Evaluation of the American College of Sports Medicine submaximal treadmill running test for predicting VO2max

The purpose of this study was to assess the validity of the American College of Sports Medicine's (ACSM's) submaximal treadmill running test in predicting VO2max. Twenty-one moderately well-trained men aged 18-34 years performed 1 maximal treadmill test to determine maximal oxygen uptake (M VO2max) and 2 submaximal treadmill tests using 4 stages of continuous submaximal exercise. Estimated VO2max was predicted by extrapolation to age-predicted maximal heart rate (HRmax) and calculated in 2 ways: using data from all submaximal stages between 110 b·min(-1) and 85% HRmax (P VO2max-All), and using data from the last 2 stages only (P VO2max-2). The measured VO2max was overestimated by 3% on average for the group but was not significantly different to predicted VO2max (1-way analysis of variance [ANOVA] p = 0.695; M VO2max = 53.01 ± 5.38; P VO2max-All = 54.27 ± 7.16; P VO2max-2 = 54.99 ± 7.69 ml·kg(-1)·min(-1)), although M VO2max was not overestimated in all the participants--it was underestimated in 30% of observations. Pearson's correlation, standard error of estimate (SEE), and total error (E) between measured and predicted VO2max were r = 0.646, 4.35, 4.08 ml·kg(-1)·min(-1) (P VO2max-All) and r = 0.642, 4.21, 3.98 ml·kg(-1)·min(-1) (P VO2max-2) indicating that the accuracy in prediction (error) was very similar whether using P VO2max-All or P VO2max-2, with up to 70% of the participants predicted scores within 1 SEE (～4 ml·kg(-1)·min(-1)) of M VO2max. In conclusion, the ACSM equation provides a reasonably good estimation of VO2max with no difference in predictive accuracy between P VO2max-2 and P VO2max-All, and hence, either approach may be equally useful in tracking an individual's aerobic fitness over time. However, if a precise knowledge of VO2max is required, then it is recommended that this be measured directly.     

儿童最大有氧活动能力的发展特征

本文报告了我国４６３名１０－１９岁儿童青少年的最大有氧活动能力的发展特征。在青春早期,男女童的最大吸氧量绝对值均随年龄增长而增加,男童由１．７５升／分增至３．１０升／分,女童由１．４４升／分增至２．０７升／分,女童增长较少;以后女童即稳定于这一水平,男童仍略有增长。按身高及按最大心率计标的相对值与其有相似的特征。按体重和瘦体重计算的相对值,在男女童都未见随年龄增长的规律。男童ＶＯ２ｍａｘ绝对值及各     

Validation of the Cosmed Fitmate for prediction of maximal oxygen consumption

The main purpose of this study was to assess the validity of the Cosmed Fitmate (FM) for the prediction of maximal oxygen consumption (VO(2)max). In addition, this study examined whether measuring submaximal VO(2), rather than predicting it, can improve upon the prediction of VO(2)max. Participants for the study were 48 young to middle-age adults (32 men, 16 women), with a mean age of 31 yr. Each participant completed a submaximal and maximal treadmill test on 2 separate occasions. During the submaximal test, VO(2)max was predicted using the FM. This device extrapolates the linear regression relating heart rate (HR) and measured VO(2) at submaximal work rates to age-predicted maximum HR (HR = 220 - age). The criterion measure was obtained using a graded, maximal treadmill test, with VO(2) measured by the Douglas bag (DB) method. There was no significant difference between VO(2)max predicted by the FM and VO(2)max measured by the DB method. The results of this study showed that a strong positive correlation (r = 0.897) existed between VO(2)max predicted by the FM and VO(2)max measured by the DB method, with a standard error of the estimate (SEE) = 3.97 ml·kg(-1)·min(-1). There was a significant difference in VO(2)max predicted by the American College of Sports Medicine (ACSM) metabolic equations and VO(2)max measured by the DB method (p = 0.01). The correlation between these variables was r = 0.758 (SEE = 5.26 ml·kg(-1)·min(-1)). These findings indicate that a small, portable, and easy-to-use metabolic system provides valid estimates of VO(2)max, and improves upon predictive accuracy, compared to using generalized ACSM metabolic equations.     

Errors in predicting maximal oxygen consumption in pregnant women.

This study was designed to determine the accuracy of estimated values of maximal heart rate (HRmax) and oxygen consumption (VO2) during pregnancy. We measured HR and maximal VO2 (VO2max) at rest and during cycle (CE) and treadmill exercise (TE) tests with rapidly increasing exercise intensities during gestation and after delivery. Pregnancy was found to affect the linear relationship of HR and %VO2max so that the intercept increases with advancing gestation and the slope decreases. Estimated maximal HR (HRmax, est), 220 - age (yr) x beats/min, overestimated measured HRmax by 8% (CE) and 5% (TE). For VO2max estimated by Astrand's nomogram (VO2max, est1) and by linear extrapolation of submaximal values of HR and VO2 to HRmax, est (VO2max, est2), individual errors were large (SD 17-28%). Mean VO2max, est1 overestimated measured VO2max by 20% during CE but not during TE (-2%) and elicited the erroneous impression that VO2max decreases during CE in pregnancy. Mean VO2max, est2 values were not significantly different from measured VO2max values. This apparent accuracy resulted from two opposing errors: 1) HRmax, est overestimated HRmax, and 2) above 70% VO2max the slope of the HR-%VO2max relationship was significantly reduced. Therefore neither method to estimate VO2max can replace the measurement of VO2max.     

Maximal oxygen consumption test during arm exercise--reliability and validity.

The reliability and validity of a continuous progressive arm test, in which maximal 02 consumption (V02 max arm) is determined, were analyzed. Forty-one men (28.2 +/- 8.8 yr) performed the test twice. Eighteen additional men (22.6 +/- 5.6 yr) performed the arm test, as well as the treadmill run, in which maximal O2 consumption VO2max leg) was determined. The validity of the VO2 max arm test was computed, using VO2 max leg as a criterion for the individual's aerobic capacity. The reliability coefficients of VO2 max arm, VEmax arm, and HRmax arm were 0.94, 0.98, and 0.76, respectively, indicating a high reliability of the testmthe validity coefficient of VO2max arm was only 0.74. The regression equation of VO2max leg on VO2max arm was y = 24.4 + 0.9 +/- 4.4 (Syx). These findings indicate that, following the suggested protocol, the individual repeatedly uses the same muscles and does reach an all-out stage. However, different individuals apparently are aided by their trunk and leg muscles to different degrees, which lowers the validity of this test as a predictor of aerobic capacity.     

Cardiovascular changes associated with decreased aerobic capacity and aging in long-distance runners

Fifty-five male runners aged between 30 to 80 years were examined to determine the relative roles of various cardiovascular parameters which may account for the decrease in maximal oxygen uptake (VO2max) with aging. All subjects had similar body fat composition and trained for a similar mileage each week. The parameters tested were VO2max, maximal heart rate (HRmax), cardiac output (Q), and arteriovenous difference in oxygen concentration (Ca-Cv)O2 during graded, maximal treadmill running. Average body fat and training mileage were roughly 12% and 50 km.week-1, respectively. The average 10-km run-time slowed significantly by 6.0%.decade-1 [( 10-km run-time (min) = 0.323 x age (years) + 24.4] (n = 49, r = 0.692, p less than 0.001]. A strong correlation was found between age and VO2max [( VO2max (ml.kg-1.min-1) = -0.439 x age + 76.5] (n = 55, r = -0.768, p less than 0.001]. Thus, VO2max decreased by 6.9%.decade-1 along with reductions of HRmax (3.2%.decade-1, p less than 0.001) and Q (5.8%.decade-1, p less than 0.001), while no significant change with age was observed in estimated (Ca-Cv)O2. It was concluded that the decline of VO2max with aging in runners was mainly explained by the central factors (represented by the decline of HR and Q in this study), rather than by the peripheral factor (represented by (Ca-Cv)O2).     

Intensity of official Futsal matches

The purpose of this study was to assess the intensity of official Futsal matches, expressed in different ways. Fourteen male professional Futsal players from a First Division Brazilian team volunteered to participate in this study. Maximal oxygen uptake (VO(2)max) and the heart hate (HR) and oxygen uptake (VO(2)) correlation were determined for each player. The match intensity was estimated from the players' average HR measured during 13 National Futsal League matches. The HR measurements were obtained while the players were in the court but the values recorded while the players were sitting on the bench were not considered. In addition, these HR values were used to estimate the intensity of the effort expressed as a percentage of the maximal HR (% HRmax), percentage of VO(2)max (% VO(2)max), kilocalories per minute (kcal·min(-1)), and total caloric expenditure. The mean intensity of the matches was 86.4 ± 3.8% HRmax, 79.2 ± 9.0% VO(2)max, 18.0 ± 2.2 kcal·min(-1), and 313 ± 9.3 kcal. It was concluded that official Futsal matches have high intensity when expressed in the different ways used in this study. The information provided by this research can be used for planning the athletes' workouts, diets, and resting periods.     

Age, sex, race, initial fitness, and response to training: the HERITAGE Family Study.

Effects of age, sex, race, and initial fitness on training responses of maximal O(2) uptake (VO(2 max)) are unclear. Data were available on 435 whites and 198 blacks (287 men and 346 women), aged 17-65 yr, before and after standardized cycle ergometer training. Individual responses varied widely, but VO(2 max) increased significantly for all groups. Responses by men and women and by blacks and whites of all ages varied widely. There was no sex difference for change (Delta) in VO(2 max) (ml. kg(-1). min(-1)); women had lower initial values and greater relative (%) increases. Blacks began with lower values but had similar responses. Older subjects had a lower Delta but a similar percent change. Baseline VO(2 max) correlated nonsignificantly with DeltaVO(2 max) but significantly with percent change. There were high, medium, and low responders in all age groups, both sexes, both races, and all levels of initial fitness. Age, sex, race, and initial fitness have little influence on VO(2 max) response to standardized training in a large heterogeneous sample of sedentary black and white men and women.     

Sustainability of critical power determined by a 3-minute all-out test in elite cyclists

Critical power (CP) is a theoretical workload representative of an athlete's maximal sustainable pace. Recent research has validated a 3-minute all-out test on a cycle ergometer for determining CP; however, few studies have investigated the sustainability of CP using this test. The purpose of this study was to determine the sustainability of CP established during the 3-minute test and the determinants of sustainability. A group of elite cyclists (N = 21) performed a VO2max test, 3-minute all-out test, and a time to exhaustion (TTE) trial at CP on 3 different days separated by at least 24 hours. Expired gases were collected during all trials and analyzed for VO2 and VCO2. Heart rate was measured by telemetry. Multiple regression was used to determine predictors of sustainability with significance predetermined at p < 0.05. VO2max was measured at 58.9 ± 5.6 ml·kg(-1)·min(-1), ventilation breakpoint at 44.9 ± 5.7 ml·kg(-1)·min(-1) (75% VO2max), and maximum heart rate at 179 ± 10 b·min(-1). Peak power (PP) in the 3-minute all-out test was measured at 738 ± 170 W, and CP was determined at 305 ± 32 W or 79% of VO2max. The VO2 at CP was 55.4 ± 6.9 ml·kg(-1)·min(-1), representing 94% of measured VO2max. The mean TTE at CP was 14.79 ± 8.38 minutes. The difference score of PP - CP significantly predicted TTE (r = 0.65, p < 0.05). No other measured variables contributed to this prediction. Based on sustainability, these data suggest that the 3-minute all-out test may overestimate CP in elite cyclists, which could lead to overtraining if CP determined with this test is used to identify training intensities.     

Skinfold thickness is related to cardiovascular autonomic control as assessed by heart rate variability and heart rate recovery

The purpose of this study was to determine if heart rate recovery (HRR) and heart rate variability (HRV) are related to maximal aerobic fitness and selected body composition measurements. Fifty men (age = 21.9 ± 3.0 years, height = 180.8 ± 7.2 cm, weight = 80.4 ± 9.1 kg, volunteered to participate in this study. For each subject, body mass index (BMI), waist circumference (WC), and the sum of skinfolds across the chest, abdomen, and thigh regions (SUMSF) were recorded. Heart rate variability (HRV) was assessed during a 5-minute period while the subjects rested in a supine position. The following frequency domain parameters of HRV were recorded: normalized high-frequency power (HFnu), and low-frequency to high-frequency power ratio (LF:HF). To determine maximal aerobic fitness (i.e., VO2max), each subject performed a maximal graded exercise test on a treadmill. Heart rate recovery was recorded 1 (HRR1) and 2 (HRR2) minutes during a cool-down period. Mean VO2max and BMI for all the subjects were 49.5 ± 7.5 ml·kg(-1)·min(-1) and 24.7 ± 2.2 kg·m(-2), respectively. Although VO2max, WC, and SUMSF was each significantly correlated to HRR and HRV, only SUMSF had a significant independent correlation to HRR1, HRR2, HFnu, LF:HF (p < 0.01). The results of the regression procedure showed that SUMSF accounted for the greatest variance in HRR1, HRR2, HFnu, and LF:HF (p < 0.01). The results of this study suggest that cardiovascular autonomic modulation is significantly related to maximal aerobic fitness and body composition. However, SUMSF appears to have the strongest independent relationship with HRR and HRV, compared to other body composition parameters and VO2max.     

Cardiovascular response to punching tempo

Eighteen trained volunteers (12 men and 6 women: age = 22.0 +/- 2.8 years, height = 170.79 +/- 7.67 cm, weight = 71.54 +/- 12.63 kg) participated in 2-minute, randomized fitness boxing trials, wearing 0.34-kg punching gloves, at various tempos (60, 72, 84, 96, 108, and 120 b.min(-1)). During each trial, oxygen uptake (VO(2)), heart rate (HR), and ventilation (VE) were measured continuously. A rating of perceived exertion (RPE) was attained at the conclusion of each trial. Subjects were able to attain VO(2) values ranging from 26.83 to 29.75 ml.kg(-1).min(-1), which correspond to 67.7-72.5% of VO(2)max. The HR responses yielded results ranging from 167.4 to 182.2 b.min(-1), or 85 to 93% of HRmax. No significant difference (p > 0.05) was seen with VO(2) between trials, although a significant difference (p < 0.05) was observed with HR, VE, and RPE. It appears that boxing speed is associated with increased VE, HR response, and perceived effort but not with VO(2). Energy expenditure values ranged from 9.8 to 11.2 kcal.min(-1) for the boxing trials. These results suggest that fitness boxing programs compare favorably with other exercise modalities in cardiovascular response and caloric expenditure.     

Human ventilatory responsiveness to hypoxia is unrelated to maximal aerobic capacity.

Ventilatory responsiveness to hypoxia (HVR) has been reported to be different between highly trained endurance athletes and healthy sedentary controls. However, a linkage between aerobic capacity and HVR has not been a universal finding. The purpose of this study was to examine the relationship between HVR and maximal oxygen consumption (VO2 max) in healthy men with a wide range of aerobic capacities. Subjects performed a HVR test followed by an incremental cycle test to exhaustion. Participants were classified according to their maximal aerobic capacity. Those with a VO2 max of >or=60 ml x kg(-1) x min(-1) were considered highly trained (n = 13); those with a VO2 max of 50-60 ml x kg(-1) x min(-1) were considered moderately-trained (n = 18); and those with a VO2 max of <50 ml x kg(-1) x min(-1) were considered untrained (n = 24). No statistical differences were detected between the three groups for HVR (P > 0.05), and the HVR values were variable within each group (range: untrained = 0.28-1.61, moderately trained = 0.23-2.39, and highly trained = 0.08-1.73 l x min.%arterial O2 saturation(-1)). The relationship between HVR and VO2 max was not statistically significant (r = -0.1723; P > 0.05). HVR was also unrelated to maximal minute ventilation and ventilatory equivalents for O2 and CO2. We found that a spectrum of hypoxic ventilatory control is present in well-trained endurance athletes and moderately and untrained men. We interpret these observations to mean that other factors are more important in determining hypoxic ventilatory control than physical conditioning per se.     

Maximal aerobic capacity across age in healthy Hispanic and Caucasian women.

We tested the hypothesis that the age-related decline in maximal aerobic capacity, as measured by maximal oxygen uptake (VO(2 max)), is greater in Hispanic than in Caucasian women. We studied 146 healthy sedentary women aged 20-75 yr: 53 Hispanic (primarily of Mexican descent) and 93 Caucasian (non-Hispanic white). The groups did not differ in mean age, body mass, percent body fat, estimated physical activity-related energy expenditure, or education-based socioeconomic status (SES). During maximal exercise, respiratory exchange ratio, rating of perceived exertion, and percent predicted maximal heart rate were similar across age and ethnicity, suggesting equivalent maximum voluntary efforts in all subjects. VO(2 max) (ml x kg(-1) x min(-1)) was inversely related to age (P < 0.01) in Caucasian (r =-0.68) and Hispanic (r = -0.61) women. The absolute rate of decline in VO(2 max) with age was the same in the two groups (-0.31 ml x kg(-1) x min(-1) x yr(-1)). The relative rate of decline (% from age 25 yr) also was similar in the Caucasian (-9.0%) and Hispanic (-9.2%) women. When subjects of all ages were pooled, mean levels of VO(2 max) were similar in the two groups (approximately 28 ml x kg(-1) x min(-1)). These results, the first to our knowledge in Hispanics, indicate that mean levels of VO(2 max), as well as the rate of decline in VO(2 max) with age, are similar in healthy sedentary Hispanic and Caucasian women of similar SES. Thus it does not appear that Hispanic ethnicity per se modulates maximal aerobic capacity in this population.     

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)     

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.     

Running economy and maximal oxygen consumption after 4 weeks of oral Echinacea supplementation

The purpose of this investigation was to determine the effects of 4 weeks of oral Echinacea (ECH) supplementation on erythropoietin (EPO), red blood cell (RBC) count, running economy (RE), and VO2max. Twenty-four men aged 24.9 ± 4.2 years, height 178.9 ± 7.9 cm, weight 87.9 ± 14.6 kg, body fat 19.3 ± 6.5% were grouped using a double-blind design and self-administered an 8,000-mg·d(-1) dosage of either ECH or placebo (PLA) in 5 × 400 mg × 4 times per day for 28 days. Blood samples were collected and analyzed for RBCs and EPO using automated flow cytometery and enzyme-linked immunosorbent assay. Maximal graded exercise tests (GXTs) were administered to measure VO2max, RE, and heart-rate responses. Analysis of variance was used to determine statistically significant differences (P ≤ 0.05). The EPO increased significantly in ECH at 7 days (ECH: 15.75 ± 0.64, PLA: 10.01 ± 0.73 mU·ml(-1)), 14 days (ECH: 18.88 ± 0.71, PLA: 11.02 ± 0.69 mU·ml(-1)), and 21 days (ECH: 16.06 ± 0.55, PLA: 9.20 ± 0.55 mU·ml(-1)). VO2max increased significantly in ECH (ECH: 1.47 ± 1.28, PLA: -0.13 ± 0.52%). Running economy improved significantly in ECH as indicated by a decrease in submaximal VO2max during the first 2 stages of the GXT (stage 1: ECH -1.50 ± 1.21, PLA 0.60 ± 1.95%; stage 2: ECH -1.67 ± 1.43, PLA 0.01 ± 1.03%). These data suggest that ECH supplementation results in significant increases in EPO, VO2max, and running economy.     

Predicting maximal aerobic capacity (VO2max) from the critical velocity test in female collegiate rowers

The objective of this study was to examine the relationship between the critical velocity (CV) test and maximal oxygen consumption (VO2max) and develop a regression equation to predict VO2max based on the CV test in female collegiate rowers. Thirty-five female (mean ± SD; age, 19.38 ± 1.3 years; height, 170.27 ± 6.07 cm; body mass, 69.58 ± 0.3 1 kg) collegiate rowers performed 2 incremental VO2max tests to volitional exhaustion on a Concept II Model D rowing ergometer to determine VO2max. After a 72-hour rest period, each rower completed 4 time trials at varying distances for the determination of CV and anaerobic rowing capacity (ARC). A positive correlation was observed between CV and absolute VO2max (r = 0.775, p < 0.001) and ARC and absolute VO2max (r = 0.414, p = 0.040). Based on the significant correlation analysis, a linear regression equation was developed to predict the absolute VO2max from CV and ARC (absolute VO2max = 1.579[CV] + 0.008[ARC] - 3.838; standard error of the estimate [SEE] = 0.192 L·min(-1)). Cross validation analyses were performed using an independent sample of 10 rowers. There was no significant difference between the mean predicted VO2max (3.02 L·min(-1)) and the observed VO2max (3.10 L·min(-1)). The constant error, SEE and validity coefficient (r) were 0.076 L·min(-1), 0.144 L·min(-1), and 0.72, respectively. The total error value was 0.155 L·min(-1). The positive relationship between CV, ARC, and VO2max suggests that the CV test may be a practical alternative to measuring the maximal oxygen uptake in the absence of a metabolic cart. Additional studies are needed to validate the regression equation using a larger sample size and different populations (junior- and senior-level female rowers) and to determine the accuracy of the equation in tracking changes after a training intervention.     

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.