Finger and forearm vasodilatatory changes after local cold acclimation

To determine the vascular changes induced by local cold acclimation, post-ischaemia and exercise vasodilatation were studied in the finger and the forearm of five subjects cold-acclimated locally and five non-acclimated subjects. Peak blood flow was measured by venous occlusion plethysmography after 5 min of arterial occlusion (PBFisc), after 5 min of sustained handgrip at 10% maximal voluntary contraction (PBFexe), and after 5 min of both treatments simultaneously (PBFisc + exe). Each test was performed at room temperature (25 degrees C, SE 1 C) (non-cooled condition) and after 5 min of 5 degrees C cold water immersion (cooled condition). After the cold acclimation period, the decrease in skin temperature was more limited in the cold-acclimated compared to the non-acclimated (P less than 0.01). The PBFisc was significantly reduced in the cooled condition only in the cold-acclimated subjects (finger: 8.4 ml.100 ml-1.min-1, SE 1.1, P less than 0.01; forearm: 5.8 ml.100 ml-1.min-1, SE 1.5, P less than 0.01) compared to the non-cooled condition. Forearm PBFexe was significantly decreased in the cooled condition only in the cold-acclimated subjects (non-cooled: 7.4 ml.100 ml-1.min-1, SE 1.2; cooled: 3.9 ml.100 ml-1.min-1, SE 2.6, P less than 0.05) indicating that muscle blood flow was also reduced.(ABSTRACT TRUNCATED AT 250 WORDS)     

Effect of short-term energy intake level and exercise on oxygen consumption in men

The influence of short-term energy intake and cycle exercise on oxygen consumption in response to a 1.5 MJ test meal was investigated in ten young, adult men. On the morning after a previous day's "low-energy" intake (LE regimen) of 4.5 MJ, the mean resting oxygen consumption increased by 0.7 ml X kg-1 X min-1 after the test meal (P less than 0.025). After a "high-energy" intake (HE regimen) of 18.1 MJ, the resting measurement was unchanged (+0.4 ml X kg-1 X min-1) after the meal (n.s.). These trends are the reverse of what would be expected if oxygen consumption in response to feeding is a factor in the acute control of body weight. The mean fasting oxygen consumption during cycle exercise at 56% of VO2max (constant work) for both LE and HE prior intakes was not different at 31.1 ml X kg-1 X min-1. Oxygen consumption during exercise increased after feeding by 0.5 ml X kg-1 X min-1 on the LE regimen (n.s.) and decreased by 1.2 ml X kg-1 X min-1 on the HE regimen (n.s.). These results are also the reverse of what would be expected if oxygen consumption in response to exercise is related to short-term energy intake.     

Human tolerance to heat strain during exercise: influence of hydration.

This study determined whether 1) exhaustion from heat strain occurs at the same body temperatures during exercise in the heat when subjects are euhydrated as when they are hypohydrated, 2) aerobic fitness influences the body temperature at which exhaustion from heat strain occurs, and 3) curves could be developed to estimate exhaustion rates at a given level of physiological strain. Seventeen heat-acclimated men [maximal oxygen uptake (VO2max) from 45 to 65 ml.kg-1.min-1] attempted two heat stress tests (HSTs): one when euhydrated and one when hypohydrated by 8% of total body water. The HSTs consisted of 180 min of rest and treadmill walking (45% VO2max) in a hot-dry (ambient temperature 49 degrees C, relative humidity 20%) environment. The required evaporative cooling (Ereq) exceeded the maximal evaporative cooling capacity of the environment (Emax); thus thermal equilibrium could not be achieved and 27 of 34 HSTs ended by exhaustion from heat strain. Our findings concerning exhaustion from heat strain are 1) hypohydration reduced the core temperature that could be tolerated; 2) aerobic fitness, per se, did not influence the magnitude of heat strain that could be tolerated; 3) curves can be developed to estimate exhaustion rates for a given level of physiological strain; and 4) exhaustion was rarely associated with a core temperature up to 38 degrees C, and it always occurred before a temperature of 40 degrees C was achieved. These findings are applicable to heat-acclimated individuals performing moderate-intensity exercise under conditions where Ereq approximates or exceeds Emax and who have high skin temperatures.     

Comparison in men of physiological responses to exercise of increasing intensity at low and moderate ambient temperatures

In six male subjects the sweating thresholds, heart rate (fc), as well as the metabolic responses to exercise of different intensities [40%, 60% and 80% maximal oxygen uptake (VO2max)], were compared at ambient temperatures (Ta) of 5 degrees C (LT) and 24 degrees C (MT). Each period of exercise was preceded by a rest period at the same temperature. In LT experiments, the subjects rested until shivering occurred and in MT experiments the rest period was made to be of exactly equivalent length. Oxygen uptake (VO2) at the end of each rest period was higher in LT than MT (P less than 0.05). During 20-min exercise at 40% VO2max performed in the cold no sweating was recorded, while at higher exercise intensities sweating occurred at similar rectal temperatures (Tre) but at lower mean skin (Tsk) and mean body temperatures (Tb) in LT than MT experiments (P less than 0.001). The exercise induced VO2 increase was greater only at the end of the light (40% VO2max) exercise in the cold in comparison with MT (P less than 0.001). Both fc and blood lactate concentration [1a]b were lower at the end of LT than MT for moderate (60% VO2max) and heavy (80% VO2max) exercises. It was concluded that the sweating threshold during exercise in the cold environment had shifted towards lower Tb and Tsk. It was also found that subjects exposed to cold possessed a potentially greater ability to exercise at moderate and high intensities than those at 24 degrees C since the increases in Tre, fc and [1a]b were lower at the lower Ta.     

Thermoregulatory, cardiovascular, and muscular factors related to exercise after precooling

The effect of slightly lowered body temperature on endurance time and possibly related physiological factors was studied in seven male volunteers exercising on a cycle ergometer at an ambient temperature (Ta) of 18 degrees C. Work load was increased to 40% in a stepwise manner (phase I, min 0-16) followed by a period at 80% of peak oxygen consumption (VO2) sustained to exhaustion. On one day, exercise was preceded by a double cold exposure (precooling test, PRET), resulting in a 204-kJ/m2 negative heat storage and a 4 and 0.2 degrees C lower mean skin and core temperature at the start of exercise compared with the control test (CONT). Core temperature dropped further during exercise in PRET. Endurance time at 80% of peak VO2 was increased by 12% (P less than 0.05) in PRET. Heart rate (HR) was decreased throughout PRET (P less than 0.05); oxygen pulse and arteriovenous O2 difference were significantly increased in phase I of PRET, whereas the PRET-CONT differences in stroke volume and cardiac output were not significant. In phase II of PRET (min 16-28, heavy exercise) sweat rate (SR) and heat conductivity, indicating forearm blood flow, were lower (-39%, P less than 0.001; -37%). Pedal rate (PR) was 9% lower (P less than 0.01) in phase II of PRET. At the termination of exercise, PRET-CONT differences in HR, SR, and PR had disappeared.     

Effect of training on the dose-response relationship for insulin action in men

Seven endurance-trained subjects [maximal O2 consumption (VO2max) 64 +/- 1 (SE) ml.min-1.kg-1] were subjected to three sequential hyperinsulinemic euglycemic clamps 15 h after having performed their last training session (T). Results were compared with findings in seven untrained subjects (VO2max 44 +/- 2 ml.min-1.kg-1) studied both at rest (UT) and after 60 min of bicycle exercise at 150 W (UT-ex). In T and UT-ex compared with UT, sensitivity for insulin-mediated whole-body glucose uptake was higher [insulin concentrations eliciting half-maximal glucose uptake being 44 +/- 2 (T) and 43 +/- 4 (UT-ex) vs. 52 +/- 3 microU/ml (UT), P less than 0.05] and responsiveness was higher [13.4 +/- 1.2 (T) and 10.9 +/- 0.7 (UT-ex) vs. 9.5 +/- 0.7 mg.min-1.kg-1 (UT), P less than 0.05]. Furthermore, responsiveness was higher (P less than 0.05) in T than in UT-ex. Insulin-stimulated O2 uptake and maximal glucose oxidation rate were higher in T than in UT and UT-ex. Insulin-stimulated conversion or glucose to glycogen and muscle glycogen synthase was higher in T than in UT and UT-ex. However, glycogen storage in vastus lateralis muscle was found only in UT-ex. No change in any glucoregulatory hormone or metabolite could explain the increased insulin action in trained subjects. It is concluded that physical training induces an adaptive increase in insulin responsiveness of whole-body glucose uptake, which does not reflect increased glycogen deposition in muscle.(ABSTRACT TRUNCATED AT 250 WORDS)     

Glucagon chronically impairs hepatic and muscle glucose disposal

Defects in insulin secretion and/or action contribute to the hyperglycemia of stressed and diabetic patients, and we hypothesize that failure to suppress glucagon also plays a role. We examined the chronic impact of glucagon on glucose uptake in chronically catheterized conscious depancreatized dogs placed on 5 days of nutritional support (NS). For 3 days of NS, a variable intraportal infusion of insulin was given to maintain isoglycemia (approximately 120 mg/dl). On day 3 of NS, animals received a constant low infusion of insulin (0.4 mU.kg-1.min-1) and either no glucagon (CONT), basal glucagon (0.7 ng.kg-1.min-1; BasG), or elevated glucagon (2.4 ng.kg-1.min-1; HiG) for the remaining 2 days. Glucose in NS was varied to maintain isoglycemia. An additional group (HiG+I) received elevated insulin (1 mU.kg-1.min-1) to maintain glucose requirements in the presence of elevated glucagon. On day 5 of NS, hepatic substrate balance was assessed. Insulin and glucagon levels were 10+/-2, 9+/-1, 7+/-1, and 24+/-4 microU/ml, and 24+/-5, 39+/-3, 80+/-11, and 79+/-5 pg/ml, CONT, BasG, HiG, and HiG+I, respectively. Glucagon infusion decreased the glucose requirements (9.3+/-0.1, 4.6+/-1.2, 0.9+/-0.4, and 11.3+/-1.0 mg.kg-1.min-1). Glucose uptake by both hepatic (5.1+/-0.4, 1.7+/-0.9, -1.0+/-0.4, and 1.2+/-0.4 mg.kg-1.min-1) and nonhepatic (4.2+/-0.3, 2.9+/-0.7, 1.9+/-0.3, and 10.2+/-1.0 mg.kg-1.min-1) tissues decreased. Additional insulin augmented nonhepatic glucose uptake and only partially improved hepatic glucose uptake. Thus, glucagon impaired glucose uptake by hepatic and nonhepatic tissues. Compensatory hyperinsulinemia restored nonhepatic glucose uptake and partially corrected hepatic metabolism. Thus, persistent inappropriate secretion of glucagon likely contributes to the insulin resistance and glucose intolerance observed in obese and diabetic individuals.     

Predictors of sweat loss in man during prolonged exercise

Nineteen healthy male subjects, differing in training status and Vo2max (52 +/- 1 ml.min-1.kg-1, mean +/- SEM; 43-64 ml.min-1.kg-1, range), exercised for 1 h at an absolute workload of 192 +/- 8 W (140-265 W); this was equivalent to 70 +/- 1% Vo2max (66-74%). Each exercise test was performed on an electrically braked cycle ergometer at a constant ambient temperature (22.5 +/- 0.0 degrees C) and relative humidity (85 +/- 0%). Nude body weight was recorded prior to and after each exercise test. Absolute sweat loss (body weight loss corrected for respiratory weight loss) during each test was 910 +/- 82 g (426-1665 g); this was equivalent to 1.3 +/- 0.1% (0.7-2.2%) of pre-exercise body weight (relative sweat loss). Weighted mean skin temperature and rectal temperature increased after 5 min of exercise from 30.5 +/- 0.3 degrees C and 37.2 +/- 0.1 degrees C respectively to 32.5 +/- 0.2 degrees C and 38.8 +/- 0.1 degrees C respectively, recorded immediately prior to the end of exercise. Bivariate linear regression and Pearson's correlation demonstrated absolute sweat loss was related to Vo2max (r = 0.72, p less than 0.001), absolute exercise workload (r = 0.66, p less than 0.01), body surface area (r = 0.62, p less than 0.01), weight (r = 0.60, p less than 0.01) and height (r = 0.53, p less than 0.05). Relative sweat loss was related to VO2max (r = 0.77, P less than 0.001) and absolute exercise workload (R = 0.59, P less than 0.01).(ABSTRACT TRUNCATED AT 250 WORDS)     

Effect of high-intensity endurance training on isokinetic muscle power

The purpose of this study was to determine the effects of high-intensity endurance training on isokinetic muscle power. Six male students majoring in physical-education participated in high intensity endurance training on a cycle ergometer at 90% of maximal oxygen uptake (VO2max) for 7 weeks. The duration of the daily exercise session was set so that the energy expenditure equalled 42 kJ.kg-1 of lean body mass. Peak knee extension power was measured at six different speeds (30 degrees, 60 degrees, 120 degrees, 180 degrees, 240 degrees, and 300 degrees.s-1) with an isokinetic dynamometer. After training, VO2max increased significantly from mean values of 51.2 ml.kg-1.min-1, SD 6.5 to 56.3 ml.kg-1.min-1, SD 5.3 (P less than 0.05). Isokinetic peak power at the lower test speeds (30 degrees, 60 degrees and 120 degrees.s-1) increased significantly (P less than 0.05). However, no significant differences in muscle peak power were found at the faster velocities of 180 degrees, 240 degrees, and 300 degrees.s-1. The percentage improvement was dependent on the initial muscle peak power of each subject and the training stimulus (intensity of cycle ergometer exercise).     

Effect of endurance training on excessive CO2 expiration due to lactate production in exercise

We attempted to determine the change in total excess volume of CO2 output (CO2 excess) due to bicarbonate buffering of lactic acid produced in exercise due to endurance training for approximately 2 months and to assess the relationship between the changes of CO2 excess and distance-running performance. Six male endurance runners, aged 19-22 years, were subjects. Maximal oxygen uptake (VO2max), oxygen uptake (VO2) at anaerobic threshold (AT), CO2 excess and blood lactate concentration were measured during incremental exercise on a cycle ergometer and 12-min exhausting running performance (12-min ERP) was also measured on the track before and after endurance training. The absolute magnitudes in the improvement due to training for CO2 excess per unit of body mass per unit of blood lactate accumulation (delta la-) in exercise (CO2 excess.mass-1.delta la-), 12-min ERP, VO2 at AT (AT-VO2) and VO2max on average were 0.8 ml.kg-1.l-1.mmol-1, 97.8 m, 4.4 ml.kg-1. min-1 and 7.3 ml.kg-1.min-1, respectively. The percentage change in CO2 excess.mass-1.delta la- (15.7%) was almost same as those of VO2max (13.7%) and AT-VO2 (13.2%). It was found to be a high correlation between the absolute amount of change in CO2 excess.mass-1.delta la-, and the absolute amount of change in AT-VO2 (r = 0.94, P less than 0.01).(ABSTRACT TRUNCATED AT 250 WORDS)     

Effect of physical training on the responses of serum adrenocorticotropic hormone during prolonged exhausting exercise

The purpose of this study was to investigate the effects of physical training on the responses of serum adrenocorticotropic hormone (ACTH) and cortisol concentration during low-intensity prolonged exercise. Five subjects who had fasted for 12 h cycled at the same absolute intensity that elicited 50% of pre-training maximal oxygen uptake (VO2max), either until exhaustion or for up to 3 h, before and after 7 weeks of vigorous physical training [mean daily energy consumption during training exercise, 531 kcal (2230 kJ)]. In the pretraining test, serum ACTH and cortisol concentrations did not increase during the early part of the exercise. Increases in concentrations of both hormones occurred in all subjects when blood glucose concentration decreased during the later phase of the exercise. The mean values and SEM of serum ACTH and cortisol concentrations at the end of the exercise were 356 ng.l-1, SEM 79 and 438 micrograms.l-1, SEM 36, respectively. After the physical training, VO2max of the subjects improved significantly from the mean value of 50.2 ml.kg-1.min-1, SEM 2.5 to 57.3 ml.kg-1.min-1, SEM 2.0 (P less than 0.05). In the post-training test, exercise time to exhaustion was prolonged in three subjects. Comparing the pre- and post training values observed after the same length of time that the subjects had exercised in the pre-training test, the post-training values of serum ACTH (44 ng.l-1, SEM 3) and cortisol (167 micrograms.l-1, SEM 30) concentration were less than the pre-training value (P less than 0.05).(ABSTRACT TRUNCATED AT 250 WORDS)     

Dynamics of hepatic lactate and glucose balances during prolonged exercise and recovery in the dog

The present experiments were undertaken to assess dynamics of hepatic lactate and glucose balance in the over-night-fasted dog during 150 min of moderate-intensity treadmill exercise and 90 min of exercise recovery. Catheters were implanted chronically in an artery and portal and hepatic veins 16 days before experimentation. 3-3H-glucose was infused to determine hepatic glucose uptake, as well as tracer-determined glucose production by isotope dilution (Ra). At rest, net hepatic lactate output was 0.33 +/- 0.15 mg.kg-1.min-1 and increased to 2.26 +/- 0.82 mg.kg-1.min-1 after 10 min of exercise, after which it fell such that the liver was a net lactate consumer by the end of exercise and through recovery. In contrast to the rapid release of lactate, net hepatic glucose output rose gradually from 2.58 +/- 0.20 mg.kg-1.min-1 at rest to 8.87 +/- 0.85 mg.kg-1.min-1 after 60 min of exercise, beyond which it did not change significantly until the cessation of exercise. Hepatic glucose uptake at rest was 1.38 +/- 0.42 mg.kg-1.min-1 and did not change appreciably during exercise or recovery. Absolute hepatic glucose output (net glucose output plus uptake) rose from 3.96 +/- 0.45 mg.kg-1.min-1 at rest to 10.20 +/- 1.09 mg.kg-1.min-1 after 60 min of exercise and was 9.65 +/- 1.15 mg.kg-1.min-1 at 150 min of exercise. Ra rose from 3.34 +/- 0.21 mg.kg-1.min-1 to 7.58 +/- 0.73 and 8.59 +/- 0.77 mg.kg-1.min-1 at 60 and 150 min, respectively.(ABSTRACT TRUNCATED AT 250 WORDS)     

Thermoregulatory responses to upper body exercise

The purpose of this study was to compare thermoregulatory responses between upper body and lower body exercise. Nine male subjects performed 60 min of arm crank (AC) and cycle (CY) exercise at the same absolute intensity (oxygen uptake = 1.61 X min-1) and at the same relative intensity (60% of ergometer specific peak oxygen uptake) in a temperate (24 degrees C, 20% rh) environment. During the absolute intensity experiments, rectal temperature and sweating rate responses were essentially the same for both modes of exercise. In addition, no differences were found for chest, back, arm, or thigh skin temperatures, but calf skin temperature was significantly (P less than 0.05) lower during arm crank than cycle exercise. During the relative intensity experiments, thermoregulatory responses were lower during arm crank than cycle exercise. In addition, we found no difference between esophageal and rectal temperature values elicited by arm crank exercise. These results indicate that the examined thermoregulatory responses are independent of the skeletal muscle mass employed and dependent upon the absolute metabolic intensity.     

Endurance training slows down the kinetics of heart rate increase in the transition from moderate to heavier submaximal exercise intensities

To find out whether endurance training influences the kinetics of the increases in heart rate (fc) during exercise driven by the sympathetic nervous system, the changes in the rate of fc adjustment to step increments in exercise intensities from 100 to 150 W were followed in seven healthy, previously sedentary men, subjected to 10-week training. The training programme consisted of 30-min cycle exercise at 50%-70% of maximal oxygen uptake (VO2max) three times a week. Every week during the first 5 weeks of training, and then after the 10th week the subjects underwent the submaximal three-stage exercise test (50, 100 and 150 W) with continuous fc recording. At the completion of the training programme, the subjects' VO2max had increased significantly (39.2 ml.min-1.kg-1, SD 4.7 vs 46 ml.min-1.kg-1, SD 5.6) and the steady-state fc at rest and at all submaximal intensities were significantly reduced. The greatest decrease in steady-state fc was found at 150 W (146 beats.min-1, SD 10 vs 169 beats.min-1, SD 9) but the difference between the steady-state fc at 150 W and that at 100 W (delta fc) did not decrease significantly (26 beats.min-1, SD 7 vs 32 beats.min-1, SD 6). The time constant (tau) of the fc increase from the steady-state at 100 W to steady-state at 150 W increased during training from 99.4 s, SD 6.6 to 123.7 s, SD 22.7 (P less than 0.01) and the acceleration index (A = 0.63.delta fc.tau-1) decreased from 0.20 beats.min-1.s-1, SD 0.05 to 0.14 beats.min-1.s-1, SD 0.04 (P less than 0.02). The major part of the changes in tau and A occurred during the first 4 weeks of training. It was concluded that heart acceleration following incremental exercise intensities slowed down in the early phase of endurance training, most probably due to diminished sympathetic activation.     

Lymphocyte proliferation responses after exercise in men: fitness, intensity, and duration effects

This study investigated the effects of intensity and duration of exercise on lymphocyte proliferation as a measure of immunologic function in men of defined fitness. Three fitness groups--low [maximal O2 uptake (VO2max) = 44.9 +/- 1.5 ml O2.kg-1.min-1 and sedentary], moderate (VO2max = 55.2 +/- 1.6 ml O2.kg-1.min-1 and recreationally active), and high (VO2max = 63.3 +/- 1.8 ml O2.kg-1.min-1 and endurance trained)--and a mixed control group (VO2max = 52.4 +/- 2.3 ml O2.kg-1.min-1) participated in the study. Subjects completed four randomly ordered cycle ergometer rides: ride 1, 30 min at 65% VO2max; ride 2, 60 min at 30% VO2max; ride 3, 60 min at 75% VO2max; and ride 4, 120 min at 65% VO2max. Blood samples were obtained at various times before and after the exercise sessions. Lymphocyte responses to the T cell mitogen concanavalin A were determined at each sample time through the incorporation of radiolabeled thymidine [( 3H]TdR). Despite differences in resting levels of [3H]TdR uptake, a consistent depression in mitogenesis was present 2 h after an exercise bout in all fitness groups. The magnitude of the reduction in T cell mitogenesis was not affected by an increase in exercise duration. A trend toward greater reduction was present in the highly fit group when exercise intensity was increased. The reduction in lymphocyte proliferation to the concanavalin A mitogen after exercise was a short-term phenomenon with recovery to resting (preexercise) values 24 h after cessation of the work bout. These data suggest that single sessions of submaximal exercise transiently reduce lymphocyte function in men and that this effect occurs irrespective of subject fitness level.     

The influence of cardiorespiratory fitness on the decrement in maximal aerobic power at high altitude

There are conflicting reports in the literature which imply that the decrement in maximal aerobic power experienced by a sea-level (SL) resident sojourning at high altitude (HA) is either smaller or larger for the more aerobically "fit" person. In the present study, data collected during several investigations conducted at an altitude of 4300 m were analyzed to determine if the level of aerobic fitness influenced the decrement in maximal oxygen uptake (VO2max) at HA. The VO2max of 51 male SL residents was measured at an altitude of 50 m and again at 4300 m. The subjects' ages, heights, and weights (mean +/- SE) were 22 +/- 1 yr, 177 +/- 7 cm and 78 +/- 2 kg, respectively. The subjects' VO2max ranged from 36 to 60 ml X kg -1 X min -1 (mean +/- SE = 48 +/- 1) and the individual values were normally distributed within this range. Likewise, the decrement in VO2max at HA was normally distributed from 3 ml X kg-1 X min-1 (9% VO2max at SL) to 29 ml X kg-1 X min-1 (54% VO2max at SL), and averaged 13 +/- 1 ml X kg-1 X min-1 (27 +/- 1% VO2max at SL). The linear correlation coefficient between aerobic fitness and the magnitude of the decrement in VO2max at HA expressed in absolute terms was r = 0.56, or expressed as % VO2max at SL was r = 0.30; both were statistically significant (p less than 0.05).(ABSTRACT TRUNCATED AT 250 WORDS)     

Sex difference in maximal oxygen uptake. Effect of equating haemoglobin concentration

Ten men and 11 women were studied to determine the effect of experimentally equating haemoglobin concentration ([Hb]) on the sex difference in maximal oxygen uptake (VO2max). VO2max was measured on a cycle ergometer using a continuous, load-incremented protocol. The men were studied under two conditions: 1) with normal [Hb] (153 g X L-1) and 2) two days following withdrawal of blood, which reduced their mean [Hb] to exactly equal the mean of the women (134 g X L-1). Prior to blood withdrawal, VO2max expressed in L X min-1 and relative to body weight and ride time on the cycle ergometer test were greater (p less than .01) in men by 1.11 L X min-1 (47%), 4.8 ml X kg-1 min-1 (11.5%) and 5.9 min (67%), respectively, whereas VO2max expressed relative to fat-free weight (FFW) was not significantly different. Equalizing [Hb] reduced (p less than .01) the mean VO2max of the men by 0.26 L X min-1 (7.5%), 3.2 ml X kg-1 min-1 (6.9%) or 4.1 ml X kg FFW-1 min-1 (7.7%), and ride time by 0.7 min (4.8%). Equalizing [Hb] reduced the sex difference for VO2max less than predicted from proportional changes in the oxygen content of the arterial blood and arteriovenous oxygen content difference during maximal exercise. It was concluded that the sex difference in [Hb] accounts for a significant, but relatively small portion of the sex difference in VO2max (L X min-1). Other factors such as the dimensions of the oxygen transport system and musculature are of greater importance.     

Long-term cold adaptation in the rat

1. To determine whether long-term cold exposure induces insulative adaptation in the rat, two groups of eight adult animals each were exposed to 4 and 25 degrees C, respectively, for 18 months. 2. At any ambient temperature between -5 and 30 degrees C, the cold adapted animals had a higher rate of oxygen uptake, and higher unfurred skin temperatures than the controls. 3. At ambient temperatures below thermoneutrality, whole body thermal resistance increased continuously in both groups of animals. 4. It is concluded that long-term exposure does not induce insulative adaptation, and that thermal resistance is not maximal at the lower critical temperature.     

Rectal and rectal vs. esophageal temperatures in paraplegic men during prolonged exercise

This study investigated the rectal (Tre), esophageal (Tes), and skin (Tsk) temperature changes in a group of trained traumatic paraplegic men pushing their own wheelchairs on a motor-driven treadmill for a prolonged period in a neutral environment. There were two experiments. The first experiment (Tre and Tsk) involved a homogeneous group (T10-T12/L3) of highly trained paraplegic men [maximum O2 uptake (VO2max) 47.5 +/- 1.8 ml.kg-1.min-1] exercising for 80 min at 60-65% VO2max.Tre and Tsk (head, arm, thigh, and calf) and heart rate (HR) were recorded throughout. O2 uptake (VO2), minute ventilation (VE), CO2 production (VCO2), and heart rate (HR) were recorded at four intervals. During experiment 1 significant changes in HR and insignificant changes in VCO2, VE, and VO2 occurred throughout prolonged exercise. Tre increased significantly from 37.1 +/- 0.1 degrees C (rest) to 37.8 +/- 0.1 degrees C after 80 min of exercise. There were only significant changes in arm Tsk. Experiment 2 involved a nonhomogeneous group (T5-T10/T11) of active paraplegics (VO2max 39.9 +/- 4.3 ml.kg-1.min-1) exercising at 60-65% VO2max for up to 45 min on the treadmill while Tre and Tes were simultaneously recorded. Tes rose significantly faster than Tre during exercise (dT/dt 20 min: Tes 0.050 +/- 0.003 degrees C/min and Tre 0.019 +/- 0.005 degrees C/min), and Tes declined significantly faster than Tre at the end of exercise. Tes was significantly higher than Tre at the end of exercise. Our results suggest that during wheelchair propulsion by paraplegics, Tes may be a better estimate of core temperature than Tre.     

Effects of airflow and work load on cardiovascular drift and skin blood flow

Cardiovascular drift (CVD) can be defined as a progressive increase in heart rate (HR), decreases in stroke volume (SV) and mean arterial pressure (MAP), and a maintained cardiac output (Q) during prolonged exercise. To test the hypothesis that the magnitude of CVD would be related to changes in skin blood flow ( SkBF ), eight healthy, moderately trained males performed 70-min bouts of cycle ergometry in a 2 X 2 assortment of airflows (less than 0.2 and 4.3 m X s-1) and relative work loads (43.4% and 62.2% maximal O2 uptake). Ambient temperature and relative humidity were controlled to mean values of 24.2 +/- 0.8 degrees C and 39.5 +/- 2.4%, respectively. Q, HR, MAP, SkBF , skin and rectal temperatures, and pulmonary gas exchange were measured at 10-min intervals during exercise. Between the 10th and 70th min during exercise at the higher work load with negligible airflow, HR and SkBF increased by 21.6 beats X min-1 and 14.0 ml X 100 ml-1 X min-1, respectively, while SV and MAP decreased by 16.4 ml and 11.3 mmHg. The same work load in the presence of 4.3 m X s-1 airflow resulted in nonsignificant changes of 7.6 beats X min-1, 4.0 ml X (100 ml-1 X min)-1, -2.7 ml, and -1.7 mmHg for HR, SkBF , SV, and MAP. Since nonsignificant changes in HR, SkBF , SV, and MAP were observed at the lower work load in both airflow conditions, the results emphasize that CVD occurs only in conditions which combine high metabolic and thermal circulatory demands.(ABSTRACT TRUNCATED AT 250 WORDS)