Changes in adrenal and testicular activity monitored by salivary sampling in males throughout marathon runs

Summary Measurement of cortisol and testosterone in saliva samples provided by marathon runners at 6.4 km (4-mile) intervals has been used for monitoring acute changes in adrenal and testicular activity, and the changes compared with mean values in timed samples on five rest days.The collection of mixed whole saliva was well accepted; the missed sample rate in the 8 runners in the Cardiff marathon was less than 10%. On rest days, salivary cortisol and testosterone were within the normal male range and showed a circadian rhythm; mean values at 08.00 h (23.5 nmol L^–1; 258 pmol L^–1 p<0.001, p<0.001 respectively) were higher than at 22.00 h (2.8 nmol L^–1; 130 pmol L^–1). In samples collected at 09.00 h, immediately prior to the Cardiff marathon, cortisol (25.1 nmol L^–1) and testosterone (304 pmol L^–1) were higher than the mean values (14.9 nmol L^–1; 209 pmol L^–1) on non-run days. Concentrations of both steroids increased during the marathon; testosterone peaked (442 pmol L^–1) at 21 miles, whereas cortisol continued to increase, being maximal (87.9 nmol L^–1) at 30 min after completion of the run. Four of the runners in the Cardiff marathon also participated in the Bristol marathon and the changing patterns in salivary hormones were strictly comparable.Salivary sampling would appear to be of value in monitoring acute and rhythmic changes in endocrine function in marathon runners. The temporal relationship between changes in salivary cortisol and testosterone are consistent with direct inhibition of testicular secretion by high cortisol concentrations.     

The inhibiting effect of atropine on growth hormone release during exercise

Summary The effects of atropine upon changes in the circulating levels of growth hormone (GH), cortisol, lactate, glucose, and free fatty acids (FFA) were studied during exercise using both constant and progressively increasing work loads. At low work loads, atropine had no effect upon the changes in either cortisol or lactate levels, but the normal exercise-induced rise in GH was abolished or markedly reduced. At higher work loads, especially when prolonged, the usual rises in cortisol and lactate were enhanced by atropine, but the rise in GH was diminished and delayed. In no circumstances were the changes in FFA or glucose significantly affected by atropine.We regard the effect of atropine upon changes in cortisol and lactate responses as secondary to its cardiovascular effect, but suggest that the inhibition of GH release may be evidence of a cholinergic mechanism in the control of GH release during exercise.     

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.     

Glucoregulatory hormones in man at high altitude

Summary Concentrations of glucose, lactic acid, free fatty acid (FFA), insulin, cortisol and growth hormone (GH) in the blood were monitored in 15 euglycaemic men (sojourners, SJ) at sea level (SL) and while at altitudes of 3500 m and 5080 m, in acclimatised low landers (ALL) and in high altitude natives (HAN). In SJ, blood glucose and insulin concentrations showed a significant increase on the 3rd and 7th day after arrival at high altitude (HA), thereafter returning to sea level values and remaining the same during the entire period of their stay at 3500 m. Subsequently, on arrival at higher altitude (5080 m) the glucose concentrations again showed an increase over the preceding values and returned to SL values on day 41 while at 5080 m. A significant increase in cortisol concentrations was seen on day 3 after arrival at HA and the increased levels were maintained until day 21 at 3500 m. The cortisol concentrations on day 30 after arrival at 5080 m came down to SL values and remained unchanged thereafter. No appreciable change in GH and FFA was seen during the sojourn at HA. On the other hand, blood lactic acid concentration decreased significantly. There was no difference between the fasting glucose concentrations in ALL at 3500 m and in HAN at 3500 m and 4200 m compared to values of SJ at SL, whereas ALL at 4200 m had higher glucose values. Concentrations of plasma insulin and GH in ALL and HAN were higher than the values of SJ at SL, whereas cortisol values did not show any difference. These observations indicated that at HA the glucose values were high for the insulin concentration observed and might have been due to increased secretion of GH by the pituitary gland.     

Influence of prolonged continuous exercise on hormone responses to subsequent exercise in humans

This study examined the possibility that fatigue may modify the hormone responses to exercise. A group of 12 endurance trained athletes ran for 2 h (blood lactate concentrations of approximately 2 mmol·l^–1) in order to induce fatigue. The subjects exercised for 10 min at 70% maximal oxygen uptake before (1st test) and after (2nd test) the 2 h run to assess hormone responsiveness. A 1 min anaerobic power test was performed to assess muscle power. Cortisol, growth hormone, testosterone and insulin concentrations were determined before and after the 1st and 2nd tests. The 1st test resulted in increases in concentrations (P<0.05) of cortisol and growth hormone, a decrease in insulin concentration (P<0.01) and no change in testosterone concentration. The 2 h run caused decreases of insulin, increases of growth hormone concentration and variable responses in the concentrations of cortisol and testosterone. The 2nd test decreased insulin concentration further (P<0.05), but responses of the concentrations of testosterone, growth hormone and cortisol were variable. In 6 subjects (group A) cortisol displayed an increase [mean (SD)] from baseline concentrations [+304.0 (60.0) nmol·l^–1], while in the other 6 subjects (group B) a decrease or no change was seen [+3.1 (5.3) nmol·l^–1 ,between groups, P<0.05]. Growth hormone concentration was substantially higher in group A [+14.7 (4.8) ng·ml^–1] than group B [+6.0 (2.9) ng·ml^–1] following the 2nd test. In group A anaerobic muscle power was higher, while in group B it was lower, after the 2 h run than before the 2 h run (P<0.05). The findings suggest that fatigue from prolonged endurance activity may introduce a resetting in the pituitary-adrenocortical component of the endocrine system, expressed either by intensified or by suppressed endocrine functions. Electronic Publication     

Hormonal responses to three training protocols in rowing

The aim of this study was to examine the acute responses of serum growth hormone, testosterone, and cortisol to three training protocols in rowing. Six young rowers, members of the national team, carried out three frequently used protocols in rowing, i.e., an endurance, a moderate interval, and a resistance protocol, on separate days in a counterbalanced design. Blood samples were collected before, immediately after, and 4 h after exercise for the determination of growth hormone, testosterone, cortisol, and creatine kinase. All three protocols caused marked increases in growth hormone, the most spectacular being that immediately after the endurance protocol. The change in testosterone concentration immediately after the endurance protocol was significantly higher than the changes after the other two protocols. Cortisol concentration was significantly higher immediately after the endurance protocol than after the other two protocols, but remained relatively low in all cases, suggesting that these protocols did not considerably promote catabolism in muscle tissue. Based on these data, endurance training caused greater responses of the three hormones studied compared to interval or resistance training. In fact, resistance training (at intensities above 85% of 1RM) did not cause any significant changes in the three hormones. We therefore propose that evaluation of training programmes designed for elite athletes should include measurements of hormonal changes in order to ascertain that the programmes do cause the expected adaptations.     

Effect of altitude training on serum creatine kinase activity and serum cortisol concentration in triathletes

In this investigation we evaluated the effect of a 5-week training program at 1860 m on serum creatine kinase (CK) activity and serum cortisol concentration in national-caliber triathletes for the purpose of monitoring the response to training in a hypobaric hypoxic environment. Subjects included 16 junior-level female (n = 8) and male (n = 8) triathletes who were training for the International Triathlon Union (ITU) World Championships. After an initial acclimatization period, training intensity and/or volume were increased progressively during the 5-week altitude training camp. Resting venous blood samples were drawn at 0700 hours following a 12-h overnight fast and were analyzed for serum CK activity and serum cortisol concentration. Subjects were evaluated before [7–10 days pre-altitude (SL 1)] and after [7–10 days post-altitude (SL 2)] the 5-week training camp at 1860 m. At altitude, subjects were evaluated within 24–36 h after arrival (ALT 1), 7 days after arrival (ALT 2), 18 days after arrival (ALT 3), and 24–36 h prior to leaving the altitude training camp (ALT 4). A repeated-measures analysis of variance was used to evaluate differences over time from SL 1 to SL 2. Compared to SL 1, serum CK activity increased approximately threefold (P < 0.05) within the initial 24–36 h at altitude (ALT 1), and increased by an additional 70% (P < 0.05) after the 1st week of altitude training (ALT 2). Serum CK activity remained significantly elevated over the duration of the experimental period compared to pre-altitude baseline levels. Serum cortisol concentration was increased (P < 0.05) at the end of the 5-week altitude training period (ALT 4) relative to SL 1, ALT 1 and ALT 3. These data suggest that: (1) the initial increase in serum CK activity observed in the first 24–36 h at altitude was due primarily to acute altitude exposure and was independent of increased training intensity and/or training volume, (2) the subsequent increases in serum CK activity observed over the duration of the 5-week altitude camp were probably due to the combined effects of altitude exposure and increased training load, and (3) the increase in serum cortisol concentration observed at the end of the altitude training camp reflects the additive effect of 5 weeks of altitude exposure in combination with a progressively increased training intensity and/or volume. Accepted: 5 June 1999     

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.     

The influence of exercise on dental pain thresholds and the release of stress hormones

Different levels of exercise (50-200 W) were produced by a bicycle ergometer. In all six subjects the heart rate and blood pressure were increased with increasing work load. Dental pain thresholds tended to increase with increasing work load, too. Plasma ACTH levels were above the normal range during the whole experiment in all subjects, whereas plasma cortisol and prolactin levels were elevated only in one subject. Growth hormone levels had a tendency to elevation at 200 W. There was no correlation between the release of cortisol, prolactin or ACTH and the dental pain threshold elevation. However, there was significant correlation between the release of growth hormone and the dental pain threshold elevation. The results indicate that physical exercise at submaximal work loads is enough to produce a pain threshold elevation in some subjects, with a minor coactivation of stress mechanisms.     

Influence of training on the response of androgen plasma concentrations to exercise in swimmers

In eight top-level male endurance swimmers the aerobic performance and the response to exercise of total testosterone (T), free testosterone (fT), sex hormone binding globulin (SHBG), non-SHBG-bound testosterone (NST) and cortisol (C) were evaluated during a training season. The swimmers participated in three test sessions which occurred 6, 12 and 24 weeks after the beginning of the season. During each session, after a standard warm-up, the swimmers performed a set of 15 × 200-m freestyle, with a 20-s rest between repetitions, at a predetermined individual speed. Three blood samples were collected: before warm-up, at the end of the set, and after 1 h of recovery. A few days before each session, the individual swimming velocity associated with a 4 mmol · l^–1 blood lactate concentration (₄) was assessed as a standard of aerobic performance. The values of ₄ were lower in the second session than in the third one. The concentrations of C, which increased after the exercise, showed the highest values in the second session. The values of T and the T: SHBG ratio increased after the exercise but returned to their initial concentrations during the recovery period. The values of fT and NST increased after the exercise in the first and third sessions. In the initial two sessions, when the aerobic performance was still low, the concentrations of NST decreased to below the initial values after recovery. In session III, when the adaptation to the training workload was complete, NST returned to resting concentrations after recovery. The results would suggest that stressful stimuli produced by an increase in training volume may induce changes in androgen metabolism during exercise. In this respect, NST would appear to be a better index of metabolic response than T, T/SHBG and fT.     

Moderate endurance training has no effect on the parathyroid function of heart transplant patients

The benefit of retraining for heart transplant recipients (HTR) is now well established. The rehabilitation of these patients can be compromised by osteopenia and bone fractures. The resting levels of parathyroid hormone (PTH) and exercise-induced increases are higher in HTR than in healthy controls. To evaluate the effect of a moderate endurance training programme on parathyroid activity, six HTR, an average of 18 months after transplant, and seven healthy sedentary controls have been studied. None of the subjects had a history of bone disease. Two exercise tests (square wave endurance exercise tests, SWEET) with identical work rates were performed before and after training. Intact PTH, ionized calcium (Ca²⁺), phosphorus (Pi) and pH were measured at rest, during exercise and in the recovery periods. Training consisted of a 45-min SWEET three times a week for 6 weeks. Levels of Ca²⁺, Pi and PTH showed a significant increase during the exercise session in both groups. Ca²⁺ and Pi levels decreased rapidly after the cessation of exercise whereas PTH reached a peak at the 10th min of the recovery in both groups. This increase in PTH was significantly higher in HTR than in controls. However, despite a significant improvement of total endurance work (+28% in HTR, +29% in controls) this endurance training had no effect on resting levels of PTH, plasma Ca²⁺ or Pi, nor on their exercise-induced variations. The exercise-induced decrease in pH was less pronounced after training which is evidence of training. We conclude that a short endurance training programme does not alter the moderate hyperparathyroidism of HTR. The effect of such a training programme on bone mass and bone mineral density needs now to be evaluated. Accepted: 4 February 1997     

The effect of exercise on the production and clearance of testosterone in well trained young men

Summary Tritium-labelled testosterone was infused into four well-trained subjects at rest and during one hour of exercise at about 60% of their maximum aerobic power. This exercise regime led to a mean increase of 27% (range 10–51%) in plasma testosterone concentration. At the same time there were significant decreases in the estimated hepatic plasma flow (EHPF) (45%; range 28–67%), metabolic clearance rate of testosterone (MCR_T) (29%; range 18–37%) and plasma volume (8.2%; range 3–10%). The production rate of testosterone decreased by 10% (range 9–22%) but this was not statistically significant. The ratio MCR_T: EHPF increased in 3 out of 4 subjects in response to exercise but there was considerable inter-subject variation both at rest and during exercise. These findings suggest that the exercise-induced elevation of testosterone level is due solely to the reduction in the rate at which testosterone is cleared from the plasma. The principal cause of the reduction in MCR_T is probably the reduction in EHPF but the variation in the ratio MCR_T: EHPF suggests that changes in the extrahepatic clearance of testosterone may also be involved.     

State, not trait, neuroendocrine function predicts costly reactive aggression in men after social exclusion and inclusion

Social exclusion increases aggressive behaviour, and the possible neuroendocrine underpinnings of the effect are largely unknown. Here, we examined the extent to which testosterone and cortisol responses to social exclusion would predict subsequent reactive aggression. Men were randomly assigned to a social exclusion (SE) or inclusion (SI) condition of ‘Cyberball’, a computer ball-toss game. Aggression was then measured using the Point Subtraction Aggression Paradigm (PSAP). Saliva was collected at three points for the measurement of testosterone and cortisol. Regression analyses indicated that testosterone concentrations 10-min into the PSAP (controlling for pre- and post-Cyberball testosterone) were positively correlated with aggressive behaviour, irrespective of SI/SE. Post hoc analyses for the conditions separately, however, suggested the relationship was stronger for SI men (R²_change = 13.3%, F_1,29 = 5.28, p = 0.03) than for SE men (R²_change = 1.8%, F_1,26 = 0.49, p = 0.49). Aggressive behaviour was also positively correlated with cortisol concentrations 10-min into the PSAP (controlling for pre- and post-Cyberball cortisol) irrespective of SE/SI. When both hormones were included in the regression model, the interaction of baseline ‘Cortisol’ × ‘Testosterone’ × ‘Experimental Group’ approached significance (R²_change = 5.4%, F_1,55 = 3.53, p = 0.07), but no significant effects were observed in either group alone. The findings add to evidence that individual differences in state neuroendocrine function map onto variability in human social behaviour.     

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.     

Effects of heavy resistance training on maximal and explosive force production, endurance and serum hormones in adolescent handball players

To determine the effects of 6-weeks of heavy-resistance training on physical fitness and serum hormone status in adolescents (range 14–16 years old) 19 male handball players were divided into two different groups: a handball training group (NST, n = 10), and a handball and heavy-resistance strength training group (ST, n = 9). A third group of 4 handball goalkeepers of similar age served as a control group (C, n = 4). After the 6-week training period, the ST group showed an improvement in maximal dynamic strength of the leg extensors (12.2%; P < 0.01) and the upper extremity muscles (23%; P < 0.01), while no changes were observed in the NST and C groups. Similar differences were observed in the maximal isometric unilateral leg extension forces. The height of the vertical jump increased in the NST group from 29.5 (SD 4) cm to 31.4 (SD 5) cm (P < 0.05) while no changes were observed in the ST and C groups. A significant increase was observed in the ST group in the velocity of the throwing test [from 71.7 (SD 7) km · h⁻¹ to 74.0 (SD 7) km · h⁻¹; P < 0.001] during the 6-week period while no changes were observed in the NST and C groups. During a submaximal endurance test running at 11 km · h⁻¹, a significant decrease in blood lactate concentration occurred in the NST group [from 3.3 (SD 0.9) mmol · l⁻¹ to 2.4 (SD 0.8) mmol · l⁻¹; P < 0.01] during the experiment, while no change was observed in the ST or C groups. Finally, a significant increase (P < 0.01) was noted in the testosterone:cortisol ratio in the C group, while the increase in the NST group approached statistical significance (P < 0.08) and no changes in this ratio occurred in the ST group. The present findings suggested that the addition of 6-weeks of heavy resistance training to the handball training resulted in gains in maximal strength and throwing velocity but it compromised gains in leg explosive force production and endurance running. The tendency for a compromised testosterone:cortisol ratio observed in the ST group could have been associated with a state of overreaching or overtraining. Accepted: 22 April 1999     

Growth hormone and prolactin response to rehydration during exercise: effect of water and carbohydrate solutions

Summary The effect of progressive rehydration with either water or a carbohydrate solution on the plasma growth hormone (GH) and prolactin (PRL) response to exercise was examined together with plasma somatostatin. Five subjects underwent four 3-h experimental sessions at 36°C in which 25-min exercise periods alternated with 5-min rest periods. The sessions were conducted without fluid replacement (DH) or under rehydration with either water or isosmotic carbohydrate solutions AISO (acid) or NISO (neutral). The fluid was given every 10 min after the 1st h of exercise. Plasma GH increased significantly (p < 0.01) under DH after 2 and 3 h of exercise; this increase was prevented by rehydration with water, AISO and NISO. Plasma glucose was significantly higher following AISO and NISO rehydration compared with DH. This possibly influenced the GH response, but there was no difference between plasma glucose levels under DH and water rehydration at any time. The solutions tended to attenuate the increase in heart rate, rectal temperature and plasma cortisol, suggesting that the lack of GH response under rehydration conditions is a result of decreasing physiological stress levels. The GH response could not be explained by plasma somatostatin, which tended to decline in all sessions. Plasma PRL did not increase in any of the sessions, confirming that exercise without rehydration is a more potent stimulator of GH than of PRL. It is concluded that progressive rehydration with water is sufficient to prevent the exercise-induced increase in plasma GH.     

高原出血性休克羊的氧运送,氧耗量及心功能变化

本文探讨高原邮血性休克氧运送，氧耗量及血流动力学变化特征。出生生长于３６５８米高原绵羊以Ｗｉｇｇｅｒ氏方法引起出血休克。其结果如下：（１）在低血压期及再输血后５ｈ氧运送量，氧耗量及心输出量减少，但动脉－混合静脉血氧含量差增加，ＰａＯ２及动脉血含氧无明显变化。这些结果表明氧耗量下降是心输出量减少的结果。（２）两侧心室的心泵血功能和等容收缩及弛张期功能降低，回输血后所有上述指标恢复正常，这表明心功能障     

Effects of training at simulated altitude on performance and muscle metabolic capacity in competitive road cyclists

Summary Differences between the effects of training at sea level and at simulated altitude on performance and muscle structural and biochemical properties were investigated in 8 competitive cyclists who trained for 3–4 weeks, 4–5 sessions/week, each session consisting of cycling for 60–90 min continuously and 45–60 min intermittently. Four subjects, the altitude group (AG), trained in a hypobaric chamber (574 torr=2300 m above sea level), and the other four at sea level (SLG). Before and after training work capacity was tested both at simulated altitude (574 torr) and at sea level, by an incremental cycle ergometer test until exhaustion. Work capacity was expressed as total amount of work performed. Venous blood samples were taken during the tests. Leg muscle biopsies were taken at rest before and after the training period. AG exhibited an increase of 33% in both sea level and altitude performance, while SLG increased 22% at sea level and 14% at altitude. Blood lactate concentration at a given submaximal load at altitude was significantly more reduced by training in AG than SLG. Muscle phosphofructokinase (PFK) activity decreased with training in AG but increased in SLG. All AG subjects showed increases in capillary density. In conclusion, work capacity at altitude was increased more by training at altitude than at sea level. Work capacity at sea level was at least as much improved by altitude as by sea level training. The improved work capacity by training at altitude was paralleled by decreased exercise blood lactate concentration, increased capillarization and decreased glycolytic capacity in leg muscle.     

Effect of anaerobic and aerobic exercise of equal duration and work expenditure on plasma growth hormone levels

Summary Growth hormone (GH) and lactic acid levels were measured in five normal males before, during and after two different types of exercise of nearly equal total duration and work expenditure. Exercise I (aerobic) consisted of continuous cycling at 100 W for 20 min. Exercise II (anaerobic) was intermittent cycling for one minute at 285 W followed by two minutes of rest, this cycle being repeated seven times. Significant differences (P<0.01) were observed in lactic acid levels at the end of exercise protocols (20 min) between the aerobic (I) and anaerobic (II) exercises (1.96±0.33 mM·l^–1 vs 9.22±0.41 mM·l^–1, respectively). GH levels were higher in anaerobic exercise (II) than in aerobic (I) at the end of the exercise (20 min) (2.65±0.95 g·l^–1 vs 0.8±0.4 g·l^–1;P<0.10) and into the recovery period (30 min) (7.25±6.20 g·l^–1 vs 2.5±2.9 g·l^–1;P<0.05, respectively).