Enzyme levels of the NADH shuttle systems: measurements in isolated muscle fibres from humans of differing physical activity

The aim of the present study was to investigate enzyme levels of the malate-aspartate and alpha-glycerophosphate shuttles in type I (slow-twitch) and type II (fast-twitch) fibres of human skeletal muscle. The influence of endurance training on these levels was also elucidated. Biopsy specimens were obtained from the lateral part of the quadriceps femoris muscle of six untrained and six endurance-trained subjects. Type I vs. type II. In both groups the type I fibres exhibited higher levels of the TCA cycle marker enzyme citrate synthase (CS), as well as of the malate-aspartate shuttle enzymes (cytoplasmic and mitochondrial malate dehydrogenase (cMDH, mMDH), and aspartate aminotransferase (cASAT, mASAT]. A more pronounced difference between type I and type II fibres was noted for cMDH (58%) than for mMDH (16%), cASAT (20%), mASAT (18%) and CS (25%). In contrast to these enzymes, the levels of cytoplasmic glycerol-3-phosphate dehydrogenase (cGPDH), the enzyme representative of the alpha-glycerophosphate shuttle, were higher (25%) in the type II fibres. Endurance-trained vs. untrained. In the endurance-trained group, both fibre types were characterized by higher levels of CS (mean for both fibre types: 48%) as well as of mitochondrial malate-aspartate shuttle enzymes (mMDH: 47%, mASAT: 48%) than in the corresponding fibre types in the untrained group, while the differences in the levels of cytoplasmic malate-aspartate shuttle enzymes (cMDH: 13%, cASAT: 16%) were not statistically significant. Nor were the differences in cGPDH levels (8%) between the untrained and endurance-trained groups statistically significant. It is concluded that in human skeletal muscle, malate-aspartate shuttle enzymes are expressed to a higher degree in type I (slow) fibres than in type II (fast) fibres, with cMDH exhibiting the most marked difference. The single fibre analysis indicated that the muscle's activity level might exert a greater influence on the mitochondrial isoenzymes than on the cytoplasmic ones. In contrast to the malate-aspartate shuttle enzymes, the alpha-glycerophosphate shuttle is expressed to a higher degree in type II fibres and its capacity appears to not be influenced by endurance training. The present studies demanded considerable methodological investigations which also are presented in this paper.     

Activities of key enzymes in the energy metabolism of human myocardial and skeletal muscle

Activities of total creatine kinase (CK), its isoenzyme MB (CK-MB), total lactate dehydrogenase (LD) and its isoenzyme LD1, phosphofructokinase (PFK), aspartate aminotransferase (ASAT) and citrate synthase (CS) were determined in skeletal muscle biopsies obtained from physically trained and untrained men and in myocardial biopsies from patients subjected to open heart surgery because of valve disease. The LD1, ASAT and CS activities were higher in trained than in untrained skeletal muscle and still higher in heart muscle than in either trained or untrained skeletal muscle. The CK-MB activity was higher in trained than untrained skeletal muscle and the myocardial CK-MB activity was similar to that in trained skeletal muscle. Total CK activity was slightly lower in trained than in untrained skeletal muscle and the myocardial CK activity was approximately one third of the skeletal muscle CK. Both the PFK and the total LD activity was of similar magnitude in the different muscle types. In conclusion, as estimated by enzyme activities, the oxidative capacity is 2-3 times larger in myocardial than in skeletal muscle, while the glycolytic capacity as estimated by PFK appears to be the same.     

Enzyme levels in pools of microdissected human muscle fibres of identified type. Adaptive response to exercise

Enzyme activities were determined in pools of type I (slow twitch) and II A and II B (fast twitch) fibres of the thigh muscle from individuals engaged to a high degree in physical training of an endurance character and from non-endurance-trained controls. The endurance-trained (ET) group had significantly higher activity levels of the mitochondrial enzymes citrate synthase, malate dehydrogenase, and 3-OH-acylCoA dehydrogenase both in type I (2.1X, 1.7X, 1.4X) and in type II A (2.3X, 1.8X, 1.4X) and II B fibres (2.0X, 1.5X, 1.5X) than the non-endurance-trained (NET) group. Of the glycolytic enzymes, phosphofructokinase (PFK) in type I fibres was significantly higher (1.8X) in the ET than in the NET group whereas glyceraldehydephosphate dehydrogenase (GAPDH) in type I fibres was similar in the two groups. In type II fibres both PFK and GAPDH levels tended to be higher in the ET group. Lactate dehydrogenase (LDH) of both fibre types were not different in the two groups. Type I fibres differed significantly from type II fibres for all the six enzymes measured in both groups. However, no significant difference between fibres of types II A and II B was found. The results indicate that fibres of types I, II A and II B in human skeletal muscle all possess great adaptability with regard to their oxidative capacity. Furthermore, the data suggest that extensive endurance training may enhance the glycolytic capacity in both type I and type II fibres although the glycolytic capacity of the muscle as a whole generally is low in endurance trained subjects owing to a predominance of type I fibres. It is concluded that further studies are needed to determine whether there is a metabolic distinction between fibres of types II A and II B.     

Enzyme levels in pools of microdissected human muscle fibres of identified type: Adaptive response to exercise

Enzyme activities were determined in pools of type I (slow twitch) and IIA and II B (fast twitch) fibres of the thigh muscle from individuals engaged to a high degree in physical training of an endurance character and from non-endurance-trained controls. The endurance-trained (ET) group had significantly higher activity levels of the mitochondrial enzymes citrate synthase, malate dehydrogenase, and 3-OH-acylCoA dehydrogenase both in type I (2.1×, 1.7×, 1.4×) and in type IIA (2.3×, 1.8×, 1.4×) and IIB fibres (2.0×, 1.5 ×, 1.5×) than the non-endurance-trained (NET) group. Of the glycolytic enzymes, phosphofructokinase (PFK) in type I fibres was significantly higher (I.8×) in the ET than in the NET group whereas glyceraldehydephosphate dehydrogenase (GAPDH) in type I fibres was similar in the two groups. In type II fibres both PFK and GAPDH levels tended to be higher in the ET group. Lactate dehydrogenase (LDH) of both fibre types were not different in the two groups. Type 1 fibres differed significantly from type II fibres for all the six enzymes measured in both groups. However, no significant difference between fibres of types IIA and IIB was found. The results indicate that fibres of types I, IIA and IIB in human skeletal muscle all possess great adaptability with regard to their oxidative capacity. Furthermore, the data suggest that extensive endurance training may enhance the glycolytic capacity in both type I and type II fibres although the glycolytic capacity of the muscle as a whole generally is low in endurance trained subjects owing to a predominance of type I fibres. It is concluded that further studies are needed to determine whether there is a metabolic distinction between fibres of types IIA and IIB.     

Age- and training-related changes in the collagen metabolism of rat skeletal muscle

Summary The effects of ageing and life-long endurance training on the collagen metabolism of skeletal muscle were evaluated in a longitudinal study. Wistar rats performed treadmill running 5 days a week for 2 years. The activities of collagen biosynthesis enzymes, prolyl-4-hydroxylase and galactosylhydroxylysyl glucosyltransferase, were highest in the muscles of the youngest animals, decreased up to the age of 2 months and from then on remained virtually unchanged. The enzyme activity in young animals was higher in the slow collagenous soleus muscle than in the rectus femoris muscle. The enzyme activity in the soleus muscle was higher for older trained rats than older untrained rats. The relative proportion of type I collagen increased and that of type III collagen decreased with age, suggesting a more marked contribution by type I collagen to the agerelated accumulation of total muscular collagen. The results show that collagen biosynthesis decreases with maturation and that life-long endurance training maintains a higher level of biosynthesis in slow muscles.     

The GLUT4 density in slow fibres is not increased in athletes. How does training increase the GLUT4 pool originating from slow fibres?

The influence of training on GLUT4 expression in slow- and fast-twitch skeletal muscle fibres was studied in male endurance-trained athletes and control subjects. The trained state was ensured by elevated maximal oxygen uptake (29%), as well as citrate synthase (60%) and 3-hydroxy-acyl-CoA dehydrogenase (38%) activities in muscle biopsy samples of the vastus lateralis. GLUT4 densities in slow- and fast-twitch fibres were measured by the use of a newly developed, sensitive method combining immunohistochemistry with morphometry, and no effect of training was found. GLUT4 density was higher in slow-twitch fibres compared to fast-twitch fibres (P<0.05) when biopsy samples from untrained subjects were examined. In athletes GLUT4 density was identical in slow- and fast-twitch fibres. Slow-twitch fibre diameters were 10% larger in the athletes (P<0.01), and slow-twitch fibre fractions were 140% of the fraction in the control group. Thus, GLUT4 originating from slow-twitch fibres was increased by 30% (P<0.02) in athletes. We conclude that long-lasting endurance training increases slow-twitch fibre GLUT4 expression by means of an elevated slow-twitch fibre mass in human skeletal muscle.     

Exercise-induced reversal of age-related declines of oxidative reactions, mitochondrial yield, and flavins in skeletal muscle of the rat

The ability of gastrocnemius muscle homogenates to catalyze the oxidation of succinate, glutamate + malate, pyruvate + malate, palmitoyl-coenzyme A, decanoylcarnitine and palmitoylcarnitine in the presence of ADP decreased by approximately 32% in sedentary male Sprague-Dawley rats between the ages of 9 and 25 months. Following 21 weeks of treadmill training (running), such homogenates from 25-month-old animals catalyzed oxidations 55% more rapidly than those from 25-month-old sedentary rats, and 17% faster than those from 9-month-old sedentary rats. Total and peptide-bound flavin of gastrocnemius muscles also declined between 9 and 25 months of age and were elevated in the 25-month-old endurance trained rats to levels greater than both 9- and 25-month-old sedentary animals. The yield of protein in the mitochondrial fraction from the quadriceps femoris muscle decreased between 9 and 25 months and was restored to the 9-month level by endurance training. The kinetic characteristics of the isolated mitochondria were not influenced by age or exercise. These data indicate that 2-year-old rats retain the capacity to increase skeletal muscle oxidative capacity and mitochondrial population density in response to endurance training.     

Changes in maximal aerobic power,aerobic capacity,and muscle enzyme activities at two stages of the annual training cycle in ski-runners

Summary Changes of cardiorespiratory capacity, of the activity of seven enzymes involved in energy metabolism and of laboratory endurance were investigated in a group of nine male ski-runners before and after exhausting training and a competing period during the winter.Despite the decrease in laboratory endurance and total work oxygen consumption between the investigations, O₂ max, O₂-pulse max and O₂ debt did not change; and O₂-pulse per kg b.w. showed a significant increase.In biopsy samples of the vastus lateralis muscle, the activity of enzymes of carbohydrate metabolism, both anaerobic and total (triose phosphate dehydrogenase — TPDH, lactate dehydrogenase — LDH, hexokinase — HK), and of total aerobic metabolism (citrate synthetase — CS, malate dehydrogenase — MDH), was decreased during this period by 27 to 59% (mean values for different enzymes). The mean activity of cytoplasmic glycerol phosphate dehydrogenase (GPDH) and of hydroxyacyl — CoA dehydrogenase (HOADH) did not change, although the activity of the latter enzyme was decreased in the muscle of those ski-runners who were trained predominantly for speed, and it was increased in those trained mainly for endurance.The changes in activity of the muscle enzymes associated with glycolysis (TPDH and LDH) and of MDH, connected with metabolism and hydrogen transport between cytoplasmic and aerobic mitochondrial compartments, correlate inversely with those of aerobic capacity (total work O₂ consumption).     

Effect of 2 weeks of endurance training on uncoupling protein 3 content in untrained human subjects

AIM: The mitochondrial uncoupling protein-3 (UCP3) is able to lower the proton gradient across the inner mitochondrial membrane, thereby uncoupling substrate oxidation from ATP production and dissipating energy as heat. What the effect of endurance training on UCP3 is, is still controversial. Endurance-trained athletes are characterized by lower levels of UCP3, but longitudinal studies in rodents reported no effect of endurance training on muscular UCP3 levels. Here, we examined the effect of a 2-week training programme on skeletal muscle UCP3 protein content in untrained human subjects, and hypothesized that UCP3 will be reduced after the training programme. METHODS: Nine untrained men [age: 23.3 +/- 3.2 years; BMI: 22.6 +/- 2.6 kg m(-2); maximal power output (W(max)): 3.8 +/- 0.6 W kg(-1) body weight] trained for 2 weeks. Before and at least 72 h after the training period, muscle biopsies were taken for determination of UCP3 protein content. RESULTS: UCP3 protein content tended to be lower after the training programme [95 +/- 10 vs. 109 +/- 12 arbitrary units (AU), P = 0.08]. Cytochrome c content tended to increase with 33% in response to endurance training (52 +/- 6 vs. 39 +/- 6 AU, P = 0.08). The ratio UCP3 relative to cytochrome c tended to decrease significantly upon endurance training (2.0 +/- 0.4 vs. 3.2 +/- 0.6 AU, P = 0.01). CONCLUSION: A short-term (2-week) endurance training programme decreased UCP3 protein levels and significantly reduced the ratio of UCP3 to cytochrome c.     

Effects of glutamine deprivation on glucose and amino acid metabolism in tissue culture.

The effects of glutamine deprivation on cultured skeletal muscle cells were analyzed by incubating 10-day-old myotube preparations in glutamine free Dulbecco's modified Eagle medium containing 10% fetal calf serum for up to 48 h. Under these conditions net glutamine production was not observed, but active ammonia production (average rate = 1.0 nmol/min . mg protein) continued despite glutamine withdrawal. Glutamine deprivation was associated with a progressive depletion of intracellular aspartate and glutamate. Maximal aspartate depletion correlated with a 15-fold increase in the intracellular lactate:pyruvate ratio and a 3-fold decrease in the estimated intracellular glutamate:(alpha-ketoglutarate) (ammonia) ratio. Despite wide shifts in cell metabolite concentrations, the mass action ratios of alanine and aspartate aminotransferase approximated the expected equilibria constants. These results suggest that 1) glutamine deprivation is associated with a marked reduction of aspartate, and the maintenance of aspartate depletion is due in part to the tendency of aspartate aminotransferase to maintain the metabolites of this reaction at a near equilibrium level; 2) the transport of reducing equivalents from the cytosolic to the mitochondrial compartments via the malate-aspartate shuttle may be limited under conditions of aspartate depletion.     

Enzyme activities in muscle and connective tissue of M. vastus lateralis in habitually training and sedentary 33 to 70-year-old men

A cross-sectional study was carried out to examine the activities of certain enzymes representing aerobic and anaerobic energy metabolism as well as the biosynthesis of collagen of M. vastus lateralis in 23 male endurance athletes in habitual training, aged 33 to 70 years. 23 sedentary healthy men of corresponding ages were selected for the control group. The mean maximal oxygen uptake of the trained subjects was 53.6 ml · kg^?1 · min^?1 and that of the control subjects 36.3 ml · kg^?1 · min^?1. As compared to the control group the trained subjects had significantly higher values in the muscle malate dehydrogenase, succinate dehydrogenase and prolyl hydroxylase activities, whereas the opposite was true in the activity of lactate dehydrogenase. In hexokinase and creatine phosphokinase no marked differences between the groups were observed. The results showed that endurance training leads to increased activities of oxidative enzymes in the skeletal muscle. The adaptation changes were also observed in old men. The increased activity of prolyl hydroxylase may reflect the general enzymatic adaptation to physical training. A possibility exists that the turnover of muscle collagen in endurance athletes is continuously faster than that in sedentary men of corresponding ages.     

Effect of endurance training on the capacity of red and white skeletal muscle of mouse to oxidize carboxyl-14C-labelled palmitate.

Three groups of mice were trained for 1, 4 and 5 months according to different running programs on a motor driven treadmill and the fatty acid oxidation capacity (FAO) and the activities of some enzymes of energy metabolism (cytochrome c oxidase, malate dehydrogenase, triosephosphate dehydrogenase, and lactate dehydrogenase) were determined from m. quadriceps femoris (MQF). Endurance training increased the FAO [5-month training 4 days/week, 30 min/day 22% (p less than 0.05); 1-month training, 7 days/week, 150 min/day 37% (p less than 0.001); 4-month training, 5 days/week, 60 min/day 24% (p less than 0.05)]. The activities of cytochrome c oxidase and malate dehydrogenase increased approx. 30% (p less than 0.001) whereas triosephosphate dehydrogenase and lactate dehydrogenase activities were not prominently influenced by training. The predominantly red part of MQF of untrained animals oxidized palmitate four times faster than the predominantly white part. The activities of cytochrome c oxidase and malate dehydrogenase were two times higher showing pronounced FAO in the red part. Endurance training increased the FAO and activities of oxidative enzymes in the red and white parts and in the whole muscle relatively equally resulting in similar differences between the muscle types after training. The absolute increase in the FAO of the red muscle was, however, manyfold when compared in chemical units to the white muscle.     

Effect of methionine sulfoximine on pyruvate dehydrogenase, citric acid cycle enzymes and aminotransferases in the subcellular fractions isolated from rat cerebral cortex

The effect of acute and subacute doses of L-methionine-DL-sulfoximine (MSI) were studied on the activities of pyruvate dehydrogenase, enzymes of citric acid cycle and aspartate and alanine aminotransferases in the mitochondria, synaptosomes and cytosol of rat brain. In general, the activities of pyruvate dehydrogenase and of the citric acid cycle enzymes, except malate dehydrogenase (malate----oxaloacetate), were elevated in all 3 subcellular fractions. Malate dehydrogenase activity (malate----oxaloacetate) was suppressed in the mitochondria while the activity of this enzyme in the reverse direction was enhanced in the cytosol. Activities of aspartate and alanine aminotransferases were suppressed under these conditions. As the effects of MSI on these enzymes were similar to those observed upon the administration of ammonium salts, it is suggested that the hyperammonemic state induced by MSI might derange the operation of the malate-aspartate shuttle. Increased activities of citric acid cycle enzymes in the cytosol suggested the existence of a small population of mitochondria which was highly vulnerable either to ammonia or to MSI.     

The malate-aspartate NADH shuttle components are novel metabolic longevity regulators required for calorie restriction-mediated life span extension in yeast

Recent studies suggest that increased mitochondrial metabolism and the concomitant decrease in NADH levels mediate calorie restriction (CR)-induced life span extension. The mitochondrial inner membrane is impermeable to NAD (nicotinamide adenine dinucleotide, oxidized form) and NADH, and it is unclear how CR relays increased mitochondrial metabolism to multiple cellular pathways that reside in spatially distinct compartments. Here we show that the mitochondrial components of the malate-aspartate NADH shuttle (Mdh1 [malate dehydrogenase] and Aat1 [aspartate amino transferase]) and the glycerol-3-phosphate shuttle (Gut2, glycerol-3-phosphate dehydrogenase) are novel longevity factors in the CR pathway in yeast. Overexpressing Mdh1, Aat1, and Gut2 extend life span and do not synergize with CR. Mdh1 and Aat1 overexpressions require both respiration and the Sir2 family to extend life span. The mdh1Deltaaat1Delta double mutation blocks CR-mediated life span extension and also prevents the characteristic decrease in the NADH levels in the cytosolic/nuclear pool, suggesting that the malate-aspartate shuttle plays a major role in the activation of the downstream targets of CR such as Sir2. Overexpression of the NADH shuttles may also extend life span by increasing the metabolic fitness of the cells. Together, these data suggest that CR may extend life span and ameliorate age-associated metabolic diseases by activating components of the NADH shuttles.     

Effect of 2 weeks of endurance training on uncoupling protein 3 content in untrained human subjects

Aim: The mitochondrial uncoupling protein‐3 (UCP3) is able to lower the proton gradient across the inner mitochondrial membrane, thereby uncoupling substrate oxidation from ATP production and dissipating energy as heat. What the effect of endurance training on UCP3 is, is still controversial. Endurance‐trained athletes are characterized by lower levels of UCP3, but longitudinal studies in rodents reported no effect of endurance training on muscular UCP3 levels. Here, we examined the effect of a 2‐week training programme on skeletal muscle UCP3 protein content in untrained human subjects, and hypothesized that UCP3 will be reduced after the training programme. Methods: Nine untrained men [age: 23.3 ± 3.2 years; BMI: 22.6 ± 2.6 kg m^?2; maximal power output (W_max): 3.8 ± 0.6 W kg^?1 body weight] trained for 2 weeks. Before and at least 72 h after the training period, muscle biopsies were taken for determination of UCP3 protein content. Results: UCP3 protein content tended to be lower after the training programme [95 ± 10 vs. 109 ± 12 arbitrary units (AU), P = 0.08]. Cytochrome c content tended to increase with 33% in response to endurance training (52 ± 6 vs. 39 ± 6 AU, P = 0.08). The ratio UCP3 relative to cytochrome c tended to decrease significantly upon endurance training (2.0 ± 0.4 vs. 3.2 ± 0.6 AU, P = 0.01). Conclusion: A short‐term (2‐week) endurance training programme decreased UCP3 protein levels and significantly reduced the ratio of UCP3 to cytochrome c.     

Effect of Endurance Training on the Capacity of Red and White Skeletal Muscle of Mouse to Oxidize Carboxyl-14C-labelled Palmitate

Three groups of mice were trained for 1, 4 and 5 months according to different running programs on a motor driven treadmill and the fatty acid oxidation capacity (FAO) and the activities of some enzymes of energy metabolism (cytochrome c oxidase, malate dehydrogenase, triosephosphate dehydrogenase, and lactate dehydrogenase) were determined from m. quadriceps femoris (MQF). Endurance training increased the FAO [5-month training, 4 days/week, 30 min/day 22% (p<0.05); 1-month training, 7 days/week, 150 min/day 37% (p<0.001); 4-month training, 5 days/week, 60 min/day 24% (p<0.05)]. The activities of cytochrome c oxidase and malate dehydrogenase increased approx. 30% (p< 0.001) whereas triosephosphate dehydrogenase and lactate dehydrogenase activities were not prominently influenced by training. The predominantly red part of MQF of untrained animals oxidized palmitate four times faster than the predominantly white part. The activities of cytochrome c oxidase and malate dehydrogenase were two times higher showing pronounced FAO in the red part. Endurance training increased the FAO and activities of oxidative enzymes in the red and white parts and in the whole muscle relatively equally resulting in similar differences between the muscle types after training. The absolute increase in the FAO of the red muscle was, however, manyfold when compared in chemical units to the white muscle.     

Dissociation of training effects on skeletal muscle mitochondrial enzymes and myoglobin in man

The effect of endurance training on skeletal muscle myoglobin concentration in man was investigated. 8 healthy sedentary males (20-31 yrs) trained on cycle ergometers 40 min/day, 4 days a week for 8 weeks. The work consisted of continuous exercise at a work load that during the last 5 weeks corresponded to 75% of the pretraining maximal oxygen uptake (VO2 max). The training program resulted in a 7% increase in VO2 max (p less than 0.01). The activities of the mitochondrial enzymes citrate synthase (CS), succinate dehydrogenase (SDH) and cytochrome c oxidase (Cyt-c-ox) in the quadriceps femoris muscle, as indicators of muscle respiratory capacity, increased by 62-82% (p less than 0.01). The metabolic adaptation of skeletal muscle was further indicated by a 17% increase in the work load corresponding to a blood lactate concentration of 4 mmol/l, as determined by a progressive exercise test (p less than 0.05). There was, however, no change in the myoglobin concentration of the thigh muscle with training (-1%, NS). It is suggested that endurance exercise in man at 75% of the maximal oxygen uptake does not severely tax the functions of myoglobin in skeletal muscle.     

Skeletal muscle and heart antioxidant defences in response to sprint training

Although endurance training enhances the antioxidant defence of different tissues, information on the effect of sprint training is scanty. We examined the effect of sprint training on rat skeletal muscle and heart antioxidant defences. Male Wistar rats, 16–17 weeks old, were sprint trained on a treadmill for 6 weeks. Total glutathione levels and activities of glutathione peroxidase, glutathione reductase, glutathione S-transferase and superoxide dismutase in heart and various skeletal muscles were compared in trained and control sedentary animals. Lactate dehydrogenase and citrate synthase enzyme activities were measured in muscle to test the effects of training on glycolytic and oxidative metabolism. Sprint training significantly increased lactate dehydrogenase activity in predominantly fast glycolytic muscles and enhanced total glutathione contents of the superficial white quadriceps femoris, mixed gastrocnemius and fast-glycolytic extensor digitorum longus muscles. Oxidative metabolic capacity increased in plantaris muscle only. Compared with the control group, glutathione peroxidase activities in gastrocnemius, extensor digitorum longus muscles and heart also increased in sprint trained rats. Glutathione reductase activities increased significantly in the extensor digitorum longus muscle and heart. Glutathione S-transferase activity was also higher in the sprint trained extensor digitorum longus muscle. Sprint training did not influence glutathione levels or glutathione-related enzymes in the soleus muscle. Superoxide dismutase activity remained unchanged in skeletal muscle and heart. Sprint training selectively enhanced tissue antioxidant defences by increasing skeletal muscle glutathione content and upregulating glutathione redox cycle enzyme activities in fast and mixed fibre leg muscles and heart.