The effect of moderate altitude on post-exercise blood lactate

Summary Post-exercise blood lactate levels were studied after a short exhaustive bicycle ride in 3 males at sea level control, at altitude (2300 m) and on return to sea level. The short exhaustive bicycle ride was performed at a work rate of 2730 kpm · min^–1 and ride times ranged from 55 to 105 sec. Compared to sea level controls, performance time of the tests at altitude were of similar intensity and duration. Although the changes were small, the oxygen uptakes during the ride and oxygen debts following the rides increased with each test. However, in comparison with sea level controls the blood lactate concentrations were reduced. The reduction on the average reached 44% after 4 days at altitude, and 51% after 22 days at altitude. This reduction in blood lactate concentration of the same subject at altitude as compared with his sea level values may indicate a decrease in the activity of the glycolytic pathway relative to the activity of the aerobic pathway. This appears to be a contradiction to what would be expected in the mild hypoxic conditions present at altitude.Work done while at the University of Michigan, Ann Arbor, Michigan.This study was supported in part by a grant from the Fitness and Amateur Sport Directorate, Ottawa, Canada.     

Benefits of training at moderate altitude versus sea level training in amateur runners

After more than 25 years of research on altitude training (AT) there is no consensus regarding either the training programme at altitude or the effects of AT on performance at sea level. Based on a review of the research work on AT, we investigated combined base training and interval training at moderate altitude and compared immediate and delayed effects on sea level performance with those following similar sea level training (SLT). The altitude group (AG, 10 male amateur runners) trained at 2315 m (natural altitude) and the sea level group (SLG, 12 male amateur runners) at 187 m. Both groups performed 7 days of base training (running on a trail) lasting between 60 and 90 min a day and 5 days of interval training (speed and hill runs) for between 10 and 45 min a day. Incremental exercise tests were performed 1 week before (t ₁), 3 days after (t ₂) and 16 days after (t ₃) the 12-day main training period. Within AG, exercise performance improved fromt ₁ tot ₂ by 8% (P<0.05) and fromt ₂ tot ₃ by 8% (P<0.05). Maximum oxygen uptake ( ) increased fromt ₂ tot ₃ by 10% (P<0.05). Within SLG exercise performance increased fromt ₂ tot ₃ by 8% (P<0.05). Att ₃, relative and absolute in AG were significantly higher in comparison with SLG (P=0.005 andP=0.046 respectively). The improved performance 3 days after AT may be explained in part by an increased oxygen uptake at submaximal exercise intensities without a change in . Further enhancement in performance 2 weeks after AT, however, seems to have been due to the clearly enhanced . Progressive cardiovascular adjustments might have contributed primarily to the time-dependent improvements observed after AT, possibly by an enhanced stroke volume overcompensating the reduced heart rates during submaximal exercise. In conclusion, our findings would suggest that training at a moderate natural altitude improves performance at sea level more than SLT. Combining base and interval training with regulation of intensity by training at constant heart rates during acclimatization at altitude would seem to be a successful training regimen for amateur runners. Most beneficial effects became apparent during the subsequent SLT around 2 weeks after return from altitude. Therefore, we are convinced that AT should be reconsidered as a potent tool for enhancing aerobic capacity, at least in non-elite athletes.     

Further increase in high density lipoprotein in trained males after enhanced training

Summary Eight well-trained males were studied before, during and after 6 months of a progressively increased amount of endurance training in order to elucidate the effects on the apoproteins and apo-lipoproteins. Initially high HDL-cholesterol levels were revealed (1.62±0.15 mmol×l^–1, mean ± SE.). After a transient but not significant, slight decline at the onset of the increased training program (1.57±0.06 mmol×l^–1) HDL-cholesterol increased gradually to the end of the training period (1.92±0.12 mmol×l^–1). There was an increased aerobic capacity as judged by maximal oxygen uptake and by lactate concentration during standardized submaximal work. However, at the end of the training period, a levelling off in maximal oxygen uptake was revealed, while HDL-cholesterol was still increasing. The present data demonstrate that HDL can be influenced by training at all levels of aerobic capacity.     

Blood lactate production and recovery from anaerobic exercise in trained and untrained boys

Summary Blood lactate production and recovery from anaerobic exercise were investigated in 19 trained (AG) and 6 untrained (CG) prepubescent boys. The exercises comprised 3 maximal test performances; 2 bicycle ergometer tests of different durations (15 s and 60 s), and running on a treadmill for 23.20±2.61 min to measure maximal oxygen uptake. Blood samples were taken from the fingertip to determine lactate concentrations and from the antecubital vein to determine serum testosterone. Muscle biopsies were obtained from vastus lateralis. Recovery was passive (seated) following the 60 s test but that following the treadmill run was initially active (10 min), and then passive. Peak blood lactate was highest following the 60 s test (AG, 13.1±2.6 mmol·l^–1 and CG, 12.8±2.3 mmol·l^–1). Following the 15 s test and the treadmill run, peak lactate values were 68.7 and 60.6% of the 60 s value respectively. Blood lactate production was greater (p<0.001) during the 15s test (0.470±0.128 mmol·l^–1·s^–1) than during the 60s test (0.184±0.042 mmol·l^–1·s^–1). Although blood lactate production was only nonsignificantly greater in AG, the amount of anaerobic work in the short tests was markedly greater (p<0.05-0.01) in AG than CG. Muscle fibre area (type II%) and serum testosterone were positively correlated (p<0.05) with blood lactate production in both short tests. Blood lactate elimination was greater (p<0.001) at the end of the active recovery phase than in the next (passive) phase. It is concluded that blood lactate production in prepubescent boys is related to serum testosterone level and muscle type II fibre area, indicating the role of maturation and training. Submaximal exercise is likely to increase blood lactate removal during recovery.     

Serum hormones and physical performance capacity in young boy athletes during a 1-year training period

Summary Serum hormones and physical performance capacity in boy athletes (AG;n = 19) were investigated during a 1-year training period (between the ages of 11.6 and 12.6 years). Six young untrained boys served as the control group (CG). The mean serum testosterone concentration increased significantly in AG (P<0.05) following the training period from 2.92 nmol·l^–1, SD 1.04 to 5.81 nmol·l^–1, SD 1.33. Significant differences were not observed in the cortisol, sex hormone binding globulin and growth hormone levels during the follow-up period. The AG clearly increased speed (P<0.001), speed-strength (P<0.01-P<0.001) and anaerobic capacity (P<0.001) whereas CG had only slight increases (NS) in physical performance capacity during a 1-year period. During the last 6-month training period significant positive correlations (r=0.490–0.58;P<0.05 -P<0.01) were observed in AG between the relative changes in testosterone, testosterone: cortisol ratio and growth hormone and the relative performance change in speed, maximal isometric force and endurance, respectively. At the end of the period significant positive correlations were observed in all subjects between the level of testosterone and speed-strength (r=0.52–0.64;P<0.01 -P<0.001) and anaerobic capacity (r=0.49;P<0.05). It was concluded that an increase in anabolic activity with the synchronous training already has positive effects on trainability and physical performance capacity at an early stage in puberty.     

Effects of chronic hypoxia and endurance training on muscle capillarity in rats

Skeletal muscle capillarity expressed as capillary density (CD), and number of capillaries per fibre (C/F), as well as the mean fibre cross-sectional area (FCSA), were determined in the extensor digitorum longus (EDL), plantaris (PLA) and soleus (SOL) muscles of four groups of eight rodents trained on a swimming exercise programme (T) or maintained sedentary (S), at sea level (SL) or at simulated altitude (HA), barometric pressure 61.7 kPa (463 torr) for 12 weeks. It was shown that both HA exposure and endurance training decreased body and skeletal muscles weights (P<0.001). However, neither HA exposure nor endurance training induce any variation in relative importance in the skeletal muscle mass. Altitude exposure and endurance training had increasing effects on CD in all muscles studied (P<0.001). This study confirms the fact that altitude exposure has no direct effect on capillary development. On the other hand, the capillary supply of the several slow- and fast- twitch skeletal muscles studied is increased by endurance training. This real enhancement in capillary network is ascertained by an increase in the C/F ratio (+7%, +26%, +16%, in PLA, EDL, and SOL muscles, respectively at sea level, and +19.5%, +30%, and +14% respectively at HA). These results indicate that the effects of chronic exercise on skeletal muscle capillarity estimated by the C/F ratio, are greater in an hypobaric environment than in a SL environment.     

Effects of 8 weeks' endurance training on skeletal muscle metabolism in 56–70-year-old sedentary men

Summary The effects of 8 weeks' endurance training on muscle metabolism at rest and after a submaximal bicycle ergometer exercise were studied in 31 previously sedentary men, aged 56–70. Training consisted of 3–5 one hour exercise bouts per week including walking-jogging, swimming, gymnastics and ball games. The effects of training were similar to those previously reported for younger men. Mean maximal oxygen uptake increased (11%), as did the resting values for muscle glycogen concentration, the enzymes representing aerobic energy metabolism (malate dehydrogenase, succinate dehydrogenase), and also some of the anaerobic enzymes (creatine phosphokinase, lactate dehydrogenase). Lactate production during submaximal work decreased. The enzyme activities were lower following acute exercise both before and after training.     

Beneficial effects of exercising at moderate altitude on red cell oxygen transport and on exercise performance

The effect of a ascent to moderate altitude (2,300 m) and altitude training on the O₂-transport properties of Hb and their possible consequences on tissue oxygenation during exercise were studied on six control and six training subjects. A rapid increase in P-50 values (+2.4 mm Hg, 0.32 kPa) was measured within one day after ascent. At the end of the stay at altitude (13th day) P-50 values were higher in subjects performing training than in controls. At altitude a slow but constant increase in 2,3-DPG, pyruvate kinase activity and reticulocyte count was found, which was more pronounced in training subjects as compared to controls. Ascent to altitude resulted in a decreased maximal performance capacity (–9%), but both groups recovered during the stay. In training subjects maximal exercise performance was increased after descent. Exercise at altitude was performed at a lower heart rate (controls: –10/min; training: –18/min) and at a lower lactate concentration (–4 mmol/l). These data indicate a positive effect of adaptation to altitude on exercise performance. Training itself shifts the ODC to the right and adds this effect to the effects of passive altitude adaptation on the O₂-binding properties of hemoglobin.Parts of this study have been presented at the ISOTT meeting in Nijmegen, The Netherlands, 1984     

Increased left ventricular muscle mass after long-term altitude training in athletes

The effects of long-term altitude training on altitude and sea-level physiological characteristics in elite endurance athletes were investigated. Seven Swedish elite cross-country skiers (five men, two women; mean age 27 years) spent 1 month training at 1900 m above sea level in Italy. Rollerski treadmill tests were performed before and 5 and 11 days after the altitude sojourn; three tests were also performed at altitude. Before and 1, 11 and 35 days after the altitude camp, echocardiographic and blood volume measurements were performed. The heart rates at both maximal (P < 0.05) and submaximal (P < 0.01) work loads were decreased by 5–9 beats min^?1 at altitude. The haemoglobin concentration and haematocrit increased quickly at altitude with a corresponding decrease on return to sea level. The blood volume (7%) and total haemoglobin (3%) tended to be higher day 11 post-altitude (NS). There were no significant changes in diastolic internal diameter or wall thickness of the left ventricle, but the calculated cardiac left ventricular muscle mass was increased post-altitude (9–10%, P < 0.01). The maximal oxygen uptake increased in six of the seven skiers after the altitude training (day 11, mean 3%, NS). In conclusion, training at moderate altitude may cause a reduction in heart rates during exercise. Moreover, after long-term training at altitude, there may be an increase in the cardiac left ventricular muscle mass.     

Effect of various types of acute exercise and exercise training on the insulin sensitivity of rat soleus muscle measured in vitro

Effects of acute exercise varying in duration and intensity, as well as of two training regimes (endurance and sprint training) on the sensitivity of the soleus muscle of rat to insulin was measured in vitro and compared in rats. As an index of the muscle insulin sensitivity the hormone concentration in the incubation medium which would produce half maximum stimulation of lactate production (LA) and glycogen synthesis was determined. A single bout of moderate endurance exercise (60 min treadmill running at 20 m×min^–1, 0° inclination) increased the rate of LA production at the hormone concentrations used and increased the sensitivity of the process to insulin at 0.25 and 2 h but not 24 h after termination of exercise. Similar though less pronounced effects were found after heavy endurance exercise (30 min at 25 m×min^–1, 10°), but sprint exercise (6×10 s bouts at 43 m×min^–1, 0°) had no influence on the insulin sensitivity of the soleus muscle. The rate of glycogen synthesis in vitro was accelerated after endurance exercise, but the sensitivity of this process to insulin was unaffected by the preceding exercise. Endurance training for 5 weeks caused marked enhancement of sensitivity of both LA production and glycogen synthesis to insulin, which persisted for at least 48 h after the last training session. No changes in the soleus muscle sensitivity to insulin were found after sprint training. It is concluded that the increased insulin sensitivity of glucose utilization by skeletal muscle which occurs after endurance exercise and particularly during endurance training can substantially contribute to improved carbohydrate tolerance. Sprint exercise does not produce any changes in muscle insulin sensitivity, at least in the soleus muscle of the rat.Dedicated to the late Professor Stanislaw Kozlowski     

The effect of ski training at altitude and racing on pituitary,adrenal and testicular function in men

Summary The effect of similar prolonged exercise on hormonal changes was studied at sea level and at moderate altitude. Four cross-country skiers participated in a 30-km race and five biathlonists in a 20-km race at sea level in Finland and during altitude training and racing at 1650 m in Les Saisies, France. Venous blood samples were taken at both altitudes before the race between 0800 and 0900 hours and 25–35 min after the race. Resting blood samples were also taken before and after the altitude training and the period of racing. Serum testosterone concentration was higher before the race at altitude than at sea level (19%, P<0.02), and 30 min after the race growth hormone (GH) concentration was higher at sea level than at moderate altitude (P<0.002). There were not significant differences in serum luteinising hormone between the altitudes. Serum cortisol concentration was higher after the altitude training and the period of racing than before (P<0.02) but no difference was observed in testosterone. We concluded, that since the profiles of the anabolic-catabolic hormone concentrations measured are indicators of the performance level of athletes, our data indicated that to follow them during altitude training could be beneficial in optimizing training programme for individual athletes. We also concluded, that the lower GH concentration after racing at moderate altitude may have been a consequence of decreased racing speed and/or increased physical performance.     

Muscle Metabolism and Enzyme Activities after Training in Boys 11–13 Years Old

The effect of training on the skeletal muscle metabolism of 11-to 13-year-old boys was examined. In one experiment changes in blood lactate, and muscle lactate, CP, ATP, and glycogen were determined at rest and following exercise before and after 4 months of training. The concentrations of glycogen, CP and ATP at rest were higher (P<0.01) following training. Blood and muscle lactate were 23 and 56 % higher after maximal work following training. A greater reduction in muscle glycogen occurred during maximal work after training but the pattern for ATP and CP depletion was unchanged. In a second experiment boys trained by pedalling a bicycle ergometer an average of 30 min 3 times a week for 6 weeks. Biopsy samples of the vastus lateralis were examined for oxidative (succinate dehydrogenase) and anaerobic (phosphofructokinase) capacity before and after training. The fiber composition and relative oxidative capacity in the fibers was determined histochemically. Succinate dehydrogenase and phosphofructokinase activities increased 30 and 83 %, respectively, following training. Fiber distribution was unchanged by training but the oxidative capacity of both fiber types appeared to increase.     

The respiratory system as an exercise limiting factor in normal sedentary subjects

Summary The present study was undertaken to investigate the respiratory system as an exercise limiting factor. Breathing and cycle endurance (i.e. the time until exhaustion at a given performance level) as well as physical working capacity 170 (i.e. the exercise intensity corresponding to a heart rate of 170 beats -min^–1 on a cycle ergometer) were determined in four healthy sedentary subjects. Subsequently, the subjects trained their respiratory system for 4 weeks by breathing daily about 901 · min^–1 for 30 min. Otherwise they continued their sedentary lifestyle. Immediately after the respiratory training and 18 months later, all performance tests carried out at the beginning of the study were repeated. The respiratory training increased breathing endurance from 4.2 (SD 1.9) min to 15.3 (SD 3.8) min. Cycle endurance was improved from 26.8 (SD 5.9) min to 40.2 (SD 9.2) min whereas physical working capacity 170 remained essentially the same. During the endurance cycling test in the respiratory untrained state, the subjects continuously increased their ventilation up to hyperventilation [ventilation at exhaustion = 96.9 (SD 23.6) 1 · min^–1] while after the respiratory training they reached a respiratory steady-state without hyperventilation [ventilation at exhaustion = 63.3 (SD 14.5) 1 · min^–1]. The absence of this marked hyperventilation was the cause of the impressive increase of cycle endurance in normal sedentary subjects after respiratory training. The effects gained by the respiratory training were completely lost after 18 months. Our results indicated that the respiratory system was an exercise limiting factor during an endurance test in normal sedentary subjects.     

The lactate paradox revisited in lowlanders during acclimatization to 4100 m and in high-altitude natives

Chronic hypoxia has been proposed to induce a closer coupling in human skeletal muscle between ATP utilization and production in both lowlanders (LN) acclimatizing to high altitude and high-altitude natives (HAN), linked with an improved match between pyruvate availability and its use in mitochondrial respiration. This should result in less lactate being formed during exercise in spite of the hypoxaemia. To test this hypothesis six LN (22–31 years old) were studied during 15 min warm up followed by an incremental bicycle exercise to exhaustion at sea level, during acute hypoxia and after 2 and 8 weeks at 4100 m above sea level (El Alto, Bolivia). In addition, eight HAN (26–37 years old) were studied with a similar exercise protocol at altitude. The leg net lactate release, and the arterial and muscle lactate concentrations were elevated during the exercise in LN in acute hypoxia and remained at this higher level during the acclimatization period. HAN had similar high values; however, at the moment of exhaustion their muscle lactate, ADP and IMP content and Cr/PCr ratio were higher than in LN. In conclusion, sea-level residents in the course of acclimatization to high altitude did not exhibit a reduced capacity for the active muscle to produce lactate. Thus, the lactate paradox concept could not be demonstrated. High-altitude natives from the Andes actually exhibit a higher anaerobic energy production than lowlanders after 8 weeks of acclimatization reflected by an increased muscle lactate accumulation and enhanced adenine nucleotide breakdown.     

Effects of endurance training at high altitude on diaphragm muscle properties

The biochemical, histochemical, and structural changes induced by endurance training and long-term exposure to high altitude were studied in the diaphragm muscle of rats exposed to simulated altitude (HA: n = 16; P _b = 62 kPa, 463 Torr; 4000 m) and compared to animals maintained at sea-level (SL: n = 16). Half of the animals in each group were trained (T) by swimming for 12 weeks, the other half were kept sedentary (S). Except for a small decrease in type I fibres in the HA-S group (–7%, P<0.05), in favour of type IIab and type IIb fibres, neither high-altitude exposure nor endurance training had an overall effect on fibre type distribution. The mean fibre cross-sectional area was found to be unaffected by altitude and/or chronic exercise. Capillary density was shown to be increased by both high-altitude exposure (P<0.02) and training (P<0.001), whereas capillary growth, estimated by the capillary/fibre ratio, was unaffected in both cases. Following endurance training, a modest increase in citrate synthase was shown to occur to the same extent in the HA-T and SL-T groups (+15% and + 16% respectively, NS). Hexokinase increased following training (P<0.05) and high-altitude exposure (P<0.001). In normoxic and hypoxic animals, endurance training enhanced the ratio of the heart-specific lactate dehydrogenase isozyme LDH1 to total LDH activity (+59%, P<0.01; +92%, P<0.05 respectively). It may be hypothesized that the increased glucose phosphorylation capacity observed in diaphragm muscle contributes to the reduction of glycogen utilization during exercise.     

Uniqueness of interval and continuous training at the same maintained exercise intensity

Summary The present study sought to evaluate the inconsistencies previously observed regarding the predominance of continuous or interval training for improving fitness. The experimental design initially equated and subsequently maintained the same relative exercise intensity by both groups throughout the program. Twelve subjects were equally divided into continuous (CT, exercise at 50% maximal work) or interval (IT, 30 s work, 30 s rest at 100% maximal work) training groups that cycled 30 min day^–1, 3 days week^–1, for 8 weeks. Following training, aerobic power (VO_2max), exercising work rates, and peak power output were all higher (9–16%) after IT than after CT (5–7%). Vastus lateralis muscle citrate synthase activity increased 25% after CT but not after IT. A consistent increase in adenylate kinase activity (25%) was observed only after IT. During continuous cycling testing the CT group had reduced blood lactate (1a_b) levels and respiratory quotient at both the same absolute and relative (70% VO_2max) work rates after training, while the IT group displayed similar changes only at the same absolute work rates. By contrast, both groups responded similarly during intermittent cycling testing with lower 1a_b concentrations seen only at absolute work rates. These results show that, of the two types of training programs currently employed, IT produces higher increases in VO_2max and in maximal exercise capacity. Nevertheless, CT is more effective at increasing muscle oxidative capacity and delaying the accumulation of 1a_b during continuous exercise.     

The effect of training on responses of Β-endorphin and other pituitary hormones to insulin-induced hypoglycemia

Summary We studied whether the previously reported intensified -endorphin response to exercise after training might result from a training-induced general increase in anterior pituitary secretory capacity. Identical hypoglycemia was induced by insulin infusion in 7 untrained (Skeletal muscle enzyme activity, fiber composition and in relation to distance running performance 49±4 ml · (kg · min)^–1, mean and SE) and 8 physically trained (Skeletal muscle enzyme activity, fiber composition and in relation to distance running performance 65±4 ml · (kg · min)^–1) subjects. In response to hypoglycemia, levels of -endorphin and prolactin immunoreactivity in serum increased similarly in trained (from 41±2 pg · ml^–1 and 6±1 pg · ml^–1 before hypoglycemia to 103±11 pg · ml^–1 and 43±9 pg · ml^–1 during recovery, P<0.05) and untrained (from 35±7 pg · ml^–1 and 7±2 pg · ml^–1 to 113±18 pg · ml^–1 and 31±8 pg · ml^–1 P<0.05) subjects. Growth hormone (GH) was higher 90 min after glucose nadir in trained (61±13 mU · l^–1) than in untrained (25±6 mU · l^–1) subjects (P<0.05). Levels of thyrotropin (TSH) changed in neither of the groups. It is concluded that, in contrast to what has been formerly proposed, training does not result in a general increase in secretory capacity of the anterior pituitary gland. TSH responds to hypoglycemia neither in trained nor in untrained subjects. Finally, differences in -endorphin responses to exercise between trained and untrained subjects cannot be ascribed to differences in responsiveness to hypoglycemia.     

Diurnal variations of serum erythropoietin at sea level and altitude

This study tested the hypothesis that the diurnal variations of serum-erythropoietin concentration (serum-EPO) observed in normoxia also exist in hypoxia. The study also attempted to investigate the regulation of EPO production during sustained hypoxia. Nine subjects were investigated at sea level and during 4 days at an altitude of 4350 m. Median sea level serum-EPO concentration was 6 (range 6–13) U·l^–1. Serum-EPO concentration increased after 18 and 42 h at altitude, [58 (range 39–240) and 54 (range 36–340) U·l^–1, respectively], and then decreased after 64 and 88 h at altitude [34 (range 18–290) and 31 (range 17–104) U·l^–1, respectively]. These changes of serum-EPO concentration were correlated to the changes in arterial blood oxygen saturation (r = –0.60,P = 0.0009), pH (r = 0.67,P = 0.003), and in-vivo venous blood oxygen half saturation tension (r = –0.68,P = 0.004) but not to the changes in 2, 3 diphosphoglycerate. After 64 h at altitude, six of the nine subjects had down-regulated their serum-EPO concentrations so that median values were three times above those at sea level. These six subjects had significant diurnal variations of serum-EPO concentration at sea level; the nadir occurred between 0800–1600 hours [6 (range 4–13) U·l^–1], and peak concentrations occurred at 0400 hours [9 (range 8–14) U·l^–1,P = 0.02]. After 64 h at altitude, the subjects had significant diurnal variations of serum-EPO concentration; the nadir occurred at 1600 hours [20 (range 16–26) U·l^–1], and peak concentrations occurred at 0400 hours [31 (range 20–38) U·l^–1,P = 0.02]. This study demonstrated diurnal variations of serum-EPO concentration in normoxia and hypoxia, with comparable time courses of median values. The results also suggested that EPO production at altitude is influenced by changes in pH and haemoglobin oxygen affinity.     

Buffer capacity and lactate accumulation in skeletal muscle of trained and untrained men

Buffer capacity (β) of skeletal muscle has been determined in trained (n=7) and in sedentary subjects (n=8). The trained subjects were active in ball games where a high degree of anaerobic energy utilization is required. Percentage fibre type occurrence in the thigh muscle was not significantly different in the two groups. However, there was a tendency towards a higher proportion of type I (slow-twitch) fibres (61.5±11.6% vs. 50.2±12.5%) and a lower proportion of type IIB fibres (2.1±3.5% vs 14.1±16.3%) in the trained subjects. The proportion of the cross-sectional area of the muscle biopsies that was made up of type I or type II fibres was not different in the two groups. All subjects performed an isometric contraction of the knee extensors to fatigue at 61% of their maximal voluntary contraction force. Muscle biopsies were taken from the quadriceps femoris muscle at rest and immediately after contraction. The buffer capacity of muscle was calculated from: β= (Muscle lactate (work)-Muscle lactate (rest))/(Muscle pH (rest) -Muscle pH (work)). A higher buffer capacity (p<0.05) was observed in the trained subjects (β=194±30 mmolxpH^-1xkg^-1 dry wt.) compared to the sedentary group (β=164±20) (mean±SD). An unexpected finding was that muscle lactate after contraction to fatigue was lower (30%, p<0.01) and muscle pH was higher (6.80±0.06 vs. 6.61±0.12, p<0.01) in the trained subjects than in the sedentary controls. Creatine phosphate stores were almost completely depleted in both groups. Post-exercise lactate values were related to the proportion of type II fibres in the muscle (p<0.01). There was, however, no statistical correlation betwe β and fibre type occurrence (p>0.05). In summary, the present results indicate that skeletal muscle buffer capacity can be changed by training in man. Furthermore, it is concluded that the lower lactate accumulation and pH decline after an isometric contraction to fatigue that was observed in the trained compared to the sedentary subjects is related to the training per se. However, the tendency towards a lower type I (slowtwitch) fibre percentage in the trained subjects is likely to have contributed to the observed differences.     

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

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