Physical training under the influence of beta-blockade in rats. II: Effects on vascular reactivity

Summary Rats were treated by daily swimming or running exercises for 7 weeks. One group of rats was also trained under the influence of propranolol, while another group received daily propranolol injections only.The rat groups trained without beta blockade maintained a higher tail skin temperature when exposed to 5 C after the 7-week training period. This phenomenon was not observable in the animals having received their training under the influence of beta-blockade. Both rat groups trained without beta-blockade showed increased vasodilatatory response to isoprenaline, as judged from a higher elevation of the tail skin temperature in response to the drug. This response was absent in the animal group having performed its training periods under the influence of propranolol. After the injection of phenylephrine the trained rats had a higher tail skin temperature than did the controls or propranolol-treated rats.The present results suggest an elevated sensitivity of beta₂-adrenoceptors and/or decreased sensitivity of alpha-adrenoceptors in trained rats. It is suggested that for the development of these changes repeated activation of the sympathetic nervous system by exercise periods is needed. That is why they are preventable if the training is performed under the influence of beta-blockade.     

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.     

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.     

Physical training under the influence of beta blockade in rats: Effect on adrenergic responses

Summary Rats were trained by daily swimming or running exercises with and without daily propranolol injections. Both training methods resulted in cardiac enlargement, but only swimming exercise caused hypertrophy of the brown adipose tissue. These changes were antagonized by beta blockade. The size of the adrenals reflected the stress of the treatments, but other known stress parameters, such as the size of the thymus or sexual organs dit not. Only swimming training without beta blockade sensitized the rats to the calorigenic action of noradrenaline. The cooling rate of the rats in water, when taking into account the insulative capacity of the body, was decreased in swimming-trained as well as in propranolol-treated rats but increased in running-trained rats. The latter two changes may be due to circulatory alterations, while the delayed body cooling in swimming-trained rats probably results from increased heat production capacity. Training-induced resting bradycardia and enhanced tachycardic response to isoprenaline were observable only in the animal groups trained without beta blockade. The pressor response to noradrenaline tended to be higher in the trained groups and the propranolol-treated group than in the controls and was smaller in the animal groups trained under the influence of beta blockade. On the other hand, the hypotonic response to isoprenaline was smaller in the propranolol-treated and running-trained animals. The results emphasize the importance of the sympathetic nervous system in the adaptation of an organism to physical training.     

Muscle enzyme adaptation to training and tapering-off in spinal-cord-injured humans

The activity of muscle metabolic enzymes depends on the amount and type of physical training. We examined muscle enzyme adaptation to prolonged training followed by a period of lowered activity in spinal-cord-injured individuals (SCI). Ten SCI [mean age 35 (SEM 2) years , mean body mass 78 (SEM 4) kg, mean time post-injury 12 (SEM 2) years and range of lesion C5–T4] were given 12 months of functional electrical stimulation of an upright cycling motion for 30 min a day, three times a week, followed by 6 months of training once a week. Activities of glycolytic (hexokinase HK, lactate dehydrogenase LDH) and oxidative (citrate synthase CS, 3-hydroxyacyl-CoA dehydrogenase HAD) enzymes were determined in biopsies of the vastus lateralis muscle taken at 0, 3, 6, 12, and 18 months of training. The degree of sympathoadrenergic activity was evaluated from arterial concentrations of catecholamines in response to acute exercise. Training three times a week induced increases (P<0.05) in HK (150%), LDH (40%), CS (100%), and HAD (70%) activities that reached a plateau after 3 months. Peak oxygen uptake and power output during exercise by electrical stimulation rose continuously over the first 12 months. After reducing the amount of training by two-thirds, HK, LDH and CS activities remained elevated above basal levels (P<0.05), whereas HAD, power output and maximal oxygen uptake returned to pretraining levels (P>0.05). It is concluded that most improvements in glycolytic and mitochondrial oxidative enzyme activities induced by long-term training can be maintained in spinal-cord-injured individuals despite a marked reduction in training frequency unrelated to performance or to the degree of sympathoadrenergic impairment. Electronic Publication     

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.     

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 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.     

Effects of two high-intensity intermittent training programs interspaced by detraining on human skeletal muscle and performance

Summary The purpose of this study was to investigate the effects of repeated high-intensity intermittent training programs interspaced by detraining on human skeletal muscle and performances. First, nineteen subjects were submitted to a 15-week cycle ergometer training program which involved both continuous and high-intensity interval work patterns. Among these 19 subjects, six participated in a second 15-week training program after 7 weeks of detraining. Subjects were tested before and after each training program for maximal aerobic power and maximal short-term ergocycle performances of 10 and 90 s. Muscle biopsy from the vastus lateralis before and after both training programs served for the determination of creatine kinase (CK), hexokinase, phosphofructokinase (PFK), lactate dehydrogenase (LDH), malate dehydrogenase, 3-hydroxyacyl-CoA dehydrogenase (HADH) and oxoglutarate dehydrogenase (OGDH) activities. The first training program induced significant increases in all performances and enzyme activities but not in CK. Seven weeks of detraining provoked significant decreases in maximal aerobic power and maximal 90 s ergocycle performance. While the interruption of training had no effect on glycolytic enzyme markers (PFK and LDH), oxidative enzyme activities (HADH and OGDH) declined. These results suggest that a fairly long interruption in training has negligeable effects on glycolytic enzymes while a persistent training stimulus is required to maintain high oxidative enzyme levels in human skeletal muscle. The degree of adaptation observed after the second training program confirms that the magnitude of the adaptive response to exercise-training is limited.     

Different metabolic responses to exercise training programmes in single rat muscle fibres

Summary The aim of this report is to elucidate the effects of exercise training on metabolic properties of different muscle fibre types of the rat hindlimb. Single muscle fibres were dissected from soleus (SOL) or extensor digitorum longus (EDL) muscles of Wistar strain male rats trained on a treadmill for 16 weeks. Each fibre was typed histochemically (SO, slow-twitch oxidative; FOG, fast-twitch oxidative glycolytic; FG, fast-twitch glycolytic). Then glycolytic and oxidative enzymes (CK, LDH, PFK, PK, SDH, and MDH) activities were measured biochemically. Slow,-type fibres (SO) were hypertrophied following endurance training and fast-twitch fibres (FOG and FG) were hypertrophied following sprint training. In EDL muscles the distribution of the slow-type fibres was reduced following the sprint training. The activity of glycolytic enzymes increased significantly in the fast-type fibres (FOG and FG) following sprint training, while oxidative enzymes activities increased in both fast (FOG and FG) and slow (SO) muscle fibres following the endurance training. Neither glycolytic nor oxidative enzymes' activities always increased equally in all types of fibre following exercise training. Consequently, the metabolic profiles in each type of single muscle fibre were affected differently by different intensities of exercise training. These results suggest that the functional (enzymes activity) and structural (muscle fibre hypertrophy) changes of skeletal muscle fibre following exercise training appeared gradually, and would be controlled by different factors.     

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.     

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).     

Species-specific effects of chronic nerve stimulation upon tibialis anterior muscle in mouse,rat, guinea pig,and rabbit

Tibialis anterior (TA) muscle of mouse, rat, guinea pig, and rabbit was indirectly stimulated for 10 h/day at 10 Hz up to 28 days. Changes in the activity levels of hexokinase (HK), phosphofructokinase (PFK) glyceraldehydephosphate dehydrogenase (GAPDH), lactate dehydrogenase (LDH), creatine kinase (CK), citrate synthase (CS), malate dehydrogenase (MDH), 3-hydroxyacyl-CoA dehydrogenase (HADH), and -hydroxybutyrate dehydrogenase (HBDH) were compared. Although the direction of changes in the enzyme activity pattern was in accordance with previous findings on rabbit TA, the magnitude of the responses varied markedly between themammals under study. Mouse TA was almost unaffected. A major effect of chronic stimulation in rat, guinea pig and rabbit was an increase in enzyme activities of aerobic-oxidative metabolism. According to intrinsic differences of the muscles under study, the increases varied among the species and appeared to be inversely related to the basal levels of these enzymes in the unstimulated muscles. Conversely, glycolytic enzyme activities (PFK, GAPDH, LDH) markedly decreased in rat, guinea pig, and rabbit, and were only slightly reduced in mouse. Changes in HK and HBDH activities displayed the largest variations in the induced change between species. These results indicate species-specific patterns of metabolic adaptation to increased contractile activity.     

Enzyme adaptations of human skeletal muscle during bicycle short-sprint training and detraining

The effect of sprint training and detraining on supramaximal performances was studied in relation to muscle enzyme adaptations in eight students trained four times a week for 9 weeks on a cycle ergometer. The subjects were tested for peak oxygen uptake (V˙O_{2 peak}), maximal aerobic power (MAP) and maximal short-term power output (W˙_max) before and after training and after 7 weeks of detraining. During these periods, biopsies were taken from vastus lateralis muscle for the determination of creatine kinase (CK), adenylate kinase (AK), glycogen phosphorylase (PHOS), hexokinase (HK), phosphofructokinase (PFK), lactate dehydrogenase (LDH) and its isozymes, 3-hydroxy-acyl-CoA dehydrogenase (HAD) and citrate synthase (CS) activities. Training induced large improvements in W˙_max (28%) with slight increases (3%) in V˙O_{2 peak}} (P < 0.10). This was associated with a greater glycolytic potential as shown by higher activities for PHOS (9%), PFK (17%) and LDH (31%) after training, without changes in CK and oxidative markers (CS and HAD). Detraining induced significant decreases in V˙O_{2 peak} (4%), MAP (5%) and oxidative markers (10–16%), while W˙_max and the anaerobic potential were maintained at a high level. This suggests a high level in supramaximal power output as a result of a muscle glycogenolytic and glycolytic adaptation. A long interruption in training has negligible effects on short-sprint ability and muscle anaerobic potential. On the other hand, a persistent training stimulus is required to maintain high aerobic capacity and muscle oxidative potential. This may contribute to a rapid return to competitive fitness for sprinters and power athletes.     

Determination of metabolic profiles on single muscle fibres of different types

Summary Single muscle fibres separated from extensor digitorum longus (EDL) as well as soleus (SOL) in the Wistar strain male rat in relaxing solution were typed histochemically, then glycolytic and oxidative enzyme activities were determined on the same fibres. Glycolytic enzyme lactate dehydrogenase (LDH), phosphofructokinase (PFK), pyruvate kinase (PK) and creatine kinase (CK) showed highest activities in fast-twitch glycolytic (FG), lower in fast-twitch oxidative glycolytic (FOG) and lowest in slow-twitch oxidative (SO) fibres. Also oxidative enzyme succinate dehydrogenase (SDH) and malate dehydrogenase (MDH) showed highest activities in SO, lower in FOG and lowest in FG fibres. The activities of LDH, PFK, PK and CK in FOG fibres separated from EDL showed higher activity compared to those separated from SOL, whereas the opposite result was obtained for the activities of SDH and MDH. Enzyme activities in a single muscle fibre type were not distinguishable from those of another type, and the activity profiles overlapped over a considerable range. The correlations among the separate enzyme activities of CK, LDH and MDH obtained from the same single fibre overlapped over a considerable range.     

Metabolic changes in the quadriceps femoris muscle of obese people

1. In biopsy samples of the lateral part of m. quadriceps femoris of 49 obese and 14 lean persons the activities of the following enzymes were investigated: triosephosphate dehydrogenase (TPDH), glycerolphosphate: nad dehydrogenase (GPDH), lactate dehydrogenase (LDH), hexokinase (HK), malate: NAD dehydrogenase (MDH), citrate synthase (CS) and hydroxyacyl-CoA dehydrogenase (HOADH). 2. The muscles of obese had an increased activity ratio of TPDH to CS and to HK, respectively, caused in muscles of female obese subjects by an increase of TPDH activity, in those of obese men rather by a decrease of CS and HK activities. 3. Cluster analysis brough to light the existence of three major groups. Group 1 (low activity-low LDH group), consisting of muscles of female obese subjects only, exhibited low activities of all enzymes investigated, that of LDH being so low as to possibly induce a serious deficiency of anerobic metabolism under working conditions. Group 2 (medium enzyme activity group) was characterized by medium enzyme activities, similar to that of lean controls (included in this group). This consisted of subjects of both sex. Group 3 (high enzyme activity group) consisted of obese of both sex. It was distinguished by high enzyme activities, especially of LDH. It is suggested that the groups of similar enzyme activity patterns might reflect different stages, types and/or genesis of obesity.     

M. Quadriceps femoris of Man,a muscle with an unusual enzyme activity pattern of energy supplying metabolism in mammals

1. The following enzyme activities were estimated in needle-biopsy samples of the lateral part of the human quadriceps femoris muscle: triosephosphate dehydrogenase (TPDH), lactate dehydrogenase (LDH), NAD : glycerol-3-phosphate dehydrogenase (GPDH), hexokinase (HK), NAD: malate dehydrogenase (MDH), citrate synthase (CS) and hydroxyacyl-CoA dehydrogenase. 2. Although the enzyme activities in muscles of women were lesser than in those of men, no difference was found in the calculated enzyme activity ratios. There is thus no sex-dependent metabolic type-differentiation in this muscle. 3. The human quadriceps femoris is a low-activity muscle, in comparison with muscles of homoiotherm laboratory animals. The enzyme activity ratio of TPDH to CS, characterizing the glycolytic pyruvate formation to aerobic oxidative capacities, shows this muscle to be of an intermediate type in this respect, similarly as the extensor digitorum longus of the rat. The relatively very high capacity of glucose phosphorylation (HK), the high aerobic regeneration of cytoplasmic dehydrogenated NAD (GPDH) and the very low anaerobic regeneration (LDH), show the unusually high proportion of carbohydrates (glucose) which can be broken down aerobically.     

Response of ventilatory muscles of the rat to endurance training

The effect of endurance training on the oxidative and glycolytic potentials of the diaphragm and intercostal muscles of rats has been studied. Training consisted of treadmill running (28 m/min, 60 min/day, 5 days/wk) for periods ranging from 8–26 weeks. Exercise of similar duration and intensity produced a glycogen depletion in the diaphragm and intercostal muscles of nontrained rats. Oxidative potential was estimated from the activity of the mitochondrial marker enzyme succinate dehydrogenase (SDH). The activities of phosphorylase (PHOS), hexokinase (HK), and lactate dehydrogenase (LDH) were determined as well as the distribution of the LDH isozymes. SDH activity averaged 44 (42–51) and 17 (10–22)% (P<0.01) greater in the plantaris and diaphragm muscles, respectively, after 8–12 weeks of endurance running as compared to the sedentary animals. There was no change in the SDH activity of the intercostal muscles or in the activities of the glycolytic enzymes. There was also no change in the distribution of the isozymes of LDH. Extending the duration of the training program to 26 weeks did not produce any additional alteration in the magnitude of the adaptation observed after the initial training period. Comparative studies of different types of muscles demonstrated that the diaphragm, although having a fiber composition somewhat similar to that of a fast-twitch skeletal muscle, has a metabolic profile that is intermediate between pure slow twitch skeletal muscle and cardiac muscle.     

Swim training does not protect mice from skeletal muscle oxidative damage following a maximum exercise test

We investigated whether swim training protects skeletal muscle from oxidative damage in response to a maximum progressive exercise. First, we investigated the effect of swim training on the activities of the antioxidant enzymes, superoxide dismutase (SOD), catalase (CAT) and glutathione peroxidase (GPx), in the gastrocnemius muscle of C57Bl/6 mice, 48 h after the last training session. Mice swam for 90 min, twice a day, for 5 weeks at 31°C (± 1°C). The activities of SOD and CAT were increased in trained mice (P < 0.05) compared to untrained group. However, no effect of training was observed in the activity of GPx. In a second experiment, trained and untrained mice were submitted to a maximum progressive swim test. Compared to control mice (untrained, not acutely exercised), malondialdehyde (MDA) levels were increased in the skeletal muscle of both trained and untrained mice after maximum swim. The activity of GPx was increased in the skeletal muscle of both trained and untrained mice, while SOD activity was increased only in trained mice after maximum swimming. CAT activity was increased only in the untrained compared to the control group. Although the trained mice showed increased activity of citrate synthase in skeletal muscle, swim performance was not different compared to untrained mice. Our results show an imbalance in the activities of SOD, CAT and GPx in response to swim training, which could account for the oxidative damage observed in the skeletal muscle of trained mice in response to maximum swim, resulting in the absence of improved exercise performance.     

Variability in the magnitude of response of metabolic enzymes reveals patterns of co-ordinated expression following endurance training in women

Skeletal muscles improve their oxidative fatty acid and glucose metabolism following endurance training, but the magnitude of response varies considerably from person to person. In 20 untrained young women we examined interindividual variability in training responses of metabolic enzymes following 6 weeks of endurance training, sufficient to increase maximal oxygen uptake by 10 ± 8% (mean ± SD). Training led to increases in mitochondrial enzymes [succinate dehydrogenase (SDH; 47 ± 78%), cytochrome c oxidase (52 ± 70%) and ATP synthase (63 ± 69%)] and proteins involved in fatty acid metabolism [3-hydroxyacyl CoA dehydrogenase (69 ± 92%) and fatty acid transporter CD36 (86 ± 31%)]. Increases in enzymes of glucose metabolism [phosphofructokinase (29 ± 94%) and glucose transporter 4 (18 ± 65%)] were not significant. There was no relationship between changes in maximal oxygen uptake and the changes in the metabolic proteins. Considerable interindividual variability was seen in the magnitude of responses. The response of each enzyme was proportional to the change in SDH; individuals with a large increase in SDH also showed high gains in all other enzymes, and vice versa. Peroxisome proliferator-activated receptor γ coactivator 1α protein content increased after training, but was not correlated with changes in the metabolic proteins. In conclusion, the results revealed co-ordinated adaptation of several metabolic enzymes following endurance training, despite differences between people in the magnitude of response. Differences between individuals in the magnitude of response might reflect the influence of environmental and genetic factors that govern training adaptations.