Submaximal Oxygen Uptake Research Articles

THEORETICAL HIP AND KNEE EXTENSOR TORQUES AS A FUNCTION OF PREFERRED HIP ANGLE AND CRANK ANGLE IN CYCLISTS 281

A previous study (Heil et al., MSSE 26(5):S63, 1994) found that submaximal oxygen uptake (˙VO2) was minimized as a quadratic function of preferred hip angle (HA) across nine combinations of seat-tube (70°, 80°, 90°) and trunk angle (10°, 20°, 30°) in competitive cyclists during submaximal cycle ergometry. These observations may have been the result of training-specific alterations in the hip and/or knee extensor torque capabilities. The present study evaluated this theory by creating theoretical torque-angle curves for individual muscles participating in either hip or knee extension during the power-phase of bicycle pedaling. Sagittal-view kinematics of the hip and knee joints from the previous study(n=13) were used as input to the model. Based upon a two-component Hill-type model, the maximal theoretical torques (TMAX) of four hip (gluteus maximus (GM), 3 hamstrings) and four knee extensors (rectus femoris (RF), 3 vasti) as a function of changes in joint and crank angles were calculated. The algorithms for TMAX combined muscle, tendon, and sarcomere architecture data from the literature with moment-arm length and force-length algorithms. The results indicated: 1) Changes in TMAX were greatest for GM and RF; 2) TMAX magnitude for GM and RF increased with an increase in mean HA, while peak TMAX values occurred earlier in the crank cycle for GM and later for RF. Thus, TMAX magnitude and timing for GM and RF may explain the previously observed relationship between preferred HA and˙VO2.

Total radical trapping antioxidant potential (TRAP) and exercise

The relationship between physical activity, physical fitness and total radical trapping antioxidant potential (TRAP) was examined in the Northern Ireland Health and Activity Survey. This was a cross-sectional population study (n = 1600) using a two-stage probability sample of the population. TRAP was calculated using the sum of the individual serum antioxidant concentrations (urate, protein thiols, ascorbate, alpha tocopherol and bilirubin) multiplied by their respective stoichiometric values. Physical fitness was determined by estimation of VO2max by extrapolation from submaximal oxygen uptake, and physical activity was recorded by computer-assisted interview. Mean serum TRAP concentrations were significantly higher in males (653 +/- 8.2 mumol/l, mean +/- SEM) compared to females (564 +/- 8.0 mumol/l) (p < 0.0001). Both male and female smokers had significantly lower TRAP values than non-smokers (males p < 0.0001, females p = 0.02). In females, there was a positive relationship of TRAP with age (p < 0.001) and body mass index (p < 0.001) but a negative relationship with physical fitness (p < 0.05). The known beneficial effects of exercise and activity do not appear to be directly mediated through increased antioxidant status.

Arm crank exercise with static leg FNS in persons with spinal cord injury

Persons with spinal cord injury experience considerable difficulty, during aerobic exercise, in achieving even moderate levels of oxygen uptake. Therefore, the effect of static functional neuromuscular stimulation (FNS) on this parameter during arm crank exercise (ACE) was investigated. Eight subjects with spinal cord injury, lesion levels range C6-T12, performed ACE at 60% and 80% of VO2peak, both with and without concurrent FNS of the lower limbs. ACE was performed with no FNS, with FNS at 40 milliamperes (mA), and with FNS at 80 mA. Significant differences in oxygen uptake were found between ACE without FNS and ACE with FNS-80 mA at 60% VO2peak (10% increase, 12.5 ml.kg-1.min-1 to 13.7 ml.kg-1.min-1, P < 0.05), and between ACE without FNS and ACE with FNS-80 mA at 80% VO2peak (16%, increase, 14.8 ml.kg-1.min-1 to 17.2 ml.kg-1.min-1, P < 0.01). A 10% difference between ACE without FNS and ACE with FNS-40 mA, did not reach significance. These data indicate that, in this population of subjects with spinal cord injury, (a) FNS can increase submaximal ACE oxygen uptake, and (b) that such increases are enhanced both at higher levels of FNS and of work load. Implications for wellness are discussed.

Effects of Cast-Bracing of the Knee on Physical Performance in Healthy Subjects

Effects of application of a hinged cast-brace on thigh muscle strength and physical performance tests were studied in eight healthy volunteers. The cast-brace was applied to one leg for four weeks. The subjects were free to move around. The extra loading by the cast-brace was determined in a progressive uphill walk test on a treadmill with measurements of oxygen uptake, heart rate and plasma lactate concentration. Submaximal oxygen uptake in the uphill walk test was raised significantly (average 9%) on the day after application. After four weeks of cast-brace wearing the submaximal oxygen uptake in the uphill walk test had decreased, but remained elevated (average 4%) even one day after removal. Heart rate was significantly higher (average 7%) during cast application and after removal. Plasma lactate concentration, however, was not influenced. To investigate the effect of four weeks cast-bracing various performance tests to judge the thigh muscle function were taken before application and after removal. No significant changes in peak torque of knee flexion and extension, in physiologic variables at submaximal running pace during treadmill exercise, maximal running speed, 60 m dash, or in jump height were found. In conclusion, cast-bracing of a healthy knee for four weeks has no significant effects on physical performance after removal.

Adding ??-2 agonism does not improve ??-1 blockade exercise responses in hypertensives

We tested the hypothesis that celiprolol, a beta-1 adrenoceptor antagonist with the ancillary property of beta-2-mediated vasodilation, would increase blood flow to active muscles during exercise and result in less impairment of exercise performance compared with the beta-1 antagonist atenolol. After an initial 3-wk washout phase, 11 untrained hypertensive men participated in a 6-wk crossover study of the two drugs. Each treatment phase was followed by a 3-wk placebo phase. Resting forearm and calf vascular resistance measured by venous occlusion plethysmography and submaximal and maximal bicycle ergometry exercise responses were evaluated at the end of each treatment and placebo phase. Celiprolol significantly decreased resting forearm and calf vascular resistance whereas atenolol had no significant effect. Neither beta-blocker significantly affected submaximal exercise oxygen uptake, rate of perceived exertion, minute ventilation, or respiratory exchange ratio. Both beta-blockers significantly and similarly decreased peak oxygen uptake; celiprolol 23.9 +/- 1.7, atenolol 24.9 +/- 1.7, placebo 27.3 +/- 1.3 ml.kg-1.min-1. Our findings suggest that during exercise while on beta-blockade, other factors such as sympathetic vasoconstriction or local metabolic vasodilation may override beta-2-mediated vasodilation. Thus, the addition of beta-2 agonism to beta-1 antagonism decreases resting vascular resistance but offers no advantage over conventional beta-1 blockade therapy during exercise.

Aerobic Capacity and Grade-Walking Economy of Children 5–9 Years Old: A Longitudinal Study

Maximal oxygen uptake (VO2max), submaximal grade-walking oxygen uptake, and anthropometric measures were measured in a group of 19 children in 1988 and in 1992. The children were 5.2 ± .9 years old in 1988 and 9.2 ± 1.0 in 1992. The VO2max did not change relative to body weight over the 4 years (44.6 ml·kg−1·min−1 in 1988 versus 43.3 ml·kg−1·min−1 in 1992). Lower specific weight-relative oxygen uptakes were seen at the submaximal work levels in 1992 than in 1988, indicating an improvement in grade-walking economy.

Effects of Varying Levels of Hypohydration on Ratings of Perceived Exertion

To investigate the effects of varying levels of hypohydration on ratings of perceived exertion (RPE) during moderate and heavy submaximal exercise, and at the lactate threshold (LT) and ventilatory threshold (VT), 9 male subjects cycled under states of euhydration (EU), moderate hypohydration (MH), and severe hypohydration (SH). The desired level of hypohydration was achieved over a 36-hr period by having subjects cycle at 50% VO2max in a 38 degrees C environment on two occasions while controlling fluid intake and diet. During submaximal exercise, oxygen uptake, ventilation, heart rate, blood lactate, and RPE were not significantly different among treatments. Hypohydration did not significantly alter LT or VT, or perceptual responses at LT or VT. It is concluded that hypohydration of up to 5.6% caused by fluid manipulation and exercise in the heat over a 36-hr period does not alter RPE or the lactate or ventilatory threshold, nor RPE at the lactate and ventilatory thresholds measured during moderate and heavy submaximal cycling in a neutral (22 degrees C) environment.

An Examination of the Anaerobic Capacity of Children Using Maximal Accumulated Oxygen Deficit

The purpose of this study was to determine the anaerobic capacity of children using the maximal accumulated oxygen deficit technique (AOD). Eighteen healthy children (9 boys, 9 girls) with a mean age of 10.6 years volunteered as subjects. Peak oxygen uptake and submaximal steady-state oxygen uptake tests were conducted against progressive constant work rates on a Cybex cycle ergometer. Supramaximal work rates were predicted from the linear regression of submaximal steady-state work rates and oxygen uptakes to equal 110, 130, and 150% of peak oxygen uptake. Results indicated a significant interaction in the responses of both sexes when the accumulated oxygen deficit data were expressed in both absolute and relative terms. The profile of accumulated oxygen deficits across the three intensities indicated a downward shift in the girls responses between the 110 and 150% supramaximal tests. This trend was not evident in the boys’ responses. Intraclass correlations conducted on test-retest data indicated that compared to the boys, the reliability of the girls in the accumulated oxygen deficits in liters and ml·kg−1 was poorer.

Effect of hand paddle aids on oxygen uptake during arm-stroke-only swimming.

Cardiorespiratory responses during arm-stroke-only swimming with and without the aid of paddle were compared in seven trained swimmers. Water flow rate was started at 0.80 m.s-1 and was increased by 0.05 m.s-1 every 2 min up. to 1.00 m.s-1. Subsequently, the flow rate was increased by 0.05 m.s-1 every minute until exhaustion. At given submaximal water flow rates, oxygen uptake, heart rate (fc), pulmonary ventilation (VE) and respiratory frequency (fR) during swimming using hands alone (H) were significantly higher than when aided by paddles (P). There were no significant differences in tidal volume (VT) between H and P. The subjects were able to swim significantly faster using paddles (P < 0.05); however, no significant differences between H and P were found in peak oxygen uptake (VO2peak, Fc, VE, FR, VT and the blood lactate concentration at which VO2peak was obtained (P > 0.05). These results would suggest that the ability to swim faster with paddles does not depend on higher energy production but may be attributed to higher propelling efficiency.

Cardiovascular responses in paraplegic subjects during arm exercise.

The purpose of this study was to examine cardiovascular responses during arm exercise in paraplegics compared to a well-matched control group. A group of 11 male paraplegics (P) with complete spinal cord-lesions between T6 and T12 and 11 male control subjects (C), matched for physical activity, sport participation and age performed maximal arm-cranking exercise and submaximal exercise at 20%, 40% and 60% of the maximal load for each individual. Cardiac output (Qc) was determined by the CO2 rebreathing method. Maximal oxygen uptake was significantly lower and maximal heart rate (fc) was significantly higher in P compared to C. At the same oxygen uptakes no significant differences were observed in Qc between P and C; however, stroke volume (SV) was significantly lower and fc significantly higher in P than in C. The lower SV in P could be explained by an impaired redistribution of blood and, therefore, a reduced ventricular filling pressure, due to pooling of venous blood caused by inactivity of the skeletal muscle pump in the legs and lack of sympathetic vasoconstriction below the lesion. In conclusion, in P maximal performance appears to have been limited by a smaller active muscle mass and a lower SV despite the higher fc,max. During submaximal exercise, however, this lower SV was compensated for by a higher fc and, thus at the same submaximal oxygen uptake, Qc was similar to that in the control group.

The relationship between body mass and oxygen uptake during running in humans

Oxygen uptake during treadmill running was measured at submaximal and maximal intensities in six different groups of endurance athletes (N = 134) and in seven endurance-trained men. The relationship between body mass (M) and oxygen uptake (VO2) was evaluated by deriving the exponent b in the equation VO2 = a.Mb. Thus, if b = 1, the oxygen uptake increases in proportion to body mass and oxygen uptake per kg is independent of body mass; if b less than 1, than the oxygen uptake per kg is inversely related to body mass. The exponent b was found to be less than unity for all groups for both submaximal (b = 0.76, s = 0.06) and maximal oxygen uptake (b = 0.71, s = 0.05). These results indicate that neither submaximal nor maximal oxygen uptake increases in proportion to body mass during running. The relationship between submaximal oxygen uptake and body mass observed in this study may explain why the oxygen uptake per kg of body mass has been found to be higher for children than for adults.

Cardiovascular response to maximal cycle exercise duringpregnancy and at two and seven months postpartum

We examined the cardiovascular response at rest and during upright cycle exercise in nine women during pregnancy (25.6 +/- 3.0 weeks' gestation) and at 2 months (8.8 +/- 1.8 weeks) and 7 months (30.0 +/- 2.5 weeks) post partum. Antepartum resting cardiac output, heart rate, and stroke volume were higher, whereas the arterial-venous oxygen difference was lower than both postpartum values. The antepartum resting oxygen uptake did not differ from 2 months post partum but was higher than at 7 months post partum. Cardiac output during submaximal exercise was greater antepartum than at both postpartum tests. Submaximal antepartum oxygen uptake, heart rate, and stroke volume were generally higher, and the arterial-venous oxygen difference was lower than at 7 months post partum. The slope of the antepartum cardiac output versus oxygen uptake relationship did not differ from the value at 2 months post partum, (6.16 +/- 1.38 and 5.84 +/- 1.34, p greater than 0.05) but was higher than at 7 months post partum (5.22 +/- 0.78, p less than 0.05). There were no significant differences in maximal oxygen uptake or heart rate among the three testing periods. Maximal cardiac output and stroke volume were higher antepartum than at 2 and 7 months post partum, whereas the arterial-venous oxygen difference was lower than at 7 months post partum. There were few significant differences in resting, submaximal, or maximal measurements between the two postpartum conditions. These data suggest that the augmented cardiac response to exercise during pregnancy is reduced by 2 months post partum but that additional time may be required for a complete resolution of the cardiovascular changes induced by pregnancy.

Exercise Oxygen Uptake in 3- through 6-Year-Old Children.

This study compared submaximal and maximal oxygen uptake (V̇O2 max) in children ages 3-4 and 5-6 years. Methods appropriate for this age group were developed to elicit maximal performance on the exercise tests. Subjects (N = 22) performed progressive treadmill walking tests. The criteria used to determine whether V̇O2 max was reached were a plateauing of oxygen uptake, HR > 195, and an R > 1.00. The V̇O2 max for the 3- and 4-year-olds (44.5 ml•kg-1•min-1) was not significantly different from that of the 5- and 6-year-olds (44.1 ml•kg-1•min-1). At submaximal levels, 5- and 6-year-olds had significantly lower relative oxygen uptake, indicating better economy in walking. A large proportion of children met testing criteria for V̇O2 max. Test-retest results indicated that the tests were reliable.

Anaerobic energy production and O2 deficit‐debt relationship during exhaustive exercise in humans.

1. Eight subjects performed one-legged, dynamic, knee-extensor exercise, first at 10 W followed by 10 min rest, then at an intense, exhaustive exercise load (65 W) lasting 3.2 min. After 60 min recovery, exercise was performed for 8-10 min each at 20, 30, 40 and 50 W. Measurements of pulmonary oxygen uptake, heart rate, blood pressure, leg blood flow, and femoral arterial-venous differences of oxygen content and lactate were performed as well as determination of ATP, creatine phosphate (CP) inosine monophosphate (IMP) and lactate concentrations on biopsy material from the quadriceps muscle before and immediately after the intense exercise, and at 3, 10 and 60 min into recovery. 2. Individual linear relations (r = 0.95-1.00) between the power outputs for submaximal exercise and oxygen uptakes (leg and pulmonary) were used to estimate the energy demand during intense exercise. Pulmonary and leg oxygen deficits determined as the difference between energy demand and oxygen uptake were 0.46 and 0.48 l (kg active muscle)-1, respectively. Limb and pulmonary oxygen debts (oxygen uptake during 60 min of recovery - pre-exercise oxygen uptake) were 0.55 and 1.65 l (kg active muscle)-1, respectively. 3. During the intense exercise, muscle [ATP] decreased by 30% and [CP] by 60% from resting concentrations of 6.2 and 22.4 mmol (kg wet wt)-1, respectively, and [IMP] increased to 1.1 mmol (kg wet wt)-1. Muscle [lactate] increased from 2 to 28.1 mmol (kg wet wt)-1, and the concomitant net lactate release was 14.8 mmol (kg wet wt)-1 or about 1/3 of the total net lactate production. During recovery 70% of the accumulated lactate was released to the blood, and the nucleotides and CP returned to about 40 and 85% of pre-exercise values at 3 and 10 min of recovery, respectively. 4. Total reduction in ATP and CP (and elevation of IMP) during the intense exercise amounted to 16.4 mmol ATP (kg wet wt)-1, which together with the lactate production accounted for 83.1 mmol ATP (kg wet wt)-1. In addition 6-8 mmol ATP (kg wet wt)-1 are made available related to accumulation of glycolytic intermediates including pyruvate (and alanine). Estimated leg oxygen deficit corresponded to an ATP production of 94.7 mmol ATP kg-1; this value included 3.1 mmol kg-1 related to unloading of HbO2 and MbO2.(ABSTRACT TRUNCATED AT 400 WORDS)

Role of leg vasculature in the cardiovascular response to arm work in wheelchair-dependent populations.

To assess the effects of leg vasculature on cardiovascular dynamics during submaximal arm work, oxygen uptake (VO2), cardiac output (Q) and heart rate (HR) were measured during arm-crank ergometry (ACE) at 35 W (45% peak ACE VO2) in five able-bodied subjects, five wheelchair-dependent paraplegics, and five wheelchair-dependent bilateral amputees who represented the conditions of active, passive, and absence of leg musculature respectively. Arteriovenous oxygen difference (a-v O2) and stroke volume (SV) were calculated from VO2, Q and HR. An index of leg fluid accumulation and leg blood flow was measured in the paraplegics and able-bodied subjects during rest and ACE. VO2, Q, and a-v O2 during ACE were not statistically different among the three groups. However, paraplegics exhibited higher HR (P less than 0.05) and lower SV (P less than 0.06) during exercise compared to both amputees and able-bodied subjects. Greater (P less than 0.05) leg fluid accumulation was measured in paraplegics compared to able-bodied subjects, although no statistically significant differences in leg blood flow were observed. Although our results are limited to a small number of subjects, these data suggest that an active muscle pump contributes significantly to elevated venous return and stroke volume during ACE. The legs of the paraplegic appear to act as a reservoir for fluid accumulation which may limit cardiac filling, particularly during moderate arm work to support wheelchair function.

Cardiovascular responses to upper body exercise in normals and cardiac patients

This review summarizes and contrasts the cardiovascular responses elicited during dynamic upper body exercise (UBE) with those associated with lower body exercise (LBE). Information was obtained from studies which utilized arm-crank and/or cycle ergometers. At any given submaximal oxygen uptake (VO2), cardiac output (Q) is similar for UBE and LBE; however, heart rate (HR) is higher and stroke volume (SV) lower during UBE. Peripheral resistance and systolic and diastolic blood pressure are greater during UBE. Maximal Q, HR, SV, workload, and VO2 are less for UBE. As observed with healthy individuals, cardiac patients experience greater physiological stress for any given VO2 during UBE. UBE offers a satisfactory but perhaps not equivalent alternative to LBE for evaluation of angina and ischemic responses to exercise. The central and peripheral responses to either upper or lower body exercise appear to be independent of the muscle mass but directly related to the ergometer specific relative exercise intensity. The control mechanisms which govern these responses appear to be a centrally mediated activation of medullary centers coupled with a chemoreflex arising in the exercising skeletal muscle.

Energy and thermal regulation during bed rest and spaceflight.

In planning for long-duration (1- to 2-yr) space missions (microgravity), the availability of oxygen, water, and food is critical for survival. If astronauts would consume approximately 3,100 kcal and 2.2 liters of fluid per day, the requirements for a 2-yr flight would be 2,263,000 kcal and 1,606 liters for each astronaut. These estimates, based on limited microgravity simulation and flight data, include 1 h/day of moderate isotonic exercise. Each 30-min/day reduction in exercise training time would save 110,869 kcal and 91 liters of water per year. One daily 5-h extravehicular sortie at an average work rate of 1.7 l/min would require an additional 529,250 kcal and 1,095 liters of water per year. Results from microgravity simulation (bed rest) experiments suggest that 1) there is uncertainty whether basal metabolism is unchanged, 2) submaximal ergometer exercise oxygen uptake appears to be unchanged or lower, and 3) without vigorous exercise training near peak levels, the peak oxygen uptake is definitely reduced. In addition, the equilibrium level of exercise core temperature is elevated excessively by approximately 0.5 degrees C after bed-rest acclimation. Changes in the efficiency of work or metabolism in any or all of these conditions could affect nutritional requirements for long spaceflights. Further research is necessary to elucidate the metabolic factors that would be changed and the energy cost of intra- and extravehicular activity during prolonged exposure to microgravity.

Human cardiovascular adjustments to acute hypoxaemia.

Traditionally, cardiovascular adjustments to hypoxaemia are viewed as resultants of competing local vasodilation and vasoconstriction via arterial chemoreflexes with net effects of increased cerebral and coronary blood flows (local) and reduced flow to visceral organs and muscle (reflex). Although true in asphyxia, breathing activates lung mechanoreceptors which reduce vagal outflow and apparently, in humans, abolishes sympathetic vasomotor activity (SNA). During rest, moderate to severe hypoxaemia (PaO2 = 35 to 27 mmHg) caused no splanchnic, cutaneous or muscle vasoconstriction. Local vasodilator effects of hypoxaemia were not sufficient to overwhelm vasoconstriction; splanchnic arterioles responded normally to infused noradrenalin (NA) during hypoxaemia. Possibly, central effects of hypoxaemia blunt SNA or peripheral, prejunctional effects impair neuronal release of NA. Persistent orthostatic tolerance with normal skeletal muscle vasoconstriction and retained spinal venomotor reflexes during hypoxaemia argue against prejunctional inhibition of NA release. Results so far suggest that beyond a certain threshold, hypoxaemia centrally inhibits SNA. In contrast to rest, even moderate hypoxaemia during exercise markedly increases plasma NA concentration (and SNA), but the usual relationship among splanchnic blood flow, plasma NA and heart rate was not observed--NA and heart rate rose together, whereas the predicted splanchnic vasoconstriction was not observed. In moderate hypoxaemia, muscle blood flow and cardiac output are greater than in normoxia at a given submaximal oxygen uptake; but at maximal oxygen uptake, blood pressure, total vascular conductance and maximal cardiac output are unaffected. Given the fixed upper limit to cardiac output and the greater capacity of active muscle to vasodilate and exceed cardiac pumping capacity during hypoxaemia, we conclude that blood pressure is maintained by baroreflex- (not chemoreflex-) mediated vasoconstriction in the active muscle which must be the primary target of increased SNA and the source of NA.

Influence of diuretic-induced dehydration on competitive running performance.

A diuretic drug (40 mg of furosemide) was utilized to study the effects of dehydration (D) on competitive running performance, without prior thermal or exercise stress. Eight men competed in randomized races of 1,500, 5,000, and 10,000 m, while normally hydrated (H) and with mean plasma volume reductions of 9.9, 12.3, and 9.9%, respectively. As a result of the reduced body water (change in body weight = -1.9, -1.6, and -2.1%), mean outdoor performance times on a running track increased 0.16 min, 1.31 min (P less than 0.05), and 2.62 min (P less than 0.05) in the 1,500-m, 5,000-m, and 10,000-m trials. Running performance decrements due to dehydration were more strongly correlated with changes in body weight (r = -0.79, -0.65, and -0.40) than with urine volume or plasma volume differences. In addition, subjects were studied during submaximal and maximal treadmill exercise while H and D (mean change in plasma volume = -7.1%). Neither submaximal nor maximal oxygen uptake was significantly altered (P greater than 0.05) as a consequence of D. Mean treadmill run time to volitional exhaustion was reduced by 41.4 s (P less than 0.05) during the D treadmill trial. Therefore, it appears that competitive performance in trials of long duration (5,000 and 10,000 m) was affected to a greater extent by D than the shorter 1,500-m event, even though submaximal and maximal oxygen uptake was not altered.

Cardiorespiratory alterations consequent to endurance exercise training during chronic beta-adrenergic blockade with atenolol and propranolol

A study was undertaken to determine if normal healthy subjects can increase their endurance capacity consequent to endurance training during chronic β-adrenergic blockade. Forty-seven subjects, 17 to 34 years of age, were randomly assigned to 1 of 3 treatments (placebo, propranolol, 160 mg/day, and atenolol, 100 mg/day) and then completed a 15-week aerobic exercise training program. All groups reduced their submaximal steady-state heart rates consequent to training; submaximal oxygen uptake was slightly reduced; submaximal stroke volume was increased only in the placebo and atenolol groups; submaximal cardiac output was generally lower; and arterial-mixed venous oxygen difference was increased after training in all 3 groups, suggesting decreased muscle blood flow and increased oxidative capacity. Maximal oxygen uptake, and maximal treadmill time were increased in all 3 groups after training. However, while still on medication the atenolol group had significantly greater increases In maximal oxygen uptake and maximal treadmill time compared with the propranolol group. Because most patients will remain on medication, these results suggest a distinct advantage for cardloselective blocking agents. It is concluded that β-adrenergic blockade does not reduce the ability of normal healthy subjects to gain the benefits associated with cardiorespiratory endurance training.