Oxygen consumption following exercise of moderate intensity and duration.

To study the effects of exercise intensity and duration on excess postexercise oxygen consumption (EPOC), 8 men [age = 27.6 (SD 3.8) years, VO2max = 46.1 (SD 8.5) ml min-1 kg-1] performed four randomly assigned cycle-ergometer tests (20 min at 60% VO2max, 40 min at 60% VO2max, 20 min at 70% VO2max, and 40 min at 70% VO2max). O2 uptake, heart rate and rectal temperature were measured before, during, and for 1 h following the exercise tests. Blood for plasma lactate measurements was obtained via cannulae before, and at selected times, during and following exercise. VO2 rapidly declined to preexercise levels following each of the four testing sessions, and there were no differences in EPOC between the sessions. Blood lactate and rectal temperature increased (P < 0.05) with exercise, but had returned to preexercise levels by 40 min of recovery. The results indicate that VO2 returned to resting levels within 40 min after the end of exercise, regardless of the intensity (60% and 70% VO2max) or duration (20 min and 40 min) of the exercise, in men with a moderate aerobic fitness level.     

Sex differences in endurance capacity and metabolic response to prolonged, heavy exercise

In order to test for possible sex differences in endurance capacity, groups of young, physically active women (n = 6) and men (n = 7) performed bicycle ergometer exercise at 80% and 90% of their maximal oxygen uptakes (VO2 max). The groups were matched for age and physical activity habits. At 80% VO2 max the women performed significantly longer (P less than 0.05), 53.8 +/- 12.7 min vs 36.8 +/- 12.2 min, respectively (means +/- SD). Mid-exercise and terminal respiratory exchange ratio (R) values were significantly lower in women, suggesting a later occurrence of muscle glycogen depletion as a factor in their enhanced endurance. At 90% VO2 max the endurance times were similar for men and women, 21.2 +/- 10.3 min and 22.0 +/- 5.0 min, respectively. The blood lactate levels reached in these experiments were only marginally lower (mean differences 1.5 to 2 mmol X l-1) than those obtained at VO2 max, suggesting high lactate levels as a factor in exhaustion. The changes in body weight during the 80% experiments and the degree of hemoconcentration were not significantly different between men and women.     

The effect of exercise intensity and duration on the oxygen deficit and excess post-exercise oxygen consumption

Nine males with mean maximal oxygen consumption (VO2max) = 63.0 ml.kg-1.min-1, SD 5.7 and mean body fat = 10.6%, SD 3.1 each completed nine counterbalanced treatments comprising 20, 50 and 80 min of treadmill exercise at 30, 50 and 70% VO2max. The O2 deficit, 8 h excess post-exercise oxygen consumption (EPOC) and EPOC:O2 deficit ratio were calculated for all subjects relative to mean values obtained from 2 control days each lasting 9.3 h. The O2 deficit, which was essentially independent of exercise duration, increased significantly (P less than 0.05) with intensity such that the overall mean values for the three 30%, 50% and 70% VO2max workloads were 0.83, 1.89 and 3.09 l, respectively. While there were no significant differences (P greater than 0.05) between the three EPOCs after walking at 30% VO2max for 20 (1.01 l), 50 (1.43 l) and 80 min (1.04 l), respectively, the EPOC thereafter increased (P less than 0.05) with both intensity and duration such that the increments were much greater for the three 70% VO2max workloads (EPOC: 20 min = 5.68 l; 50 min = 10.04 l; 80 min = 14.59 l) than for the three 50% VO2max workloads (EPOC: 20 min = 3.14 l; 50 min = 5.19 l; 80 min = 6.10 l). An analysis of variance indicated that exercise intensity was the major determinant of the EPOC since it explained five times more of the EPOC variance than either exercise duration or the intensity times duration interaction. The mean EPOC:O2 deficit ratio ranged from 0.8 to 4.5 and generally increased with both exercise intensity and duration.(ABSTRACT TRUNCATED AT 250 WORDS)     

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.     

Endurance training of older men: responses to submaximal exercise.

The purpose of this study was to quantify the exercise response of older subjects on a time-to-fatigue (TTF) submaximal performance test before and after a training program. Eight older men (67.4 +/- 4.8 yr) performed two maximal treadmill tests to determine maximum oxygen uptake (VO2max) and ventilation threshold (TVE) and a constant-load submaximal exercise treadmill test that required an oxygen uptake (VO2) between TVE and VO2max. The submaximal test, performed at the same absolute work rate before and after the training program, was performed to volitional fatigue to measure endurance time. The men trained under supervision at an individualized pace representing approximately 70% of VO2max (80% maximum heart rate) for 1 h, four times per week for 9 wk. Significant increases were demonstrated for VO2max (ml.kg-1.min-1; 10.6%); maximal ventilation (VE, l/min; 11.6%), and TVE (l/min; 9.8%). Weight decreased 2.1%. Performance time on the TTF test increased by 180% (7.3 +/- 3.0 to 20.4 +/- 13.5 min). The similar end points for VO2, VE, and heart rate during the TTF and maximal treadmill tests established that the TTF test was stopped because of physiological limitations. The increase in performance time among the subjects was significantly correlated with improvements in VO2max and TVE, with the submaximal work rate representing a VO2 above TVE by 88% of the difference between TVE and VO2max pretraining and 73% of this difference on posttraining values.     

Effect of carbohydrate feedings during high-intensity exercise

To determine the upper limits of steady-state exercise performance and carbohydrate oxidation late in exercise, seven trained men were studied on two occasions during prolonged cycling that alternated every 15 min between approximately 60% and approximately 85% of VO2max. When fed a sweet placebo throughout exercise, plasma glucose and respiratory exchange ratio (R) declined (P less than 0.05) from 5.0 +/- 0.1 mM and 0.91 +/- 0.01 after 30 min (i.e., at 85% VO2max) to 3.7 +/- 0.3 mM and 0.79 +/- 0.01 at fatigue (i.e., when the subjects were unable to continue exercise at 60% VO2max). Carbohydrate feeding throughout exercise (1 g/kg at 10 min, then 0.6 g/kg every 30 min) increased plasma glucose to approximately 6 mM and partially prevented this decline in carbohydrate oxidation, allowing the men to perform 19% more work (2.74 +/- 0.13 vs. 2.29 +/- 0.09 MJ, P less than 0.05) before fatiguing. Even when fed carbohydrate, however, by the 3rd h of exercise, R had fallen from 0.92 to 0.87, accompanied by a reduction in exercise intensity from approximately 85% to approximately 75% VO2max (both P less than 0.05). These data indicate that carbohydrate feedings enable trained cyclists to exercise at up to 75% VO2max and to oxidize carbohydrate at up to 2 g/min during the later stages of prolonged intense exercise.     

The effects of alterations in dietary carbohydrate intake on the performance of high-intensity exercise in trained individuals

This study was designed to examine the effects of alterations in dietary carbohydrate (CHO) intake on the performance of high-intensity exercise lasting approximately 10 min (EXP 1) and 30 min (EXP 2). Trained subjects exercised to exhaustion on four occasions on a cycle ergometer at 90% of maximal oxygen consumption (VO2max; EXP 1, n = 5) and 80% of VO2max (EXP 2, n = 7). The first two tests were familiarisation trials and were carried out following the subjects' normal diet. Normal training was continued but standardised during the periods of dietary control. The subsequent two tests were performed 2 weeks apart after 7 days of dietary manipulation. The two diets were a 70% and a 40% CHO diet, isoenergetic with each subject's normal diet and administered in a randomised order. At both exercise intensities, time to exhaustion following the high CHO and low CHO diets was not different [mean (SD) EXP 1: 11.56 (3.78) min and 8.95 (2.35) min, P = 0.22; EXP 2: 26.9 (7.4) min and 26.5 (6.5) min, P = 0.90]. No differences in resting blood metabolite concentrations were found apart from a lower beta-hydroxybutyrate (beta-HB) level following the high CHO diet in EXP 2. Blood lactate was higher after exercise at 90% of VO2max following the high CHO diet. Blood lactate was higher, and beta-HB lower during exercise at 80% of VO2max following the high CHO diet. No differences were found in the other blood metabolites tested. The respiratory exchange ratio after 15 min of exercise at 80% of VO2max was higher on the high CHO diet. No differences in oxygen uptake, heart rate (EXP 2) or ratings of perceived exertion (both experiments) were found between conditions. These results indicate that moderate changes in diet composition during training do not affect the performance of high-intensity exercise in trained individuals when the total energy intake is moderately high.     

Plasma catecholamines and heart rate at the beginning of muscular exercise in man

The relationship between the time course of heart rate and venous blood norepinephrine (NE) and epinephrine (E) concentrations was studied in 7 sedentary young men before and during 3 bicycle exercises of 5 min each (respectively 23 +/- 2.8%, 45 +/- 2.6% and 65 +/- 2.4% VO2max, mean +/- SE). During the low level exercise the change in heart rate is monoexponential (tau = 5.7 +/- 1.2 s) and no increment above the resting level of NE (delta NE) or of E (delta E) occurs. At the medium and highest intensity of exercise: a) the change in heart rate is biexponential, tau for the fast and the slow component averaging about 3 and 80 s respectively; b) delta NE (but not delta E) increases continuously with time of exercise; c) at the 5th min of exercise heart rate increments are related to delta NE; d) between 20 s and 5 min, at corresponding sampling times, the heart rate of the slow component is linearly related to delta NE. At exercise levels higher than 33% VO2max the increase in heart rate described by the slow component of the biexponential kinetic could be due to an augmented sympathetic activity revealed by increased NE blood levels.     

Effect of exercise intensity and duration on postexercise metabolism

Data are reported on the net recovery O2 consumption (VO2) for nine male subjects (mean age 21.9 yr, VO2max 63.0 ml.kg-1.min-1, body fat 10.6%) used in a 3 (independent variables: intensities of 30, 50, and 70% VO2max) x 3 (independent variables: durations of 20, 50, and 80 min) repeated measures design (P less than or equal to 0.05). The 8-h mean excess postexercise O2 consumptions (EPOCs) for the 20-, 50-, and 80-min bouts, respectively, were 1.01, 1.43, and 1.04 liters at 30% VO2max (6.8 km/h); 3.14, 5.19, and 6.10 liters at 50% VO2max (9.5 km/h); and 5.68, 10.04, and 14.59 liters at 70% VO2max (13.4 km/h). The mean net total O2 costs (NTOC = net exercise VO2 + EPOC) for the 20-, 50-, and 80-min bouts, respectively, were 20.48, 53.20, and 84.23 liters at 30% VO2max; 38.95, 100.46, and 160.59 liters at 50% VO2max; and 58.30, 147.48, and 237.17 liters at 70% VO2max. The nine EPOCs ranged only from 1.0 to 8.9% of the NTOC (mean 4.8%) of the exercise. These data, therefore, indicate that in well-trained subjects the 8-h EPOC per se comprises a very small percentage of the NTOC of exercise.     

Gastric emptying during walking and running: effects of varied exercise intensity

Gastric emptying is increased during running (50%-70% maximal aerobic uptake, VO2max) as compared to rest. Whether this increase varies as a function of mode (i.e. walking vs running) and intensity of treadmill exercise is unknown. To examine the gastric emptying characteristics of water during treadmill exercise performed over a wide range of intensities relative to resting conditions, 10 men ingested 400 ml of water prior to each of six 15 min exercise bouts or 15 min of seated rest. Three bouts of walking exercise (1.57 m.s-1) were performed at increasing grades eliciting approximately 28%, 41% or 56% of VO2max. On a separate day, three bouts of running (2.68 ms-1) exercise were performed at grades eliciting approximately 57%, 65% or 75% of VO2max. Gastric emptying was increased during treadmill exercise at all intensities excluding 75% VO2max as compared to rest. Gastric emptying was similar for all intensities during walking and at 57% and 65% VO2max during running. However, running at 74% VO2max decreased the volume of original drink emptied as compared to all lower exercise intensities. Stomach secretions were markedly less during running as compared to walking and rest. These data demonstrate that gastric emptying is similarly increased during both moderate intensity (approximately 28%-65% VO2max) walking or running exercise as compared to resting conditions. However, gastric emptying decreases during high intensity exercise. Increases in gastric emptying during moderate intensity treadmill exercise may be related to increases in intragastric pressure brought about by contractile activity of the abdominal muscles.     

Changes in the leucocyte count during and after brief intense exercise.

Twelve healthy male volunteers exercised at 200 W on a cycle ergometer for 8 min or until exhausted, if sooner. Retrospectively, subjects fell into two groups. During the last minute of exercise at 200 W, those in group 1 (n = 5) had a mean respiratory exchange ratio (R) of 1.06 (SD 0.01) and were working at a mean of 79% (SD 4%) of their maximum oxygen consumption (VO2max) as measured in a separate incremental load test. For subjects in group 2 (n = 7), R was 1.31 (SD 0.08) and their VO2 was maximal (mean 101%. SD 3%). Plasma lactate, and adrenaline concentrations rose to higher levels during exercise in subjects in group 2 than in those in group 1. At the finish of exercise, the leucocyte count and the plasma lactate concentration immediately began to fall in subjects in group 1 whereas in group 2 subjects both rose for several minutes before falling. Plasma catecholamine concentrations fell rapidly in both groups during recovery.     

Effects of prolonged exercise at a similar percentage of maximal oxygen consumption in trained and untrained subjects

Six trained male cyclists and six untrained but physically active men participated in this study to test the hypothesis that the use of percentage maximal oxygen consumption (%VO2max) as a normalising independent variable is valid despite significant differences in the absolute VO2max of trained and untrained subjects. The subjects underwent an exercise test to exhaustion on a cycle ergometer to determine VO2max and lactate threshold. The subjects were grouped as trained (T) if their VO2max exceeded 60 ml.kg-1.min-1, and untrained (UT) if their VO2max was less than 50 ml.kg-1.min-1. The subjects were required to exercise on the ergometer for up to 40 min at power outputs that corresponded to approximately 50% and 70% VO2max. The allocation of each exercise session (50% or 70% VO2max) was random and each session was separated by at least 5 days. During these tests venous blood was taken 10 min before exercise (- 10 min), just prior to the commencement of exercise (0 min), after 20 min of exercise (20 min), at the end of exercise and 10 min postexercise (+ 10 min) and analysed for concentrations of cortisol, [Na+], [K+], [Cl-], glucose, free fatty acid, lactate [la-], [NH3], haemoglobin [Hb] and for packed cell volume. The oxygen consumption (VO2) and related variables were measured at two time intervals (14-15 and 34-35 min) during the prolonged exercise tests. Rectal temperature was measured throughout both exercise sessions. There was a significant interaction effect between the level of training and exercise time at 50% VO2max for heart rate (fc) and venous [la-].(ABSTRACT TRUNCATED AT 250 WORDS)     

Sweat ammonia excretion during submaximal cycling exercise

This study was undertaken to investigate whether part of the ammonia formed during muscular exercise was excreted with the sweat. Male medical students volunteered for the experiment. They exercised 30 min on a bicycle ergometer at 80 and 40% of the predetermined maximal O2 uptake (VO2max). Exercise at 80% VO2max was performed twice, at room temperature (20 degrees C) and in a cold room (0 degrees C), whereas exercise at 40% was performed only at room temperature (20 degrees C). Blood was collected from the antecubital vein immediately before and after exercise. Sweat was collected from the hypogastric region by use of gauze pads. It was shown that the plasma ammonia level was elevated after exercise at 80% VO2max and remained stable after exercise at 40% VO2max. The volume of sweat produced during exercise at 80% VO2max at 20 degrees C was 428 +/- 138 ml and at 0 degrees C 245 +/- 86 ml and during exercise at 40% VO2max was 183 +/- 69 ml. The ammonia concentration in the sweat after exercise at 80% VO2max at 20 degrees C was 7,140 mumol/l and at 0 degrees C 11,816 mumol/l. After exercise at 40% VO2max, it was 2,076 mumol/l. The total ammonia lost through the sweat during exercise at 80% VO2max was similar at both temperatures, despite the difference in the sweat volume (at 20 degrees C, 3,360 +/- 2,080 mumol; at 0 degrees C, 3,310 +/- 1,250 mumol). During exercise at 40% VO2max, it was 350 +/- 230 mumol. These results show that part of ammonia formed during exercise is lost with sweat. The amount lost increases with increased work rate and the plasma ammonia concentration.     

Heart rate overshoot at the beginning of muscle exercise.

A characteristic notch in the heart rate (fc) on-response at the beginning of square-wave exercise is described in 7 very fit marathon runners and 12 sedentary young men, during cycle tests at 30% and 60% of maximal oxygen consumption (VO2max). The fc notch revealed a fc overshoot with respect to the fc values predicted from exponential beat-by-beat fitted models. While at 30% of VO2max all subjects showed a fc overshoot, at 60% of VO2max it occurred in the marathon runners but not in the sedentary subjects. The mean time of occurrence of the fc overshoot from the onset of the exercise was 16.7 (SD 4.7) s and 12.2 (SD 3.2) s at 30% of VO2max in the runners and the sedentary subjects respectively, and 23.8 (SD 8.8) s at 60% of VO2max in the runners. The amplitude of the overshoot, with respect to rest, was 41 (SD 12) beats.min-1 and 31 (SD 4) beats.min-1 at 30% of VO2max in the runners and the sedentary subjects respectively, and 46 (SD 19) beats.min-1 at 60% of VO2max in the runners. The existence and the amplitude of the fc overshoot may have been related to central command and muscle heart reflex mechanisms and thus may have been indicators of changes in the balance between sympathetic and parasympathetic activity occurring in fit and unfit subjects.     

Plasma Met-enkephalin and catecholamine responses to intense exercise in humans.

Native and cryptic Met-enkephalin and catecholamines are coreleased in response to stress. However, it is not known whether Met-enkephalin and catecholamines exhibit concurrent temporal relationships in response to exercise. The purpose of this investigation was to examine the corelease of catecholamines and Met-enkephalin in endurance-trained (n = 6) and untrained (n = 6) male subjects during a 6-min bout of exercise: 4 min at 70% of maximal O2 uptake (VO2max) followed by 2 min at 120% VO2max. Peak catecholamine levels were found at 1 min of recovery. In trained subjects, native Met-enkephalin peaked during exercise at 70% VO2max, declined during exercise at 120% VO2max, and returned to basal levels by 1 min of recovery. In the untrained subjects, native Met-enkephalin peaked at 120% VO2max (6 min) and returned to baseline by 5 min of recovery. In both groups, cryptic Met-enkephalin peaked at 70% VO2max and returned to basal levels during exercise at 120% VO2max. These data demonstrate that during exercise there is a temporal dissociation in plasma levels of Met-enkephalin and catecholamines.     

Effect of exercise on cerebral perfusion in humans at high altitude.

The effects of submaximal and maximal exercise on cerebral perfusion were assessed using a portable, recumbent cycle ergometer in nine unacclimatized subjects ascending to 5,260 m. At 150 m, mean (SD) cerebral oxygenation (rSO2%) increased during submaximal exercise from 68.4 (SD 2.1) to 70.9 (SD 3.8) (P < 0.0001) and at maximal oxygen uptake (.VO2(max)) to 69.8 (SD 3.1) (P < 0.02). In contrast, at each of the high altitudes studied, rSO2 was reduced during submaximal exercise from 66.2 (SD 2.5) to 62.6 (SD 2.1) at 3,610 m (P < 0.0001), 63.0 (SD 2.1) to 58.9 (SD 2.1) at 4,750 m (P < 0.0001), and 62.4 (SD 3.6) to 61.2 (SD 3.9) at 5,260 m (P < 0.01), and at .VO2(max) to 61.2 (SD 3.3) at 3,610 m (P < 0.0001), to 59.4 (SD 2.6) at 4,750 m (P < 0.0001), and to 58.0 (SD 3.0) at 5,260 m (P < 0.0001). Cerebrovascular resistance tended to fall during submaximal exercise (P = not significant) and rise at .VO2(max), following the changes in arterial oxygen saturation and end-tidal CO(2). Cerebral oxygen delivery was maintained during submaximal exercise at 150 m with a nonsignificant fall at .VO2(max), but at high altitude peaked at 30% of .VO2(max) and then fell progressively at higher levels of exercise. The fall in rSO2 and oxygen delivery during exercise may limit exercise at altitude and is likely to contribute to the problems of acute mountain sickness and high-altitude cerebral edema.     

Water immersion delays the oxygen uptake response to sitting arm-cranking in humans

We investigated the effect of central hypervolaemia during water immersion up to the xiphoid process on the oxygen uptake (VO2) and heart rate (HR) response to arm cranking. Seven men performed a 6-min arm-cranking exercise at an intensity requiring a VO2 at 80% ventilatory threshold both in air [C trial, 29 (SD 9) W] and immersed in water [WI trial, 29 (SD 11) W] after 6 min of sitting. The VO2 (phase 2) and HR responses to exercise were obtained from a mono-exponential fit [f(t) = baseline + gain x (1 - e(-(t-TD)/tau))]. The response was evaluated by the mean response time [MRT; sum of time constant (tau) and time delay (TD)]. No significant difference in VO2 and HR gains between the C and WI trials was observed [VO2 0.78 (SD 0.1) vs 0.80 (SD 0.2) l x min(-1), HR 36 (SD 7) vs 37 (SD 8) beats x min(-1), respectively]. Although the HR MRT was not significantly different between the C and WI trials [17 (SD 3), 19 (SD 8) s, respectively), VO2 MRT was greater in the WI trial than in the C trial [40 (SD 6), 45 (SD 6) s, respectively; P < 0.05]. Assuming no difference in VO2 in active muscle between the two trials, these results would indicate that an increased oxygen store and/or an altered response in muscle blood distribution delayed the VO2 response to exercise.     

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.     

Effect of previous supramaximal work on lacticaemia during supra-anaerobic threshold exercise

Twelve male and female subjects (eight trained, four untrained) exercised for 30 min on a treadmill at an intensity of maximal O2 consumption (% VO2max) 90.0%, SD 4.7 greater than the anaerobic threshold of 4 mmol.l-1 (Than = 83.6% VO2max, SD 8.9). Time-dependent changes in blood lactate concentration [( lab]) during exercise occurred in two phases: the oxygen uptake (VO2) transient phase (from 0 to 4 min) and the VO2 steady-state phase (4-30 min). During the transient phase, [lab] increased markedly (1.30 mmol.l-1.min-1, SD (0.13). During the steady-state phase, [lab] increased slightly (0.02 mmol.l-1.min-1, SD 0.06) and when individual values were considered, it was seen that there were no time-dependent increases in [lab] in half of the subjects. Following hyperlacticaemia (8.8 mmol.l-1, SD 2.0) induced by a previous 2 min of supramaximal exercise (120% VO2max), [lab] decreased during the VO2 transient (-0.118 mmol.l-1.min-1, SD 0.209) and steady-state (-0.088 mmol.l-1.min-1, SD 0.103) phases of 30 min exercise (91.4% VO2max, SD 4.8). In conclusion, it was not possible from the Than to determine the maximal [lab] steady state for each subject. In addition, lactate accumulated during previous supramaximal exercise was eliminated during the VO2 transient phase of exercise performed at an intensity above the Than. This effect is probably largely explained by the reduction in oxygen deficit during the transient phase. Under these conditions, the time-course of changes in [lab] during the VO2 steady state was also affected.     

Pulmonary gas exchange during exercise in women: effects of exercise type and work increment.

Exercise-induced arterial hypoxemia (EIAH) has been reported in male athletes, particularly during fast-increment treadmill exercise protocols. Recent reports suggest a higher incidence in women. We hypothesized that 1-min incremental (fast) running (R) protocols would result in a lower arterial PO(2) (Pa(O(2))) than 5-min increment protocols (slow) or cycling exercise (C) and that women would experience greater EIAH than previously reported for men. Arterial blood gases, cardiac output, and metabolic data were obtained in 17 active women [mean maximal O(2) uptake (VO(2 max)) = 51 ml. kg(-1). min(-1)]. They were studied in random order (C or R), with a fast VO(2 max) protocol. After recovery, the women performed 5 min of exercise at 30, 60, and 90% of VO(2 max) (slow). One week later, the other exercise mode (R or C) was similarly studied. There were no significant differences in VO(2 max) between R and C. Pulmonary gas exchange was similar at rest, 30%, and 60% of VO(2 max). At 90% of VO(2 max), Pa(O(2)) was lower during R (mean +/- SE = 94 +/- 2 Torr) than during C (105 +/- 2 Torr, P < 0.0001), as was ventilation (85.2 +/- 3.8 vs. 98.2 +/- 4.4 l/min BTPS, P < 0.0001) and cardiac output (19.1 +/- 0.6 vs. 21.1 +/- 1.0 l/min, P < 0.001). Arterial PCO(2) (32.0 +/- 0.5 vs. 30.0 +/- 0.6 Torr, P < 0.001) and alveolar-arterial O(2) difference (A-aDO(2); 22 +/- 2 vs. 16 +/- 2 Torr, P < 0.0001) were greater during R. Pa(O(2)) and A-aDO(2) were similar between slow and fast. Nadir Pa(O(2)) was 相似文献