Effect of high-intensity intermittent swimming training on fatty acid oxidation enzyme activity in rat skeletal muscle

We previously reported that high-intensity exercise training significantly increased citrate synthase (CS) activity, a marker of oxidative enzyme, in rat skeletal muscle to a level equaling that attained after low-intensity prolonged exercise training (Terada et al., J Appl Physiol 90: 2019-2024, 2001). Since mitochondrial oxidative enzymes and fatty acid oxidation (FAO) enzymes are often increased simultaneously, we assessed the effect of high-intensity intermittent swimming training on FAO enzyme activity in rat skeletal muscle. Male Sprague-Dawley rats (3 to 4 weeks old) were assigned to a 10-day period of high-intensity intermittent exercise training (HIT), low-intensity prolonged exercise training (LIT), or sedentary control conditions. In the HIT group, the rats repeated fourteen 20 s swimming sessions with a weight equivalent to 14-16% of their body weight. Between the exercise sessions, a 10 s pause was allowed. Rats in the LIT group swam 6 h/day in two 3 h sessions separated by 45 min of rest. CS activity in the triceps muscle of rats in the HIT and LIT groups was significantly higher than that in the control rats by 36 and 39%, respectively. Furthermore, 3-beta hydroxyacyl-CoA dehydrogenase (HAD) activity, an important enzyme in the FAO pathway in skeletal muscle, was higher in the two training groups than in the control rats (HIT: 100%, LIT: 88%). No significant difference in HAD activity was observed between the two training groups. In conclusion, the present investigation demonstrated that high-intensity intermittent swimming training elevated FAO enzyme activity in rat skeletal muscle to a level similar to that attained after 6 h of low-intensity prolonged swimming exercise training.     

The effects of high-intensity exercise on skeletal muscle neutrophil myeloperoxidase in untrained and trained rats

The primary purpose of this study was to examine the effects of high-intensity acute exercise on neutrophil infiltration in different muscle fiber types of untrained rats and to compare postexercise neutrophil accumulation in muscles of untrained and trained animals. The effect of high-intensity acute exercise on blood neutrophil degranulation reaction in trained animals was also elucidated. Neutrophil enzyme myeloperoxidase (MPO) was determined as a measure of neutrophil migration into muscles and blood neutrophil degranulation. Male albino rats were subjected to acute exercise and 5 weeks of training. The used model of intensive acute exercise consisted of 5, 15, and 25 intermittent swimming bouts with the addition of weight (8% of total body mass) for 1-min each, followed by 1.5-min rest intervals. MPO was analyzed in quadriceps muscle (white and red portion) and in soleus muscle 24 h after acute exercise. MPO content in resting blood plasma and neutrophils was determined 48-h following the completion of a training process. In addition, MPO content in the trained rats was measured immediately (in blood plasma and neutrophils) after and 24 h (in muscles) following a single-bout of exercise to exhaustion. The remaining two-third of the trained animals were exposed to a single-bout of nonstop swimming with the addition of 6% body mass until exhaustion. These animals were sacrificed immediately and 24 h after loaded swimming to analyze leukocyte count, MPO content in blood plasma and neutrophils and in muscles, respectively. About 24 h after exercise MPO concentrations in the red portion of quadriceps muscle and in soleus muscle were 4–7-fold higher as compared to the white portion of m. quadriceps. There was an association between the quantity of repetitive bouts of swimming and MPO content in the muscles. The duration of swimming to exhaustion of trained rats was 3.8-fold longer than untrained sedentary control. At rest, plasma MPO concentration was found to be 40% higher in trained rats compared to untrained controls (P < 0.05). Postexercise plasma MPO concentrations were significantly higher both in untrained (+137%; P < 0.05) and trained (+81%; P < 0.05) rats compared to resting values. At rest neutrophil MPO concentration was found to be 33% lower in trained rats compared to untrained controls (P < 0.05). There were no significant differences in muscle MPO concentrations between untrained and trained rats at rest. A single-bout of exercise to exhaustion produced a greater increase in MPO content in untrained compared to trained rats. The data suggest that postexercise neutrophil infiltration is more intensive in red fibers types compared to white fiber types. A smaller neutrophil infiltration in muscles of trained animals after exhaustive exercise suggests a protective effect of previous training to muscle injury.Portions of this paper were presented by V. Morozov in 2003 at the 6th ISEI Symposium on Exercise Muscle Metabolism and Immune Function, Copenhagen.     

Effects of high-intensity intermittent swimming on PGC-1alpha protein expression in rat skeletal muscle

AIM: The aim of the present investigation was to elucidate the effects of exercise intensity on exercise-induced expression of peroxisome proliferator-activated receptor gamma coactivator-1alpha (PGC-1alpha) protein in rat skeletal muscle. METHODS: We measured PGC-1alpha content in the skeletal muscles of male Sprague-Dawley rats (age: 5-6 weeks old; body weight: 150-170 g) after a single session of high-intensity intermittent exercise (HIE) or low-intensity prolonged swimming exercise (LIE). During HIE, the rats swam for fourteen 20-s periods carrying a weight (14% of body weight), and the periods of swimming were separated by a 10-s pause. LIE rats swam with no load for 6 h in two 3-h sessions, separated by 45 min of rest. RESULTS: After HIE, the PGC-1alpha protein content in rat epitrochlearis muscle had increased by 126, 140 and 126% at 2, 6 and 18 h, respectively, compared with that of the age-matched sedentary control rats' muscle. Immediately, 6 and 18-h after LIE, the PGC-1alpha protein content in the muscle was significantly elevated by 84, 95 and 67% respectively. The PGC-1alpha protein content observed 6 h after HIE tended to be higher than that observed after LIE. However, there was no statistically significant difference between the two values (P = 0.12). CONCLUSION: The present investigation suggests that irrespective of the intensity of the exercise, PGC-1alpha protein content in rat skeletal muscle increases to a comparable level when stimuli induced by different protocols are saturated. Further, HIE is a potent stimulus for enhancing the expression of PGC-1alpha protein, which may induce mitochondrial biogenesis in exercise-activated skeletal muscle.     

Exercise training in rats impairs the replenishment of white adipose tissue after partial lipectomy

The aim of this study was to evaluate the effect of exercise training on the metabolism of rats following the partial removal of fat pads. Three-month-old male Wistar rats were subjected to the partial removal (L) of retroperitoneal white adipose tissue (RET) and epididymal white adipose tissue (EPI), or a sham operation (Sh). Seven days after surgery, both sets of rats were subdivided into exercised (LE or ShE) (swimming 90 min/day, 5 days/week, 6 weeks) and sedentary (LS or ShS) groups. Partial removal of the fat pads increased the lipogenesis rates in both the RET and EPI and decreased the weight and lypolysis rate of the EPI, while the RET weight was not significantly affected by lipectomy. In both lipectomized and sham-operated groups, exercise training caused a reduction in carcass lipid content, food intake, RET and EPI weights, and RET lipogenesis rate. On the other hand, the exercise training increased the percentage of diet-derived lipid accumulation in both tissues, either in sham and lipectomized rats. These results confirmed that regrowth is not uniform and depends on the particular fat pad that is excised. They also demonstrated that exercise training following the partial removal of fat pads modified adipose tissue metabolism, impaired the replenishment of adipose tissue, and decrease body adiposity.     

The effect of high-intensity intermittent swimming on post-exercise glycogen supercompensation in rat skeletal muscle

A single bout of prolonged endurance exercise stimulates glucose transport in skeletal muscles, leading to post-exercise muscle glycogen supercompensation if sufficient carbohydrate is provided after the cessation of exercise. Although we recently found that short-term sprint interval exercise also stimulates muscle glucose transport, the effect of this type of exercise on glycogen supercompensation is uncertain. Therefore, we compared the extent of muscle glycogen accumulation in response to carbohydrate feeding following sprint interval exercise with that following endurance exercise. In this study, 16-h-fasted rats underwent a bout of high-intensity intermittent swimming (HIS) as a model of sprint interval exercise or low-intensity prolonged swimming (LIS) as a model of endurance exercise. During HIS, the rats swam for eight 20-s sessions while burdened with a weight equal to 18% of their body weight. The LIS rats swam with no load for 3 h. The exercised rats were then refed for 4, 8, 12, or 16 h. Glycogen levels were almost depleted in the epitrochlearis muscles of HIS- or LIS-exercised rats immediately after the cessation of exercise. A rapid increase in muscle glycogen levels occurred during 4 h of refeeding, and glycogen levels had peaked at the end of 8 h of refeeding in each group of exercised refed rats. The peak glycogen levels during refeeding were not different between HIS- and LIS-exercised refed rats. Furthermore, although a large accumulation of muscle glycogen in response to carbohydrate refeeding is known to be associated with decreased insulin responsiveness of glucose transport, and despite the fact that muscle glycogen supercompensation was observed in the muscles of our exercised rats at the end of 4 h of refeeding, insulin responsiveness was not decreased in the muscles of either HIS- or LIS-exercised refed rats compared with non-exercised fasted control rats at this time point. These results suggest that sprint interval exercise enhances muscle glycogen supercompensation in response to carbohydrate refeeding as well as prolonged endurance exercise does. Furthermore, in this study, both HIS and LIS exercise prevented insulin resistance of glucose transport in glycogen supercompensated muscle during the early phase of carbohydrate refeeding. This probably led to the enhanced muscle glycogen supercompensation after exercise.     

Effects of high‐intensity intermittent swimming on PGC‐1α protein expression in rat skeletal muscle

Aim: The aim of the present investigation was to elucidate the effects of exercise intensity on exercise‐induced expression of peroxisome proliferator‐activated receptor γ coactivator‐1α (PGC‐1α) protein in rat skeletal muscle. Methods: We measured PGC‐1α content in the skeletal muscles of male Sprague–Dawley rats (age: 5–6 weeks old; body weight: 150–170 g) after a single session of high‐intensity intermittent exercise (HIE) or low‐intensity prolonged swimming exercise (LIE). During HIE, the rats swam for fourteen 20‐s periods carrying a weight (14% of body weight), and the periods of swimming were separated by a 10‐s pause. LIE rats swam with no load for 6 h in two 3‐h sessions, separated by 45 min of rest. Results: After HIE, the PGC‐1α protein content in rat epitrochlearis muscle had increased by 126, 140 and 126% at 2, 6 and 18 h, respectively, compared with that of the age‐matched sedentary control rats’ muscle. Immediately, 6 and 18‐h after LIE, the PGC‐1α protein content in the muscle was significantly elevated by 84, 95 and 67% respectively. The PGC‐1α protein content observed 6 h after HIE tended to be higher than that observed after LIE. However, there was no statistically significant difference between the two values (P = 0.12). Conclusion: The present investigation suggests that irrespective of the intensity of the exercise, PGC‐1α protein content in rat skeletal muscle increases to a comparable level when stimuli induced by different protocols are saturated. Further, HIE is a potent stimulus for enhancing the expression of PGC‐1αprotein, which may induce mitochondrial biogenesis in exercise‐activated skeletal muscle.     

Vitamin C supplementation does not alter high-intensity endurance training-induced mitochondrial biogenesis in rat epitrochlearis muscle

The purpose of this study was to investigate whether vitamin C supplementation prevents high-intensity intermittent endurance training-induced mitochondrial biogenesis in the skeletal muscle. Male Wistar-strain rats were assigned to one of five groups: a control group, training group, small dose vitamin C supplemented training group, middle dose vitamin C supplemented training group, and large dose vitamin C supplemented training group. The rats of the trained groups were subjected to intense intermittent swimming training. The vitamin C supplemented groups were administrated vitamin C for the pretraining and training periods. High-intensity intermittent swimming training without vitamin C supplementation significantly increased peroxisome proliferator-activated receptor-γ coactivator-1α protein content and citrate synthase activity in the epitrochlearis muscle. The vitamin C supplementation did not alter the training-induced increase of these regardless of the dose of vitamin C supplementation. The results demonstrate that vitamin C supplementation does not prevent high-intensity intermittent training-induced mitochondrial biogenesis in the skeletal muscle.     

Interaction of exercise and diet on GLUT-4 protein and gene expression in Type I and Type II rat skeletal muscle

We determined the interaction of exercise and diet on glucose transporter (GLUT-4) protein and mRNA expression in type I (soleus) and type II [extensor digitorum longus (EDL)] skeletal muscle. Forty-eight Sprague Dawley rats were randomly assigned to one of two dietary conditions: high-fat (FAT, n=24) or high-carbohydrate (CHO, n=24). Animals in each dietary condition were allocated to one of two groups: control (NT, n=8) or a group that performed 8 weeks of treadmill running (4 sessions week-1 of 1000 m @ 28 m min-1, RUN, n=16). Eight trained rats were killed after their final exercise bout for determination of GLUT-4 protein and mRNA expression: the remainder were killed 48 h after their last session for measurement of muscle glycogen and triacylglycerol concentration. GLUT-4 protein expression in NT rats was similar in both muscles after 8 weeks of either diet. However, there was a main effect of training such that GLUT-4 protein was increased in the soleus of rats fed with either diet (P < 0.05) and in the EDL in animals fed with CHO (P < 0.05). There was a significant diet-training interaction on GLUT-4 mRNA, such that expression was increased in both the soleus (100% upward arrowP < 0.05) and EDL (142% upward arrowP < 0.01) in CHO-fed animals. Trained rats fed with FAT decreased mRNA expression in the EDL ( downward arrow 45%, P < 0.05) but not the soleus ( downward arrow 14%, NS). We conclude that exercise training in CHO-fed rats increased both GLUT-4 protein and mRNA expression in type I and type II skeletal muscle. Despite lower GLUT-4 mRNA in muscles from fat-fed animals, exercise-induced increases in GLUT-4 protein were largely preserved, suggesting that control of GLUT-4 protein and gene expression are modified independently by exercise and diet.     

High-intensity exercise and muscle glycogen availability in humans.

This study investigated the effects of muscle glycogen availability on performance and selected physiological and metabolic responses during high-intensity intermittent exercise. Seven male subjects completed a regimen of exercise and dietary intake (48 h) to either lower and keep low (LOW-CHO) or lower and then increase (HIGH-CHO) muscle glycogen stores, on two separate occasions at least a week apart. On each occasion the subjects completed a short-term (<10 min) and prolonged (>30 min) intermittent exercise (IEX) protocol, 24 h apart, which consisted of 6-s bouts of high-intensity exercise performed at 30-s intervals on a cycle ergometer. Glycogen concentration (mean +/- SEM) in m. vastus lateralis before both IEx(short) and IEx(long) was significantly lower following LOW-CHO [180 (14), 181 (17) mmol kg (dw)(-1)] compared with HIGH-CHO [397 (35), 540 (25) mmol kg (dw)(-1)]. In both IEx(short) and IEx(long), significantly less work was performed following LOW-CHO compared with HIGH-CHO. In IEx(long), the number of exercise bouts that could be completed at a pre-determined target exercise intensity increased by 265% from 111 (14) following LOW-CHO to 294 (29) following HIGH-CHO (P < 0.05). At the point of fatigue in IEx(long), glycogen concentration was significantly lower with the LOW-CHO compared with HIGH-CHO [58 (25) vs. 181 (46) mmol kg (dw)(-1), respectively]. The plasma concentrations of adrenaline and nor-adrenaline (in IEx(short) and IEx(long)), and FFAand glycerol (in IEx(long)), increased several-fold above resting values with both experimental conditions. Oxygen uptake during the exercise periods in IEx(long), approached 70% of Vo2max. These results suggest that muscle glycogen availability can affect performance during both short-term and more prolonged high-intensity intermittent exercise and that with repeated exercise periods as short as 6 s, there can be a relatively high aerobic contribution.     

High-intensity exercise and muscle glycogen availability in humans

This study investigated the effects of muscle glycogen availability on performance and selected physiological and metabolic responses during high-intensity intermittent exercise. Seven male subjects completed a regimen of exercise and dietary intake (48 h) to either lower and keep low (LOW-CHO) or lower and then increase (HIGH-CHO) muscle glycogen stores, on two separate occasions at least a week apart. On each occasion the subjects completed a short-term (<10 min) and prolonged (>30 min) intermittent exercise (IEX) protocol, 24 h apart, which consisted of 6-s bouts of high-intensity exercise performed at 30-s intervals on a cycle ergometer. Glycogen concentration (mean ± SEM) in m. vastus lateralis before both IEx_short and IEx_long was significantly lower following LOW-CHO [180 (14), 181 (17) mmol kg (dw)^–1] compared with HIGH-CHO [397 (35), 540 (25) mmol kg (dw)^–1]. In both IEx_short and IEx_long, significantly less work was performed following LOW-CHO compared with HIGH-CHO. In IEx_long, the number of exercise bouts that could be completed at a pre-determined target exercise intensity increased by 265% from 111 (14) following LOW-CHO to 294 (29) following HIGH-CHO (P < 0.05). At the point of fatigue in IEx_long, glycogen concentration was significantly lower with the LOW-CHO compared with HIGH-CHO [58 (25) vs. 181 (46) mmol kg (dw)^–1, respectively]. The plasma concentrations of adrenaline and nor-adrenaline (in IEx_short and IEx_long), and FFA and glycerol (in IEx_long), increased several-fold above resting values with both experimental conditions. Oxygen uptake during the exercise periods in IEx_long approached 70% of V o_2max. These results suggest that muscle glycogen availability can affect performance during both short-term and more prolonged high-intensity intermittent exercise and that with repeated exercise periods as short as 6 s, there can be a relatively high aerobic contribution.     

Human skeletal muscle fiber type alteration with high-intensity intermittent training

Summary The response of muscle fiber type proportions and fiber areas to 15 weeks of strenuous high-intensity intermittent training was investigated in twenty-four carefully ascertained sedentary (14 women and 10 men) and 10 control (4 women and 6 men) subjects. The supervised training program consisted mainly of series of supramaximal exercise lasting 15 s to 90 s on a cycle ergometer. Proportions of muscle fiber type and areas of the fibers were determined from a biopsy of the vastus lateralis before and after the training program. No significant change was observed for any of the histochemical charactertics in the control group. Training significantly increased the proportion of type I and decreased type IIb fibers, the proportion of type IIa remained unchanged. Areas of type I and IIb fibers increased significantly with training. These results suggest that high-intensity intermittent training in humans may alter the proportion of type I and the area of type I and IIb fibers and in consequence that fiber type composition in human vastus lateralis muscle is not determined solely by genetic factors.     

The effect of exercise on the contractile properties of single skinned fast- and slow-twitch skeletal muscle fibres from the adult rat

The effects of long-term endurance exercise on the contractile properties of single skinned muscle fibres from adult rats, were investigated. Adult (4-month-old) male rats were subjected to a 16-week, high-intensity endurance swimming programme, where animals carried a load (corresponding to 2% of body wt), during all 2-h training sessions. At the conclusion of the training period, muscle fibres isolated from the extensor digitorum longus (EDL), and soleus (SOL), could be classified into distinct classes or fibre types on the basis of their Ca²⁺- and Sr²⁺-activated contractile characteristics. The fast-twitch EDL comprised two fibre populations, while the slow-twitch SOL was found to be composed of three distinct fibre types. Endurance swimming modified the contractile characteristics of fibres from both the EDL and SOL, but exerted greater influence on those of the SOL. This was illustrated by significant increases in the sensitivity to Ca²⁺ and Sr²⁺, and a lower threshold for contraction by these activating ions, in the exercised group. Not one of the total of 272 fibres sampled, exhibited mixed fast- and slow-twitch contractile characteristics, often associated with exercise-induced fibre type transformations. Thus, high-intensity endurance swimming induced changes in some single muscle fibre contractile properties of adult rats, but did not cause major changes in fibre type distribution.     

Effect of physical training on the development of hypertension in the spontaneously hypertensive rat

The effect of chronic physical exercise on the development of hypertension was measured in spontaneously hypertensive rats (SHR) and their progenitor normotensive wistar-kyoto controls (WK). Starting 4–5 weeks after birth groups of rats were subjected to swimming exercise 1 h×day^–1, 4 days×weeks^–1 for a total period of 11 weeks. Control rats were handled daily without exercise. Both in trained SHR and WK a significant delay in increase in body weight was observed. Physical training caused a small, but significant (P<0.001) reduction in systolic blood pressure of SHR, whereas it did not affect blood pressure in WK. Heart rate was significantly (P<0.001) lower in both trained SHR and WK than in their non-trained controls. At the end of the training period the degree of training was tested by measuring muscle cytochrome oxidase activity and relative heart weight. Cytochrome oxidase activity in gastrocnemius muscle was higher in the trained animals, although the difference was only significant (P<0.05) for WK. Training also caused a significant (P<0.01) increase in the ratio heart weight to body weight in WK. Both trained and non-trained SHR have a ca. 25% higher relative heart weight than WK controls. SHR hearts did not further hypertrophy as a consequence of physical exercise.These data indicate that swim training induces a trained state in both SHR and WK. Moreover, this form of training causes a slight, but significant attennation of the development of hypertension in SHR.     

Effect of systemic hypoxia on GLUT4 protein expression in exercised rat heart

Altitude training is a common method used to enhance endurance performance in athletes. We have examined the interactive effect of exercise training and chronic hypoxic on glycogen storage and GLUT4 protein expression in cardiac muscles. Thirty-two male Sprague-Dawley rats were weight balanced and assigned to one of the following four groups: control, exercise, hypoxia, and hypoxia-exercise. Rats with hypoxic treatment (breathing 14% O(2) for 12 hr/d) were exposed under normobaric conditions. The training protocol consisted of swimming for two 3-hr periods per day for 4 weeks. Glycogen content, GLUT4 protein, and mRNA of all rats were determined 16 hr after treatments. Four-week exercise training without hypoxia significantly elevated myocardial glycogen level by 45%. The chronic hypoxic-exercise training elevated the myocardial glycogen level by 67% above control level, significantly greater than the exercise group. Chronic hypoxia, exercise training, and hypoxia-exercise training significantly elevated GLUT4 protein by 40-70% in cardiac muscles. Chronic hypoxia significantly elevates the GLUT1 protein level independent of exercise training. The new finding in this study was that GLUT4 gene expression in cardiac muscle can be stimulated by exercise training with hypoxia treatments. This molecular adaptation appears to be associated with the observed increase in glycogen storage of the muscle.     

Impact of treadmill locomotor training on skeletal muscle IGF1 and myogenic regulatory factors in spinal cord injured rats

The objective of this study was to determine the impact of treadmill locomotor training on the expression of insulin-like growth factor I (IGF1) and changes in myogenic regulatory factors (MRFs) in rat soleus muscle following spinal cord injury (SCI). Moderate, midthoracic (T₈) contusion SCIs were produced using a NYU (New York University) impactor. Animals were randomly assigned to treadmill training or untrained groups. Rats in the training group were trained starting at 1 week after SCI, for either 3 bouts of 20 min over 1.5 days or 10 bouts over 5 days. Five days of treadmill training completely prevented the decrease in soleus fiber size resulting from SCI. In addition, treadmill training triggered increases in IGF1, MGF and IGFBP4 mRNA expression, and a concurrent reduction of IGFBP5 mRNA in skeletal muscle. Locomotor training also caused an increase in markers of muscle regeneration, including small muscle fibers expressing embryonic myosin and Pax7 positive nuclei and increased expression of the MRFs, myogenin and MyoD. We concluded that treadmill locomotor training ameliorated muscle atrophy in moderate contusion SCI rats. Training-induced muscle regeneration and fiber hypertrophy following SCI was associated with an increase in IGF1, an increase in Pax7 positive nuclei, and upregulation of MRFs.     

GLUT-4 expression is not consistently higher in type-1 than in type-2 fibres of rat and human vastus lateralis muscles; an immunohistochemical study

In whole muscle homogenates, the glucose transporter-4 (GLUT-4) content is reported to be higher in muscles consisting predominantly of oxidative (type-1) muscle fibres than in muscles consisting predominantly of glycolytic (type-2) fibres. From these findings, it has been deduced that in rat muscle, oxidative fibres have an intrinsically higher level of GLUT-4 protein than glycolytic fibres. No data is available concerning human muscle. Moreover, the fibre-type-specific expression of GLUT-4 has not yet been examined directly. In this study, the relative abundance of GLUT-4 protein expression in individual fibres of different types within a muscle was compared directly in immunohistochemical assays. The human vastus lateralis muscle and a selection of rat muscles were studied using a novel GLUT-4 antiserum. It is concluded that the pattern of fibre-type-specific GLUT-4 expression differs between human and rats and varies between the different muscles studied, indicating that non-fibre-type-specific factor(s) affect expression of GLUT-4. The observation that within a muscle a fibre-type-specific expression of GLUT-4 was observed indicates that fibre-type-specific factors contribute to GLUT-4 expression as well. Thus, it can be postulated that both fibre-type-dependent and fibre-type-independent factors affect GLUT-4 expression.     

High‐Intensity Resistance Training with Insufficient Recovery Time Between Bouts Induce Atrophy and Alterations in Myosin Heavy Chain Content in Rat Skeletal Muscle

The aim of this study was to test whether high‐intensity resistance training with insufficient recovery time between bouts, could result in a decrease of muscle fiber cross‐sectional area (CSA), alter fiber‐type frequencies and myosin heavy chain (MHC) isoform content in rat skeletal muscle. Wistar rats were divided into two groups: trained (Tr) and control (Co). Tr group were subjected to a high‐intensity resistance training program (5 days/week) for 12 weeks, involving jump bouts into water, carrying progressive overloads based on percentage body weight. At the end of experiment, animals were sacrificed, superficial white (SW) and deep red (DR) portions of the plantaris muscle were removed and submitted to mATPase histochemical reaction and SDS‐PAGE analysis. Throughout the experiment, both groups increased body weight, but Tr was lower than Co. There was a significant reduction in IIA and IID muscle fiber CSA in the DR portion of Tr compared to Co. Muscle fiber‐type frequencies showed a reduction in Types I and IIA in the DR portion and IID in the SW portion of Tr compared to Co; there was an increase in Types IIBD frequency in the DR portion. Change in muscle fiber‐type frequency was supported by a significant decrease in MHCI and MHCIIa isoforms accompanied by a significant increase in MHCIIb isoform content. MHCIId showed no significant differences between groups. These data show that high‐intensity resistance training with insufficient recovery time between bouts promoted muscle atrophy and a transition from slow‐to‐fast contractile activity in rat plantaris muscle. Anat Rec, 2011. © 2011 Wiley‐Liss, Inc.     

Comparison of the Effects of Physical Exercise,Cold Acclimation and Repeated Injections of Isoprenaline on Rat Muscle Enzymes

The metabolic effects on rat cardiac and skeletal muscle of a strenuous program of swimming, of cold acclimation and of isoprenaline treatment (0.3 mg/kg daily for 5 five-day weeks) were compared. Exercised and cold-exposed rats gained less body weight than did controls or isoprenaline-treated rats. In all treated groups the heart and the interscapular brown adipose tissue hypertrophied. The size of the adrenals increased only in isoprenaline-treated animals. Cold-acclimation and physical training increased and isoprenaline treatment reduced or did not affect the activities of succinate dehydrogenase, rnalate dehydrogenase and citrate synthase of cardiac muscle. In skeletal muscle all treatments resulted in increased activities of these enzymes. Of the anaerobic enzymes analysed, only the activity of hexokinase increased in response to the treatments used. This increase was the same in cardiac as in skeletal muscle, but it was significantly greater with isoprenaline-treatment than with training or with cold-acclimation. The activities of lactate dehydrogenase and phosphofructokinase did not differ significantly. All treatments improved cold resistance, but only swimming exercise and cold acclimation significantly increased tolerance to exercise. It is concluded that prolonged stimulation of adrenergic β-receptors by catecholamines is responsible for the metabolic changes observed.     

Effects of high-intensity intermittent training on carnitine palmitoyl transferase activity in the gastrocnemius muscle of rats

We examined the capacity of high-intensity intermittent training (HI-IT) to facilitate the delivery of lipids to enzymes responsible for oxidation, a task performed by the carnitine palmitoyl transferase (CPT) system in the rat gastrocnemius muscle. Male adult Wistar rats (160-250 g) were randomly distributed into 3 groups: sedentary (Sed, N = 5), HI-IT (N = 10), and moderate-intensity continuous training (MI-CT, N = 10). The trained groups were exercised for 8 weeks with a 10% (HI-IT) and a 5% (MI-CT) overload. The HI-IT group presented 11.8% decreased weight gain compared to the Sed group. The maximal activities of CPT-I, CPT-II, and citrate synthase were all increased in the HI-IT group compared to the Sed group (P < 0.01), as also was gene expression, measured by RT-PCR, of fatty acid binding protein (FABP; P < 0.01) and lipoprotein lipase (LPL; P < 0.05). Lactate dehydrogenase also presented a higher maximal activity (nmol·min⁻¹·mg protein⁻¹) in HI-IT (around 83%). We suggest that 8 weeks of HI-IT enhance mitochondrial lipid transport capacity thus facilitating the oxidation process in the gastrocnemius muscle. This adaptation may also be associated with the decrease in weight gain observed in the animals and was concomitant to a higher gene expression of both FABP and LPL in HI-IT, suggesting that intermittent exercise is a “time-efficient” strategy inducing metabolic adaptation.