Calculation of record-time in the 800-meter run: predictive value of Margaria's equation

Margaria's equation (1976)--describing the relationship between the minimum time necessary to cover a distance equal or longer than 1,000 m (record-time TR) and the maximal oxygen consumption (VO2 max)--has been modified in order to be applied to the calculation of TR in the 800 m foot race. Fifteen subjects participated in this study (VO2 max = 63 +/- 3.5 ml O2 X kg-1 X min-1, measured TR = 131 +/- 10 seconds). It has been found the TR calculated from Margaria's equation (TRc) are underestimated (TRc = 104 +/- 10 seconds). By taking into account the actual energy cost of running (0.19 ml O2 X kg-1 X m-1) and the kinetics of VO2 at the onset of exercise, TRc averaged 133 +/- 8.5 seconds. Moreover, the relationship between TRc and measured TR (TRm) is highly significant (TRc = 50.4 + 0.65 TRm; r = 0.75; P less than 0.01). These results validate Margaria's equation modifications.     

Relationship between record time and maximal oxygen consumption in middle-distance running.

The relationship between record time (tr) and maximal oxygen uptake (VO2max) has been examined in 69 male physical education students who had taken part in 800-m and 1500-m footraces. It was found that tr and VO2max were inversely related. The relationships tr = f(VO2max) have been fitted by two exponential equations: tr (1500 m) = 698e-0.0145VO2max; tr (800 m) = 272e-0.011VO2max; P less than 0.001. A mathematical formulation of the energy conservation principle in supramaximal running, based on the exponential increase of the oxygen uptake as a function of time with a rate constant of 0.025 s-1 has been applied to the tr calculation from VO2max. As calculated tr were highly correlated to measured tr (P less than 0.001), it was concluded that the relationships tr = f(VO2max) can be interpreted on the basis of the model described in this study.     

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.     

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.     

Development of a submaximal test to predict elliptical cross-trainer VO2max

The purpose of this study was to develop an equation to predict VO2max from a submaximal elliptical cross-trainer test. Fifty-four apparently healthy subjects (25 men and 29 women, mean +/- SD age: 29.5 +/- 7.1 years, height: 173.3 +/- 12.6 cm, weight: 72.3 +/- 7.9 kg, percent body fat: 17.3 +/- 5.0%, and elliptical cross-trainer VO2max: 43.9 +/- 7.2 ml x kg(-1) x min(-1)) participated in the study and were randomly assigned to an original sample group (n = 40) and a cross-validation group (n = 14). Each subject completed an elliptical cross-trainer submaximal (3 5-minute submaximal stages) and a VO2max test on the same day, with a 15-minute rest period in between. Stepwise multiple regression analyses were used to develop an equation for estimating elliptical cross-trainer VO2max from the data of the original sample group. The accuracy of the equation was tested by using data from the cross-validation group. Because there was no shrinkage in R2 between the original sample group and the cross-validation group, data were combined in the final prediction equation (R2 = 0.732, standard error of the estimate = 3.91 ml x kg(-1) x min(-1), p < 0.05): VO2max = 73.676 + 7.383(gender) - 0.317(weight) + 0.003957(age x cadence) - 0.006452(age x heart rate at stage 2). The correlation coefficient between the predicted and measured VO2max values was r = 0.86. Dependent t-tests resulted in no significant differences (p > 0.05) between predicted (43.8 ml x kg(-1) x min(-1)) and measured (43.9 ml x kg(-1) x min(-1)) VO2max measurements. Results indicate that the protocol and equation developed in the current study can be used by exercise professionals to provide acceptably accurate estimates of VO2max in non-laboratory-based settings.     

Prediction of VO2max during cycle exercise in pregnant women

We measured maximal O2 uptake (VO2max) during stationary cycling in 40 pregnant women [aged 29.2 +/- 3.9 (SD) yr, gestational age 25.9 +/- 3.3 wk]. Data from 30 of these women were used to develop an equation to predict the percent VO2max from submaximal heart rates. This equation and the submaximal VO2 were used to predict VO2max in the remaining 10 women. The accuracy of VO2max values estimated by this procedure was compared with values predicted by two popular methods: the Astrand nomogram and the VO2 vs. heart rate (VO2-HR) curve. VO2max values estimated by the derived equation method in the 10 validation subjects were only 3.7 +/- 12.2% higher than actual values (P greater than 0.05). The Astrand method overestimated VO2max by 9.0 +/- 19.4% (P greater than 0.05), whereas the VO2-HR curve method underestimated VO2max by only 1.6 +/- 10.3% in the same 10 subjects (P greater than 0.05). Both the Astrand and the VO2-HR curve methods correlated well with the actual values when all 40 subjects were considered (r = 0.77 and 0.85, respectively), but the VO2-HR curve method had a lower SE of prediction than the Astrand method (8.7 vs. 10.4%). In a comparison group of 10 nonpregnant sedentary women (29.9 +/- 4.5 yr), an equation relating %VO2max to HR nearly identical to that obtained in the pregnant women was found, suggesting that pregnancy does not alter this relationship. We conclude that extrapolating the VO2-HR curve to an estimated maximal HR is the most accurate method of predicting VO2max in pregnant women.     

Modeling: optimal marathon performance on the basis of physiological factors

This paper examines current concepts concerning "limiting" factors in human endurance performance by modeling marathon running times on the basis of various combinations of previously reported values of maximal O2 uptake (VO2max), lactate threshold, and running economy in elite distance runners. The current concept is that VO2max sets the upper limit for aerobic metabolism while the blood lactate threshold is related to the fraction of VO2max that can be sustained in competitive events greater than approximately 3,000 m. Running economy then appears to interact with VO2max and blood lactate threshold to determine the actual running speed at lactate threshold, which is generally a speed similar to (or slightly slower than) that sustained by individual runners in the marathon. A variety of combinations of these variables from elite runners results in estimated running times that are significantly faster than the current world record (2:06:50). The fastest time for the marathon predicted by this model is 1:57:58 in a hypothetical subject with a VO2max of 84 ml.kg-1.min-1, a lactate threshold of 85% of VO2max, and exceptional running economy. This analysis suggests that substantial improvements in marathon performance are "physiologically" possible or that current concepts regarding limiting factors in endurance running need additional refinement and empirical testing.     

Aerobic performance of female marathon and male ultramarathon athletes.

The aerobic performance of thirteen male ultramarathon and nine female marathon runners were studied in the laboratory and their results were related to their times in events ranging in distance from 5 km to 84.64 km. The mean maximal aerobic power output (VO2 max) of the men was 72.5 ml/kg . min compared with 58.2 ml/kg . min (p less than 0.001) in the women but the O2 cost (VO2) for a given speed or distance of running was the same in both sexes. The 5 km time of the male athletes was closely related to their VO2 max (r = -0.85) during uphill running but was independent of relative power output (%VO2 max). However, with increasing distance the association of VO2 max with male athletic performance diminished (but nevertheless remained significant even at 84.64 km), and the relationship between %VO2 max and time increased. Thus, using multiple regression analysis of the form: 42.2 km (marathon) time (h) = 7.445 - 0.0338 VO2 max (ml/kg . min) - 0.0303% VO2 max (r = 0.993) and 84.64 km (London-Brighton) time (h) = 16.998 - 0.0735 VO2 max (ml/kg . min) - 0.0844% VO2 max (r = 0.996) approximately 98% of the total variance of performance times could be accounted for in the marathon and ultramarathon events. This suggests that other factors such as footwear, clothing, and running technique (Costill, 1972) play a relatively minor role in this group of male distance runners. In the female athletes the intermediate times were not available and they did not compete beyond 42.2 km (marathon) distance but for this event a similar association though less in magnitude was found with VO2 max (r = -0.43) and %VO2 max (= -0.49). The male athletes were able to sustain 82% VO2 max (range 80--87%) in 42.2 km and 67% VO2 max (range 53--76%) in 84.64 km event. The comparable figure for the firls in the marathon was 79% VO2 max (ranges 68--86%). Our data suggests that success at the marathon and ultramarathon distances is crucially and (possibly) solely dependent on the development and utilisation of a large VO2 max.     

Determination of the velocity associated with the longest time to exhaustion at maximal oxygen uptake

The so-called velocity associated with VO2max, defined as the minimal velocity which elicits VO2max in an incremental exercise protocol (v(VO2max)), is currently used for training to improve VO2max. However, it is well known that it is not the sole velocity which elicits VO2max and it is possible to achieve VO2max at velocities lower and higher than v(VO2max). The goal of this study was to determine the velocity which allows exercise to be maintained the longest time at v(VO2max). Using the relationship between time to exhaustion at VO2max in the all-out runs at 90%, 100%, 120% and 140% of v(VO2max) and distance run at VO2max, the velocity which elicits the longest time to exhaustion at VO2max (CV') was determined. For the six subjects tested (physical education students), this velocity was not significantly different from v(VO2max) (16.96+/-0.92 km x h(-1) vs 17.22+/-1.12 km x h(-1), P = 0.2 for CV' and v(VO2max), respectively) and these two velocities were correlated (r = 0.88, P = 0.05).     

Crossvalidation of two heart rate-based equations for predicting VO2max in white and black men

The purpose of this investigation was to crossvalidate 2 equations that use the ratio of maximal heart rate (HRmax) to resting HR (HRrest) for predicting maximal oxygen consumption (VO2max) in white and black men. One hundred and nine white (n = 51) and black (n = 58) men completed a maximal exercise test on a treadmill to determine VO2max. The HRrest and HRmax were used to predict VO2max via the HRindex and HRratio equations. Validity statistics were done to compare the criterion versus predicted VO2max values across the entire cohort and within each race separately. For the entire group, VO2max was significantly overestimated with the HRindex equation, but the HRratio equation yielded no significant difference compared with the criterion. In addition, there were no significant differences shown between VO2max and either HR-based prediction equation for the white subgroup. However, both equations significantly overestimated VO2max in the black group. Furthermore, large standard error of estimates (ranging from 6.92 to 7.90 ml·kg(-1)·min(-1)), total errors (ranging from 8.30 to 8.62 ml·kg(-1)·min(-1)), and limits of agreement (ranging from upper limits of 16.65 to lower limits of -18.25 ml·kg(-1)·min(-1)) were revealed when comparing the predicted to criterion VO2max for both the groups. Considering the results of this investigation, the HRratio and HRindex methods appear to crossvalidate and prove useful for estimating the mean VO2max in white men as a group but not for an age-matched group of black men. However, because of inflated values for error, caution should be exercised when using these methods to predict individual VO2max.     

A new approach to assessing maximal aerobic power in children: the Odense School Child Study

In two experiments maximal aerobic power (VO2max) calculated from maximal mechanical power (Wmax) was evaluated in 39 children aged 9-11 years. A maximal multi-stage cycle ergometer exercise test was used with an increase in work load every 3 min. In the first experiment oxygen consumption was measured in 18 children during each of the prescribed work loads and a correction factor was calculated to estimate VO2max using the equation VO2max = 12.Wmax + 5.weight. An appropriate increase in work rate based on height was determined for boys (0.16 W.cm-1) and girls (0.15 W.cm-1) respectively. In the second experiment 21 children performed a maximal cycle ergometer exercise test twice. In addition to the procedure in the first experiment a similar exercise test was performed, but without measurement of oxygen uptake. Calculated VO2max correlated significantly (p less than 0.01) with those values measured in both boys (r = 0.90) and girls (r = 0.95) respectively, and the standard error of estimation for VO2max (calculated) on VO2max (measured) was less than 3.2%. Two expressions of relative work load (%VO2max and %Wmax) were established and found to be closely correlated. The relative work load in %VO2max could be predicted from the relative work load in %Wmax with an average standard error of 3.8%. The data demonstrate that calculated VO2max based on a maximal multi-stage exercise test provides an accurate and valid estimate of VO2max.     

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)     

Oxygen uptake kinetics in trained athletes differing in VO2max

Previous work has shown that when VO2 kinetics are compared for endurance trained athletes and untrained subjects, the highly trained athletes have a faster response time. However, it remains to be determined whether the more rapid adjustment of VO2 toward steady state in athletes is due to VO2max differences or training adaptation alone. One approach to this problem is to study the time course of VO2 kinetics at the onset of work in athletes who differ in VO2max but have similar training habits. Therefore, the purpose of these experiments was to compare the time course of VO2 kinetics at the onset of exercise in athletes with similar training routines but who differ in VO2max. Ten subjects (VO2max range 50-70 ml . kg-1 . min-1) performed 6-minutes of cycle ergometer exercise at approximately 50% VO2max. Ventilation and gas exchange were monitored by open circuit techniques. The data were modeled with a single component exponential function incorporating a time delay, (TD); delta VO2t = delta VO2ss (1-e-t-TD/tau), where tau is the time constant delta VO2t is the increase in VO2 at time t and delta VO2ss is the steady-rate increment above resting VO2. Kinetic analysis revealed a range of VO2 half times from 21.6 to 36.0 s across subjects with a correlation coefficient of r = -0.80 (p less than 0.05) between VO2max and VO2 half time. These data suggest that in highly trained individuals with similar training habits, those with a higher VO2max achieve a more rapid VO2 adjustment at the onset of work.     

Ambulatory estimates of maximal aerobic power from foot -ground contact times and heart rates in running humans.

Seeking to develop a simple ambulatory test of maximal aerobic power (VO(2 max)), we hypothesized that the ratio of inverse foot-ground contact time (1/t(c)) to heart rate (HR) during steady-speed running would accurately predict VO(2 max). Given the direct relationship between 1/t(c) and mass-specific O(2) uptake during running, the ratio 1/t(c). HR should reflect mass-specific O(2) pulse and, in turn, aerobic power. We divided 36 volunteers into matched experimental and validation groups. VO(2 max) was determined by a treadmill test to volitional fatigue. Ambulatory monitors on the shoe and chest recorded foot-ground contact time (t(c)) and steady-state HR, respectively, at a series of submaximal running speeds. In the experimental group, aerobic fitness index (1/t(c). HR) was nearly constant across running speed and correlated with VO(2 max) (r = 0.90). The regression equation derived from data from the experimental group predicted VO(2 max) from the 1/t(c). HR values in the validation group within 8.3% and 4.7 ml O(2) x kg(-1) x min(-1) (r = 0.84) of measured values. We conclude that simultaneous measurements of foot-ground constant times and heart rates during level running at a freely chosen constant speed can provide accurate estimates of maximal aerobic power.     

Role of muscle loss in the age-associated reduction in VO2 max

A progressive decline in maximal O2 consumption (VO2max) expressed traditionally as per kilogram body weight generally occurs with advancing age. To investigate the extent to which this decline could be attributable to the age-associated loss of metabolically active tissue, i.e., muscle, we measured 24-h urinary creatinine excretion, an index of muscle mass, in 184 healthy nonobese volunteers, ages 22-87 yr, from the Baltimore Longitudinal Study of Aging who had achieved a true VO2max during graded treadmill exercise. A positive correlation was found between VO2max and creatinine excretion in both men (r = 0.64, P less than 0.001) and women (r = 0.47, P less than 0.001). As anticipated, VO2max showed a strong negative linear relationship with age in both men and women. Creatinine excretion also declined with age in men and women. When VO2max was normalized for creatinine excretion, the variance in the VO2max decline attributable to age declined from 60 to 14% in men and from 50 to 8% in women. Thus comparing the standard age regression of VO2max per kilogram body weight with that in which VO2max is normalized per milligram creatinine excretion, the decline in VO2max between a hypothetical 30 yr old and a 70 yr old was reduced from 39 to 18% in men and from 30 to 14% in women. We conclude that in both sexes, a large portion of the age-associated decline in VO2max in non-endurance-trained individuals is explicable by the loss of muscle mass, which is observed with advancing age.     

Prediction of maximal VO2 from a submaximal StairMaster test in young women

The StairMaster 4000 PT is a popular step ergometer which provides a submaximal test protocol (SM Predicted VO(2)max) for the prediction of VO(2)max (ml.kg(-1).min(-1)). The purpose of this study was to evaluate the SM Predicted VO(2)max protocol by comparing it to results from a VO(2)max treadmill test in 20 young healthy women aged 20-25 years. Subjects were 10 step-trained (ST) women who had performed aerobic activities and exercised on a step ergometer for 20-30 minutes at least 3 times per week for the past 3 months, and 10 non-step-trained (NST) women who had performed aerobic activities no more than twice a week during the past 3 months and had no previous experience on a step ergometer. The SM Predicted VO(2)max protocol used 2 steady state heart rates between approximately 115-150 b.min(-1) to estimate VO(2)max. The Bruce maximal treadmill protocol (Actual VO(2)max) was used to measure VO(2)max by open circuit spirometry. Each subject performed both tests within a 7-day period. The means and standard deviations for the Actual VO(2)max tests were 39.8 +/- 6.1 ml.kg(-1).min(-1) for the ST group, 37.6 +/- 6.3 ml.kg(-1).min(-1) for the NST group, and 38.7 +/- 6.2 ml.kg(-1).min(-1) for the Total group (N = 20); and for the SM Predicted VO(2)max tests, means and standard deviations were 40.78 +/- 14.0 ml.kg(-1).min(-1), 30.9 +/- 4.8 ml.kg(-1).min(-1) and 35.9 +/- 11.4 ml.kg(-1).min(-1). There was no significant difference (p > 0.05) between the means of the Actual VO(2)max and SM Predicted VO(2)max test for the Total group (N = 20) or the ST group (n = 10), but a significant difference (p < 0.05) was shown for the NST group. The coefficient of determination (R(2)) and standard error of estimate (SEE) for the SM Predicted VO(2)max and Actual VO(2)max tests were R(2) = 0.18, SEE = 5.72 ml.kg(-1).min(-1) for the Total group; R(2) = 0.00, SEE = 6.68 ml.kg(-1).min(-1) for the NST group; and R(2) = 0.33, SEE = 5.32 ml.kg(-1).min(-1) for ST group. In conclusion, the SM Predicted VO(2)max test has acceptable accuracy for the ST group, but significantly underpredicted the NST group by almost 7 ml; and, as demonstrated by the high SEEs, it has a low level of precision for both ST and NST subjects.     

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.     

Slow upward drift of VO2 during constant-load cycling in untrained subjects

The oxygen uptake kinetics during constant-load exercise when sitting on a bicycle ergometer were determined in 7 untrained subjects by measuring breath-by-breath VO2 during continuous exercise to volitional exhaustion (mean endurance time = 1160 +/- 172 s) at a pedal frequency of 70 revolutions.min-1. The power output, averaging 189.5 W, was set at 82.5% of that eliciting the individual VO2max during a 5 min incremental exercise test. Throughout the exercise period, the VO2 kinetics could be appropriately described by a two-component exponential equation of the form: VO2(t) = Ya[1 - exp(-kat)] + Yb[1 - exp(-kbt)] where VO2 is net oxygen consumption and t the time from work onset. VO2 measured at the end of exercise was close to VO2max (98% VO2max) and the mean values of Ya, ka, Yb and kb amounted to 1195 ml O2.min-1, 0.034 s-1, 1562 ml O2.min-1, and 0.005 s-1 respectively. The initial rate of increase in VO2 predicted from the above equation is slower than that calculated, for the same work intensity, on the basis of the data obtained by Morton (1985) in trained subjects. For t greater than 480 s, however, the two models yield substantially equal results.     

The influence of exercise duration at VO2 max on the off-transient pulmonary oxygen uptake phase during high intensity running activity

The purpose of this study was to examine the influence of time run at maximal oxygen uptake (VO2 max) on the off-transient pulmonary oxygen uptake phase after supra-lactate threshold runs. We hypothesised: 1) that among the velocities eliciting VO2 max there is a velocity threshold from which there is a slow component in the VO2-off transient, and 2) that at this velocity the longer the duration of this time at VO2 max (associated with an accumulated oxygen kinetics since VO2 can not overlap VO2 max), the longer is the off-transient phase of oxygen uptake kinetics. Nine long-distance runners performed five maximal tests on a synthetic track (400 m) while breathing through the COSMED K4b2 portable, telemetric metabolic analyser: i) an incremental test which determined VO2 max, the minimal velocity associated with VO2 max (vVO2 max) and the velocity at the lactate threshold (vLT), ii) and in a random order, four supra-lactate threshold runs performed until exhaustion at vLT + 25, 50, 75 and 100% of the difference between vLT and vVO2 max (vdelta25, vdelta50, vdelta75, vdelta100). At vdelta25, vdelta50 (= 91.0 +/- 0.9% vVO2 max) and vdelta75, an asymmetry was found between the VO2 on (double exponential) and off-transient (mono exponential) phases. Only at vdelta75 there was at positive relationship between the time run at VO2 max (%tlimtot) and the VO2 recovery time constant (Z = 1.8, P = 0.05). In conclusion, this study showed that among the velocities eliciting VO2 max, vdelta75 is the velocity at which the longer the duration of the time at VO2 max, the longer is the off-transient phase of oxygen uptake kinetics. It may be possible that at vdelta50 there is not an accumulated oxygen deficit during the plateau of VO2 at VO2 max and that the duration of the time at VO2 max during the exhaustive runs at vdelta100, could be too short to induce an accumulating oxygen deficit affecting the oxygen recovery.