Adaptation of muscle to exercise. Increase in levels of palmityl Coa synthetase, carnitine palmityltransferase, and palmityl Coa dehydrogenase, and in the capacity to oxidize fatty acids

Exercise increases fat oxidation at rest unrelated to changes in energy balance or lipolysis

The hypothesis that exercise increases fat oxidation at rest independently of changes in energy balance, body composition, and/or lipolysis was tested in 21 volunteers. After a period of energy balance, volunteers were randomly allocated to one of four groups: control, overfed (OF), overfed and exercised (OF-EX), and exercised (EX). OF and OF-EX were overfed 50% excess of energy balance calories; OF-EX and EX spent 50% excess of energy balance calories during daily exercise sessions. Exercise increased fat oxidation at rest independently of dietary intake (OF-EX = + 22 +/- 2.4, EX = + 23 +/- 1.5 mg/min) and reduced carbohydrate oxidation (OF-EX = - 49 +/- 6.2, EX = - 46 +/- 5.4 mg/min). Volunteers in the OF group had an increase in carbohydrate oxidation (85 +/- 5.9 mg/min) and a decline in fat oxidation (- 33 +/- 1.4 mg/min). Protein oxidation did not change in any group. These changes occurred without a direct relation with changes in lipolysis and persisted even when expressed as a percentage or as an absolute equivalent of resting metabolic rate in calories. Thus exercise, independent of changes in energy intake and body composition and not related to changes in lipolysis, increases fat oxidation at rest, which may explain the beneficial effects of exercise in weight loss programs.

The membrane-associated 40 KD fatty acid binding protein (Berk's protein), a putative fatty acid transporter is present in human skeletal muscle

Muscle tissue (1.1 +/- 0.1 grams) was obtained from seven healthy individuals (3 males, 4 females) using an open incision approach before and after ingestion of either 75 grams of dextrose (N=5) or water (N=2). Purified sarcolemmal membranes from the muscle were prepared using a sucrose step gradient. A polyclonal antibody raised against the purified (99%) rat hepatocyte 40 KD membrane fatty acid binding protein (mFABP-L) was used to probe for this putative transporter in the muscle membranes using Western blot. A single band at the 40 KD MW band was identified which reacted antigenically with the protein purified from rat livers. These response of Berk's protein 60-75 minutes after dextrose ingestion (or water) was erratic and no specific trend could be identified. Our data demonstrate that the 40 KD mFABP-L originally isolated from rat liver is also present in human skeletal muscle membrane. This protein may be involved in transport of fatty acids across the membrane of skeletal muscle, however its physiological role in human fatty acid metabolism remains to be established.

Palmitate oxidation in muscle mitochondria of patients with the juvenile form of neuronal ceroid-lipofuscinosis

The finding that the intracellular storage material in juvenile neuronal ceroid lipofuscinosis (JNCL) consists of the subunit c of ATP synthase prompted us to study energy conservation in JNCL patients. The activities of respiratory chain enzymes in isolated muscle mitochondria from 8 JNCL cases were normal, but oxidation of palmitate was reduced in 6 patients. The degree of reduction was related to the age of the patients. None of the patients had clinical symptoms or laboratory findings of impaired energy conservation, which suggest that the reduced palmitate oxidation was not associated with a major defect in fatty acid oxidation.

Mitochondrial biogenesis in striated muscle

Mitochondrial biogenesis (synthesis) has been observed to occur in skeletal muscle in response to chronic use. It also occurs in cardiac muscle during growth and hypertrophy, and it may be impaired during the aging process. This review summarizes the literature on the processes of mitochondrial biogenesis at the biochemical and molecular levels, with particular reference to striated muscles. Mitochondrial biogenesis involves the expression of nuclear and mitochondrial genes and the coordination of these two genomes, the synthesis of proteins and phospholipids and their import into the organelle, and the incorporation of these lipids and proteins into their appropriate locations within the matrix, inner or outer membranes. The emphasis is on the regulation of these events, with information derived in part from other cellular systems. Although descriptions of mitochondrial content changes in heart and skeletal muscle during altered physiological states are plentiful, much work is needed at the molecular level to investigate the regulatory processes involved. A knowledge of biochemical and molecular biology techniques is essential for continued progress in the field. This is a promising area, and potential new avenues for future research are suggested.

A randomized study of the effects of aerobic exercise by lactating women on breast-milk volume and composition

BACKGROUND

The potential risks and benefits of regular exercise during lactation have not been adequately evaluated. We investigated whether regular aerobic exercise had any effects on the volume or composition of breast milk.

METHODS

Six to eight weeks post partum, 33 sedentary women whose infants were being exclusively breast-fed were randomly assigned to an exercise group (18 women) or a control group (15 women). The exercise program consisted of supervised aerobic exercise (at a level of 60 to 70 percent of the heart-rate reserve) for 45 minutes per day, 5 days per week, for 12 weeks. Energy expenditure, dietary intake, body composition, and the volume and composition of breast milk were assessed at 6 to 8, 12 to 14, and 18 to 20 weeks post partum. Maximal oxygen uptake and the plasma prolactin response to nursing were assessed at 6 to 8 and 18 to 20 weeks.

RESULTS

The women in the exercise group expended about 400 kcal per day during the exercise sessions but compensated for this energy expenditure with a higher energy intake than that recorded by the control women (mean [+/- SD], intake, 2497 +/- 436 vs. 2168 +/- 328 kcal per day at 18 to 20 weeks; P < 0.05). Maximal oxygen uptake increased by 25 percent in the exercising women but by only 5 percent in the control women (P < 0.001). There were no significant differences between the two groups in maternal body weight or fat loss, the volume or composition of the breast milk, the infant weight gain, or maternal prolactin levels during the 12-week study.

CONCLUSIONS

In this study, aerobic exercise performed four or five times per week beginning six to eight weeks post partum had no adverse effect on lactation and significantly improved the cardiovascular fitness of the mothers.

Metabolic adaptations to endurance training in older individuals

The purpose of this study was to describe the effects of moderate intensity exercise training on the muscle energy utilization, blood flow, and exercise performance of four sedentary older individuals (58 +/- 4 yrs). Subjects trained the dominant forearm each day for 12 weeks. The nondominant arm was not trained and served as a within-subject control. 31P nuclear magnetic resonance spectroscopy (31P NMRS) was used to identify the power output in watts (W) at the onset, or threshold, of intracellular acidosis (IT) in the exercising muscle during progressive exercise tests to fatigue. After 6 weeks of training, power output at the IT increased by 14% (p < 0.05) in the dominant arm; however, an additional 6 weeks of the same exercise program failed to produce a further increase in IT power. IT power of the nondominant forearm was not changed. In the dominant forearm, endurance time for a submaximal wrist flexion test was increased 34% and 58% at 6 and 12 weeks, respectively. Maximal voluntary strength was not affected by training, nor was resting or exercising blood flow. The training program delayed the onset of intracellular acidosis during progressive exercise and increased the capacity for submaximal work. These effects did not appear to depend on an increase in muscle blood flow.

The effect of exercise on the riboflavin status of adult men

Six sedentary to moderately active men with biochemical signs of riboflavin deficiency were studied under metabolic ward conditions to examine the effects of physical activity on riboflavin status. All participants were subjected to additional exercise (EXER) for an 18 d period between two maintenance (M1 and M2) periods (16 and 13 d respectively) of habitual physical activity. Energy balance and riboflavin intake were maintained throughout the study. Riboflavin status, as judged by a significant reduction in erythrocyte glutathione reductase (EC 1.6.4.2) activation coefficient (EGR-AC), improved on changing from home (1.53 (SD 0.14)) to period M1 (1.36 (SD 0.21)) diets. The exercise period, however, resulted in a significant deterioration in riboflavin status (1.57 (SD 0.31)) which persisted in the subsequent period M2 (1.54 (SD 0.15)). There was a concomitant fall in the urinary excretion of riboflavin only in the EXER period, when results were expressed as a percentage of the dietary intake of riboflavin. These results suggest an increased demand for the vitamin for selective biochemical functions during exercise. However, the energy cost of walking (treadmill 4 km/h), 50 W and 100 W work-loads (bicycle ergometer) as well as delta mechanical efficiency (DME) did not change during the three metabolic periods. The urinary excretion of riboflavin was inversely related to DME (r -0.49; P < 0.05) and directly correlated with haemoglobin levels (r 0.63; P < 0.005). The present study suggests that riboflavin status further deteriorates during a short period of increased physical activity in individuals whose riboflavin status is marginal.

Mitochondrial actaptations to chronic muscle use: Effect of iron deficiency

1. The effects of chronic muscle use on mitochondrial structure, enzymes and gene expression is reviewed. The role of iron deficiency in modulating this adaptation is discussed. 2. Chronic muscle use and disuse alter mitochondrial composition and affect mitochondrial subpopulations differentially. This has implications for an understanding of organelle assembly. 3. Iron deficiency decreases mitochondrial functional mass within muscle by reducing the level of heme and non-heme iron-containing components. This alters the metabolic response during exercise and results in a reduced endurance performance. 4. Both iron deficiency and chronic muscle use represent contrasting experimental models for the study of mitochondrial function and biogenesis.

The relationship of voluntary running to fibre type composition, fibre area and capillary supply in rat soleus and plantaris muscles

Twenty 4-week-old Wistar rats exercised voluntarily in running wheels each day for 45 days. Fibre type composition, fibre cross-sectional area and the number of capillaries around a fibre of the slow-twitch soleus and fast-twitch plantaris muscles were examined and compared with animals which had no access to running wheels. The exercise group had a higher percentage of fast-twitch oxidative glycolytic (FOG) fibres and a lower percentage of fast-twitch glycolytic (FG) fibres in the deep portion of the plantaris muscle. The area of FOG fibres in the surface portion of the plantaris muscle was also greater in the exercise group. In the exercised animals, there was a positive relationship between the running distance and the area of FOG fibres in both the deep and surface portions of the plantaris muscle. In addition, the running distance correlated positively with the percentage of FOG fibres and negatively with that of FG fibres in the deep portion of the plantaris muscle. There were no relationships between the running distance and fibre type composition, or fibre area and capillary supply in the soleus muscle. These results suggested that the increase in the percentage and area of FOG fibres in the fast-twitch muscle was closely related to voluntary running.

Acute and chronic responses of skeletal muscle to endurance and sprint exercise. A review

Skeletal muscle adapts to the stress of endurance and sprint exercise and training. There are 2 main types of skeletal muscle fibre--slow twitch (ST) and fast twitch (FTa, FTb, FTc). Exercise may produce transitions between FT and ST fibres. Sprint training has decreased the proportion of ST fibres and significantly increased the proportion of FTa fibres, while endurance training may convert FTb to FTa fibres, and increase the proportion of ST fibres (i.e. FTb----FTa----FTc----ST). However, the high proportion of ST fibres documented for elite endurance athletes may be simply the result of natural selection. ST fibres function predominantly during submaximal exercise, whereas FT fibres are recruited as exercise intensity approaches VO2max and/or glycogen stores are depleted. Long distance runners have greater ST and FT fibre areas than untrained controls. However, doubt remains as to whether the ST or FT fibre area is greatest in endurance athletes. Increases in FT fibre area seem to occur during the first 2 months of training whereas ST fibre areas appear to increase after 2 to 6 months of training. Sprint training leads to the preferential use of FT fibres and male, but not female sprinters have larger FT fibres than untrained controls. Mitochondrial proteins and oxidative enzymes, as opposed to VO2max, are important determinants of the duration of endurance exercise. Endurance training increases intramuscular glycogen stores in both FT and ST fibres and produces a 'glycogen-sparing' effect which is characterised by an increased free fatty acid (FFA) metabolism. The activity of glycogen synthase is also increased by endurance training. Sprint training increases glycogen concentrations similarly in all fibre types, reduces the rate of glycogen utilisation at submaximal workloads and allows supramaximal workloads to be maintained for longer periods of time. During endurance exercise the pattern of glycogen depletion varies between muscle fibre types and between muscle groups. Glycogen stores in ST fibres are utilised initially, followed by stores in FTa then FTb fibres. Sprint activities are associated with a much greater rate of glycogen depletion. However, it is unlikely that glycogen depletion causes fatigue during sprinting. Sprint work is associated with a preferential depletion of glycogen from FTb then FTa and ST fibres. Endurance training appears to increase triglyceride stores adjacent to mitochondria and ST fibres have greater triglyceride stores than FT fibres. Endurance exercise is associated with a preferential use of triglycerides from ST fibres and endogenous triglycerides may account for over 50% of the total lipid oxidised during exercise.(ABSTRACT TRUNCATED AT 400 WORDS)

Weight set-point theory and the high-density lipoprotein concentrations of long-distance runners

Long-distance runners have higher high-density lipoprotein (HDL)-cholesterol concentrations and lower adiposity than sedentary men. Most cross-sectional studies claim that the runners' elevated HDL-cholesterol is not due to the runners' leanness. However, when cross-sectional studies use analysis of covariance (ANCOVA) to adjust for adiposity, or when they compare runners with lean sedentary men, they make an incorrect tacit assumption. They assume that the relationship between change in adiposity and change in HDL-cholesterol in men who have lost fat by running is the same as the cross-sectional difference in HDL-cholesterol between naturally fat and lean sedentary men. Regression slopes for HDL-cholesterol versus adiposity during and at the end of 1 year of running in 35 initially sedentary men suggest this assumption is incorrect; the increase in HDL-cholesterol that accompanies weight loss (-4.28 +/- 1.01 mg/100 mL per kg/m2) is considerably greater than the increase in HDL-cholesterol that is associated with lower adiposity cross-sectionally (-0.78 +/- 0.46 mg/100 mL per kg/m2). These results suggest the following theory: long-distance runners have the HDL metabolism of men who are below their sedentary set-point weight rather than the HDL metabolism of men who are naturally lean without exercising or dieting. This theory was applied to data from 23 published comparisons between long-distance runners and sedentary men.(ABSTRACT TRUNCATED AT 250 WORDS)

A sensitive method for measuring ATP-formation in rat muscle mitochondria

A sensitive method for the measurement of the ATP production rate in isolated skeletal muscle mitochondria is presented. Mitochondrial suspensions were prepared by differential centrifugation from approximately 80 mg of soleus muscle. ATP production rates were measured luminometrically, utilizing a reagent based upon firefly luciferase, which emits light proportional to the ATP concentration. In a group of 10 rats the ATP production rates were measured with the following substrate combinations: pyruvate + malate, palmitoyl-L-carnitine + malate, alpha-ketoglutarate, succinate + rotenone and succinate alone. The variance of the method including tissue preparation, protein determination and the luminometric determination of ATP production was estimated to be 10-14% for the various substrates. Compared to values in the literature, the present results show a good agreement for the substrates pyruvate + malate and palmitoyl-L-carnitine + malate, but lower rates were obtained in our study for alpha-ketoglutarate and succinate + rotenone. The advantage of the luminometric method is its high sensitivity. Only 30-40 mg of tissue is required for a complete determination, compared to 1-2 g for a similar assay of oxygen consumption. The method is intended for use in human subjects and will facilitate studies of mitochondrial respiration both in patients of different age groups and in healthy subjects.

Lipid depletion and repletion in skeletal muscle following a marathon

Intramuscular lipid content was investigated in muscle biopsies from 10 well-trained endurance athletes before, immediately after, and 1, 3, 5, and 7 days after a marathon. Diets were controlled throughout the entire period of the study. Triglyceride content was ultrastructurally determined by the use of stereological methods. The volume percent lipid significantly decreased after the marathon and was lowest at 3 days post-marathon, rising slightly but still 35% lower than the pre-marathon value by 7 days post-marathon. Glycogen granules were abundant and tightly packed in the pre-marathon biopsies, scarce immediately post-marathon, and abundant, but less tightly packed, 7 days post-marathon. Post-marathon fluctuations in the volume percentages of mitochondria indicated possible fluid shifts within the muscle fibers: dehydration immediately post-marathon followed by rehydration with possible edema. Assuming the content of mitochondria remained constant throughout the recovery period, the ratio of the volume percentage of lipid to the volume percentage of mitochondria indicated that lipid content may have reached pre-marathon levels after 7 days post-marathon.

The effect of detraining and reduced training on the physiological adaptations to aerobic exercise training

In previously sedentary individuals, regularly performed aerobic exercise results in significant improvements in exercise capacity. The development of peak exercise performance, as typified by competitive endurance athletes, is dependent upon several months to years of aerobic training. The physiological adaptations associated with these improvements in both maximal exercise performance, as reflected by increases in maximal oxygen uptake (VO2max), and submaximal exercise endurance include increases in both cardiovascular function and skeletal muscle oxidative capacity. Despite prolonged periods of aerobic training, reductions in maximal and submaximal exercise performance occur within weeks after the cessation of training. These losses in exercise performance coincide with declines in cardiovascular function and muscle metabolic potential. Significant reductions in VO2max have been reported to occur within 2 to 4 weeks of detraining. This initial rapid decline in VO2max is likely related to a corresponding fall in maximal cardiac output which, in turn, appears to be mediated by a reduced stroke volume with little or no change in maximal heart rate. A loss in blood volume appears to, at least partially, account for the decline in stroke volume and VO2max during the initial weeks of detraining, although changes in cardiac hypertrophy, total haemoglobin content, skeletal muscle capillarisation and temperature regulation have been suggested as possible mediating factors. When detraining continues beyond 2 to 4 weeks, further declines in VO2max appear to be a function of corresponding reductions in maximal arterial-venous (mixed) oxygen difference. Whether reductions in oxygen delivery to and/or extraction by working muscle regulates this progressive decline is not readily apparent. Changes in maximal oxygen delivery may result from decreases in total haemoglobin content and/or maximal muscle blood flow and vascular conductance. The declines in skeletal muscle oxidative enzyme activity observed with detraining are not causally linked to changes in VO2max but appear to be functionally related to the accelerated carbohydrate oxidation and lactate production observed during exercise at a given intensity. Alternatively, reductions in submaximal exercise performance may be related to changes in the mean transit time of blood flow through the active muscle and/or the thermoregulatory response (i.e. degree of thermal strain) to exercise. In contrast to the responses observed with detraining, currently available research indicates that the adaptations to aerobic training may be retained for at least several months when training is maintained at a reduced level. Reductions of one- to two-thirds in training frequency and/or duration do not significantly alter VO2max or submaximal endurance time provided the intensity of each exercise session is maintained.(ABSTRACT TRUNCATED AT 400 WORDS)

Exercise-induced transient hyperlipidemia in the racehorse

Effects of graded intensity exercise on plasma lipids was studied in Standardbred and Finnishbred Trotters. The rate of lipolysis indicated by the elevated plasma concentrations of glycerol increased parallel with the intensity of the trot in the Standardbreds, but not as clearly in the Finnishbred trotters. During the exercise plasma triglyceride concentration increased significantly and the increase correlated with the intensity of the exercise as well as the activity of lipolysis. Together with the increase in plasma triglycerides, there was a parallel increase in the pre-beta fraction of lipoproteins which suggests that the hepatic synthesis of triglycerides was increased. It was calculated that about one third of the nonesterified fatty acids released in lipolysis during the high-intensity exercise is oxidized and the remainder is used for resynthesis of triglycerides. Since there were interstrain differences in the concentrations of triglycerides and glycerol after the high-intensity exercise it is suggested that the differences may be of some value in the estimation of recovery after submaximal exercise.

Biochemical aspects of peripheral muscle fatigue. A review

Muscular fatigue is of critical importance to performance and as such has been the subject of numerous investigations. However, a clear cause remains elusive. Although many factors have been identified, this review deals only with those which occur distal to the neuromuscular junction. Factors discussed include: energy supply (ATP/creatine phosphate, glycogen, oxygen, and free fatty acids); the accumulation of metabolites (lactate/hydrogen ions, calcium, ammonium, electrolyte and water shifts); and, the special case of eccentric work. The results of many studies using various methodologies are examined. Peripheral fatigue appears to be a complex series of interactions with variable influence on the development of fatigue depending upon the nature of the work performed.

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.

Carnitine status, plasma lipid profiles, and exercise capacity of dialysis patients: effects of a submaximal exercise program

Carnitine status, blood lipid profiles, and exercise capacity were evaluated in a combined group of hemodialysis (N = 4) and continuous ambulatory peritoneal dialysis (N = 6) patients before and after an 8-week submaximal exercise program. Maximal aerobic capacity (VO2max) was only 18.5 +/- 5.9 (mean +/- SD) mL O2/kg/min, well below the expected 30 to 35 mL O2/kg/min for age-matched sedentary controls. Plasma short-chain acylated carnitine levels, which were two to three times normal values, were reduced after the exercise program, but the long-chain acylcarnitines were significantly reduced during acute exercise. Muscle biopsies of the vastus lateralis were performed at rest in five patients prior to and after the 8-week exercise program. Total carnitine in skeletal muscle was 3.09 (.076 SD) mumol/g ww, with only 11.3% acylated prior to the exercise program, which was much lower than the 4.25 +/- 1.27 mumol/g ww, with 28.5% acylated in a group of healthy athletic subjects (N = 28). Muscle free carnitine concentrations decreased significantly following the 8-week training period, with only a slight reduction in total carnitine. The percent of acylated carnitine was therefore significantly increased (P less than 0.05) from 11.3% to 25.2% after the experimental period. Pretraining carnitine palmitoyl transferase activity at rest was 0.57 +/- 0.28 nmol palmitoyl carnitine formed/5 min/mg mitochondrial protein, which was not changed by exercise training v 1.80 +/- 0.51 nmol/5 min/mg protein in 28 healthy normals (P less than 0.001). Free fatty acid concentrations were reduced significantly during acute exercise as a result of the exercise training program whereas other plasma lipids were not altered. (ABSTRACT TRUNCATED AT 250 WORDS)

Leucine metabolism in thyrotoxicosis: plasma aminogram and 3-methylhistidine excretion before and after treatment

Previous studies have suggested increased protein catabolism and altered muscle metabolism in hyperthyroid patients. In this experiment we investigated parameters of protein and leucine metabolism before and after treatment of hyperthyroidism. While confined in a metabolic ward, patients' daily caloric intake was based on the resting energy expenditure and an allowance for 16 hours of light physical activity. We found no significant difference in plasma aminogram and urinary 3-methylhistidine excretion (an index of protein catabolism) before and after treatment. On the other hand, hyperthyroidism appeared to increase the rates of oxidation, turnover, and plasma clearance of endogenous leucine. However, only the 60% increase in the rate of leucine oxidation was statistically significant. We conclude that in spite of increased catabolism, basal levels of branched-chain amino acids are well maintained in plasma of hyperthyroid patients consuming a diet that compensates for their hypermetabolic state.

Effects of L-carnitine loading on the aerobic and anaerobic performance of endurance athletes

L-Carnitine (L-C), a well known physiological carrier across the inner mitochondrial membrane of activated long chain fatty acids and acceptor of acyl groups from acyl-CoA, has been recently synthesised industrially. This has made it possible to study the effects of L-C loading (4 g X d(-1) by mouth over a period of 2 weeks) on the aerobic and anaerobic performance of 6 long distance competitive walkers. As a result of the treatment: 1) mean total, free and esterified serum L-C both at rest and shortly after completing a 120 min walk at about 65% of the individual maximal aerobic power (VO2max) were significantly increased; 2) VO2max increased 6%, from 54.5 +/- 3.7 (S.D.) to 57.8 +/- 4.7 m1O2 X kg(-1) X min(-1) (P less than 0.02); 3) blood lactate concentration (Lab) as a consequence of short bouts repeated exercise (series of 10, 15 and 20 jumps off both feet on a force platform) was unchanged; 4) heart rate, pulmonary ventilation, oxygen consumption, and respiratory quotient in the same conditions as for 1) were unchanged. It is concluded that, in trained athletes, as a consequence of L-C loading VO2max is slightly but significantly raised, probably as a result of an activation of substrate flow through the TCA cycle, whereas the lipid contribution to metabolism in prolonged submaximal exercise remains unchanged.

Lack of relationship between changes in adiposity and plasma lipids following endurance training

In order to study the effect of alterations in fat morphology and metabolism induced by exercise-training on plasma lipids, 13 healthy young men were subjected to a 20-week aerobic training program on bicycle. Training significantly increased maximal aerobic power (VO2 max) (P less than 0.001) and decreased per cent body fat (P less than 0.001). A significant reduction of mean adipocyte diameter and an increase in isolated fat cell epinephrine-stimulated lipolysis were also observed following training. However, with the exception of total cholesterol, no changes were noted in plasma lipids. Neither before nor after training were triglycerides and high density lipoprotein cholesterol (HDL-C) correlated with VO2 max, fat cell diameter and adipocyte-stimulated lipolysis. The present study demonstrates that an important fat loss (mean loss of fat = 3 kg) and a significant gain in VO2 max induced by endurance training do not necessarily produce an increase in HDL-C levels in normal male subjects. Moreover, changes in VO2 max, body fatness and in fat cell epinephrine-stimulated lipolysis produced by endurance training are not related to modifications in plasma lipids in healthy men.

Elevation of tissue coenzyme Q (ubiquinone) and cytochrome c concentrations by endurance exercise in the rat

Six months of enforced and voluntary endurance training of young female Wistar rats resulted in significant decreases of body weight and gastrocnemius muscle wet weight and protein content, and increases in heart weight and protein content, and liver protein content. The coenzyme Q and cytochrome c concentrations of cardiac, gastrocnemius, and deep red region of the vastus lateralis muscles were increased, while small or nonsignificant trends toward increases in cytochrome c and coenzyme Q were seen in kidney, brain, lung, liver, internal + external oblique muscles, and the superficial white region of the vastus lateralis muscle. These results are discussed with regard to several roles for coenzyme Q in cellular function.

The effect of exercise training on glycogen, glycogen synthase and phosphorylase in muscle and liver

It is thought that exercise training in both man and the rat results in a protective effect against the depletion of carbohydrate stores during exercise (glycogen-sparing). However there has been no comprehensive study of the effects of training on glycogen anabolic and catabolic enzymes with liver or muscle. The aim of this study was to examine whether changes in these enzymes occur and whether these changes may provide an explanation for the glycogen-sparing which results from exercise training. Male rats were trained by a treadmill running program at three different workloads. In addition, there were three control groups: free eating (SF), food restricted (SR), and one SF with a single bout of exercise prior to sacrifice. Exercise training was associated with a 60-150% increase in glycogen synthase and phosphorylase and a 50-70% increase in glycogen content in soleus, an intermediate muscle, but not in extensor digitorum longus (EDL), a white muscle nor in liver. The increase in glycogen synthase and phosphorylase in intermediate muscle was proportional to the degree of training and there was a significant correlation between glycogen content, glycogen synthase, and phosphorylase activity in intermediate muscle. Cytochrome c oxidase activity, an indicator of respiratory capacity, increased 50% in gastrocnemius of trained rats and was significantly correlated with glycogen synthase and phosphorylase in soleus. These results indicate a significant effect of exercise training on glycogen anabolic and catabolic enzymes in intermediate muscle, with no significant effects in white muscle or liver. The changes do not provide an explanation for glycogen-sparing, but are consistent with improved capacity of intermediate muscle for rapid glycogen mobilisation and repletion.

Response of skeletal muscle to training

Physical training induces adaptive changes in skeletal muscle. These changes are localised to the active muscle with their magnitude depending upon the nature, i.e. time and intensity, of the training regimen. The most notable changes are increased concentrations of mitochondria and glycogen. With endurance training there are major changes in metabolism in that there is a greater contribution of fat to the total metabolism during submaximal exercise. This results in a conservation of the stores of glycogen with the net result of increasing total exercise capacity. This increased use of fat during submaximal exercise appears to be more closely related to the elevations in the concentration of mitochondria in muscle than to changes in total body maximal oxygen uptake. The combination of a greater contribution of fat to the metabolism and the elevated concentration of stored glycogen are prime factors contributing to the enhanced endurance capacity after endurance training. The mechanism for the greater use of fat after endurance training is discussed. Evidence now supports the hypothesis that this is due to a tighter control over the Embden-Meyerhof pathway as a result of the greater concentration of mitochondria. The effect of heavy resistance exercise on the size and strength of skeletal muscle is discussed. Some attention is focused on the recently revived controversy concerning whether muscle enlargement is the result of a hypertrophy of pre-existing fibres or of hyperplasia. It is concluded that although there is considerable evidence to support the development of hypertrophy in response to heavy resistance exercise, the contention that a splitting of fibres occurs to produce a greater fibre number is presently poorly supported.

The effect of a 20-week endurance training program on adipose-tissue morphology and lipolysis in men and women

In order to assess the effect of endurance training on adipose-tissue morphology and lipolysis, 22 adult subjects (11 men and 11 women) took part in a 20-week ergocycle training program, four to five days a week, 40 minutes a day, at 80% of their maximal heart rate. Before and after training, they were submitted to an adipose-tissue biopsy in the suprailiac region. Fat cell weight (FCW), and lipolytic activity were determined on isolated fat cells. For the whole sample, training significantly reduced FCW (pre: 0.40 +/- 0.13 (mean +/- SD) versus post: 0.36 +/- 0.13 micrograms; P less than 0.05), percentage of fat (pre: 22.0 +/- 8.3 versus post: 19.7 +/- 8.1%; P less than 0.05), and increased adipocyte epinephrine maximal stimulated lipolysis (ESL) (pre: 1.08 +/- 0.49 versus post: 1.69 +/- 0.67 mumol glycerol/30 min/10(6) cells; P less than 0.001). No changes were observed in fat cell number. In women, however, training induced no changes in the fatness indicators (% fat, sum of skinfolds, FCW). The exercise program significantly lowered the adiposity of men (% fat: P less than 0.001; sum of skinfolds: P less than 0.01; FCW: P less than 0.05). In both sexes, a significant increase in ESL was observed after training. ESL of men, however, responded better than that of women to training (ESL of women: 1.36 +/- 0.67 versus ESL of men: 2.02 +/- 0.50 mumol glycerol/30 min/10(6) cells; P less than 0.05), with increases over pre-training values of 46% and 66% in women and men, respectively.(ABSTRACT TRUNCATED AT 250 WORDS)

Fibre type specific transformations in the enzyme activity pattern of rat vastus lateralis muscle by prolonged endurance training

The alterations in activity patterns of representative enzymes in energy metabolism were investigated in the superficial (white) and deep (red) portions of the fast vastus lateralis muscle of the adult rat in response to prolonged endurance training. It was found that following 15 weeks of extreme training (final running duration: 210 min per day, 27 m/min at 15 degree grade), increases in the activities of marker enzymes of the citric acid cycle (citrate synthase), beta-oxidation (3-hydroxyacyl CoA dehydrogenase), and ketone body utilization (3-ketoacid CoA transferase) as well as of glutamate pyruvate transaminase occurred in both regions of the muscle, with the greatest increase being observed in the superficial portion (2.6-4.2-fold). Pronounced increases were also seen for hexokinase which showed highest activities after 7 weeks of training. Conversely, decreases were noted for various glycogenolytic, glycolytic and gluconeogenic enzymes (phosphorylase, glyceraldehydephosphate dehydrogenase, pyruvate kinase, lactate dehydrogenase and fructose-1,6-diphosphatase). Reduction in the activities of these enzymes was most pronounced in the deep portion of the muscle. These results demonstrate a fundamental rearrangement of the energy metabolism of the muscle in response to prolonged, high intensity training. In the case of the deep portion of the vastus lateralis muscle, which has been shown to be composed of a large percentage of fast oxidative-glycolytic fibres (FOG), the enzyme profile becomes similar to the slow oxidative (SO) fibre. In the superficial portion which contains predominantly fast glycolytic fibres (FG), the enzyme profile becomes similar to FOG fibres.(ABSTRACT TRUNCATED AT 250 WORDS)

Daily variations of plasma glucose and insulin in physically-trained and sedentary subjects

The variations in plasma glucose and insulin levels were measured at 30-minute intervals throughout the day in physically trained and in sedentary subjects. The subjects exercised for 75 minutes at 65% of VO2max in the first experiment and refrained from heavy exercise in the second experiment. In all situations the physically trained subjects overall had lower plasma glucose and insulin levels than the nontrained subjects. In addition, the positive correlation between plasma glucose and plasma insulin levels observed in the physically trained subjects was significantly smaller than that note in the nontrained subjects, indicating reduced insulin requirements in physically-trained persons. During the period of exercise, glucose levels increased significantly in the trained subjects only. In the period that followed exercise, that is between 1:30 PM and 9:00 PM, the physically trained subjects had plasma glucose levels that were higher than those noted during the comparable hours not preceded by exercise; no comparable difference were found with insulin. Calculation of the total area for insulin indicated a reduction of insulin requirement of about 40% associated with physical training.

Altered muscle metabolism in rats after thermal injury

Burn injury is associated with an elevation in total body oxygen consumption, increased hepatic alanine uptake and conversion to glucose, and a negative nitrogen balance. The primary source of the alanine used for gluconeogenesis by the liver and of the nitrogen lost as urea is believed to be from skeletal muscle. Selected muscle regulatory enzymes and pyruvate and oleate oxidation rates were assayed for maximal activity during the postburn period. Male Sprague-Dawley rats that received 50% total body surface scald burns on the dorsum and abdomen were examined for citrate synthase (CS), phosphofructokinase (PFK), and glutamate-pyruvate transaminase (GPT) activity in uninjured muscle at 3, 7, 13, and 20 days postburn, and the ability of muscle to oxidize pyruvate and oleate was measured at 3 and 13 days after injury. Cs, PFK, and GPT activities increased significantly (p less than 0.05) by 13-20 days after injury in the soleus and diaphragm. The epitrochlearis showed no change in CS, but PFK and GPT were elevated within this time frame. The gastrocnemius muscle showed an elevated oleate oxidation rate at 13 days after injury, but no change at 3 days postburn. Pyruvate oxidation rates were unaltered. The results of this study indicate that during the postburn period several metabolic alterations occur in muscle. These adaptations include: (1) elevated CS activity which may be associated with increased oxidative capacity,, (2) increased PFK activity which implies that more substrate is being shuttled through the glycolytic pathway, (3) increased GPT activity which may reflect increased pyruvate conversion to alanine, and (4) increased oleate oxidation rates which demonstrate that muscle is utilizing more fatty acid substrates during the postburn period.

Effect of cold environment on skeletal muscle mitochondria in growing rats

Growing rats(4 weeks old) were kept for 3 weeks at 11 degrees C and 24 degrees C respectively. The cold-adapted animals showed a significantly higher oxygen consumption (64%). Volume density of subsarcolemmal and interfibrillar mitochondria as well as volume density of fat droplets were estimated in M. soleus and the diaphragm of both groups. In cold-adapted animals, the total volume of mitochondria was significantly increased by 24% in diaphragm and 37% in M. soleus. The volume of subsarcolemmal mitochondria was almost doubled in each muscle, but the volume of interfibrillar mitochondria did not change significantly. The surface of the inner mitochondrial membranes per unit volume of mitochondrion in M. soleus was significantly increased both in interfibrillar and subsarcolemmal mitochondria, whereas the surface of the outer mitochondrial membranes per unit volume of mitochondrion was increased only in the subsarcolemmal mitochondria. The volume of fat droplets in the diaphragm and M. soleus of cold adapted animals increased significantly by 62% and 150% respectively.

Palmitate oxidation in human muscle: comparison to CPT and carnitine

The evaluating of palmitate oxidation in muscle tissue may be a useful screening test for detecting defects in fatty acid metabolism in human neuromuscular disease. If the test is to be useful, it is necessary to obtain data on a wide variety of muscle illnesses for comparative purposes. We report our experience with palmitate oxidation, muscle carnitine, and carnitine palmityl transferase (CPT) activity in 148 muscles biopsies from a variety of illnesses. The efficacy of using total protein, citrate synthase, and (1-14C) pyruvate oxidation as internal references was investigated. Palmitate oxidation was significantly less than normal (P less than or equal to 0.01) in Duchenne muscular dystrophy, congenital nonprogressive myopathy, congenital muscular dystrophy, malignant hyperpyrexia, and denervation, depending on the internal reference used. Muscle carnitine levels followed a similar pattern, however, CPT activity did not. The possibility of these findings being secondary to inactivity is discussed.

Significance of skeletal muscle oxidative enzyme enhancement with endurance training

A theoretical model is proposed to explain how the increase in mitochondrial protein concentration, and therefore of the oxidative enzymes, that occurs with endurance training could operate to alter the choice of substrate during submaximal exercise in a manner such that the oxidation of fatty acids increases, glycogen depletion and lactate production are reduced, and work capacity is enhanced. The model is based on the control of enzyme activities both by enzyme and substrate concentrations. The effect of altering enzyme concentration on reaction velocities is presented on the basis of standard Henri-Michaelis-Menten kinetics. It is shown that the reaction velocity at a given substrate concentration is a function of total enzyme concentration. With an increase in total enzyme concentration there is a parallel increase in reaction velocity at the same substrate level. This would have its greatest impact at substrate levels below the Km of the enzyme. It would have an effect of enhancing fatty acid flux through the oxidative pathways while inhibiting the Embden-Meyerhof pathway. The model, as proposed, is consistent with known alterations in metabolism as they occur in man during submaximal exercise following endurance training.

Norepinephrine mobilization of free fatty acids in endurance trained rats

Wistar rats were trained to run, a male group on 6 days a week for 4 months at 28 m x min-1, and a female group on 5 days a week for 5-6 months at 31 m x min-1. Male rats were given continuous infusion of [1-14C] palmitate-albumin tracer via a jugular catheter at a constant infusion rate of 80 nCI x min-1. The effect of concurrent norepinephrine (NE) infusion on free fatty acid (FFA) mobilization was then studied in this group. NE increased plasma FFA levels similarly in both control and endurance trained male groups. Turnover of FFA, however, increased in response to NE relatively less in the trained group. Furthermore, NE caused the metabolic clearance rate of FFA (MCR) to decrease in control animals but not in runners. Colonic temperature was slightly increased by NE infusion in the control group only. Female rats were given a bolus injection of 5 microCi of [1-14C] palmitate-rat serum through a venous cannula. The disappearance of radioactivity in the circulation was measured. MCR values were higher in the trained group (p = 0.01). The effect of NE infusion on FFA levels was also studied in female animals. NE caused levels to increase in both control and trained rats. FFA concentrations were however more elevated in the control than in the trained group, before and during NE infusion. The relative increase tended to be less extensive in the trained group (p = 0.06). It is concluded that long term endurance training diminishes calorigenic and fat mobilizing actions of NE in the rat in vivo.

Lipid metabolism during exercise. II. Respiratory exchange ratio and muscle glycogen content during 4 h bicycle ergometry in two groups of healthy men

Seven physically fit (well-trained, maximal oxygen uptake 69.6 +/- 4.4 ml x kg-1 min-1) and eight less fit (moderately trained, maximal oxygen uptake 56.1 +/- 5.7 ml x kg-1 x min-1) healthy male subjects were exercised for 4 h by bicycle ergometry against a pedalling resistance calculated to cause oxygen consumption corresponding to approximately 30% of each individual's maximal oxygen uptake value. Respiratory exchange ratio was estimated at 1 h and blood glucose and lactate concentrations and muscle glycogen content at 2 h intervals. Muscle glycogen content decreased markedly during the first 2 h of exercise in the well-trained group but was similar after 4 h exercise in both groups. No major differences were observed between the two subject groups in blood variable concentrations. Calculations based on respiratory exchange ratio showed that the proportion of carbohydrates utilized in the total energy consumption was 14% in the physically fit group and 25% in the less fit group, thus supporting previous observations that more energy is derived by fat oxidation in well-trained than in less-trained individuals during submaximal work at relatively similar oxygen consumption levels.

Effects of training on VO2 max and VO2 during two running intensities in rats

Endurance training increased VO2 max significantly from 71.6 +/- 1.3 to 81.5 +/- 1.7 ml . kg-1 . min-1 in female rats. Oxygen consumption and respiratory exchange ratios were observed in rats for 1 h at rest, running at 14.3 m . min-1 on a 1% grade (easy exercise), and running at 28.7 m. min-1 on a 15% grade (hard exercise). In hard exercise untrained rats had a higher respiratory exchange ratio (0.97 vs 0.90) and exercised at a higher percent VO2 max (92 vs 74%) than trained animals. Blood lactate was higher during hard exercise than during rest or easy exercise, and higher in untrained than in trained animals during exercise. Blood glucose was significantly higher in trained than in untrained animals during hard exercise, but other wise there were no differences between treatments or groups. These results suggest enhanced lipid oxidation and carbohydrate sparing in trained during prolonged exercise as the result of training. The improvement in whole-body VO2 max due to training (13.9%) was less than the increase in tissue respiratory capacity (50--100%) reported to accompany endurance training of rats. The improvement in VO2 max of rats as the result of training was of the same magnitude as the training response usually seen in humans.