats, blood glucose and lactate were 7.6 +/- 0.2 and 1.3 +/- 0.1 mM, respectively; glucose rate of appearance (Ra) was 71.1 +/- 12.1 mumol.kg-1.min-1. MPA treatment lowered blood glucose, raised lactate, and decreased glucose Ra. Trained animals had significantly higher glucose Ra at rest and during exercise. At rest, trained MPA-treated rats had lower blood glucose, higher blood lactate, and similar glucose Ra and disappearance rates (Rd) than trained sham-injected animals. Exercising sham-injected untrained animals had increased blood glucose and glucose Ra compared with rest. Exercising trained sham-injected rats had increased blood glucose and glucose Ra and Rd but no change in blood lactate compared with untrained sham-injected animals. In the trained animals during exercise, MPA treatment increased blood lactate and decreased blood glucose and glucose Ra and Rd. There was no measurable glucose recycling in trained or untrained MPA-treated animals either at rest or during submaximal exercise. There was no difference in running time to exhaustion between trained and untrained MPA-treated rats.(ABSTRACT TRUNCATED AT 250 WORDS)     

Glucose tolerance in young and older athletes and sedentary men

Groups of endurance-trained masters athletes (60 +/- 2 yr), older untrained men (62 +/- 1 yr), lean older untrained men (61 +/- 2 yr), endurance-trained young athletes (26 +/- 1 yr), and young untrained men (28 +/- 1 yr) were studied to obtain information on the separate effects of age, physical activity, and body fatness on glucose tolerance and insulin sensitivity. Each subject underwent an oral 100-g glucose tolerance test. Skinfold thickness was determined at six sites. The trained groups had a higher maximum O2 uptake capacity and lower sum of skinfolds than their sedentary peers. The lean older untrained group had a sum of skinfolds similar to that of the young untrained group. The masters athletes, young athletes, and young untrained men exhibited similar glucose tolerance whereas the two older untrained groups had an almost twofold greater total area under the glucose curve (P less than 0.05). The masters and young athletes had significantly blunted plasma insulin responses compared with the other three groups (P less than 0.05). The young and the lean older untrained groups had similar plasma insulin responses with significantly lower insulin levels than the older untrained group (P less than 0.05). These results provide evidence that regularly performed vigorous exercise can, in some individuals, prevent the deterioration of glucose tolerance and insulin sensitivity with age.     

Effects of three-day bed rest on metabolic, hormonal and circulatory responses to an oral glucose load in endurance or strength trained athletes and untrained subjects.

The study was designed to find out (1) whether the effect of 3-day bed rest on blood glucose (BG) and plasma insulin (IRI) responses to glucose ingestion depends on preceding physical activity and (2) whether plasma adrenaline (A), noradrenaline (NA) and cardiovascular changes following a glucose load are modified by bed rest. Eleven sedentary students (22.5+/-0.3 yrs), 8 long distance runners (18.6+/-0.3 yrs) and 10 strength trained athletes (21.2+/-2.1 yrs) were examined before and after bed rest. Plasma IRI, BG, NA, A, heart rate (HR), and blood pressure (BP) were measured during 2 hrs following glucose (75 g) ingestion. The responses of BG and IRI to glucose load were calculated as incremental areas under the curves (auc). Both in athletes and untrained subjects bed rest markedly increased IRIauc, while BGauc was elevated only in sedentary subjects (p<0.05). The greatest increases in IRIauc and IRI/BG ratios were found in the endurance athletes. The data from all subjects (n = 29) revealed that the initial plasma NA and glucose-induced increases in NA and A were lowered after bed rest (p < 0.01). These effects were most pronounced in the endurance athletes. Bed rest did not influence HR or BP in any group. It is concluded that (1) the athletes have more adequate compensation for the bed-rest-induced decrement in insulin sensitivity than sedentary men; (2) three-day bed rest diminishes basal sympathetic activity and attenuates sympathoadrenal response to oral glucose; (3) endurance athletes have greater sympathetic inhibition than strength athletes or sedentary men.     

Decreased glucose tolerance but normal blood glucose levels in the field in the caviomorph rodent Ctenomys talarum: the role of stress and physical activity

Hystricomorph rodents have a divergent insulin molecule with only 1-10% of the biological activity in comparison to other mammalian species. In this study, we used the subterranean rodent Ctenomys talarum as a model and performed blood glucose tolerance tests (GTTs) with trained and untrained individuals to evaluate blood glucose regulation and the possible role of physical activity as a compensatory mechanism. Additionally, we evaluated the variations in blood glucose during acute and chronic stress and gathered data in the field to evaluate natural-occurring variations in blood glucose levels. The GTTs showed that C. talarum have a diminished capacity of regulating blood glucose levels in comparison to other mammals and suggest that unexplored differences in the compensatory mechanisms, insulin structure and/or glucose transporters exist within species of hystricomorph rodents. However, blood glucose levels in the field stayed within the normal mammalian range. Physical activity did not prove to be a compensatory mechanism for blood glucose regulation. The individuals did not display important increases in blood glucose after acute stressors and managed to adequately regulate blood glucose during chronic stress. We suggest that the species may not face a selective pressure favoring a more tightly, mammalian like, capacity of regulating blood glucose levels.     

Cardiovascular adaptations following detraining

We have recently summarized our data concerning endurance exercise training and its effect on blood pressure regulation during lower body negative pressure (LBNP). We found that endurance trained (ET) subjects were less tolerant to LBNP than their untrained (UT) counterparts. This decreased tolerance to LBNP was linked to a fitness related adaptation in cardiac compliance, an attenuated cardiopulmonary reflex regulation of peripheral vasoconstriction and an attenuated aortic-cardiac reflex. More recently we have found that 15 days of bed rest deconditioning (a severe form of detraining) in UT subjects resulted in a more responsive aortic-cardiac reflex. In severe detraining investigations, spaceflight and bed rest deconditioning a reduction in total blood and plasma volume were the manifest physiological changes. Therefore, we postulate that the increased aortic-reflex responsiveness was a compensation for the blood and plasma volume losses associated with detraining. Subsequently, we hypothesized that a generalized reduction of the normal daily aerobic activities of a healthy, young adult population would produce a moderate reduction in total blood and plasma volume and an up-regulation of the reflex blood pressure regulatory mechanisms.     

Transient responses in cardiac function below, at, and above anaerobic threshold

Exercise-induced alterations in cardiac function during graded cycling with submaximal and maximal intensities were studied in 13 trained and 13 untrained young men. Stroke volume (SV) and stroke index (SI) at rest and during submaximal and maximal exercise, determined by impedance cardiography, were consistently greater in the trained than in the less fit group. Training-induced bradycardia was evident in the trained group at rest and during submaximal exercise. Even when SV and SI were compared at the same absolute heart rate and left ventricular ejection time, those for the trained group were markedly greater than those for the untrained. SV for the untrained group was relatively diminished above the work rate corresponding to the anaerobic threshold. The difference in SV during exercise may be attributed to inadequate filling due to the smaller stretch of myocardial fibers in diastole and/or lesser systolic emptying of the left ventricle due to the reduced myocardial contractility in systole of untrained individuals.     

Dexamethasone in resting and exercising men. I. Effects on bioenergetics, minerals, and related hormones.

A placebo and a low and a high dose of dexamethasone (Dex) were administered for 4.5 days, at 3-wk intervals, to 24 healthy men, following a double-blind, random-order, crossover procedure. After the last dose the subjects performed a maximal cycling exercise, during which respiratory exchanges, electrocardiogram, and blood pressures were monitored. Blood was sampled just before and after each exercise bout. Dex showed no significant effect on fitness, sleep, exhaustion during exercise, maximal O(2) consumption, ventilatory threshold, maximal blood lactate, or rest and exercise blood pressures. On the contrary, both doses of Dex significantly decreased heart rate at rest and during maximal exercise. Blood glucose at rest was higher after both doses of Dex than after placebo; the opposite was found during exercise. Blood levels of ACTH, beta-endorphin, cortisol, and cortisol-binding globulin were lowered by Dex at rest and after exercise. Dex stimulated the increase in atrial natriuretic factor during exercise and lowered rest and postexercise aldosterone. Finally, no difference between "fit or trained" and "less fit or untrained" subjects could be found with respect to Dex effects.     

Incretion of Insulin by Pancreas and Its Inactivation in Women during Long-Term Head-down Tilt Bed Rest

An increase in insular activity in response to hyperglycemia when performing a glucose tolerance test (GTT) during normal physical activity in eight women volunteers was found to be associated with increased blood concentrations of insulin provided by an increase in secretion rate and a decrease in inactivation rate. After 81 days of stay in long-term –6° head-down tilt bed rest (bed rest), flattened glycemic curves (with low hyperglycemic lifting) observed during the GTT, what was indicated high insular activity. An increase in the insular activity was evidencing also by a smaller peak of the blood concentration of glucose from 5 min after intravenous nfusion of 20 mL of 40% glucose solution at 120 minute of the GTT. In bed rest on empty stomach no significant changes in the concentrations of insulin and C-peptide were observed. The dynamics of hormone during the GTT was showed that the appearance of flattened glycemic curves when performing GTT during bed rest was associated with more pronounced, than under the usual conditions, an increase in insulin concentration in response to hyperglycemia. An increase in the blood insulin concentration when performing GTT in bed rest was mainly provided by increased hormone secretion rate in the pancreas, but not by a decrease in its inactivation rate. If you use regular exercises for prevention of hypokinesia under conditions of bed rest, an increase in insulin concentration during GTT was mainly provided by a decrease in its inactivation rate and not by an increase in secretion rate.     

Hormonal responses to resistance exercise in long-term trained and untrained middle-aged men

This cross-sectional study compared hormonal responses to resistance exercise between trained and untrained men to investigate the adaptations of the endocrine system to long-term strength training in middle-aged men. Twenty-one middle-aged men were recruited for this study and matched into a strength-trained group (SG) (n = 10) and an untrained group (UG) (n = 11). In the SG, the individuals had practiced strength training for hypertrophy for at least 3 years. Upper- and lower-body muscle strength was measured with a 1 repetition maximum (1RM) test. Blood samples were collected at rest and after multiple sets of a superset strength training protocol (SSTP), with an intensity of 75% of 1RM values. With these blood samples, the levels of total testosterone (TT), free testosterone (FT), dehydroepiandrosterone (DHEA), cortisol, and sex hormone-binding globulin (SHBG) were determined. In addition, the TT-to-cortisol ratio and TT-to-SHBG ratio were calculated. There was no difference at rest between groups in hormonal values for TT, FT, DHEA, cortisol, the TT-to-SHBG ratio, and the TT-to-cortisol ratio. There were increases after SSTP in the levels of TT, FT, DHEA, and cortisol and the TT-to-SHBG ratio in the UG, but only FT increased in the SG. The SG demonstrated lower values in the TT-to-SHBG ratio after the training session. These results suggest the presence of alterations in anabolic and catabolic hormonal responses to resistance exercise in long-term trained middle-aged men, with the trained subjects demonstrating lower responsiveness in the hormone values. Long-term trained men seem to require a higher volume of training, at least similar to their daily workout, to stimulate greater hormone responses.     

Insulin action and secretion in endurance-trained and untrained humans

To evaluate insulin sensitivity and responsiveness, a two-stage hyperinsulinemic euglycemic clamp procedure (insulin infusions of 40 and 400 mU.m-2.min-1) was performed on 11 endurance-trained and 11 untrained volunteers. A 3-h hyperglycemic clamp procedure (plasma glucose approximately 180 mg/dl) was used to study the insulin response to a fixed glycemic stimulus in 15 trained and 12 untrained subjects. During the 40-mU.m-2.min-1 insulin infusion, the glucose disposal rate was 10.2 +/- 0.5 mg.kg fat-free mass (FFM)-1.min-1 in the trained group compared with 8.0 +/- 0.6 mg.kg FFM-1.min-1 in the untrained group (P less than 0.01). In contrast, there was no significant difference in maximally stimulated glucose disposal: 17.7 +/- 0.6 in the trained vs. 16.7 +/- 0.7 mg.kg FFM-1.min-1 in the untrained group. During the hyperglycemic clamp procedure, the incremental area for plasma insulin was lower in the trained subjects for both early (0-10 min: 140 +/- 18 vs. 223 +/- 23 microU.ml-1.min; P less than 0.005) and late (10-180 min: 4,582 +/- 689 vs. 8,895 +/- 1,316 microU.ml-1.min; P less than 0.005) insulin secretory phases. These data demonstrate that 1) the improved insulin action in healthy trained subjects is due to increased sensitivity to insulin, with no change in responsiveness to insulin, and 2) trained subjects have a smaller plasma insulin response to an identical glucose stimulus than untrained individuals.     

Exercise-induced pyruvate dehydrogenase activation is not affected by 7 days of bed rest

To test the hypothesis that physical inactivity impairs the exercise-induced modulation of pyruvate dehydrogenase (PDH), six healthy normally physically active male subjects completed 7 days of bed rest. Before and immediately after the bed rest, the subjects completed an oral glucose tolerance test (OGTT) and a one-legged knee extensor exercise bout [45 min at 60% maximal load (W(max))] with muscle biopsies obtained from vastus lateralis before, immediately after exercise, and at 3 h of recovery. Blood samples were taken from the femoral vein and artery before and after 40 min of exercise. Glucose intake elicited a larger (P ≤ 0.05) insulin response after bed rest than before, indicating glucose intolerance. There were no differences in lactate release/uptake across the exercising muscle before and after bed rest, but glucose uptake after 40 min of exercise was larger (P ≤ 0.05) before bed rest than after. Muscle glycogen content tended to be higher (0.05< P ≤ 0.10) after bed rest than before, but muscle glycogen breakdown in response to exercise was similar before and after bed rest. PDH-E1α protein content did not change in response to bed rest or in response to the exercise intervention. Exercise increased (P ≤ 0.05) the activity of PDH in the active form (PDHa) and induced (P ≤ 0.05) dephosphorylation of PDH-E1α on Ser2?3, Ser2?? and Ser3??, with no difference before and after bed rest. In conclusion, although 7 days of bed rest induced whole body glucose intolerance, exercise-induced PDH regulation in skeletal muscle was not changed. This suggests that exercise-induced PDH regulation in skeletal muscle is maintained in glucose-intolerant (e.g., insulin resistant) individuals.     

Blood oxidative stress biomarkers: influence of sex,exercise training status,and dietary intake

Background: Sex and lifestyle factors are known to influence the oxidation of protein, lipids, and DNA. Biomarkers such as protein carbonyls (PC), malondialdehyde (MDA), and 8-hydroxydeoxyguanosine (8-OHdG) have been commonly used in an attempt to characterize the oxidative status of human subjects.Objective: This study compared resting blood oxidative stress biomarkers, in relation to exercise training status and dietary intake, between men and women.Methods: Exercise-trained and sedentary men and women (with normal menstrual cycles; reporting during the early follicular phase) were recruited from the University of Memphis, Tennessee, campus and surrounding community via recruitment flyers and word of mouth. Participants were categorized by sex and current exercise training status (ie, trained or untrained). Each completed a detailed 5-day food record of all food and drink consumed. Diets were analyzed for kilocalories and macro- and micronutrient (vitamins C, E, A) intake. Venous blood samples were obtained at rest and analyzed for PC, MDA, and 8-OHdG.Results: In the 131 participants (89 men, of whom 74 were exercise trained and 15 untrained, and 42 women, of whom 22 were exercise trained and 20 untrained; mean [SD] age, 24 [4] years), PC did not differ significantly between trained men and women or between untrained men and women. However, trained participants had significantly lower plasma PC (measured in nmol · mg protein^-1) (mean [SEM] 0.0966 [0.0055]) than did untrained participants (0.1036 [0.0098]) (P < 0.05). MDA levels (measured in μmol · L^-1) were significantly lower in trained women (0.4264 [0.0559]) compared with trained men (0.6959 [0.0593]); in trained men and women combined (0.5621 [0.0566]) compared with untrained men and women combined (0.7397 [0.0718]); and in women combined (0.5665 [0.0611]) compared with men combined (0.7338 [0.0789]) (P < 0.05 for all comparisons). No significant differences were noted between any groups for 8-OHdG. Neither PC nor 8-OHdG were correlated to any dietary variable, with the exception of PC and percent of protein in untrained men (r = 0.552; P = 0.033). MDA was positively correlated to protein intake and negatively correlated to percent of carbohydrate and vitamin C intake, primarily in trained men (P ≤ 0.03).Conclusions: In this sample of young healthy adults, oxidative stress was lower in women than in men and in trained compared with untrained individuals, particularly regarding MDA. With the exception of MDA primarily in trained men, dietary intake did not appear to be correlated to biomarkers of oxidative stress.     

Exercise adaptation attenuates VEGF gene expression in human skeletal muscle

Angiogenesis is a component of the multifactoral adaptation to exercise training, and vascular endothelial growth factor (VEGF) is involved in extracellular matrix changes and endothelial cell proliferation. However, there is limited evidence supporting the role of VEGF in the exercise training response. Thus we studied mRNA levels of VEGF, using quantitative Northern analysis, in untrained and trained human skeletal muscle at rest and after a single bout of exercise. Single leg knee-extension provided the acute exercise stimulus and the training modality. Four biopsies were collected from the vastus lateralis muscle at rest in the untrained and trained conditions before and after exercise. Training resulted in a 35% increase in muscle oxygen consumption and an 18% increase in number of capillaries per muscle fiber. At rest, VEGF/18S mRNA levels were similar before (0.38 +/- 0.04) and after (1.2 +/- 0.4) training. When muscle was untrained, acute exercise greatly elevated VEGF/18S mRNA levels (16.9 +/- 6.7). The VEGF/18S mRNA response to acute exercise in the trained state was markedly attenuated (5.4 +/- 1.3). These data support the concept that VEGF is involved in exercise-induced skeletal muscle angiogenesis and appears to be subject to a negative feedback mechanism as exercise adaptations occur.     

Enhanced oxygen extraction and reduced flow heterogeneity in exercising muscle in endurance-trained men

The aim of this study was to investigate the effects of endurance training on skeletal muscle hemodynamics and oxygen consumption. Seven healthy endurance-trained and seven untrained subjects were studied. Oxygen uptake, blood flow, and blood volume were measured in the quadriceps femoris muscle group by use of positron emission tomography and [15O]O2, [15O]H2O, and [15O]CO during rest and one-legged submaximal intermittent isometric exercise. The oxygen extraction fraction was higher (0.49 +/- 0.14 vs. 0.29 +/- 0.12; P = 0.017) and blood transit time longer (0.6 +/- 0.1 vs. 0.4 +/- 0.1 min; P = 0.04) in the exercising muscle of the trained compared with the untrained subjects. The flow heterogeneity by means of relative dispersion was lower for the exercising muscle in the trained (50 +/- 9%) compared with the untrained subjects (65 +/- 13%, P = 0.025). In conclusion, oxygen extraction is higher, blood transit time longer, and perfusion more homogeneous in endurance-trained subjects compared with untrained subjects at the same workload. These changes may be associated with improved exercise efficiency in the endurance-trained subjects.     

Exercise training and the stress response in rainbow trout, Salmo gairdneri Richardson

Plasma levels of catecholamines, cortisol, and glucose were monitored in rainbow trout during a 6-week forced swimming exercise programme. Compared to resting non-exercised controls, resting trained fish had lower levels of epinephrine, norephinephrine, cortisol, and glucose during the last 3 weeks of training. Initially, trained fish that were swimming had higher levels of epinephrine than resting trained fish. After 2 weeks of exercise, swimming did not significantly elevate epinephrine levels in trained fish. Glucose levels were consistently greater in swimming fish than in resting fish. At the end of the training period, exercised trout had lower (15–20%) oxygen consumption rates while resting or swimming than unexercised fish.
After a 5-month forced swimming exercise programme plasma levels of catecholamines and glucose were monitored in trained and untrained cannulated rainbow trout after 2 min of mild agitation. Trained fish showed an immediate (within 1 min) increase in the levels of epinephrine, but not norepinephrine and a delayed (within 15 min) increase in the levels of plasma glucose. Epinephrine levels returned to pre-stress levels within 15 min. Untrained fish had no significant increase in the plasma levels of norepinephrine, epinephrine, or glucose.     

Exercise-induced cardiac hypertrophy: a correlation of blood flow and microvasculature

The effects of exercise conditioning on the myocardium were studied in seven instrumented pigs strenuously exercised for 12 wk by treadmill running. Data were compared with eight instrumented untrained pigs. O2 consumption measured during maximum exercise effort was significantly elevated in the trained pigs (71.7 +/- 4.0 vs. 56.3 +/- 3.0 ml X ml-1 X kg-1). Absolute right and left ventricular mass increased by 20 and 13%, respectively, in response to exercise. Myocyte cross-sectional area increased by 21% in the trained hearts compared with the untrained hearts. Transmural left ventricular myocardial blood flow (ml X min-1 X g-1) was not significantly different at rest, during maximum exercise, or during exercise with adenosine infusion. However, training caused an elevation of the regional epicardial blood flow noted during exercise and exercise with adenosine. In the trained pigs mean aortic pressure during maximum exercise with adenosine infusion was not significantly different compared with untrained pigs. Coronary resistance during exercise with adenosine infusion was the same in both animal groups. In the trained group capillary numerical (no./mm2) and length (mm/mm3) densities were reduced, whereas arteriolar numerical and length densities were significantly increased compared with the untrained group. Measurements of capillary luminal surface density (mm2/mm3) in the trained group were unchanged compared with the untrained group. These results suggest that strenuous exercise does not stimulate the production of new capillaries, but this is modified by the ability of existing capillaries to increase their luminal surface area to parallel increases in myocyte growth. The arteriolar data suggest that exercise promotes the formation of new arterioles.(ABSTRACT TRUNCATED AT 250 WORDS)     

Effect of 21 days head-down bed rest on heart rate and blood pressure variability and orthostatic tolerance in men

Healthy males were tested for orthostatic tolerance during and following 21 days head-down bed rest. ECG and blood pressure were measured. Ten out of the 15 subjects were able to complete the head-up tilt (HUT) test following bed rest, and changes in heart rate dynamics and blood pressure were observed in both finishers and non-finishers. Specific results are presented and discussed.     

Metabolic and hormonal response to short term fasting after endurance training in the rat

The metabolic and hormonal response to short term fasting was studied after endurance exercise training. Rats were kept running on a motor driven rodent treadmill 5 days/wk for periods up to 1 h/day for 6 wk. Trained and untrained rats were then fasted for 24 h and 48 h. Liver and muscle glycogen, blood glucose, lactate, beta OH butyrate, glycerol, plasma insulin, testosterone and corticosterone were measured in fed and fasted trained and untrained rats. 48 h fasted trained rats show a lower level of blood lactate (1.08 +/- 0.05 vs 1.33 +/- 0.08 mmol/l-1 of blood glycerol (1 +/- 0.11 vs 0.84 +/- 0.08 mmol/l-1), and of muscle glycogen. There is a significant increase in plasma corticosterone in 48 h fasted trained rats from fed values. Plasma testosterone decreases during fasting, the values are higher in trained rats. Plasma insulin decreases during fasting without any difference between the two groups. These results show higher lipolysis, and decreased glycogenolysis in trained animals during 48 h fasting. The difference between the groups in steroid hormone response could reduce neoglucogenesis and muscle proteolysis in trained animals.     

Adaptation of blood sugar regulation during muscular activity. Effects of training]

Our aim was to study the adaptation of energetic metabolism to muscular activity and the effects of training upon these adaptations. So we realized swimming and running tests on young healthy adults, selected in "trained" and "untrained". The effects of muscular activity were reflected by a raise of serum F.F.A., clearly noted in "untrained" subjects ; the levels of glucose and growth hormone both raised, but especially in "trained" subjects. Cortisol level raised in varying degrees while insulinemia presented little changes.     

Seven days of bed rest decrease insulin action on glucose uptake in leg and whole body

Impaired glucose tolerance develops in normal humans after short-term bed rest. To elucidate the mechanism, insulin action on whole body glucose uptake rate (WBGUR) and leg glucose uptake rate (LGUR) was measured by sequential euglycemic clamp technique combined with femoral arterial and venous cannulation at insulin concentrations of 10 +/- 1, 18 +/- 1, 37 +/- 2, and 360 +/- 15 microU/ml. Studies were performed before (C) and after (BR) 7 days of strict bed rest. WBGUR was significantly lower after bed rest than before (5.5 +/- 0.4 and 7.2 +/- 0.8 mg.min-1.kg-1, respectively) when insulin was 37 microU/ml. LGUR was even more markedly depressed by bed rest, being 0.6 +/- 0.1, 0.9 +/- 0.2, and 2.8 +/- 0.4 mg.min-1.kg leg-1 (BR) compared with 0.9 +/- 0.1, 1.7 +/- 0.4, and 5.9 +/- 0.5 mg.min-1.kg leg-1 (C) (P less than 0.05) at the three lower insulin concentrations. At these insulin concentrations also, lactate release and glucose oxidation and glycogen storage estimated by indirect calorimetry were lower in the leg after bed rest. At the highest insulin dose WBGUR was similar on BR and C days, while LGUR was lower after bed rest. In conclusion, 7 days of bed rest decrease whole body insulin action, a fact that is explained by decreased insulin action in inactive muscle.