Physiologic correlates to running performance in pre-pubertal distance runners

In adults, four major variables have been shown to be associated with success in distance running performance: submaximal oxygen consumption (running economy), peak oxygen consumption (Peak VO2), ventilatory threshold (VT) and fractional utilisation (FU). The primary aim of this study was to describe the relationship between the 3000 m race times of run-trained prepubertal boys to these four variables. Thirteen male run-trained pre-pubertal boys (age 11.7 +/- 1.1 yrs, mean +/- SD), volunteered to take part in a 3000 m time trial and laboratory assessment, consisting of treadmill running at four submaximal speeds (8, 9.6, 11.2 and 12.8 km.h-1) as well as a peak VO2 test. The group demonstrated a heterogeneous array of peak VO2 data. A high level of association (p < 0.05) was found between mass-relative peak VO2 and 3000 m time trial results (r = -0.83). In addition ventilatory threshold expressed as %peak VO2, VO2 at VT and estimated velocity at VT was also highly related to 3000 m time trial (r = -0.78, -0.77 and -0.77) respectively. Fractional utilisation (%peak VO2) was significantly (p < 0.05) associated with race time at the final two submaximal running speeds only (11.2 and 12.8 km.h-1) (r = 0.61 and 0.67, respectively). Respiratory Exchange Ratio (RER) was also found to be significantly (p < 0.05) associated with 3000 m race time at 11.2 and 12.8 km.h-1. Overall peak VO2 appeared to be the single most important factor associated with success at 3000 m.     

A longitudinal study of AIDS conversations between mothers and adolescents

This paper presents the results of a study on the introduced, free-ranging patas monkey population of Southwestern Puerto Rico (SWPR). It describes information on the population size, social group composition, diet, daily ranging patterns, and patas home range during a 3 year period. The patas monkey population in the study area consisted of approximately 120 individuals in four heterosexual groups and several all-male bands. Within their home ranges (26.8 km2), the population density was 4.47 individuals/km2. Home range size among the population's four heterosexual groups varied from 3.72 km2 to 15.39 km2, and minimum daily distance traveled ranged from 0.8-2.0 km. In general, the social structure and mating system of this population parallels what has been described for African populations. However, habitat use, ranging behavior, and the quality of intergroup interactions suggests that patas of this population exhibit territorial behavior.     

Malignant melanoma in Europe: changes in mortality rates (1970-90) in European Community countries

We measured metabolic rates (mL O2 h-1, converted to kcal d-1), deep body temperatures (degree C), and skin temperatures (degree C) and calculated whole-animal thermal conductances (mL O2 g-1 h-1 degree C-1) of five 3-yr-old harbor seals (Phoca vitulina concolor) at air temperatures between -20 degrees and 35 degrees C. The mean thermal neutral zone of these seals extended from a lower critical temperature of -12.9 degrees +/- 1.6 degrees C (SD) to an upper critical temperature of 28.6 degrees +/- 1.7 degrees C. Hyperthermia was observed at an ambient air temperature of 35 degrees C. Mean standard metabolic rate was 1,553.6 +/- 168.2 kcal d-1, about 1.2 times the value expected for adult animals of similar body mass (mean mass = 49.2 +/- 7.5 kg). Mean deep body temperature increased from 37.5 degrees +/- 0.30 degrees C at an ambient temperature of 30 degrees C and reached 39.3 degrees +/- 0.33 degrees C at an ambient temperature of 35 degrees C. Skin temperature decreased with decreasing ambient temperature but remained well above ambient temperature. Mean whole-animal thermal conductance decreased from an ambient temperature of 35 degrees C until it reached a minimum value of 0.007 mL O2 g-1 h-1 degree C-1 at -4.0 degrees C; it then increased with a further decrease in ambient temperature. In comparison to the thermal limits of the same seals during their first year of life, the results indicate a broadening of the thermal neutral zone with age: an 11 degrees C decrease in the lower critical temperature and a 3.5 degrees C increase in the upper critical temperature. These findings suggest that warm ambient air temperatures should not pose any particular thermoregulatory problems for larger and older harbor seals, even beyond the limits of their current annual distribution.     

Effects of artificially-induced anaemia on sudomotor and cutaneous blood flow responses to heat stress

The influence of artificially induced anaemia on thermal strain was evaluated in trained males. Heat stress trials (38.6 degrees C, water vapour pressure 2.74 kPa) performed at the same absolute work rates [20 min of seated rest, 20 min of cycling at 30% peak aerobic power (VO2pcak), and 20 min cycling at 45% VO2peak] were completed before (HST1) and 3-5 days after 3 units of whole blood were withdrawn (HST2). Mild anaemia did not elevate thermal strain between trials, with auditory canal temperatures terminating at 38.5 degrees C [(0.16), HST1] and 38.6 degrees C [(0.13), HST2; P > 0.05]. Given that blood withdrawal reduced aerobic power by 16%, this observation deviates from the close association often observed between core temperature and relative exercise intensity. During HST2, the absolute and integrated forearm sweat rate (mSW) exceeded control levels during exercise (P < 0.05), while a suppression of forehead mSW occurred (P < 0.05). These observations are consistent with a possible peripheral redistribution of sweat secretion. It was concluded that this level of artificially induced anaemia did not impact upon heat strain during a 60-min heat stress test.     

The validity of the lactate minimum test for determination of the maximal lactate steady state

PURPOSE: The purpose of this study was to investigate the validity of the lactate minimum test ([Lac-]BMIN) in the determination of the velocity at the maximal lactate steady state (V-MLSS), and to identify those physiological factors most closely associated with 8-km running performance. METHODS: Thirteen trained male runners (VO2max range 53-67 mL.kg-1.min-1) took part in an 8-km simulated race on flat roads and completed a comprehensive battery of laboratory tests. RESULTS: Performance velocity was most strongly correlated with the estimated running velocity at VO2max (r = 0.93) and with V-MLSS (r = 0.92) and velocity at lactate threshold (V-Tlac) (r= 0.93). The running velocity at the ventilatory threshold (V-Tvent) (r = 0.81) and the [Lac-]BMIN (r = 0.83) also produced good correlations with performance velocity. Performance running velocity (mean +/- SEM 16.0 +/- 0.3 km.h-1) was not significantly different from V-MLSS (15.7 +/- 0.3 km.h-1). The running velocity at [Lac-]BMIN (14.9 +/- 0.2 km.h-1) was not significantly different from the V-Tlac (15.1 +/- 0.3 km.h-1) or V-Tvent (14.9 +/- 0.2 km.h-1) was not significantly different from the V-Tlac (15.1 +/- 0.3 km.h-1) or V-Tvent (14.9 +/- 0.3 km.h-1) but was significantly lower than the V-MLSS (P < 0.05). The [Lac-]BMIN provided the lowest correlation with V-MLSS (r = 0.61) and the worst estimate of V-MLSS (SEE = 0.75 km.h-1) compared with the other measures of lactate accumulation. The V-Tlac was not significantly different from V-MLSS and provided the highest correlation (r = 0.94) and a close estimate (SEE = 0.33 km.h-1) of the V-MLSS. CONCLUSIONS: It is concluded that of the measures studied relating to blood lactate accumulation during submaximal exercise, V-Tlac provides the best estimate of the V-MLSS and the V-Tlac had equal predictive power for 8-km race performance.     

Techniques of MRI cholangiopancreatography. History, current status and future prospects

This study investigates the effects of long-term passive heat exposure and a 16-week basic military training program on heat acclimatization. Thirty recruits were tested on the zero (T1), 2nd (T2), 6th (T3), and 16th (T4) weeks of the basic military training program. The trials involved 1 hour of marching on a treadmill at 5.5 km h-1, with a 5% gradient. The subjects wore their camouflage uniforms during the trials, with simulated combat loads. The trials were conducted in a climatic chamber programmed at 32 degrees C, 60% relative humidity, 900 Wm-2 of simulated solar radiation, and wind speed of 3 m s-1. There was no fluid replacement during the trials. Because only 9 subjects attended all the trials, the results presented are based on these subjects. No significant difference was found in mean skin temperature in all the four trials. Tympanic temperature was significantly reduced (p < 0.05) only at 20 minutes. Pairwise analysis was significant (p < 0.05) only between T1 (37.18 +/- 0.38 degrees C) and T4 (36.48 +/- 0.53 degrees C). Average body temperature was significantly different only at 10 and 60 minutes (p < 0.05). A significant pairwise difference (p < 0.05) was found only between T1 (36.61 +/- 0.33 degrees C) and T4 (36.07 +/- 0.46 degrees C) in 10 minutes. No pairwise difference was found at 60 minutes. Mean heart rate (HR) was significantly reduced during the 16 weeks at 10, 20, and 30 minutes. Mean HR at 10 minutes was reduced from 152.11 +/- 14.18 beats min-1 in T1 to 130.78 +/- 10.43 beats min-1 in T4 (p < 0.001). Mean HR at 20 and 30 minutes was reduced from 156.11 +/- 17.74 beats min-1 (T1) to 137.25 +/- 11.42 beats min-1 (T4) (p < 0.001), and from 157.14 +/- 15.77 beats min-1 (T1) to 146.11 +/- 12.64 beats min-1 (T4) (p < 0.05). There was no significant difference in sweat loss and mean sweat rate during the 16 weeks. This study concluded that long-term passive heat exposure was effective at inducing heat acclimatization in terms of tympanic temperature, average body temperature, mean skin temperature, sweat loss, and mean sweat rate, but not in terms of HR. Physical training was still necessary to induce further adaptation in HR. The limiting factor to task completion during the trials was physical fitness rather than beat fitness.     

Enzymes involved in the bioactivation of 4-(methylnitrosamino)-1-(3-pyridyl)-1-butanone in patas monkey lung and liver microsomes

4-(Methylnitrosamino)-1-(3-pyridyl)-1-butanone (NNK) is a potent tobacco-specific carcinogen in animals. Our previous studies indicated that there are differences between rodents and humans for the enzymes involved in the activation of NNK. To determine if the patas monkey is a better animal model for the activation of NNK in humans, we investigated the metabolism of NNK in patas monkey lung and liver microsomes and characterized the enzymes involved in the activation. In lung microsomes, the formation of 4-oxo-1-(3-pyridyl)-1-butanone (keto aldehyde), 4-(methylnitrosamino)-1-(3-pyridyl-N-oxide)-1-butanone (NNK-N-oxide), 4-hydroxy-1-(3-pyridyl)-1-butanone (keto alcohol), and 4-(methylnitrosamino)-1-(3-pyridyl)-1-butanol (NNAL) was observed, displaying apparent Km values of 10.3, 5.4, 4.9, and 902 microM, respectively. NNK metabolism in liver microsomes resulted in the formation of keto aldehyde, keto alcohol, and NNAL, displaying apparent Km values of 8.1, 8.2, and 474 microM, respectively. The low Km values for NNK oxidation in the patas monkey lung and liver microsomes are different from those in human lung and liver microsomes showing Km values of 400-653 microM, although loss of low Km forms from human tissue as a result of disease, surgery or anesthesia cannot be ruled out. Carbon monoxide (90%) significantly inhibited NNK metabolism in the patas monkey lung and liver microsomes by 38-66% and 82-91%, respectively. Nordihydroguaiaretic acid (a lipoxygenase inhibitor) and aspirin (a cyclooxygenase inhibitor) decreased the rate of formation of keto aldehyde and keto alcohol by 10-20 % in the monkey lung microsomes. Alpha-Napthoflavone and coumarin markedly decreased the oxidation of NNK in monkey lung and liver microsomes, suggesting the involvement of P450s 1A and 2A6. An antibody against human P450 2A6 decreased the oxidation of NNK by 12-16% and 22-24% in the patas monkey lung and liver microsomes, respectively. These results are comparable to that obtained with human lung and liver microsomes. Coumarin hydroxylation was observed in the patas monkey lung and liver microsomes at a rate of 16 and 4000 pmol/min/mg protein, respectively, which was 5-fold higher than human lung and liver microsomes, respectively. Immunoblot analysis demonstrated that the P450 2A level in the individual patas monkey liver microsomal sample was 6-fold greater than in an individual human liver microsomal sample. Phenethyl isothiocyanate, an inhibitor of NNK activation in rodents and humans, decreased NNK oxidation in the monkey lung and liver microsomes displaying inhibitor concentration resulting in 50% inhibition of the activity (IC50) values of 0.28-0.8 microM and 4.2-6.8 microM, respectively. The results demonstrate the similarities and differences between species in the metabolic activation of NNK. The patas monkey microsomes appear to more closely resemble human microsomes than mouse or rat enzymes and may better reflect the activation of NNK in humans.     

Comparison of responses of men to immersion in circulating water at 40.0 and 41.5 degrees C

BACKGROUND: The recommended maximum water temperature for public hot tubs has been set at 40.0 degrees C, but no research has been published on human immersion in hot water at higher temperatures. HYPOTHESIS: We hypothesized that thermoregulatory and cardiovascular responses at two water temperatures would be proportional to the water:blood temperature gradients. METHODS: Six healthy men were immersed for 21 min in circulating hot water at 40.0 and 41.5 degrees C in separate trials in random order 1-3 wk apart. Measurements included heart rate, systolic BP, esophageal, rectal, and non-immersed skin temperatures, sweat rate, and perceived comfort. RESULTS: The rise in all body temperatures, sweat rate, and heart rate were significantly greater in the 41.5 vs. 40.0 degrees C water. Peak esophageal temperatures were 38.3 +/- 0.2 degrees C vs. 37.8 +/- 0.03 degrees C, peak sweat rates were 0.48 +/- 0.05 vs. 0.32 +/- 0.03 kg x m(-2) x h(-1), and peak heart rates were 123 +/- 7 vs. 108 +/- 5 bpm, respectively. Systolic BPs followed different patterns of response in each trial, whereas diastolic pressures were not different between trials. Comfort at each level of immersion was reduced during the 41.5 degrees C trial compared with the 40.0 degrees C in excess of that predicted by difference in esophageal temperature between the trials. CONCLUSIONS: These results suggest that risks of hyperthermia or adverse cardiovascular effects in hot tubs may not be greater in water above 40.0 degrees C unless perceptual judgment is impaired. Hypotension when standing to exit the tub occurred in both trials and may represent a potential hazard to hot tub use.     

Olympics in Atlanta: a fight against physics

Environmental stress can become so severe that athletes, in spite of proper training, heat acclimation, and hydration level, are unable to maintain thermal balance. Such incompensable conditions occur when air temperature exceeds 35 degrees C and relative humidity becomes higher than 60%. At these high environmental temperatures, the heat liberated during exercise can only be lost by evaporation of sweat, and therefore water vapor pressure sets limits on the possible rate of evaporation. Calculations are presented for the required and the maximal possible sweat evaporation rate for high-intensity, long-duration events, using marathon racing as an example. The consequence of the environmental heat stress is that the athlete must reduce the speed of running considerably to prevent potential heat injury. In certain extreme environmental conditions, sporting events should be canceled or postponed.     

Predicting competition performance in long-distance running by means of a treadmill test

PURPOSE: The purpose of this study was to examine the power of 16 parameters beside the individual anaerobic threshold (IAT) in predicting performance in various competition distances. METHODS: This study examined 427 competitive runners to test the prediction probability of the IAT and other parameters for various running distances. All runners (339 men, 88 women; ages, 32.5 +/- 10.14 yr; training, 7.1 +/- 5.53 yr; training distance, 77.9 +/- 35.63 km.wk-1) performed an increment test on the treadmill (starting speed, 6 or 8 km.h-1; increments, 2 km.h-1; increment duration, 3 min to exhaustion). The heart rate (HR) and the lactate concentrations in hemolyzed whole blood were measured at rest and at the end of each exercise level. The IAT was defined as the running speed at a net increase in lactate concentration 1.5 mmol.L-1 above the lactate concentration at LT. RESULTS: Significant correlations (r = 0.88-0.93) with the mean competition speed were found for the competition distances and could be increased using stepwise multiple regression (r = 0.953-0.968) with a set of additional parameters from the training history, anthropometric data, or the performance diagnostics. CONCLUSIONS: The running speed at a defined net lactate increase thus produces an increasing prediction accuracy with increasing distance. A parallel curve of the identity straight lines with the straight lines of regression indicates the independence of at least a second independent performance determining factor.     

Influence of body composition on rewarming from immersion hypothermia

BACKGROUND: This study was conducted to determine if the differences between efficacies of three treatments for immersion hypothermia are affected by body composition. METHODS: Twelve subjects were divided into equally sized low (LF) and high (HF) fat groups. On three occasions subjects were each immersed in cold water until esophageal temperatures (Tes) decreased to approximately 33.2 degrees C (LF) and approximately 35.8 degrees C (HF). They were then rewarmed by: 1) shivering; 2) application of external heat; or 3) treadmill exercise in a balanced design. RESULTS: For HF, the afterdrop during exercise (1.04 +/- 0.2 degrees C) was greater than during shivering (0.35 +/- 0.3 degrees C) and external heat (0.36 +/- 0.1 degree C) (p < 0.01). In LF, however, the exercise afterdrop (0.75 +/- 0.2 degree C) was greater than only external heat (0.35 +/- 0.2 degree C) (p < 0.05) but not shivering (0.58 +/- 0.4 degree C). There was a positive relationship between % fat and afterdrop for the exercise condition with a slope (95% C.I.) of 0.03 (0.01 to 0.05) degree C.% fat-1 (r2 = 0.37, p < 0.05). The exercise rewarming rate (3.48 +/- 1.1 degrees C.h-1) was greater (p < 0.01) than during both shivering (1.80 +/- 0.7 degrees C.h-1) and external heat (2.22 +/- 0.7 degrees C.h-1) in HF while no difference was seen between the three treatments (5.28 +/- 0.4, 4.86 +/- 1.1 and 5.16 +/- 0.7 degrees C.h-1, respectively) in LF. There were inverse relationships between % fat and rewarming rate in the exercise -0.12 (-0.23 to -0.01) degree C.h-1.% fat-1, (r2 = 0.38), shivering -0.27 (-0.38 to -0.16) degrees C.h-1.% fat-1, (r2 = 0.76) and external heat -0.26 (-0.35 to -0.17) degree C.h-1.% fat-1, (r2 = 0.83) conditions (p < 0.05). CONCLUSIONS: The inter-treatment differences between these techniques are accentuated in the HF, and attenuated (afterdrop) or even eliminated (rewarming rate) in the LF subgroup.     

Ambient temperature effects on thermoregulation and endurance in anticholinesterase-treated rats

In sedentary animals, physostigmine (PH) administration resulted in a decreased core temperature that is ambient temperature (Ta) dependent. PH administration in rats exercising on a treadmill (26 degrees C, 50% rh, 11m/min, 6 degrees incline) decremented endurance and increased rate of rise of core temperature (heating rate, HR). This study was undertaken to examine the effects of Ta on the endurance and thermoregulatory decrements of PH-treated running rats. Adult male rats (510-530g) were given either 0.2ml saline (C) or 100 ug/kg physostigmine salicylate in 0.2 ml saline via tail vein 15 min prior to the start of running to exhaustion at 10, 15, 26, or 30 degrees C. In both C- and PH-treated groups, endurance decreased and HR increased with increasing Ta from 15 to 30 degrees C. At 15 and 26 degrees C the C rats ran significantly (p < .05) longer and had significantly lower HR than the PH rats: C15 = 90 +/- 8 min, 0.022 +/- 0.006 degrees C/min; C26 = 67 +/- 6, 0.051 +/- 0.007; PH15 = 57 +/- 5, 0.052 +/- 0.008; and PH26 = 43 +/- 6, 0.092 +/- 0.007. At 10 and 30 degrees C there were no significant differences between C and PH-treated rats. A Ta of 30 degrees C was too high for effective cooling in either group, and at 10 degrees C both groups were able to dissipate heat despite the increased metabolic rate of the PH-treated rats. The PH-treated rat model of cholinergic drug effect is useful at a Ta of 15 and 26 degrees C.     

Thermoregulatory effects of caffeine ingestion during submaximal exercise in men

BACKGROUND: The exclusive effect of caffeine ingestion on exercise thermoregulation is unclear; data indicate that caffeine may have a positive effect, a negative effect, or no effect. METHODS: Rectal (TRE) and mean skin (TSK) temperatures, skin heat conductance (HSK), and sweat rate (MSW) were measured during 30 min of rest and subsequent 70 min of submaximal cycle-ergometer exercise (67% VO2PEAK) in 11 aerobically conditioned men (mean +/- SD 29 +/- 6 yr, 49 +/- 6 mL x min(-1) x kg(-1) VO2PEAK) under two conditions: a caffeine (10 mg x kg(-1) ingestion (CI) session and a noncaffeine ingestion (NCI) control session. RESULTS: There were no significant differences in physiological or thermoregulatory parameters during exercise: X (+/-SE) end exercise levels for the NCI and CI sessions, respectively, were VO2 = 2.50 +/- 0.09 vs. 2.55 +/- 0.09 L x min(-1); heart rate = 145 +/- 7 vs. 145 +/- 5 bpm; HSK = 30 +/- 3 vs. 28 +/- 3 kcal x m(-2) x h(-1) x degrees C(-1); MSW = 393 +/- 35 vs. 378 +/- 36 g x m(-2) x h(-1); and TRE = 38.3 +/- 0.2 vs. 38.4 +/- 0.1 degrees C. Control TSK was lower than that for CI by 0.4 to 0.5 degrees C at rest and during exercise. CONCLUSION: Ingestion of a high level (10 mg x kg(-1) of caffeine has no effect on skin heat conductance, sweating, or the rate of increase and final level of rectal temperature during moderate, submaximal leg exercise.     

Serum levels of endothelial and neural cell adhesion molecules in prostate cancer

The purpose of this study was to describe the longitudinal development of running economy [defined as the oxygen uptake (VO2) at a submaximal running speed] in males and females from teenage to young adult age using data from the Amsterdam Growth and Health Study. Submaximal VO2 (in ml.kg-1.min-1) was measured in 84 males and 98 females while they ran on a treadmill at a constant speed of 8 km.h-1 for 6 min at three different treadmill slopes (0%, 2.5% and 5%). This test was carried out six times, on the same subjects at the ages of 13, 14, 15, 16, 21, and 27 years. The longitudinal development of running economy in males and females was analysed using a two-way analysis of variance for repeated measurements. At all three slopes, a significant decrease in VO2 with increasing age was found for both males and females, implying a significant increase in running economy for both sexes. Males showed significantly higher VO2 values than females at all ages measured and for all three slopes, suggesting that females have a significantly higher running economy than males. In order to make a better comparison of the VO2 of individuals of different sizes, allometric models were used; power function ratios were constructed in which body mass was expressed to an exponential power. Following this analysis the difference in submaximal VO2 and running economy between males and females appeared even larger.     

Running intensity as determined by heart rate is the same in fast and slow runners in both the 10- and 21-km races

The aims of this study were to determine (1) whether running speed is directly proportional to heart rate (HR) during field testing and during 10- and 21-km races, and (2) whether running intensity, as estimated from HR measurements, differs in 10- and 21-km races and between slow and fast runners at those running distances. Male runners were divided into a fast (65-80 min for 21 km; n = 8) or slow (85-110 min for 21 km; n = 8) group. They then competed in 10- and 21-km races while wearing HR monitors. All subjects also ran in a field test in which HR was measured while they ran at predetermined speeds. The 10-km time was significantly less in the fast compared with the slow group (33:15 +/- 1:42 vs 40:07 +/- 3:01 min:s; mean +/- S.D.), as was 21-km time (74:19 +/- 4:30 vs 94:13 +/- 9:54 min:s) (P < 0.01). Despite the differences in running speed, the average running intensity (%HRmax) for the fast and slow groups in the 10-km race was 90 +/- 1 vs 89 +/- 3% and in the 21-km race 91 +/- 1 vs 89 +/- 2%, respectively. In addition, %HRmax was consistently lower in the field test at the comparative average running speeds sustained in the 10-km (P < 0.01) and 21-km (P < 0.001) races. Hence, factors in addition to work rate or running speed influence the HR response during competitive racing. This finding must be considered when running intensity for competitive events is prescribed on the basis of field testing performed under non-competitive conditions in fast and slow runners.     

Effects of endurance training and heat acclimation on psychological strain in exercising men wearing protective clothing

Two experiments examined the influences of endurance training and heat acclimation on ratings of perceived exertion (RPE) and thermal discomfort (RTD) during exercise in the heat while wearing two types of clothing. In experiment 1, young men underwent 8 weeks of physical training [60-80% of maximal aerobic power (VO2max) for 30-45 min day-1, 3-4 days week-1 at 20-22 degrees C dry bulb (db) temperature] followed by 6 days of heat acclimation [45-55% VO2max for 60 min day-1 at 40 degrees C db, 30% relative humidity (rh)] (n = 7) or corresponding periods of control observation followed by heat acclimation (n = 9). In experiment 2, young men were heat-acclimated for 6 or 12 days (n = 8 each). Before and after each treatment, subjects completed bouts of treadmill exercise (1.34 m s-1, 2% grade in experiment 1 and 0% grade in experiment 2) in a climatic chamber (40 degrees C db, 30% rh), wearing in turn normal light clothing (continuous exercise at 37-45% VO2max for a tolerated exposure of 116-120 min in experiment 1 and at 31-34% VO2max for 146-150 min in experiment 2) or clothing protective against nuclear, biological, and chemical agents (continuous exercise at 42-51% VO2max for a tolerated exposure of 47-52 min in experiment 1 and intermittent exercise at 23% VO2max for 97-120 min in experiment 2). In experiment 1, when wearing normal clothing, endurance training and/or heat acclimation significantly decreased RPE and/or RTD at a fixed power output. There were concomitant reductions in relative work intensity (% VO2max) [an unchanged oxygen consumption (VO2) but an increased VO2max, or a reduced VO2 with no change of VO2max], rectal temperature (Tre), mean skin temperature (Tsk), and/or heart rate (HR). When wearing protective clothing, in contrast, there were no significant changes in RPE or RTD. Although training and/or acclimation reduced %VO2max or Tre, any added sweat that was secreted did not evaporate through the protective clothing, thus increasing discomfort after training or acclimation. Tolerance times were unchanged in either normal or protective clothing. In experiment 2, when wearing normal clothing, heat acclimation significantly decreased RPE and RTD at a fixed power output, with concomitant reductions in Tre, Tsk, and HR; the response was greater after 12 than after 6 days of acclimation, significantly so for RPE and HR. When wearing protective clothing, the subjects exercised at a lower intensity for a longer duration than in the moderate exercise trial. Given this tactic, either 6 or 12 days of heat acclimation induces significant reductions RPE and/or RTD, accompanied by reductions in Tre, Tsk, and/or HR. Tolerance times in protective clothing were also increased by 11-15% after acclimation, despite some increase of sweat accumulation in the protective clothing. The results suggest that (1) neither endurance training nor heat acclimation reduce psychological strain when protective clothing is worn during vigorous exercise, because increased sweat accumulation adds to discomfort, and (2) in contrast to the experience during more vigorous exercise, heat acclimation is beneficial to the subject wearing protective clothing if the intensity of effort is kept to a level that allows permeation of sweat through the clothing. This condition is likely to be met in most modern industrial applications.     

The control of shivering and non-shivering thermogenesis in the rat

1. The effect of intraperitoneal administration of propranolol (4, 8 and 12 mg/kg) on colonic temperature was studied in twelve rats during exposure to ambient temperatures of 30, 15 and 5 degrees C. 2. At 30 degrees C, propranolol had no effect on colonic temperature; at 15 and 5 degrees C, however, 4 mg propanolol/kg induced a fall in colonic temperature of about 0-8 degrees C, whereas 8 and 12 mg propanolol/kg induced a fall of about 1-5-2-0 degrees C. 3. Assuming that the temperature regulations system of the rat has a proportional controller and that the effect of propranolol was due to the blockade of non-shivering thermogenesis, the results are interpreted as showing that shivering is activated only when heat loss exceeds the capacity for non-shivering thermogenesis.     

Physiological responses of men and women during exercise in hot environments with equivalent WBGT

Eight Japanese men and women participated in this study. They were randomly exposed to two environments: hot-dry; HD (Ta = 40 degrees C, rh 30%, wet bulb globe temperature (WBGT) = 32 degrees C) and hot-wet; HW (Ta = 31 degrees C, rh = 80%, WBGT = 32 degrees C) for 110 min. During the exposure, they rested on a bicycle ergometer for 20 min during rest and 30 min during recovery, then they pedaled it with an intensity of 40% VO2 max for 60 min. Tre, Tsk, and HR were recorded every minute. Total sweat loss and dripping were measured by independent bed balances which was connected to a computer processing with an accuracy of 1 g throughout the experiment. Sweat sodium concentration at forearm and back sites were collected by sweat capsule technique. These results showed that delta Tre, Tsk, evaporated sweat, dripping sweat, body heat storage of both sexes in HD were significantly higher than these in HW during exercise. HR of men in HD at the end of recovery was slightly higher than that of women. Whereas the sweat sodium concentration at forearm and back sites in both sexes remained unchanged either in HD or HW environment, it was found that HD was more stressful than HW environment under equivalent WBGT.     

Effects of ambient temperature on the capacity to perform prolonged cycle exercise in man

Eight healthy males performed four rides to exhaustion at approximately 70% of their VO2max obtained in a neutral environment. Subjects cycled at ambient temperatures (Ta) of 3.6 +/- 0.3 (SD), 10.5 +/- 0.5, 20.6 +/- 0.2, and 30.5 +/- 0.2 degrees C with a relative humidity of 70 +/- 2% and an air velocity of approximately 0.7 m.s-1. Weighted mean skin temperature (Tsk), rectal temperature (Tre), and heart rate (HR) were recorded at rest, during exercise and at exhaustion. Venous samples were drawn before and during exercise and at exhaustion for determination of hemoglobin, hematocrit, blood metabolites, and serum electrolytes and osmolality. Expired air was collected for calculation of VO2 and R which were used to estimate rates of fuel oxidation. Ratings of perceived exertion (RPE) were also obtained. Time to exhaustion was significantly influenced by Ta (P = 0.001): exercise duration was shortest at 30.5 degrees C (51.6 +/- 3.7 min) and longest at 10.5 degrees C (93.5 +/- 6.2 min). Significant effects of Ta were also observed on VE, VO2, R, estimated fuel oxidation, HR, Tre, Tsk, sweat rate, and RPE. This study demonstrates that there is a clear effect of temperature on exercise capacity which appears to follow an inverted U relationship.     

Intracellular application of calmidazolium increases Ca2+ current through activation of protein kinase A in cultured vascular smooth muscle cells

This study compared markers of the metabolic processes occurring in male and female adolescent triathletes from two age groups (over 15 years of age [O15] and under 15 years of age [U15]) during a laboratory based duathlon. Participants were tested on three separate occasions; two peak VO2 tests on a treadmill and cycle ergometer, and a third session involved a simulated duathlon (2 km run, 12 km ride and 4 km run for the O15 group or 1 km run, 8 km ride and 2 km run for the U15). Data collection included performance speed, cardiorespiratory responses and blood borne markers of exercise metabolism. The performance speeds selected by the two age groups did not differ. The mean relative percentage of VO2peak at which subjects participated were 79+/-3, 77+/-4%, for the O15 males and females, and 71+/-5 and 82+/-2%, for the U15 males and females, respectively. While the plasma metabolites of ammonia [NH3] and lactate [La] were not different between age groups and sex (p>0.05) there were however, higher concentrations recorded during the cycling phase when compared with the running phases (p < 0.05). The respective mean concentrations for NH3 and La were 80.5+/-5.6 microM, and 4.9+/-0.3 microM for cycling, and 56.3+/-2.7 microM, and 2.7+/-0.2 microM for the combined running phases.