Effects of oral propranolol and exercise protocol on indices of aerobic function in normal man

The exercise responses to two different progressive, upright cycle ergometer tests were studied in nine healthy, young subjects either with no drug (ND) or following 48 h or oral propranolol (P) (40 mg q.i.d.). The ergometer tests increased work rate by 30 W either every 30 s or every 4 min. Propranolol caused a significant (p less than 0.05) reduction in peak oxygen uptake (VO2) during both the 30-s and 4-min tests (30-s ND, 3949 +/- 718 mL X min-1 (means +/- SD); 30-s P, 3408 +/- 778 mL X min-1; 4-min ND, 4058 +/- 409 mL X min-1; 4-min P, 3725 +/- 573 mL X min-1). There was no difference between 30-s ND and 4-min ND for peak VO2. The ventilatory anaerobic threshold was not significantly different between any test (30-s ND, 2337 +/- 434 mL O2 X min-1; 30-s P, 2174 +/- 406 mL O2 X min-1; ND, 2433 +/- 685 mL O2 X min-1; 4-min P, 2296 +/- 604 mL O2 X min-1). The VO2 at which blood lactate had increased by 0.5 mM above resting levels was significantly lower than the ventilatory anaerobic threshold for the 4-min ND (1917 +/- 489) and the 4-min P (1978 +/- 412) tests, but was not different for the 30-s ND and 30-s P tests. At exhaustion in the progressive tests, the blood PCO2 was higher (p less than 0.05) in both 30-s tests than 4-min tests.(ABSTRACT TRUNCATED AT 250 WORDS)     

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.     

Response of ventilatory and lactate thresholds to continuous and interval training

The purpose of this study was to evaluate the effects of continuous and interval training on changes in lactate and ventilatory thresholds during incremental exercise. Seventeen males were assigned to one of three training groups: group 1:55 min continuous exercise at approximately 50% maximum O2 consumption (VO2max); group 2: 35 min continuous exercise at approximately 70% VO2max; and group 3: 10 X 2-min intervals at approximately 105% VO2max interspersed with rest intervals of 2 min. All of the subjects were tested and trained on a cycle ergometer 3 day/wk for 8 wk. Lactate threshold (LT) and ventilatory threshold (VT) (in addition to maximal exercise measures) were determined using a standard incremental exercise test before and after 4 and 8 wk of training. VO2max increased significantly in all groups with no statistically significant differences between the groups. Increases (+/- SE) in LT (ml O2 X min-1) for group 1 (569 +/- 158), group 2 (584 +/- 125), and group 3 (533 +/- 88) were significant (P less than 0.05) and of the same magnitude. VT also increased significantly (P less than 0.05) in each group. However, the increase in VT (ml O2 X min-1) for group 3 (699 +/- 85) was significantly greater (P less than 0.05) than the increases in VT for group 1 (224 +/- 52) and group 2 (404 +/- 85). For group 1, the posttraining increase in LT was significantly greater than the increase in VT (P less than 0.05). We conclude that both continuous and interval training were equally effective in augmenting LT, but interval training was more effective in elevating VT.(ABSTRACT TRUNCATED AT 250 WORDS)     

Exercise and blood lymphocyte subset responses: intensity, duration, and subject fitness effects

This study examined the effect of exercise intensity and duration on the percent blood lymphocytes in men of low [LF; maximal O2 uptake (VO2max) less than 50 ml.kg-1.min-1 and sedentary], moderate (MF; VO2max = 50-60 ml.kg-1.min-1 and recreationally active), and high (HF; VO2max greater than 60 ml.kg-1.min-1 and recent training history) fitness. Thirty healthy adult men (aged 20-31 yr) participated in four randomly ordered cycle ergometer rides: ride 1 (65% VO2max, 30 min), ride 2 (30% VO2max, 60 min), ride 3 (75% VO2max, 60 min), and ride 4 (65% VO2max, 120 min). Blood samples were drawn at various times before and after the exercise sessions. Lymphocyte subsets were determined by flow cytometry using monoclonal antibodies for total T (CD3+), T-helper (CD4+), and T-suppressor (CD8+) lymphocytes and for a subset of cells expressing a natural killer (NK) cell antigen (Leu7+). Plasma catecholamines were assayed to determine exercise stress. There were sharp reductions (P less than 0.01) in the percentage of pan-T and T-helper lymphocytes immediately after exercise across all fitness levels; the magnitude of this reduction was greatest after the highest intensity (ride 3) or longest duration (ride 4) work. In contrast, the absolute number of T and T-helper cells tended to increase after exercise and significantly so in the HF subjects (P less than 0.005). There was no significant effect of exercise or subject fitness category on the percentage of T-suppressor lymphocytes, although the absolute numbers of this subset increased significantly after exercise in LF subjects. Marked increases (P less than 0.01) in the percentage of NK cells occurred immediately after exercise at all intensities and durations tested; numerical increases in total NK cells were significant in all fitness groups after the highest intensity work (ride 3; P less than 0.005). Irrespective of whether the changes were expressed as percentage or total numbers, recovery to base line occurred at 30 min after exercise. The results suggest that the exercise effect on blood lymphocyte subset percentages in men is transient and occurs across all fitness levels. Concomitant changes in plasma catecholamine concentrations are only weakly associated with these lymphocyte subset percentage responses to exercise. Furthermore, this study shows that the exercise-induced changes in lymphocyte percentages do not consistently reflect changes in the absolute numbers of cells.     

Adaptations in skeletal muscle exercise metabolism to a sustained session of heavy intermittent exercise

The purpose of this study was to investigate the hypothesis that a single, extended session of heavy exercise would be effective in inducing adaptations in energy metabolism during exercise in the absence of increases in oxidative potential. Ten healthy males [maximal aerobic power (VO(2 peak)) = 43.4 +/- 2.2 (SE) ml x kg(-1) x min(-1)] participated in a 16-h training session involving cycling for 6 min each hour at approximately 90% of maximal oxygen consumption. Measurements of metabolic changes were made on tissue extracted from the vastus lateralis during a two-stage standardized submaximal cycle protocol before (Pre) and 36-48 h after (Post) the training session. At Pre, creatine phosphate (PCr) declined (P < 0.05) by 32% from 0 to 3 min and then remained stable until 20 min of exercise at 60% VO(2 peak) before declining (P < 0.05) by a further 35% during 20 min of exercise at 75% VO(2 peak). Muscle lactate (mmol/kg dry wt) progressively increased (P < 0.05) from 4.59 +/- 0.64 at 0 min to 17.8 +/- 2.7 and 30.9 +/- 5.3 at 3 and 40 min, respectively, whereas muscle glycogen (mmol glucosyl units/kg dry wt) declined (P < 0.05) from a rest value of 360 +/- 24 to 276 +/- 31 and 178 +/- 36 at similar time points. During exercise after the training session, PCr and glycogen were not as depressed (P < 0.05), and increases in muscle lactate were blunted (P < 0.05). All of these changes occurred in the absence of increases in oxidative potential as measured by the maximal activities of citrate synthase and malate dehydrogenase. These findings are consistent with other studies, namely, that muscle metabolic adaptations to regular exercise are an early adaptive event that occurs before increases in oxidative potential.     

Endurance training decreases plasma glucose turnover and oxidation during moderate-intensity exercise in men

To assess the effects of endurance training on plasma glucose kinetics during moderate-intensity exercise in men, seven men were studied before and after 12 wk of strenuous exercise training (3 days/wk running, 3 days/wk cycling). After priming of the glucose and bicarbonate pools, [U-13C] glucose was infused continuously during 2 h of cycle ergometer exercise at 60% of pretraining peak O2 uptake (VO2) to determine glucose turnover and oxidation. Training increased cycle ergometer peak VO2 by 23% and decreased the respiratory exchange ratio during the final 30 min of exercise from 0.89 +/- 0.01 to 0.85 +/- 0.01 (SE) (P less than 0.001). Plasma glucose turnover during exercise decreased from 44.6 +/- 3.5 mumol.kg fat-free mass (FFM)-1.min-1 before training to 31.5 +/- 4.3 after training (P less than 0.001), whereas plasma glucose clearance (i.e., rate of disappearance/plasma glucose concentration) fell from 9.5 +/- 0.6 to 6.4 +/- 0.8 ml.kg FFM-1.min-1 (P less than 0.001). Oxidation of plasma-derived glucose, which accounted for approximately 90% of plasma glucose disappearance in both the untrained and trained states, decreased from 41.1 +/- 3.4 mumol.kg FFM-1.min-1 before training to 27.7 +/- 4.8 after training (P less than 0.001). This decrease could account for roughly one-half of the total reduction in the amount of carbohydrate utilized during the final 30 min of exercise in the trained compared with the untrained state.     

Maximal aerobic capacity for repetitive lifting: comparison with three standard exercise testing modes

A multi-stage, repetitive lifting maximal oxygen uptake (VO2max) test was developed to be used as an occupational research tool which would parallel standard ergometric VO2max testing procedures. The repetitive lifting VO2max test was administered to 18 men using an automatic repetitive lifting device. An intraclass reliability coefficient of 0.91 was obtained with data from repeated tests on seven subjects. Repetitive lifting VO2max test responses were compared to those for treadmill, cycle ergometer and arm crank ergometer. The mean +/- SD repetitive lifting VO2max of 3.20 +/- 0.42 l.min-1 was significantly (p less than 0.01) less than treadmill VO2max (delta = 0.92 l.min-1) and cycle ergometer VO2max (delta = 0.43 l.min-1) and significantly greater than arm crank ergometer VO2max (delta = 0.63 l.min-1). The correlation between repetitive lifting oxygen uptake and power output was r = 0.65. VO2max correlated highly among exercise modes, but maximum power output did not. The efficiency of repetitive lifting exercise was significantly greater than that for arm cranking and less than that for leg cycling. The repetitive lifting VO2max test has an important advantage over treadmill or cycle ergometer tests in the determination of relative repetitive lifting intensities. The individual curves of VO2 vs. power output established during the multi-stage lifting VO2max test can be used to accurately select work loads required to elicit given percentages of maximal oxygen uptake.     

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.     

Enhanced protein breakdown after eccentric exercise in young and older men

The effects of eccentric exercise on whole body protein metabolism were compared in five young untrained [age 24 +/- 1 yr, maximal O2 uptake (VO2max) = 49 +/- 6 ml.kg-1.min-1] and five older untrained men (age 61 +/- 1 yr, VO2max = 34 +/- 2 ml.kg-1.min-1). They performed 45 min of eccentric exercise on a cycle ergometer at a power output equivalent to 80% VO2max (182 +/- 18 W). Beginning 5 days before exercise and continuing for at least 10 days after exercise, they consumed a eucaloric diet providing 1.5 g.kg-1.day-1 of protein. Leucine metabolism in the fed state was measured before, immediately after, and 10 days after exercise, with intravenous L-[1-13C]leucine as a tracer (0.115 mumol.kg-1.min-1). Leucine flux increased 9% immediately after exercise (P less than 0.011) and remained elevated 10 days later, with no effect of age. Leucine oxidation increased 19% immediately after exercise and remained 15% above baseline 10 days after exercise (P less than 0.0001), with no effect of age. In the young men, urinary excretion of 3-methylhistidine per gram of creatinine did not increase until 10 days postexercise (P less than 0.05), but in the older men, it increased 5 days after exercise and remained high through 10 days postexercise (P less than 0.05), averaging 37% higher than in the young men. These data suggest that eccentric exercise produces a similar increase in whole body protein breakdown in older and young men, but myofibrillar proteolysis may contribute more to whole body protein breakdown in the older group.     

Step ergometry: is it task-specific training?

Maximal exercise responses were measured before and after 10 weeks of training in two groups of men, one trained on a treadmill (n = 12) and the other on a step ergometer (n = 9); the groups were pre- and post-tested on both machines to examine the specificity of the training modes. Training for both groups consisted of 3 days week-1, 30 min day-1, progressing to 50 min day-1, at an intensity of 75%-80% heart rate maximum reserve. Pre-training maximal oxygen uptake (VO2max) was significantly higher on the treadmill for both groups (X = 8.5%). VO2max increased 6.9% on the treadmill (P less than 0.05) and 6.9% (P greater than 0.05) on the step ergometer after treadmill training. The small increases may be attributed to the specificity of the testing protocols used to elicit VO2max. Significant (P less than 0.01) increases in VO2max were found for both modalities after step-ergometry training (treadmill = 11.8%; step ergometer = 23.2%). These increases resulted in equal post-test VO2max values (4.05 l min-1; 51 ml kg-1 min-1) on the step ergometer and treadmill. The significant increases in VO2max found for both modalities after step-ergometry training shows that (1) step ergometry is an effective training modality, and (2) its effects can be measured on the treadmill and therefore it is not task-specific training.     

Endurance training reduces the magnitude of exercise-induced hyperammonemia in humans

The purpose of this study was to determine the influence of endurance-type exercise training on alterations of the ammonia content of blood in exercising humans. Seven females and four males trained 6 days/wk for 7 wk alternating days of continuous cycling (40 min) and interval running (five 5-min bouts). The NH3 content of blood was determined before and during cycle ergometer (CE) exercise (4 min) at power outputs (PO) of 119, 172, and 241 W pretraining and of 163, 230, and 271 W posttraining. These PO for each occasion represent relative work loads of approximately 65, 90, and 115% of peak CE maximum O2 uptake (PCE VO2), respectively. Training increased (P less than 0.05) PCE VO2 approximately 32% (2.72 +/- 0.25 to 3.56 +/- 0.29 l/min or 38.5 +/- 1.9 to 51.2 +/- 2.3 ml X kg-1 X min-1). Both pre- and posttraining the NH3 content of blood increased (P less than 0.05) with increasing intensity of exercise. Training did not influence the measure of these responses during exercise at the same relative intensity. During exercise at the same absolute PO, approximately 168 or 235 W, however, increases in blood NH3 were less (P less than 0.05) after training. The results indicate that the magnitude of increase in blood NH3 during exercise is determined by the energy requirement of the absolute work load, relative to an individual's aerobic power.     

Exercise intensity and glucose tolerance in trained and nontrained subjects

The improved glucose tolerance and increased insulin sensitivity associated with regular exercise appear to be the result, in large part, of the residual effects of the last bout of exercise. To determine the effects of exercise intensity on this response, glucose tolerance and the insulin response to a glucose load were determined in seven well-trained male subjects [maximal O2 uptake (VO2max) = 58 ml.kg-1.min-1] and in seven nontrained male subjects (VO2max = 49 ml.kg-1.min-1) in the morning after an overnight fast 1) 40 h after the last training session (control), 2) 14 h after 40 min of exercise on a cycle ergometer at 40% VO2max, and 3) 14 h after 40 min of exercise at 80% VO2max. Subjects replicated their diets for 3 days before each test and ate a standard meal the evening before the oral glucose tolerance test. No differences in the 3-h insulin or glucose response were observed between the control trial and before exercise at either 40 or 80% VO2max in the trained subjects. In the nontrained subjects the plasma insulin response was decreased by 40% after a single bout of exercise at either 40 or 80% VO2max (7.0 X 10(3) vs. 5.0 X 10(3), P less than 0.05; 3.8 X 10(3) microU.ml-1.180 min-1, P less than 0.01). The insulin response after a single bout of exercise in the nontrained subjects was comparable with the insulin responses found in the trained subjects for the control and exercise trials.(ABSTRACT TRUNCATED AT 250 WORDS)     

Influence of a 24 h fast on high intensity cycle exercise performance in man

The influence of a 24 h fast on endurance performance and the metabolic response to maximal cycle exercise was investigated in 6 healthy men (mean +/- SD: age = 27 +/- 7 years; weight = 73 +/- 10 kg; VO2max = 46 +/- 10 ml.kg-1.min-1). Subjects performed in randomised order two exercise bouts to exhaustion separated by one week. Test rides were performed in fasted (F) and post-absorptive (normal-diet, ND) conditions on an electrically braked cycle ergometer at a workload equivalent to 100% of VO2max. Acid-base status and selected metabolites were measured on arterialised venous blood at rest prior to exercise and at intervals for 15 mins following exercise. Exercise time to exhaustion was shorter after F compared with ND (p less than 0.01). Pre-exercise blood bicarbonate (HCO3-) concentration, PCO2 and base excess (BE) were lower after F compared with ND (p less than 0.05). Prior to exercise, circulating concentrations of free fatty acids (FFA), beta-hydroxybutyrate (B-HB) and glycerol were higher after F compared with ND (p less than 0.01) but blood glucose and lactate concentration were not different. On the F treatment, after exercise, blood pH, HCO3-, and BE were all significantly higher (p less than 0.01) than on ND; blood lactate concentration was significantly lower for the whole of the post-exercise period after F compared with ND (p less than 0.01). Circulating levels of FFA and B-HB after exercise on the F treatment fell but levels of these substrates were not altered by exercise after ND.(ABSTRACT TRUNCATED AT 250 WORDS)     

Endurance training increases fatty acid turnover, but not fat oxidation, in young men.

We examined the effects of exercise intensity and a 10-wk cycle ergometer training program [5 days/wk, 1 h, 75% peak oxygen consumption (VO2 peak)] on plasma free fatty acid (FFA) flux, total fat oxidation, and whole body lipolysis in healthy male subjects (n = 10; age = 25.6 +/- 1.0 yr). Two pretraining trials (45 and 65% of VO2 peak) and two posttraining trials (same absolute workload, 65% of old VO2 peak; and same relative workload, 65% of new VO2 peak) were performed by using an infusion of [1-13C]palmitate and [1,1,2,3, 3-2H]glycerol. An additional nine subjects (age 25.4 +/- 0.8 yr) were treated similarly but were infused with [1,1,2,3,3-2H]glycerol and not [1-13C]palmitate. Subjects were studied postabsorptive for 90 min of rest and 1 h of cycling exercise. After training, subjects increased VO2 peak by 9.4 +/- 1.4%. Pretraining, plasma FFA kinetics were inversely related to exercise intensity with rates of appearance (Ra) and disappearance (Rd) being significantly higher at 45 than at 65% VO2 peak (Ra: 8.14 +/- 1.28 vs. 6.64 +/- 0.46, Rd: 8. 03 +/- 1.28 vs. 6.42 +/- 0.41 mol. kg-1. min-1) (P 相似文献   

Decline in VO2max with aging in master athletes and sedentary men

Fifteen well-trained master endurance athletes [62.0 +/- 2.3 (SE) yr] and 14 sedentary control subjects (61.4 +/- 1.4 yr) were reevaluated after an average follow-up period of approximately 8 yr to obtain information regarding the effects of physical activity on the age-related decline in maximal O2 uptake capacity (VO2max). The master athletes had been training for 10.2 +/- 2.9 yr before initial testing and continued to train during the follow-up period. The sedentary subjects' VO2max declined by an average of 3.3 ml.kg-1.min-1 (33.9 +/- 1.7 vs. 30.6 +/- 1.6, P less than 0.001) over the course of the study, a decline of 12% per decade. In these subjects maximal heart rate declined 8 beats/min (171 vs. 163) and maximal O2 pulse decreased from 0.20 to 0.18 ml.kg-1.beat (P less than 0.05). The master athletes' VO2 max decreased by an average of 2.2 ml.kg-1.min-1 (54.0 +/- 1.7 vs. 51.8 +/- 1.8, P less than 0.05), a 5.5% decline per decade. The master athletes' maximal heart rate was unchanged (171 +/- 3 beats/min) and their maximal O2 pulse decreased from 0.32 to 0.30 ml.kg-1.beat (P less than 0.05). These findings provide evidence that the age-related decrease in VO2max of master athletes who continue to engage in regular vigorous endurance exercise training is approximately one-half the rate of decline seen in age-matched sedentary subjects. Furthermore our results suggest that endurance exercise training may reduce the rate of decline in maximal heart rate that typically occurs as an individual ages.     

Improvements in exercise performance: effects of carbohydrate feedings and diet

In an effort to determine the effects of carbohydrate (CHO) feedings immediately before exercise in both the fasted and fed state, 10 well-trained male cyclists [maximum O2 consumption (VO2 max), 4.35 +/- 0.11 l/min)] performed 45 min of cycling at 77% VO2 max followed by a 15-min performance ride on an isokinetic cycle ergometer. After a 12-h fast, subjects ingested 45 g of liquid carbohydrate (LCHO), solid carbohydrate confectionery bar (SCHO), or placebo (P) 5 min before exercise. An additional trial was performed in which a high-CHO meal (200 g) taken 4 h before exercise was combined with a confectionery bar feeding (M + SCHO) immediately before the activity. At 10 min of exercise, serum glucose values were elevated by 18 and 24% during SCHO and LCHO, respectively, compared with P. At 0 and 45 min no significant differences were observed in muscle glycogen concentration or total use between the four trials. Total work produced during the final 15 min of exercise was significantly greater (P less than 0.05) during M + SCHO (194,735 +/- 9,448 N X m), compared with all other trials and significantly greater (P less than 0.05) during LCHO and SCHO (175,204 +/- 11,780 and 176,013 +/- 10,465 N X m, respectively) than trial P (159,143 +/- 11,407 N X m). These results suggest that, under conditions when CHO stores are less than optimal, exercise performance is enhanced with the ingestion of 45 g of CHO 5 min before 1 h of intense cycling.(ABSTRACT TRUNCATED AT 250 WORDS)     

Effect of beta-blockade on the drift in O2 consumption during prolonged exercise

The effect of beta-adrenergic blockade on the drift in O2 consumption (VO2 drift) typically observed during prolonged constant-rate exercise was studied in 14 healthy males in moderate heat at 40% of maximal O2 consumption (VO2max). After an initial maximum cycle ergometer test to determine the subjects' control VO2max, subjects were administered each of three medications: placebo, atenolol (100 mg once daily), and propranolol (80 mg twice daily), in a randomized double-blind fashion. Each medication period was 5 days in length and was followed by a 4-day washout period. On the 3rd day of each medication period, subjects performed a maximal cycle ergometer test. On the final day of each medication period, subjects exercised at 40% of their control VO2max for 90 min on a cycle ergometer in a warm (31.7 +/- 0.3 degrees C) moderately humid (44.7 +/- 4.7%) environment. beta-Blockade caused significant (P less than 0.05) reductions in VO2max, maximal minute ventilation (VEmax), maximal heart rate (HRmax), and maximal exercise time. Significantly greater decreases in VO2max, VEmax, and HRmax were associated with the propranolol compared with the atenolol treatment. During the 90-min submaximal rides, beta-blockade significantly reduced heart rate. Substantially lower values for O2 consumption (VO2) and minute ventilation (VE) were observed with propranolol compared with atenolol or placebo. Furthermore, VO2 drift and HR drift were observed under atenolol and placebo conditions but not with propranolol. Respiratory exchange ratio decreased significantly over time during the placebo and atenolol trials but did not change during the propranolol trial.(ABSTRACT TRUNCATED AT 250 WORDS)     

Ten weeks of aerobic training do not affect lower body negative pressure responses

Based mostly on cross-sectional data, it has been suggested that aerobic training may decrease lower body negative pressure (LBNP) tolerance through a hypothesized attenuation in both high- and low-pressure baroreflex gain. An experimental group (EXP) of eight male subjects [22.1 +/- 1.4 (SD) yr] underwent a 10-wk treadmill and cycle ergometer training program, which resulted in a 21% increase in maximal O2 uptake (VO2 max), 45.7 +/- 1.5 vs. 55.2 +/- 1.7 (SE) ml.kg-1.min-1; P less than 0.05]. A control group, (CON; n = 7; 27.3 +/- 5.7 yr), which did not undergo training, had no significant changes in VO2 max (49.4 +/- 3.3 vs. 48.8 +/- 3.2 ml.kg-1.min-1). Before and after training the EXP and CON groups participated in LBNP tolerance tests (terminated at presyncope) and neck pressure-suction testing (to describe the carotid sinus-heart rate baroreflex). LBNP tolerance, as defined by three different indexes, and carotid sinus-heart rate baroreflex gain were not altered in either group after training. Furthermore, there were no changes in LBNP heart rate, blood pressure, leg circumference, forearm blood flow, or forearm vascular resistance responses at any level of LBNP challenge after training. In conclusion, 10 wk of aerobic training did not change LBNP tolerance or alter the reflex cardiovascular compensatory mechanisms activated during LBNP.     

Endurance training in older men and women II. Blood lactate response to submaximal exercise

Seven men and four women (age 63 +/- 2 yr, mean +/- SD, range 61-67 yr) participated in a 12-mo endurance training program to determine the effects of low-intensity (LI) and high-intensity (HI) training on the blood lactate response to submaximal exercise in older individuals. Maximal oxygen uptake (VO2max), blood lactate, O2 uptake (VO2), heart rate (HR), ventilation (VE), and respiratory exchange ratio (R) during three submaximal exercise bouts (65-90% VO2max) were determined before training, after 6 mo of LI training, and after an additional 6 mo of HI training. VO2max (ml X kg-1 X min-1) was increased 12% after LI training (P less than 0.05), while HI training induced a further increase of 18% (P less than 0.01). Lactate, HR, VE, and R were significantly lower (P less than 0.05) at the same absolute work rates after LI training, while HI training induced further but smaller reductions in these parameters (P greater than 0.05). In general, at the same relative work rates (ie., % of VO2max) after training, lactate was lower or unchanged, HR and R were unchanged, and VO2 and VE were higher. These findings indicate that LI training in older individuals results in adaptations in the response to submaximal exercise that are similar to those observed in younger populations and that additional higher intensity training results in further but less-marked changes.     

Effects of incomplete pulmonary gas exchange on VO2 max

Recent evidence suggests that heavy exercise may lower the percentage of O2 bound to hemoglobin (%SaO2) by greater than or equal to 5% below resting values in some highly trained endurance athletes. We tested the hypothesis that pulmonary gas exchange limitations may restrict VO2max in highly trained athletes who exhibit exercise-induced hypoxemia. Twenty healthy male volunteers were divided into two groups according to their physical fitness status and the demonstration of exercise-induced reductions in %SaO2 less than or equal to 92%: 1) trained (T), mean VO2max = 56.5 ml.kg-1.min-1 (n = 13) and 2) highly trained (HT) with maximal exercise %SaO2 less than or equal to 92%, mean VO2max = 70.1 ml.kg-1.min-1 (n = 7). Subjects performed two incremental cycle ergometer exercise tests to determine VO2max at sea level under normoxic (21% O2) and mild hyperoxic conditions (26% O2). Mean %SaO2 during maximal exercise was significantly higher (P less than 0.05) during hyperoxia compared with normoxia in both the T group (94.1 vs. 96.1%) and the HT group (90.6 vs. 95.9%). Mean VO2max was significantly elevated (P less than 0.05) during hyperoxia compared with normoxia in the HT group (74.7 vs. 70.1 ml.kg-1.min-1). In contrast, in the T group, no mean difference (P less than 0.05) existed between treatments in VO2max (56.5 vs. 57.1 ml.kg-1.min-1). These data suggest that pulmonary gas exchange may contribute significantly to the limitation of VO2max in highly trained athletes who exhibit exercise-induced reductions in %SaO2 at sea level.(ABSTRACT TRUNCATED AT 250 WORDS)