Unaccustomed high mileage compared to intensity training-related neuromuscular excitability in distance runners

The influence of a 4-week unaccustomed average 103% mileage increase (ITV, increase in training volume;n = 8; average baseline mileage 85.9 km · week^–1, final mileage 174.6km · week^–1) on performance and neuromuscular excitability (NME) was tested in experienced distance runners and controlled 1 year later by a 4-week unaccustomed average 152% increase in tempo-pace and interval-runs (ITI, increase in training intensity;n = 9; baseline 9 km · week^–1, final 22.7 km · week^–1) with an average total mileage of 61.7 km · week^–1 (week 1) to 84.7 km · week^–1 (week 4). Seven athletes participated in ITV as well as in ITI. During incremental treadmill test performance at a lactate concentration of 2 mmol · l^–1 (2 LP) increased, and at 4 mmol · l^–1 (4 LP) performance did not change, whereas total running distance (TD) during the incremental test decreased in ITV compared to an increase in 2 LP, 4 LP and TD during ITI which may indicate that there was an ITV-related overtraining. The NME of the reference muscles vastus medialis and rectus femoris deteriorated in ITV (day 28 compared to 0) compared to constant values during ITI, reflecting an ITV-related overload of neuromuscular structures.     

The influence of weekly training distance on fractional utilization of maximum aerobic capacity in marathon and ultramarathon runners

Summary This study was designed to examine the interrelationships between performance in endurance running events from 10 to 90 km, training volume 3–5 weeks prior to competition, and the fractional utilization of maximal aerobic capacity (% ) during each of the events. Thirty male subjects underwent horizontal treadmill testing to determine their , and steady-state at specific speeds to allow for calculation of % sustained during competition. Runners were divided into groups of ten according to their weekly training distance (group A trained less than 60 km · week^–1, group B 60 to 100 km · week^–1, and group C more than 100 km · week^–1). Runners training more than 100 km · week^–1 had significantly faster running times (average 19.2%) in all events than did those training less than 100 km · week^–1. or % sustained during competition was not different between groups. The faster running speed of the more trained runners, running at the same % during competition, was due to their superior running economy (19.9%). Thus all of the group differences in running performance could be explained on the basis of their differences in running economy. These findings suggest either that the main effect of training more than 100 km · week^–1 may be to increase running economy, or that runners who train more than 100 km · week^–1 may have inherited superior running economy. The finding that the maximal horizontal running speed reached during the progressive maximal treadmill test was a better predictor (r=0.72) of running performance at all distances than was the (r=0.54) suggests that peak treadmill running speed can predict performance in endurance running events.     

Effect of one- and two-leg training on arm and two-leg maximum aerobic power

Summary The purpose of this study was to examine the effect of one- and two-leg training on arm and two-leg maximum aerobic power. Seven subjects cycle-trained both legs simultaneously for 30 min·day^–1, 4 days·week^–1 for 4 weeks. Nine subjects cycle-trained each leg 15 min·day^–1, 4 days· week^–1 for 4 weeks. Both groups trained at a heart rate equal to that measured at 75% of their two-leg maximum aerobic power. Thus, during each training session the groups performed 30 min of work at the same heart rate intensity. Five subjects served as a non-training control group. Arm and leg maximum oxygen uptake tests were conducted before and after training. Only two-leg training induced significant gains in arm aerobic power (P<0.0003), whereas both modes of training resulted in signifcant increases in two-leg aerobic power (P<0.0008). The data demonstrate that improvements in arm aerobic power were dependent on the quantity of leg muscle mass involved in the training, whereas gains in two-leg aerobic power occurred regardless of whether the legs were trained separately or simultaneously.     

Plasma renin activity,aldosterone and catecholamine levels when swimming and running

Summary The purpose of this study was to determine the response of plasma renin activity (PRA), plasma aldosterone concentration (PAC) and catecholamines to two graded exercises differing by posture. Seven male subjects (19–25 years) performed successively a running rest on a treadmill and a swimming test in a 50-m swimming pool. Each exercise was increased in severity in 5-min steps with intervals of 1 min. Oxygen consumption, heart rate and blood lactate, measured every 5 min, showed a similar progression in energy expenditure until exhaustion, but there was a shorter time to exhaustion in the last step of the running test. PRA, PAC and catecholamines were increased after both types of exercise. The PRA increase was higher after the running test (20.9 ng AngI · ml^–1 · h^–1) than after swimming (8.66 ng AngI · ml^–1 · h^–1). The PAC increase was slightly greater after running (123 pg · ml^–1) than swimming (102 pg · ml^–1), buth the difference was not significant. Plasma catecholamine was higher after the swimming test. These results suggest that the volume shift induced by the supine position and water pressure during swimming decreased the PRA response. The association after swimming compared to running of a decreased PRA and an enhanced catecholamine response rule out a strict dependence of renin release under the effect of plasma catecholamines and is evidence of the major role of neural pathways for renin secretion during physical exercise.     

Is exhaustive training adequate preparation for endurance performance?

Summary Our purpose was to test the significance of exhaustive training in aerobic or endurance capacity. The extent of adaptations to endurance training was evaluated by assessing the increase in physical performance capability and oxidative markers in the organs of rats trained by various exercise programs. Rats were trained by treadmill running 5 days · week^–1 at 30 m · min^–1 for 8 weeks by one of three protocols:T ₁ — 60 min · day^–1;T ₂ — 120 min · day^–1; andT ₃ — 120 min · day^–1 (3 days · week^–1) and to exhaustion (2 days · week^–1). GroupsT ₂ andT ₃ ran for longer thanT ₁ in an endurance exercise test (P<0.05), in which the animals ran at 30 m · min^–1 to exhaustion; no difference was observed between groupsT ₂ andT ₃. All 3 trained groups showed a similar increase (20–27%) in the fast-twitch oxidative-glycolytic (FOG) fibers with a concomitant decrease in the fast-twitch glycolytic (FG) fiber population in gastrocnemius (p<0.05). The capillary supply in gastrocnemius increased with the duration of exercise (p<0.05): no difference was found between groupsT ₂ andT ₃. Likewise, no distinction was seen between groupsT ₂ andT ₃ in the increase in succinate dehydrogenase activity in gastrocnemius and the heart. These results suggest that the maximal adaptive response to endurance training does not require daily exhaustive exercise.     

Plasma renin activity and plasma catecholamines in intact and splenectomized running and swimming beagle dogs

Summary The influence of splenectomy in the dog on plasma catecholamine levels and plasma renin activity during treadmill running and swimming was investigated. Plasma catecholamines were measured by a radioenzymatic assay and plasma renin activity by a radioimmunoassay. Exercise consistently increased plasma catecholamine levels before and after splenectomy (range of increase:3–38 pmol·ml^–1). Swimming, however, was a stronger stimulus than running. No change in the ratio between noradrenaline and adrenaline was found. In intact dogs exercise results in a marked increase in hematocrit due to splenic contraction (range of increase 3–8 volume %), while renal blood flow and plasma renin activity remain virtually constant. In splenectomized dogs, exercise has been reported to induce a decrease in renal blood flow. In contrast to this known effect on renal blood flow, splenectomy did not affect plasma renin activity in treadmill running dogs. In swimming dogs, however, plasma renin activity was increased after splenectomy (range of increase 3.3–6.9 ng·Ang I·ml^–1·h^–1). Possibly, a threshold in sympathetic tone is required to increase renin release in the dog.     

The effect of training on cardiovascular responses to arm exercise in individuals with tetraplegia

The aim of this study was to investigate the physiological responses to maximal and submaximal arm-cranking exercise in 21 individuals with tetraplegia (TP) and to evaluate the effect of a 3 and 6-month training period (mean frequency of 1.5 h · week^–1, mean intensity at 35% of the training time above 60% of the heart rate reserve) on these physiological responses. The TP were divided into 8 trained subjects (T), 7 untrained subjects (U) who started their training at the beginning of the study, and 6 sedentary subjects (S). All the subjects were tested at the beginning of training and after 6 months, whereas T and U were also tested in between, at 3 months. During maximal exercise, peak power output and peak oxygen uptake per kilogram bodymass were significantly higher in T (49.9 W and 14.2 ml·min^–1 · kg^–1 respectively) compared to U (20.7 W and 8.8 ml · min^–1 · kg^–1 respectively) and S (15.9 W and 7.4 ml · min^–1 · kg^–1 respectively), whereas all other peak responses showed tendencies to be higher in T. This is most likely to have been the result of participation in sport and the effect of it on performance capacity in T, although differences in completeness of the lesion may have influenced the results. No significant differences were found for submaximal and maximal responses after 3 or 6 months of training in either T and U or in S. This may have been due on the one hand to the vulnerability of the subjects to diseases and injuries and on the other hand to the low frequency of training. On an individual basis, however, remark able improvement was observed during the training period, especially for individuals in the U group. These results would suggest that a 3 or 6-month training period has no measurable positive effect on the fitness level of TP.     

Interference of strength development by simultaneously training for strength and endurance

Summary The purpose of this study was to determine how individuals adapt to a combination of strength and endurance training as compared to the adaptations produced by either strength or endurance training separately. There were three exercise groups: a strength group (S) that exercised 30–40 min·day^–1, 5 days·week^–1, an endurance group (E) that exercised 40 min·day^–1, 6 days·week^–1; and an S and E group that performed the same daily exercise regimens as the S and E groups. After 10 weeks of training, VO_{2 max} increased approx. 25% when measured during bicycle exercise and 20% when measured during treadmill exercise in both E, and S and E groups. No increase in VO_{2 max} was observed in the S group. There was a consistent rate of development of leg-strength by the S group throughout the training, whereas the E group did not show any appreciable gains in strength. The rate of strength improvement by the S and E group was similar to the S group for the first 7 weeks of training, but subsequently leveled off and declined during the 9th and 10th weeks. These findings demonstrate that simultaneously training for S and E will result in a reduced capacity to develop strength, but will not affect the magnitude of increase in VO_{2 max}.This research was supported by a University of Illinois at Chicago Circle Research Board Grant and by a NIH Biomedical Research Support Grant (HEW RR07158-2) to the University of Illinois at Chicago Circle     

Effect of exercise training on aortic collagen content in spontaneously hypertensive rats (SHR)

Summary We investigated the effects of exercise training on the amount of aortic collagen and systolic blood pressure in spontaneously hypertensive rats (SHR). Ten-week old SHR were trained either by forced treadmill running (26.8 m·min^–1 h·day^–1, five times a week, 0% incline) or by voluntary running in revolving wheels (7,800 m·day^–1 at peak) for 8 weeks. Succinate dehydrogenase (SDH) activity measured as a marker of an endurance training effect was 13% higher (P<0.01) in the soleus of forced-exercised animals than in that of sedentary ones. (6.56±0.17 mol·g^–1·min^–1; mean ± SEM), whereas SDH activity in that of voluntarily-exercised group was found to be at the same level as in sedentary animals. The systolic blood pressure after training increased by 26.4 in sedentary, 21.1 in voluntarily-exercised, and 33.9 mm Hg in forced-exercised rats, when compared with the value of each group at the beginning of the training programm. A significant difference was observed in the increment of blood pressure only between the voluntarily- and forced-exercised groups (P<0.05). The amount of aortic collagen in voluntarily-trained rats (96.5±2.0 mg·g tissue^–1, 39.8±0.7 mg·100 mg protein^–1) was significantly less than that in forced-trained rats (P<0.05). These results suggest that voluntary, mild exercise training may be more effective in the reduction of collagen accumulation in the aorta associated with the suppression of blood pressure increase than forced, vigorous exercise training in SHR.     

Day-to-day changes in oxygen uptake kinetics at the onset of exercise during strenuous endurance training

Summary The aim of this study was to assess the effect of strenuous endurance training on day-to-day changes in oxygen uptake (VO₂) on-kinetics (time constant) at the onset.of exercise. Four healthy men participated in strenuous training, for 30 min·day^–1, 6 days·week^–1 for 3 weeks. The VO₂ was measured breath-by-breath every day except Sunday at exercise intensities corresponding to the lactate threshold (LT) and the onset of blood lactate accumulation (OBLA) which were obtained before training. Furthermore, an incremental exercise test was performed to determine LT, OBLA and maximal oxygen uptake (VO_2max) before and after the training period and every weekend. The 30-min heavy endurance training was performed on a cycle ergometer 5 days·week^–1 for 3 weeks. Another six men served as the control group. After training, significant reductions of the VO₂ time constant for exercise at the pretraining LT exercise intensity (P<0.05) and at OBLA exercise intensity (P<0.01) were observed, whereas the VO₂ time constants in the control group did not change significantly. A high correlation between the decrease in the VO₂ time constant and training day was observed in exercise at the pretraining LT exercise intensity (r=–0.76; P<0.001) as well as in the OBLA exercise intensity (r= –0.91; P<0.001). A significant reduction in the blood lactate concentration during submaximal exercise and in the heart rate on-kinetics was observed in the training group. Furthermore, VO₂ at LT, VO₂ at OBLA and VO_2max increased significantly after training (P<0.05) but such was not the case in the control group. These findings indicated that within a few weeks of training a rapidly improved VO₂ on-kinetics may be observed. This may be explained. by some effect of blood lactate during exercise on VO₂ on-kinetics, together with significantly improved cardiovascular kinetics at the onset of exercise.     

Comparative effects of hindlimb suspension and exercise on skeletal muscle myosin isozymes in rats

Summary The purpose of this study was to ascertain the time course of changes, whilst suspending the hindlimb and physical exercise training, of myosin light chain (LC) isoform expression in rat soleus and vastus lateralis muscles. Two groups of six rats were suspended by their tails for 1 or 2 weeks, two other groups of ten rats each were subjected to exercise training on a treadmill for 9 weeks, one to an endurance training programme (1-h running at 20 m · min^–1 5 days · week^–1), and the other to a sprint programme (30-s bouts of running at 60 m · min^–1 with rest periods of 5 min). At the end of these experimental procedures, soleus and vastus lateralis superficialis muscles were removed for myosin LC isoform determination by two-dimensional gel electrophoresis. Hindlimb suspension for 2 weeks significantly increased the proportion of fast myosin LC and decreased slow myosin LC expression in the soleus muscle. The pattern of myosin LC was unchanged in the vastus lateralis muscle. Sprint training or endurance training for 9 weeks increased the percentage of slow myosin LC in vastus lateralis muscle, whereas soleus muscle myosin LC was not modified. These data indicate that hindlimb suspension influences myosin LC expression in postural muscle, whereas physical training acts essentially on phasic muscle. There were no differences in myosin LC observed under the influence of sprint- or endurance-training programme.     

Specificity effects of run versus cycle training on ventilatory threshold

Summary This study compared the effects of 9 weeks of run (RT) versus cycle (CT) training on ventilatory threshold (Th_v) determined during treadmill (TM) and cycle ergometer (CE) graded exercise testing. Sixteen college age men were assigned to a RT or CT group and performed a TM and a CE test before and after training. Both training groups performed similar training protocols which initially consisted of continuous exercise 4 days·week^–1 at 75–80% maximum heart rate (fc,_max) for 45 min. Training intensity was later increased to 80–85% fc _max and interval training (90–95% fc,_max) was incorporated 2 days·week^–1 into the continuous training. Both groups showed significantly improved maximal oxygen consumption ( O_2max) on both TM and CE tests (P<0.01) with no significant differences between the groups. Significant Th_v increases (P<0.05) were found on TM tests for RT (n=8) and CT (n=8) groups [mean (SD); 443 (438) and 373 (568) ml O₂·min^–1, respectively] with no difference between the groups. Results from the CE tests revealed a significant Th_v increase (P<0.01) for the CT group [566 (663) ml O₂·min^–1] with no change for the RT group. The Th_v improvement noted for the RT group was significantly different (P< 0.05) comparing CE with TM tests but not for the CT group. The results indicate that CT and RT improvement in Th_v for runners is dependent upon mode of training and testing, and there is an apparent dissociation of O_2maxand Th_v specific to training.     

Training effects of cross-country skiing and running on maximal aerobic cycle performance and on blood lipids

Summary Two experiments were carried out to compare the cardiorespiratory and metabolic effects of cross-country skiing and running training during two successive winters. Forty-year-old men were randomly assigned into skiing (n = 15 in study 1,n = 16 in study 2), running (n = 16 in study 1 andn = 16 in study 2) and control (n = 17 in study 1 andn = 16 in study 2) groups. Three subjects dropped out of the programme. The training lasted 9–10 weeks with 40-min exercise sessions three times each week. The training intensity was controlled at 75%–85% of the maximal oxygen consumption (VO_2max) using portable heart rate metres and the mean heart rate was 156–157 beats·min^–1 in the training groups. In the pooled data of the two studies the mean increase in theVO_2max (in ml·min^–1·kg^–1) on a cycle ergometer was 17% for the skiing group, 13% for the running group and 2% for the control group. The increase inVO_2max was highly significant in the combined exercise group compared to the control group but did not differ significantly between the skiing and running groups. The fasting serum concentrations of lipoproteins and insulin did not change significantly in any of the groups. These results suggested that training by cross-country skiing and running of the same duration and intensity at each session for 9–10 weeks improved equally the cardiorespiratory fitness of untrained middle-aged men.     

Effects of exercise training on plasma catecholamines and blood pressure in labile hypertensive subjects

Summary Plasma catecholamine concentrations (norepinephrine, NE; epinephrine, E) were measured along with heart rate (HR) and blood pressure (BP) at rest in supine (20 min) and standing (10 min) positions and in response to cycle ergometer exercise (5 min; 60% estimated maximal aerobic power) in 12 hypertensive patients before and after 20 weeks of aerobic training on cycle ergometer (six males, one female) or by jogging (five males). In a control group of labile hypertensive patients (five males, two females), estimated maximal aerobic power as well as HR and BP at rest in the supine and standing positions and in response to exercise were not modified from the first to the second evaluation (43±4 vs 43±5 ml·kg^–1·min^–1). In comparison estimated maximal aerobic power significantly increased in both training groups (cycle: 38±4 to 43±4; jogging: 38±3 to 46±4 ml·kg^–1·min^–1). However HR and BP were not modified following training, except for small reductions in systolic (18.9 to 18 kPa: 142 to 135 mmHg) and diastolic pressures (13.3 to 12 kPa: 100 to 90 mmHg) (p<0.05) at standing rest in the cycle group. Changes in plasma E and NE concentrations at rest and in response to exercise were small and not consistent: plasma NE was lower at standing rest following cycle training, (559±95 vs 462±108 pg·ml^–1) but a similar reduction was observed in the control group (428±45 vs 321±28 pg·ml^–1); plasma E was lower at rest following cycle training (29±7 vs 12±8 pg·ml^–1), but was higher in response to exercise (137±24 vs 419±113 pg·ml^–1). These results are in accordance with previous reports which do not clearly demonstrate that physical training in hypertensive patients lowers BP and the activity or reactivity of the sympathetic system.     

The energy cost of walking or running on sand

Summary Oxygen uptake ( O₂) at steady state, heart rate and perceived exertion were determined on nine subjects (six men and three women) while walking (3–7 km · h^–1) or running (7–14 km · h^–1) on sand or on a firm surface. The women performed the walking tests only. The energy cost of locomotion per unit of distance (C) was then calculated from the ratio of O₂ to speed and expressed in J · kg^–1 · m^–1 assuming an energy equivalent of 20.9 J · ml O₂ ^–1. At the highest speedsC was adjusted for the measured lactate contribution (which ranged from approximately 2% to approximately 11% of the total). It was found that, when walking on sand,C increased linearly with speed from 3.1 J · kg^–1 · m^–1 at 3 km · h^–1 to 5.5 J · kg^–1 · m^–1 at 7 km · h^–1, whereas on a firm surfaceC attained a minimum of 2.3 J · kg^–1 · m^–1 at 4.5 km · h^–1 being greater at lower or higher speeds. On average, when walking at speeds greater than 3 km · h^–1,C was about 1.8 times greater on sand than on compact terrain. When running on sandC was approximately independent of the speed, amounting to 5.3 J · kg^–1 · m^–1, i.e. about 1.2 times greater than on compact terrain. These findings could be attributed to a reduced recovery of potential and kinetic energy at each stride when walking on sand (approximately 45% to be compared to approximately 65% on a firm surface) and to a reduced recovery of elastic energy when running on sand.     

Effects of moderate external loading on the aerobic demand of submaximal running in men and 10 year-old boys

Summary The effects of moderate external loading on the aerobic demand of submaximal running were studied in habitually active adult men (29–37 yrs) and 10 year-old boys. The load was symmetrically placed around the trunk and adjusted to correspond to 10% of body weight. Running was performed on a treadmill at 8, 10 and 11 km · h^–1 (2.2, 2.8 and 3.1 m · s^–1). A small, but consistent decrease in net oxygen uptake (gross oxygen uptake in ml · kg^–1 · min^–1 minus calculated basal metabolic rate) with load was observed in both groups at all speeds, except for the men at 8 km · h^–1. The decrease was larger for the boys and tended to enhance with speed. The boys had a higher net oxygen uptake than the adults at all unladen running velocities, whereas the difference in the loaded condition was significant only at the highest speed. The decrease in net oxygen uptake with load could not be directly correlated with differences in body weight or step frequency. It is hypothesized that a difference in the utilization of muscle elastic energy could underlie part of the age and load dependent changes observed in running economy.     

Stroke volume response to progressive exercise in athletes engaged in different types of training

Summary Using the impedance cardiography method, heart rate ( _c) matched changes on indexed stroke volume (SI) and cardiac output (CI) were compared in subjects engaged in different types of training. The subjects consisted of untrained controls (C), volleyball players (VB) who spent about half of their training time (360 min · week^–1) doing anaerobic conditioning exercises and who had a maximal oxygen uptake ( ) 41% higher than the controls, and distance runners (D) who spent all their training time (366 min·week^–1) doing aerobic conditioning exercises and who had a 26% higher than VB. The subjects performed progressive submaximal cycle ergometer exercise (10 W·min^–1) up to _c of 150 beats·min^–1. In group C, SI had increased significantly (P<0.05) at _c of 90 beats·min^–1 ( + 32%) and maintained this difference up to 110 beats·min^–1, only to return to resting values on reaching 130 beats·min^–1 with no further changes. In group VB, SI peaked (+ 54%) at _c of 110 beats·min^–1, reaching a value significantly higher than that of group C, but decreased progressively to 22010 of the resting value on reaching 150 beats·min^–1. In group D, SI peaked at _c of 130 beats·min^–1 (+ 54%), reaching a value significantly higher than that of group VB, and showed no significant reduction with respect to this peak value on reaching 150 beats·min^–1. As a consequence, the mean CI increase per _c unit was progressively higher in VB than in C (+46%) and in D than in VB (+ 105%). It was concluded that thef _c value at which SI ceased to increase during incremental exercise was closely related to the endurance component in the training programme.     

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 training and acclimation on heat tolerance in exercising men wearing protective clothing

This study examined the effectiveness of endurance training and heat acclimation in reducing the physiological strain imposed by exercising in the heat while wearing protective clothing. Seven young men underwent 8 weeks of physical training [60–80% maximal aerobic power (VO_2max) for 30–45 min · day^–1, 3–4 days · week^–1 at < 25° C] followed by 6 days of heat acclimation (45–55% VO_2max for 60 min · day^–1 at 40° C, 30% relative humidity). Nine other young men underwent corresponding periods of control observation and heat acclimation. Before and after each treatment, subjects completed a treadmill walk (4.8 km · h^–1, 2% grade) in a climatic chamber (40° C, 30% relative humidity), wearing in turn normal combat clothing or clothing protecting against nuclear, biological, and chemical (NBC) agents. Criteria for halting this test were: (1) a rectal temperature (T _re) of 39.3° C; (2) a heart rate (f _c) 95% of the subject's observed maximum, maintained for 3 min; (3) unwillingness of the subject to continue; (4) the elapse of 120 min. The training regimen increased mean VO_2max by 16% and mean plasma volume by 8%. When tested in normal combat clothing, the rates of increase in T _re and f _c were slower after training. However, when wearing NBC protective clothing, the only significant change induced by training was a higher mean skin temperature (T _sk) in the early part of the test. Heat acclimation increased the mean plasma volume of untrained subjects by 8%, but their VO_2max remained unchanged. When tested in normal combat clothing, acclimation decreased their mean values of T _re, T _sk, f _c, and metabolic rate. When wearing NBC protective clothing, the only significant decrease after acclimation was in overall T _re. In trained subjects, heat acclimation induced no further improvement in any physiological variable when wearing normal combat clothing, but reduced overall T _re and T _sk when wearing NBC protective clothing. Training- or acclimation-induced increases of sweat secretion (an average increment of 0.14–0.23 kg · h^–1) were not accompanied by any statistically significant increase in sweat evaporation when wearing NBC protective clothing. Moreover, tolerance times were unchanged in either normal combat (116–120 min) or NBC protective clothing (47–52 min). We conclude that neither endurance training nor heat acclimation do much to improve exercise tolerance when wearing NBC protective clothing in hot environments, because any added sweat secretion decreases blood volume and increases discomfort without augmenting body cooling.     

Plasma testosterone and catecholamine responses to physical exercise of different intensities in men

Summary Plasma testosterone, noradrenaline, and adrenaline concentrations during three bicycle ergometer tests of the same total work output (2160 J·kg^–1) but different intensity and duration were measured in healthy male subjects. Tests A and B consisted of three consecutive exercise bouts, lasting 6 min each, of either increasing (1.5, 2.0, 2.5 W·kg^–1) or constant (2.0, 2.0, 2.0 W·kg^–1) work loads, respectively. In test C the subjects performed two exercise bouts each lasting 4.5 min, with work loads of 4.0 W·kg^–1. All the exercise bouts were separated by 1-min periods of rest.Exercise B of constant low intensity resulted only in a small increase in plasma noradrenaline concentration. Exercise A of graded intensity caused an increase in both catecholamine levels, whereas, during the most intensive exercise C, significant elevations in plasma noradrenaline, adrenaline and testosterone concentrations occurred. A significant positive correlation was obtained between the mean value of plasma testosterone and that of adrenaline as well as noradrenaline during exercise.It is concluded that both plasma testosterone and catecholamine responses to physical effort depend more on work intensity than on work duration or total work output.This work was performed within the Scientific Exchange Programme between the Institute of Experimental Endocrinology, Slovak Academy of Sciences in Bratislava and Medical Research Centre, Polish Academy of Sciences, Warsaw/Project 10.4/