Muscle metabolite accumulation following maximal exercise

Summary Five elite flatwater kayak paddlers were studied during indoor simulated 500 and 10,000-m races, with performance times of 2 and 45 min, respectively. Muscle biopsies were obtained from the midportion of m. deltoideus immediately pre and post exercise. Concentrations of adenosine triphosphate (ATP), creatine phosphate (CP), glucose, glucose-6-phosphate (G-6-P), glycogen, and lactate were subsequently determined. Short term exercise resulted in statistically significant increases in glucose (P<0.001), G-6-P (P<0.05) and lactate (P<0.01) concentration concomitant with decreased CP (P<0.05) and glycogen (P<0.01). Following prolonged exercise, a non-significant elevation in glucose and a reduction (P<0.01) in glycogen were demonstrated.Evidently the metabolic demands for kayak competitions at 500 and 10,000 m are different. Thus, the energy contribution from glycolytic precursors and the anaerobic component is of greater relative importance in short distances than in exercise of long duration. A generalization of the findings to other athletic events of varying distances is proposed. The present data on arm-exercise is consistent with previous findings obtained in connection with leg exercises.     

Sympathetic response to maximal bicycle exercise before and after leg strength training

Summary Plasma catecholamine concentrations at rest and in response to maximal exercise on the cycle ergometer (278±15 watts, 6 min duration) have been measured on seven young active male subjects (19±1 years old; 80±3 kg; 176±3 cm) prior to and after a eight week leg strength training program (5RM, squat and leg press exercise). Strength training resulted in a significant increase in performance on squat (103±3 to 140±5 kg) and leg press exercise (180±9 to 247±15 kg) associated with a small significant increase in lean body mass (64.5±2.2 to 66.3±2.1 kg) and no change in maximal oxygen consumption (47.5±1.3 to 46.9±1.2 ml · kg^–1 · min^–1). Plasma norepinephrine (NE) and epinephrine (E) concentrations (pg · mL^–1) were not significantly different before and after training at rest (NE: 172±19 vs 187±30; E: 33±10 vs 76±16) or in response to maximal exercise (NE: 3976±660 vs 4163±1081; E: 1072±322 vs 1321±508). Plasma lactate concentrations during recovery were similar before and after training (147±5 vs 147±15 mg · dL^–1). Under the assumption that the central command is reduced for a given absolute workload on the bicycle ergometer following leg strength training, these observations support the hypothesis that the sympathetic response to exercise is under the control of information from muscle chemoreceptors.Supported by grants from NSERC, Government of Canada and FRSQ, Government of Quebec     

Effects of aerobic endurance training status and specificity on oxygen uptake kinetics during maximal exercise

The main purpose of this study was to analyze the effects of exercise mode, training status and specificity on the oxygen uptake (O₂) kinetics during maximal exercise performed in treadmill running and cycle ergometry. Seven runners (R), nine cyclists (C), nine triathletes (T) and eleven untrained subjects (U), performed the following tests on different days on a motorized treadmill and on a cycle ergometer: (1) incremental tests in order to determine the maximal oxygen uptake (O_2max) and the intensity associated with the achievement of O_2max (IO_2max); and (2) constant work-rate running and cycling exercises to exhaustion at IO_2max to determine the effective time constant of the O₂ response (O₂). Values for O_2max obtained on the treadmill and cycle ergometer [R=68.8 (6.3) and 62.0 (5.0); C=60.5 (8.0) and 67.6 (7.6); T=64.5 (4.8) and 61.0 (4.1); U=43.5 (7.0) and 36.7 (5.6); respectively] were higher for the group with specific training in the modality. The U group showed the lowest values for O_2max, regardless of exercise mode. Differences in O₂ (seconds) were found only for the U group in relation to the trained groups [R=31.6 (10.5) and 40.9 (13.6); C=28.5 (5.8) and 32.7 (5.7); T=32.5 (5.6) and 40.7 (7.5); U=52.7 (8.5) and 62.2 (15.3); for the treadmill and cycle ergometer, respectively]; no effects of exercise mode were found in any of the groups. It is concluded that O₂ during the exercise performed at IO_2max is dependent on the training status, but not dependent on the exercise mode and specificity of training. Moreover, the transfer of the training effects on O₂ between both exercise modes may be higher compared with O_2max.     

Influence of sodium bicarbonate ingestion on plasma ammonia accumulation during incremental exercise in man

Summary This investigation evaluated the influence of metabolic alkalosis on plasma ammonia (NH₃) accumulation during incremental exercise. On two occasions separated by at least 6 days, six healthy men cycled at 70, 80, and 90%g of maximum oxygen consumption ( ) for 5 min; each exercise period was followed by 5 min of seated recovery. Exercise was then performed at 100% until exhaustion. Beginning 3 h prior to exercise, subjects ingested 3.6 mmol · kg body mass^– NaHCO₃ (test, T) or 3.0 mmol · kg body mass^–1 CaCO₃ (placebo, P) (both equivalent to 0.3 g · kg^–1) over a 2-h period. Trials were performed after an overnight fast and the order of treatments was randomized. Arterialized venous blood samples for the determination of acid-base status, blood lactate and plasma NH₃ concentrations were obtained at rest before treatment, 15 s prior to each exercise bout (Pre 70%, Pre 80%, Pre 90%, and Pre 100%), and at 0, 5 (5Post), and 10 (10'Post) min after exhaustion. Additional samples for blood lactate and plasma NH₃ determination were obtained immediately after each exercise bout (Post 70%, Post 80%, Post 90%) and at 15 min after exercise (15Post). Time to exhaustion at 100% of was not significantly different between treatments [mean (SE): 173 (42) s and 184 (44) s for T and P respectively]. A significant treatment effect was observed for plasma pH with values being significantly higher on T than on P Pre 70% [7.461 (0.007) vs 7.398 (0.008)], Pre 90% [7.410 (0.010) vs 7.340 (0.016)], and 10'Post [7.317 (0.032) vs 7.242 (0.036)]. The change in plasma pH was significantly greater following the 90%g bout (Pre 100% Pre 90%) for T [–0.09 (0.02)] than for P [–0.06 (0.01)]. Blood base excess and plasma bicarbonate concentrations were significantly higher for T than P before each exercise bout but not at the point of exhaustion. During recovery, base excess was higher for T than P at 5Post and 10Post while the bicarbonate concentration was higher for T than P at 10Post. A significant treatment effect was observed for the blood lactate concentration with T on the average being higher than P [7.0 (1.0) and 6.3 (1.1) mmol · l^–1 for T and P averaged across the 12 sampling times]. Plasma NH₃ accumulation was not different between treatments at any point in time. In addition, no differences were observed between treatments in blood alanine accumulation. The results suggest that under the conditions of the present investigation metabolic alkalosis does not influence plasma NH₃ accumulation or endurance capacity during intense incremental exercise.     

Physiological responses to maximal intensity intermittent exercise

Summary Physiological responses to repeated bouts of short duration maximal-intensity exercise were evaluated. Seven male subjects performed three exercise protocols, on separate days, with either 15 (S₁₅), 30 (S₃₀) or 40 (S₄₀) m sprints repeated every 30 s. Plasma hypoxanthine (HX) and uric acid (UA), and blood lactate concentrations were evaluated pre- and postexercise. Oxygen uptake was measured immediately after the last sprint in each protocol. Sprint times were recorded to analyse changes in performance over the trials. Mean plasma concentrations of HX and UA increased during S₃₀ and S₄₀ (P<0.05), HX increasing from 2.9 (SEM 1.0) and 4.1 (SEM 0.9), to 25.4 (SEM 7.8) and 42.7 (SEM 7.5) µmol · l^–1, and UA from 372.8 (SEM 19) and 382.8 (SEM 26), to 458.7 (SEM 40) and 534.6 (SEM 37) µmol · l^–1, respectively. Postexercise blood lactate concentrations were higher than pretest values in all three protocols (P<0.05), increasing to 6.8 (SEM 1.5), 13.9 (SEM 1.7) and 16.8 (SEM 1.1) mmol · l^–1 in S₁₅, S₃₀ and S₄₀, respectively. There was no significant difference between oxygen uptake immediately after S₃₀ [3.2 (SEM 0.1) l · min^–1] and S₄₀ [3.3 (SEM 0.4) l · min^–1], but a lower value [2.6 (SEM 0.1) l · min^–1] was found after S₁₅ (P<0.05). The time of the last sprint [2.63 (SEM 0.04) s] in S₁₅ was not significantly different from that of the first [2.62 (SEM 0.02) s]. However, in S₃₀ and S₄₀ sprint times increased from 4.46 (SEM 0.04) and 5.61 (SEM 0.07) s (first) to 4.66 (SEM 0.05) and 6.19 (SEM 0.09) s (last), respectively (P<0.05). These data showed that with a fixed 30-s intervening rest period, physiological and performance responses to repeated sprints were markedly influenced by sprint distance. While 15-m-sprints could be repeated every 30 s without decreases in performance, 40-m sprint times increased after the third sprint (P<0.05) and this exercise pattern was associated with a net loss to the adenine nucleotide pool.     

Blood lactate accumulation in intermittent supramaximal exercise

Summary Blood lactate accumulation rate and oxygen consumption have been studied in six trained male runners, aged 20 to 30 years. Subjects ran on a treadmill at a rate representing 172±5% for four 45 s sessions, separated by 9 min rest periods. Oxygen consumption was measured throughout. Blood lactate was determined in samples taken from the ear and was measured at the end of each exercise session, and two, five and nine minutes later. After the fourth exercise session, the same measurements were made every five min for 30 min. 4 subjects repeated a single exercise of the same type, duration and intensity and the same measurements were taken. With repetitive intermittent exercise, gradual increases in blood lactate concentration ([LA]b) occurred, whereas its rate of accumulation ([LA]b) decreased. The amount of oxygen consumed during each 45 s exercise session remained unchanged for a given subject. After cessation of intermittent exercise, the half-time of blood lactate was 26 min, whereas it was only 15 min after a single exercise session. values, on the other hand, returned to normal after 15 to 20 min. All other conditions being equal, the gradual decrease in [LA]b during intermittent exercise could be explained if the lactate produced during the first exercise session is used during the second period, and/or if the diffusion space of lactate increases. The diffusion space seems to be multicompartmental on the basis of half-time values noted for [LA]b after intermittent exercise, compared with those noted after a single exercise session. The distinction between the rapid return to normal values and the more gradual return to normal blood lactate levels confirms that there is no simple and direct relationship between oxygen debt and the accumulation of blood lactate after muscular exercise. In practical terms, these results show that the calorific equivalent of lactic acid defined by Margaria et al. (1963) cannot be used in the case of intermittent exercise of supramaximal intensity.     

Effects of endurance training on hyperammonaemia during a 45-min constant exercise intensity

Summary Eleven laboratory-pretrained subjects (initial =54 ml·kg⁻¹·min⁻¹) took part in a study to evaluate the effect of a short endurance training programme [8–12 sessions, 1 h per session, with an intensity varying from 60% to 90% maximal oxygen consumption ] on the responses of blood ammonia (b[NH ₄ ⁺ ]) and lactate (b[la]) concentrations during progressive and constant exercise intensities. After training, during which did not increase, significant decreases in b[NH ₄ ⁺ ], b[la] and muscle proton concentration were observed at the end of the 80% constant exercise intensity, although b[NH ₄ ⁺ ] and b[la] during progressive exercise were unchanged. On the other hand, no correlations were found between muscle fibre composition and b[NH ₄ ⁺ ] in any of the exercise procedures. This study demonstrated that a constant exercise intensity was necessary to reveal the effect of training on muscle metabolic changes inducing the decrease in b[NH ₄ ⁺ ] and b[la]. At a relative power of exercise of 80% , there was no effect of muscle fibre composition on b[NH ₄ ⁺ ] accumulation.     

Resistance exercise training attenuates exercise-induced lipid peroxidation in the elderly

This study examined the effects of 6 months of resistance exercise (RX) on basal and post-aerobic exercise lipid peroxidation (LIPOX). Men and women [n=62, mean (SD) age 68.4 (6) years] were divided randomly into either a control (n=16, CON), low-intensity training [LEX n=24; 50% one-repetition maximum (1RM), 13 repetitions/exercise], or high-intensity training (HEX n=22, 80% 1RM, 8 repetitions/exercise) group. Pre- and post-training, subjects performed a graded aerobic exercise test (GXT). Blood samples were collected prior to and 10 min following each GXT. Subjects trained 3 times per week for 6 months using 12 RX machines. LIPOX was determined by measuring levels of thiobarbituric reactive acid substances (TBARS) and lipid hydroperoxides (PEROX). RX had no effect on resting LIPOX. Post-training, post-GXT TBARS were lower in the LEX and HEX groups by 14% and 18%, respectively, compared to CON (P<0.05). Post-GXT PEROX levels were lower (P<0.05) in LEX and HEX compared to CON [CON 3.51 (0.56) nmol/ml, LEX 2.89 (0.80) nmol/ml, HEX 2.99 (0.63) nmol/ml]. Serum total and non-protein (glutathione) thiols were higher in the LEX and HEX groups following training compared to CON (P<0.05). These data suggest that RX can (1) reduce serum LIPOX, (2) provide protection against oxidizing agents in vitro, and (3) provide a "cross-protection" against the oxidative stress generated by aerobic exercise, perhaps mediated by improvements in the thiol portion of the antioxidant defense. Electronic Publication     

Effects of hyperthermia on the metabolic responses to repeated high-intensity exercise

In this study, we investigated the metabolic and performance responses to hyperthermia during high-intensity exercise. Seven males completed two 30-s cycle sprints (SpI and SpII) at an environmental temperature of 20.6 (0.3) °C [mean (SD)] with 4 min recovery between sprints. A hot or control treatment preceded the sprint exercise. For the hot trial, subjects were immersed up to the neck in hot water [43°C for 16.0 (3.2) min] prior to entering an environmental chamber [44.2 (0.8)°C for 30.7 (7.1) min]. For the control trial, subjects were seated in an empty bath (15 min) and thereafter in a normal environment [20.2 (0.6)°C for 29.0 (1.9) min]. Subjects core temperature prior to exercise was 38.1 (0.3)°C in the hot trial and 37.1 (0.3)°C in the control trial. Mean power output (MPO) was significantly higher in the hot condition for SpI [683 (130) W hot vs 646 (119) W control (P<0.025)]. Peak power output (PPO) tended to be higher in the hot trial compared with the control trial for SpI [1057 (260) W hot vs 990 (245) W control (P=0.03, NS)]. These differences in power output were a consequence of a faster pedal cadence in the hot trial (P<0.025). There were no differences in sprint performance in SpII in the hot trial compared to the control trial; however, MPO was significantly reduced from SpI to SpII in the hot condition but not in the control condition (P<0.025). Plasma ammonia was higher in the hot trial at 2 min post-SpI [169 (65) mol l^-1 hot vs 70 (26) mol l^-1 control (P<0.01)], immediately and at 2 min post-SpII [231 (76) mol l^-1 hot vs 147 (72) mol l^-1 control (P<0.01)]. Blood lactate was higher in the hot trial compared with the control trial at 5 min post-SpII (P<0.025). The results of this study suggest that an elevation in core body temperature by 1°C can improve performance during an initial bout of high-intensity cycle exercise but has no further beneficial effect on subsequent power production following a 4-min recovery period.     

The distribution of rest periods affects performance and adaptations of energy metabolism induced by high‐intensity training in human muscle

The effect of the distribution of rest periods on the efficacy of interval sprint training is analysed. Ten male subjects, divided at random into two groups, performed distinct incremental sprint training protocols, in which the muscle load was the same (14 sessions), but the distribution of rest periods was varied. The `short programme' group (SP) trained every day for 2 weeks, while the `long programme' group (LP) trained over a 6‐week period with a 2‐day rest period following each training session. The volunteers performed a 30‐s supramaximal cycling test on a cycle ergometer before and after training. Muscle biopsies were obtained from the vastus lateralis before and after each test to examine metabolites and enzyme activities. Both training programmes led to a marked increase (all significant, P < 0.05) in enzymatic activities related to glycolysis (phosphofructokinase – SP 107%, LP 68% and aldolase – SP 46%, LP 28%) and aerobic metabolism (citrate synthase – SP 38%, LP 28.4% and 3‐hydroxyacyl‐CoA dehydrogenase – SP 60%, LP 38.7%). However, the activity of creatine kinase (44%), pyruvate kinase (35%) and lactate dehydrogenase (45%) rose significantly (P < 0.05) only in SP. At the end of the training programme, SP had suffered a significant decrease in anaerobic ATP consumption per gram muscle (P < 0.05) and glycogen degradation (P < 0.05) during the post‐training test, and failed to improve performance. In contrast, LP showed a marked improvement in performance (P < 0.05) although without a significant increase in anaerobic ATP consumption, glycolysis or glycogenolysis rate. These results indicate that high‐intensity cycling training in 14 sessions improves enzyme activities of anaerobic and aerobic metabolism. These changes are affected by the distribution of rest periods, hence shorter rest periods produce larger increase in pyruvate kinase, creatine kinase and lactate dehydrogenase. However, performance did not improve in a short training programme that did not include days for recovery, which suggests that muscle fibres suffer fatigue or injury.     

Comparison of incremental and steady state tests of endurance training

Summary To compare the results obtained by incremental or constant work load exercises in the evaluation of endurance conditionning, a 20-week training programme was performed by 9 healthy human subjects on the bicycle ergometer for 1 h a day, 4 days a week, at 70–80% . Before and at the end of the training programme, (1) the blood lactate response to a progressive incremental exercise (18 W increments every 2nd min until exhaustion) was used to determine the aerobic and anaerobic thresholds (AeT and AnT respectively). On a different day, (2) blood lactate concentrations were measured during two sessions of constant work load exercises of 20 min duration corresponding to the relative intensities of AeT (1st session) and AnT (2nd session) levels obtained before training. A muscle biopsy was obtained from vastus lateralis at the end of these sessions to determine muscle lactate. AeT and AnT, when expressed as % , increased with training by 17% (p<0.01) and 9% (p<0.05) respectively. Constant workload exercise performed at AeT intensity was linked before training (60% ) to a blood lactate steady state (4.8±1.4 mmol·l^–1) whereas, after training, AeT intensity (73% ) led to a blood lactate accumulation of up to 6.6±1.7 mmol·l^–1 without significant modification of muscle lactate (7.6±3.1 and 8.2±2.8 mmol·kg^–1 wet weight respectively). It is concluded that increase in AeT with training may reflect transient changes linked to lower early blood lactate accumulation during incremental exercise. Nevertheless, the results obtained at the end of the constant work load exercises were assumed to be independant of these changes, the occurrence of blood lactate accumulation being postulated to reflect a decreased removal from the blood linked to a higher relative work intensity. So, the use of incremental exercise is an incomplete procedure when evaluating endurance training effects.     

Effects of exercise training on the matrix metalloprotease response to acute exercise

Matrix metalloproteases (MMPs) in the circulation are thought to modulate the activation of growth factors, cytokines, and angiogenesis, facilitating physiological adaptations to exercise training. The purpose of this work was to characterize serum MMP-1, MMP-2, MMP-3, and MMP-9 concentrations pre- and post-eight weeks of exercise training. We tested the hypothesis that exercise training would influence serum MMP concentrations in response to an acute resistance exercise test (ARET). Participants were randomized into an 8-week training program (5 days per week) that emphasized callisthenic (CT, N = 8) or resistance (RT, N = 8) exercise. Serum MMP concentrations (MMP-1, -2, -3, -9) were assessed in men (N = 16) in response to an acute bout of high-intensity resistance exercise (six sets of 10-RM squats with 2-min inter-set rest periods) both before and after 8 weeks of training. Training resulted in a temporal shift in the peak MMP-1 concentration from post-ARET to mid-ARET in both groups. Post-training, MMP-9 concentrations were increased immediately after the ARET in the CT group as compared to pre-training ARET concentrations. RT did not alter MMP-3 and -9 concentrations. These data suggest that the mode of exercise training influences the MMP response to an acute bout of exercise, revealing a possible role of MMPs in initiating training-specific adaptations. The opinions or assertions contained herein are the private views of the author(s) and are not to be construed as official or as reflecting the views of the Army or the Department of Defense. Citations of commercial organizations and trade names in this report do not constitute an official Department of the Army endorsement or approval of the products or services of these organizations.     

Changes in erythrocyte 2,3 diphosphoglycerate in women following short term maximal exercise

15 untrained women were subjected to a walking treadmill test to determine the influence of maximal exercise upon synthesis of erythrocyte 2,3 DPG. Although there was a 9.8% increase in the 2,3 DPG content following exercise, there was a concomitant 9.4% increase in the hemoglobin level; therefore, when 2,3 DPG is expressed as a ratio to hemoglobin there was no significant change as a result of exercise stress. It was suggested that three additive factors produced during strenuous exercise: decreased pH; increased hemoglobin concentration; and increased CO₂ production result in by-product inhibition of 2,3 DPG synthesis. It is concluded that 2,3 DPG does not provide a physiologic benefit in the adaptation of the oxygen transport system to exercise.     

Dietary composition and acid-base status: limiting factors in the performance of maximal exercise in man?

Summary Seven healthy male subjects exercised to exhaustion at a workload equivalent to 100% of their maximal oxygen uptake ( ) on 3 separate occasions. Each high intensity exercise test was performed on an electrically braked cycle ergometer; the first took place after a normal diet (46±8% carbohydrate (CHO), 41±7% fat and 13±3% protein); the second after 3 days of a low CHO diet (7±3% CHO, 64±5% fat and 29±4% protein) and the third after 3 days of a high CHO diet (76±6% CHO, 14±5% fat and 10±2% protein). Acid-base status and selected metabolites were measured on arterialised venous blood at rest prior to exercise and during the post-exercise period. Plasma urea concentration and urine total acidity were measured on each day of the experiment. Exercise time to exhaustion was longer after the normal (p<0.05) and high (p<0.01) CHO diets compared with the low CHO diet. Pre-exercise plasma bicarbonate concentration and blood were higher after the high CHO diet when compared with the normal (p=0.05, p<0.05 respectively) and low CHO conditions (p<0.05, p<0.05 respectively). Pre-exercise bicarbonate was also higher after the normal CHO diet when compared with the low CHO diet (p<0.05). Mean dietary acid intake for each 3 day period of dietary variation and plasma urea immediately prior to exercise were lower after the high CHO diet when compared to both normal (p<0.01, p<0.01) and low (p<0.01, p<0.001) CHO diets. They were also lower (p<0.01, p<0.01) after the normal when compared with the low CHO diet. Urine total acidity was higher after the low CHO diet when compared with both the normal (p<0.01) and high CHO (p<0.01) diets and near significance was found (p<0.06) when comparing the normal and high CHO diets. The present exsuggests that dietary variation alone can significantly affect the acid-base balance of the blood and may thereby influence endurance time during high intensity exercise.     

The effects of high intensity training upon respiratory gas exchanges during fixed term maximal incremental exercise in man

Summary The response of respiratory gas exchanges to a 6 week high intensity training program was examined in 5 healthy males during fixed term maximal incremental treadmill exercise. Training was performed 3 d·wk^–1 and consisted of a progressive series of repeated 15 sec and 30 sec maximal runs, and weight training exercises for the leg extensor muscles. Respiratory gases during the tests were continuously monitored using an on-line system. Muscle biopsy samples were obtained from the m. vastus lateralis before and after training for histochemical determination of fibre distribution based on myosin ATP-ase activity, and fibre cross-sectional area based on NADH-Tetrazolium Reductase activity. Training significantly increased the proportion of type IIa fibres (+5.9±2.0%,p<0.001) and decreased type I fibres (–6.3±2.0%,p<0.001), the distribution of type IIb fibres remained unchanged (+0.4±0.9%). Muscle cross-sectional area also showed a significant increase after training in type I (+ 318±215 m²,p<0.05), IIa (+652±207 m²,p<0.001) and IIb (+773±196 m²,p< 0.001) fibres. During fixed term maximal incremental exercise the mean carbon dioxide output ( ) and mean respiratory exchange ratio ( ) were significantly increased (p<0.01) after training. The R-time relationship was at all times shifted to the left after training, being significantly (p<0.01) so over the final five min of exercise. No changes in mean exercise oxygen uptake ( ), maximum oxygen uptake ( ) and maximum heart rate (FHR_max) were observed between tests. These results indicate that high intensity training can significantly affect respiratory exchange during fixed term progressive exercise.     

Endurance training increases skeletal muscle lactate transport

Lactate accumulation in skeletal muscle is reduced after a period of endurance training. Explanations for this phenomena include the increased oxidative capacity of the muscle, a reduction in lactate production, and increased lactate clearance. Muscle membrane transport of lactate can be seen to be a fundamental aspect of such clearance, and transmembrane lactate flux may well be an important aspect of the training response in skeletal muscle. Therefore, the lactate transport capacity in skeletal muscle sarcolemmal membranes in endurance-trained and sedentary rats was investigated. Training consisted of 6 weeks of progressively increased treadmill exercise. Twenty-four hours before being killed, both the trained and sedentary animals completed a brief exercise bout. Studies of lactate transport (zero-trans) were conducted using highly purified sarcolemmal vesicles. When low concentrations of L-lactate (1 mm) were used a 59.4% increase in lactate transport was observed (P < 0.05). However, when a high concentration of lactate (50 mm) was used no change in lactate transport was found (P > 0.05). Several interpretations are possible for these observations: (1) that there is an alteration in the K_m but not the V_max of the lactate transport system in skeletal muscle membranes; and (2) that specific changes occur in selected isoforms of the lactate transport protein which may co-exist in 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.     

Sex difference in plasma ammonia but not in muscle inosine monophosphate accumulation following sprint exercise in humans

Since accumulation of ammonia in plasma has been shown to be lower in females than in males following sprint exercise, we hypothesised that muscle inosine monophosphate (IMP) accumulation would also be smaller in females, especially in type II fibres. A relationship between plasma ammonia and muscle IMP accumulation was expected, since ammonia and IMP are formed in equimolar amounts during the net breakdown of adenine nucleotides. The sprint-exercise-induced IMP accumulation, measured in biopsies from vastus lateralis muscle, did not differ between males (n?=?16) and females (n?=?16) either in type I fibres [males 4.6 (SD 3), females 5.7 (SD 2) mmol?·?kg^?1 dry muscle], type II fibres [males 13.2 (SD 4), females 12.6 (SD 4) mmol?·?kg^?1 dry muscle] or in mixed muscle [males 8.4 (SD 3), females 8.2 (SD 3) mmol?·?kg^?1 dry muscle]. The accumulation of plasma ammonia following the sprint was 35% lower in the females than in the males. The inter-individual variation in plasma ammonia accumulation was explained by the sex but not by the muscle IMP accumulation as tested in a multiple regression analysis. In conclusion, the smaller plasma ammonia accumulation following sprint exercise in females than in males would seem not to be explained by a smaller muscle IMP accumulation per unit muscle during sprint exercise.     

Modifications of serum glycoproteins the days following a prolonged physical exercise and the influence of physical training

Summary Eight male subjects (mean age 24.1±2.6 years) performed at intervals of 2 weeks successively a 3 h and two 2 h runs of different running speed. The days following the running there were moderate elevations of C-reactive protein, haptoglobin, alpha-1-acid glycoprotein, coeruloplasmin, transferrin, alpha-1-antitrypsin and plasminogen. There were small or no changes of albumin, alpha-2-macroglobulin and hemopexin. The elevations of the acute phase reactants were examined in three male subjects following a 2 h run before and after an endurance training period of 9 weeks. This demonstrated a decreased acute phase response after training as illustrated by the changes of C-reactive protein, haptoglobin and alpha-1-acid glycoprotein in spite of higher posttraining running speeds. Well-trained athletes have elevated levels of the serum protease inhibitors alpha-1-antitrypsin, alpha-2-macroglobulin and C₁-inhibitor. These antiproteolytic glycoproteins might limit exercise-induced inflammatory reactions.This research was supported by the Bundesinstitut für Sportwissenschaften (Köln-Lövenich)