VO2 Data Research Articles

AEROBIC TRAINING AND RECOVERY VO2 KINETICS AFTER SUPRAMAXIMAL EXERCISE

1130 The purpose of this study was to determine the effects of an aerobic training program on recovery VO2 kinetics after supramaximal exercise. Ten untrained males (age: 22.4 ± 2.1 yr.; weight: 79.5 ± 12.3 kg; height: 176.5 ± 8.5 cm; VO2max<50 ml·kg-1·min-1) completed six weeks of aerobic training. The subjects performed pre and post training VO2max tests and Anaerobic Speed Tests (ASTs). The ASTs were individually determined to produce tests of two minutes in duration (2 min AST). Recovery VO2 data was collected following the 2 min AST and fit with a double exponential function to determine the time constants (τ1 and τ2). Significant differences were evident between pre and post training relative and absolute VO2max scores (46.38 ± 3.74 ml·kg-1·min-1 vs. 51.82 ± 5.21 ml·kg-1·min-1 and 3.61 ± 0.42 L·min-1 vs. 4.00 ± 0.40 L·min-1; p<0.05). VO2 rate components were significantly decreased following the endurance training program (τ1 = 2.69 ± 0.19 min vs. 2.29 ± 1.40 min and τ2 = 43.74 ± 5.12 min vs. 39.63± 4.24 min; p<0.05). No significant relationships were evident between VO2max and the VO2 recovery rates (p>0.05). These results indicate that the recovery VO2 kinetics associated with high intensity anaerobic exercise can be decreased through aerobic training. The findings also suggest that the VO2 recovery rates associated with supramaximal work do not appear to be related to VO2max.

PRE-EXERCISE CONSUMPTION OF COMMERCIAL ENERGY BARS AFFECTS PLASMA GLUCOSE REGULATION DURING PROLONGED INTENSE CYCLING 1422

Commercially available energy bars varying in carbohydrate (CHO), fat, and protein content were consumed one hour prior to completing a series of 60km time trials on an indoor trainer (Cateye CS 1000) with each subject using their own racing bicycle. Test bars were: 76% CHO, 15% protein, 8%fat (HC); 40% CHO, 30% protein, 30% fat (MOD); 34% CHO, 8% protein, 58% fat (HF); and placebo (P) with each “meal” weighed to provide 5kcals/kg of energy. Five trained cyclists (Age 33±3 yrs; VO2 max. 5.14±0.3 L/min.) completed each trial in a randomized sequence. Diets were analyzed for the 3 days preceding each trial and the energy bars were consumed following an 8 hour fast. Plasma glucose (mg/dL), completion time, heart rate, and VO2 data were collected at each 10km interval. Data were analyzed by a two-way (trial × distance) repeated measures ANOVA(p<0.05). Initial plasma glucose was highest following consumption of the HC bar (109mg/dL), however at the 10km interval, plasma glucose had decreased to 74mg/dL and remained lower throughout the HC trial when compared to all other trials. Mean completion time was between 2 and 4 minutes slower for the HC trial when compared to the other trials, with a clear diverging relationship existing between the HC and other trials over the final 40km. HR and VO2 were not different among the four trials and were similar at each distance interval (HR ≈bpm - 79.5% HRmax; VO2≈3.66 l/min - 71.2% VO2max), excluding the 60km values (HR ≈ 163 bpm, VO2≈4.1 l/min) when additional effort was exerted over the final stages. In conclusion, ingestion of a HC energy bar one hour prior to exercise generated a hypoglycemic state and was not advantageous to 60km time trial performance.

Scaling peak VO2 for differences in body size.

This paper examined the influence of different statistical modeling techniques on the interpretation of peak VO2 data in groups of prepubertal, circumpubertal, and adult males (group 1M, N = 29; group 2M, N = 26; group 3M, N = 8) and females (group 1F, N = 33; group 2F, N = 34; group 3F, N = 16). Conventional comparisons of the simple per-body-mass ratio (ml.kg-1.min-1) revealed no significant differences between the three male groups (P < 0.05). In females, a decline in VO2 between group 2F and 3F was observed (P < 0.05). Both linear and log-linear (allometric) models revealed significant increases across all three male groups for peak VO2 adjusted for body mass (P < 0.05). In females these scaling models identified a significantly lower peak VO2 in group 1F versus groups 2F and 3F (P < 0.05). Based upon the common mass exponent identified (b = 0.80, SE = 0.04), power function ratios (y.mass0.80) were generated and the logarithms of these compared. Again, results indicated a progressive increase in peak VO2 across groups 1M to 3M (P < 0.05) and an increase between groups 1F and 2F (P < 0.05). Incorporating stature into the allometric equation reduced the mass exponent to 0.71 (SE = 0.06) with the contribution of the stature exponent shown to be 0.44 (SE = 0.20). These results indicate that conventional ratio standards do not adequately account for body size differences when investigating functional changes in peak VO2.

Physiologic correlates to running performance in pre-pubertal distance runners.

In adults, four major variables have been shown to be associated with success in distance running performance: submaximal oxygen consumption (running economy), peak oxygen consumption (Peak VO2), ventilatory threshold (VT) and fractional utilisation (FU). The primary aim of this study was to describe the relationship between the 3000 m race times of run-trained prepubertal boys to these four variables. Thirteen male run-trained pre-pubertal boys (age 11.7 +/- 1.1 yrs, mean +/- SD), volunteered to take part in a 3000 m time trial and laboratory assessment, consisting of treadmill running at four submaximal speeds (8, 9.6, 11.2 and 12.8 km.h-1) as well as a peak VO2 test. The group demonstrated a heterogeneous array of peak VO2 data. A high level of association (p < 0.05) was found between mass-relative peak VO2 and 3000 m time trial results (r = -0.83). In addition ventilatory threshold expressed as %peak VO2, VO2 at VT and estimated velocity at VT was also highly related to 3000 m time trial (r = -0.78, -0.77 and -0.77) respectively. Fractional utilisation (%peak VO2) was significantly (p < 0.05) associated with race time at the final two submaximal running speeds only (11.2 and 12.8 km.h-1) (r = 0.61 and 0.67, respectively). Respiratory Exchange Ratio (RER) was also found to be significantly (p < 0.05) associated with 3000 m race time at 11.2 and 12.8 km.h-1. Overall peak VO2 appeared to be the single most important factor associated with success at 3000 m.

Time Courses of Cardiac Output and Oxygen Uptake Following Stepwise Increases in Exercise Intensity

The adjustment of pulmonary oxygen uptake (VO2) following a step increase in work rate has been characterized as consisting of an early "cardiodynamic" component with unchanged mixed-venous O2-content ("phase 1") and a subsequent "metabolic" component ("phase 2") starting when venous blood from the muscle arrives at the lungs. The aim of the present study was to investigate whether the onset of phase 2 actually indicates the arrival of blood influenced by the altered muscle metabolism. Parallel measurements of cardiac output (Doppler technique) and VO2 (breath-by-breath measurements at the mouth) were performed in eight subjects during step increases in exercise intensity (from a 20 W baseline to either 80 W, 120 W, 160 W or 200 W). To vary the absolute cardiac output values for given muscle VO2 the subjects exercised both in upright and supine position. Individual time-courses of the arterio-venous O2 difference (a-v delta O2) were computed from cardiac output and VO2 data. Independent of body position two clear-cut phases of similar duration were seen both in VO2 and in the computed a-v delta O2. The duration of the first component with unchanged a-v delta O2 was about 20 s at the lowest step amplitudes (20-80 W and 20-120 W). It decreased to about 15 s for the 20-160 W and 20-200 W steps. At the lower exercise intensities the duration of phase 1 appears too long to be entirely due to the transit time of venous blood from the exercising muscles to the lungs.(ABSTRACT TRUNCATED AT 250 WORDS)

Variation in the aerobic demand of running among trained and untrained subjects

Variation in the aerobic demand (VO2) of submaximal running was quantified among trained and untrained subjects stratified by performance capability. Based on a retrospective analysis of seven published studies, maximal aerobic power (VO2max), and submaximal VO2 values were analyzed in three groups of trained distance runners (Category 1 (C1) (elite runners; N = 22), Category 2 (C2) (sub-elite runners; N = 41), and Category 3 (C3) (good runners; N = 16), and one group (N = 10) of untrained subjects (Category 4; C4). Results indicated that VO2max differed significantly (P < 0.05) across groups, such that C1 > C2 > C3 > C4. Analysis of submaximal VO2 data also revealed that C4 was more uneconomical than C1, C2, and C3 and that C2 and C3 were less economical than C1. Average within-group variability in submaximal VO2 was similar across categories and a marked overlap of minimum, mean and maximal economy values existed across categories. These data suggest that 1) trained subjects are more economical than untrained subjects, 2) elite runners display better economy compared to less-talented counterparts, and 3) economical and uneconomical runners can be found in all performance categories.

Relationship between IMoninvasive Cardiopulmonary Exercise Testing and Central Hemodynamics in Patients with Severe Chronic Heart Failure

In view of the frequent follow-up evaluations of patients with severe chronic heart failure, the purpose of this study was to assess whether noninvasive gas exchange parameters from cardiopulmonary exercise testing (CPX), measured at ventilatory threshold (VT), are related to invasively measured peak diastolic pulmonary artery pressure (dPAP) and peak cardiac output (CO). 23 males with severe chronic heart failure underwent CPX on a bicycle ergometer (supine; steps of 25 W/5 min) during right heart catheterization. dPAP and/or CO increased significantly from rest to VT (18 ±10-9 30 ±10 mm Hg, p < 0.01; 4.8 ± 1.4 -9 6.4 ± 2.3 liters/min, p< 0.05), but did not from VT to peak exercise (33 ± 10 mm Hg; 7.3 ± 2.5 liters/min). Data indicated severely deteriorated hemodynamics at rest and during exercise. Oxygen uptake (VO2) increased from rest (270 ± 45 ml/min) to VT (650 ± 135 ml/min at 27 ± 7 W) to peak exercise (829 ± 183 ml/min at 39 ± 23 W). VO2 data were normal for a given workload. From all CPX data at VT, only 02 pulse correlated with peak dPAP (r = -0.58; p < 0.05). Peak CO correlated with O2 pulse (r = -0.49), VO2 (r = 0.46), ventilatory equivalent for O2 (r = -0.43) and tidal volume (r = 0.43), measured at VT (p < 0.05 for all parameters). Variance of peak dPAP and peak CO could only be explained by O2 pulse at VT (58 and 49%, respectively). Noninvasive cardiopulmonary data at VT did not give sufficient information about peak dPAP and peak CO in patients with severe chronic heart failure using a steady-state protocol. This indicates that early ventilatory threshold should not be considered indicative of reduced CO due to skeletal muscle underperfusion in heart failure patients.

Examination of data normalization procedures for expressing peak VO2 data.

Peak O2 uptake (VO2) has traditionally been compared among individuals differing in body composition by dividing measured values (1/min) by fat-free mass (FFM) (i.e., ratio method). However, the ability of the ratio method to mathematically remove the confounding influence of FFM from peak VO2 has recently been questioned. Therefore, we compared the effectiveness of the ratio method vs. regression modeling to normalize peak VO2 in a large cohort of males and females for differences in FFM. Regression modeling adjusts peak VO2 according to the relationship derived from the regression of peak VO2 on FFM. Results showed that peak VO2 was 60% higher in males (3.53 +/- 1.01/min) than in females (2.22 +/- 0.6 l/min; P < 0.01). With the ratio method (i.e., peak VO2/FFM), peak VO2 was 15% higher in males (54.6 +/- 12 ml.kg FFM-1.min-1) than in females (47.4 +/- 11 ml.kg FFM-1.min-1; P < 0.01). In contrast, when a regression-based approach was employed to normalize values, no significant difference in adjusted peak VO2 was observed between males and females (3.04 +/- 0.9 vs. 3.01 +/- 1.0 l/min). In conclusion, dividing peak VO2 by FFM can produce spurious results, because this approach does not take into account the nonzero intercept. Therefore, a regression-based approach should be used to normalize peak VO2.

Continuous cardiac output monitoring by the Fick method

Current methods for longitudinal assessment of cardiac output in severely ill patients are intermittent only and in many respects appear unsatisfactory. We have developed a computerized on-line system for continuous Fick cardiac output monitoring, utilizing fiberoptic arterial and pulmonary arterial probes with a metabolic analyzer for VO2. In 15 patients, cardiac output ranged 1.9-6.8 L/min and 12 were within 5% of thermodilution values. Continuous output monitoring during interventions in two patients (saline infusion and coronary angioplasty) illustrate the utility of the technique. Two additional patients had unsatisfactory VO2 data due to low airflow velocity. The results of this pilot study suggest that cardiac output monitoring by the Fick method may have clinical and investigational uses in intensive care units and during cardiac catheterization or surgical procedures.

Ventilation and blood lactate increase exponentially during incremental exercise.

This study examined whether the ventilatory (V) compensation for metabolic acidosis with increasing O2 uptake (VO2) and CO2 output (VCO2) might be more in accord with the theoretical expectation of a progressive acceleration of proton production from carbohydrate oxidation rather than a sudden onset of blood lactate (BLa) accumulation. The interrelationships between V, VO2, VCO2 and BLa concentration, [BLa], were investigated in 10 endurance-trained male cyclists during incremental (120 +/- 15 W min-1) exercise tests to exhaustion. Regression analyses on the V, VCO2 and [BLa] vs VO2 data revealed that all were better fitted by continuous Y = A.exp.[B.VO2] + C rate laws than by threshold linear rate equations (P < 0.0001). Plots of V vs VCO2 and [BLa] were also non-linear. Ventilation increased as an exponential V = 27 +/- 4.exp.[0.37 +/- 0.03.VCO2] function of VCO2 and as a hyperbolic function of [BLa]. In opposition to the 'anaerobic (lactate) threshold' hypothesis, we suggest these data are more readily explained by a continuous development of acidosis, rather than a sudden onset of BLa accumulation, during progressive exercise.

Use of recoveryVO2 to predict running economy

The purpose of this study was to determine whether running economy (RE) could be predicted accurately using recovery VO2 values. Twelve runners (means VO2max = 61.9, SD 4.9 ml.kg-1.min-1) completed three treadmill RE sessions over a 2-week period. During each session, subjects performed three 6-min runs at 69%, 78%, and 87% VO2max. RE was calculated from a single 2-min gas collection during the last 2 min of running. Immediately following each run, recovery VO2 data obtained during randomly assigned 15-s, 20-s, or 25-s gas collections were used to predict exercise VO2. Correlations and mean absolute percentage variation (% VAR) between actual and predicted VO2 at each relative intensity and recovery period are reported. Although the relationship between actual and predicted VO2 was significant and more pronounced at higher exercise intensities, the overall magnitude of the association was low to moderate (r range = 0.50-0.81). The range of % VAR between actual and predicted aerobic demands also obscured marked underprediction (-6.5% to -12.5%) and overprediction (+10.1% to +17.4%) of actual VO2 in some subjects. These data suggest that 15-, 20-, and 25-s recovery VO2 values do not correlate strongly with steady-state VO2, nor do they adequately account for variation in individual economy profiles.

The peak oxygen uptake of British children with reference to age, sex and sexual maturity

The purposes of this study were to provide baseline data on the peak oxygen consumption (VO2) of British children, aged 11-16 years and to examine the peak VO2 of children in relation to their pubertal stage of development. The peak VO2 of 226 boys and 194 girls was determined during either treadmill running or cycle ergometry. The sexual maturity of 320 of the children was estimated using Tanner's indices. Peak VO2 increased with chronological age in both sexes and from about the age of 12 years boys exhibited significantly higher (P less than 0.05) values than girls. Boys' peak VO2 in relation to body mass was consistent over the age range studied and was superior (P less than 0.05) to girls' values at all ages. It appears that mass-related peak VO2 is independent of sexual maturity in both sexes. The more mature boys demonstrated a significantly higher (P less than 0.05) peak VO2 (1.min-1) than the less mature boys on both ergometers. The more mature girls demonstrated significantly higher (P less than 0.05) peak VO2 (1.min-1) than the less mature girls only on the cycle ergometer. On both ergometers the differences between the peak VO2 of the girls and boys were more pronounced in the mature children whether expressed in relation to body mass or not. Comparison of the results with earlier data drawn from smaller samples failed to provide evidence to suggest that British children's peak VO2 has declined in recent years. No study with which to compare our maturity peak VO2 data appears to be available.

A comparative study on different methods for the determination of energy expenditure

In order to determine energy expenditure, the Douglas Bag technique (DB) and Kofranyi-Michaelis respirometers (KM) have been widely used under field conditions for several decades. Some years ago the Oxylog (OX) method was developed, measuring simultaneously the difference of partial oxygen pressure in inspired and expired air (PO2 diff.) by two polarographic oxygen sensors. In order to compare these three methods laboratory experiments (3 test subjects, 5 different bicycle ergometer work loads, 180 measurements per apparatus) were performed. Oxygen uptake (VO2) varied between about 0.9 to 3.0 l/min. The VO2 data obtained by the DB method, which were used as a reference, and those obtained by the KM method agreed fairly well. The recorded data of OX underestimated VO2 up to 21%, with the deviation increasing with work intensity. A sufficient accuracy of recorded VO2 was observed only up to moderate work intensity. OX data calculated from ventilation volume of inspired air per minute (VI) and PO2 diff., measured by OX, were always about 19% higher than those recorded by OX. This means that the calculated VO2 values of the OX corresponded fairly well with DB values at heavy work loads. The reason for the differences between recorded and calculated OX data is still unknown. Further research is urgently needed.

Ramp work tests with three different beta-blockers in normal human subjects

The effects of beta-blockade on the responses of oxygen uptake (VO2), heart rate (HR) and blood lactate (La-) were examined during ramp cycle ergometer tests (50 W.min-1 ramp slope) in 8 healthy male volunteers. Each subject took placebo, or one of four different doses of three different beta-blockers (propranolol, metoprolol or oxprenolol) 2 h prior to each test for a total of 15 exercise tests. VO2 was measured breath-by-breath, HR was sampled once per breath, and La- was obtained every minute. Linear regression analysis was applied to VO2 and HR data to obtain the kinetic parameter total lag time (TLT) and a slope value. La- was analyzed by a continuous exponential model with the lactate slope index (LSI) being derived from the individual response curves. Submaximal exercise HR was significantly depressed at the baseline as well as during the ramp tests by beta-blockade. TLT for HR was significantly affected by beta-blockade, with a dose dependent shift from a placebo value of 16 to 26 s with placebo to a value of -40 to -60 s at the highest dose. Slope of HR was significantly depressed relative to placebo. VO2 kinetics assessed by TLT were not significantly affected by beta-blockade. This slope of the VO2 vs work rate relationship was significantly less than placebo only at the highest dose of beta-blocker. The LSI was not significantly affected by beta-blockade. In contrast with the clear impairment of HR response to exercise during beta-blockade, both the VO2 and La- responses appear to be relatively unaffected by beta-blockade during ramp exercise tests.(ABSTRACT TRUNCATED AT 250 WORDS)

Two-dimensional short-term model of oxygen uptake kinetics.

An empirical case is presented for a two-dimensional O2 uptake (VO2) response surface, taking into account both short-term time dependence and the effect of power output. The surface is of the form VO2 = Re + aWt + bW(1-e-kt) where Re is the resting level, 0 less than W less than 2,100 kpm and 0 less than t less than 480 s are the power and time variables, respectively, k is the rate constant for the transient phase of uptake, and a and b are parameters. As a more general test of this expression, VO2 data on six middle-distance runners exercising for 8 min on a cycle ergometer at 1,200, 1,600, 1,850, and 2,100 kpm/min were collected in a respiratory laboratory. Fits of the surface gave coefficients of determination (R2) averaging 0.947, although for one subject a much lower value of 0.807 was obtained. The final fitted equation for the whole group was VO2 = 0.403 + 0.0012Wt + 1.821W(1-e-0.031t) with R2 = 0.857. (VO2 was measured in liters per minute, W in thousands of kilopond-meters per minute and t in seconds). A surface fit to a multirun experiment permits a more comprehensive examination of residuals. In this instance for one subject, such an examination suggests the possibility of a damped cyclic response-control mechanism. Residual variation, however, appears large enough to obscure any possible cycle in the remaining subjects.

1206 GLUCOSE OXIDATION IN THE HUMAN NEWBORN INFANT

The contribution of glucose to oxidative metabolism was quantified in the human newborn using [U-13C]glucose and indirect respiratory calorimetry. Six infants, gestational age 39.9 ± 0.5 wks (mean ± SD), birth weight 3.06 ± 0.13 kg were studied at 43.7 ± 5.0 hrs of age following a 9.3 ± 0.4 hour fast. A primed constant rate infusion of the tracer was given for 4 to 5 hours. VO2 (ml/kg·min), VCO2 (ml/kg·min) and RQ were measured during the last 2 hours of the study. The fraction of glucose turnover oxidized (FGO) was calculated from the rate of U-13C glucose infused and the change in 13C enrichment of CO2 above baseline. Plateau was achieved after approximately 3½ hrs. The fuel mixture was calculated from VO2 and RQ data assuming an 8% protein contribution.Conclusions: Only half of the carbohydrate calories can be accounted for by oxidation of glucose turnover. These data suggest that in the fasting newborn, local tissue oxidation of glycogen makes a significant contribution to calories derived from carbohydrate.

Oxygen consumption and pressure-volume area of abnormal contractions in canine heart.

Oxygen consumption rates (VO2) of isovolumic and normally ejecting contractions are closely correlated with their systolic pressure-volume areas (PVA) in a stable canine left ventricle. PVA is the area in the pressure-volume (PV) diagram that is circumscribed by the end-systolic and end-diastolic PV relation curves and the systolic segment of the PV loop trajectory. We studied whether VO2s of abnormally loaded ejecting contractions were similarly correlated with their PVAs. Various abnormally ejecting contractions were produced in the left ventricle of the cross-circulated canine heart. VO2 and PVA data of the various abnormal contractions and the isovolumic and normally ejecting contractions were pooled together, to which the correlation and regression analyses were applied. They could be fitted by a linear regression analyses were applied. They could be fitted by a linear regression line with a high correlation coefficient and a slight scatter in each heart. We therefore conclude that PVA is the primary correlate of VO2, not only in the isovolumic and normally ejecting contractions but also in various abnormally loaded contractions in a given canine left ventricle with a stable contractile state.

Reduction in peak oxygen uptake after prolonged bed rest.

The purpose was to test the hypothesis that the magnitude of the reduction in peak oxygen uptake (VO2) after bed rest is directly proportional to the level of pre-bed rest peak VO2. Complete pre- and post-bed rest working capacity and body weight data were available from three studies involving 24 men (19-24 yr; peak VO2, 2.39-4.80 l . min-1) and 8 women (23-34 yr; peak VO2 1.47-2.58 l . min-1), who underwent bed rest for 14-20 d with no remedial treatments. Regression analysis of percent change in post-bed rest peak VO2 on pre-bed rest peak VO2 with 32 subjects resulted in correlation coefficients (r) of--0.03 (NS) for data expressed in l . min-1 and -0.17 (NS) for data expressed in ml . min-1 . kg-1. Significant correlations were found that supported the hypothesis only when peak VO2 data were analyzed separately from studies that utilized the cycle ergometer, particularly with subjects in the supine position, as opposed to data obtained from treadmill peak VO2 tests. We conclude that orthostatic factors, associated with the upright body position and relatively high levels of physical fitness from endurance training, appear to increase variability of pre- and particularly post-bed rest peak VO2 data, which would lead to rejection of the hypothesis.

Wheelchair exercise performance of the young, middle-aged, and elderly.

The purpose of this study was to quantitate the maximal power output (POmax), peak oxygen uptake (peak VO2), and maximal heart rate (HRmax) for wheelchair ergometer (WERG) exercise performed by three groups of disabled males: young adult (20-30 yr), middle-aged (50-60 yr), and elderly (80-90 yr). These subjects, who were confined to wheelchairs for similar time periods (mean = 11.7 yr), participated in progressive-intensity discontinuous test protocols on a WERG. Lower (P less than 0.01) mean POmax, peak VO2, and HRmax values were found with advancing age groups. In relationship to age, decreases in POmax and HRmax values were best described by parabolic models, whereas decreases in peak VO2 values were best described by a linear model. In comparison with young adults (83 W, 27 ml . kg-1 . min-1), surprisingly low POmax and peak VO2 values were found for the middle-aged (16 W, 10 ml . kg-1 . min-1) and elderly (7 W, 8 ml . kg-1 . min-1). When our peak VO2 data were combined with other data in the literature for upper body exercise by male disabled individuals, a decrease of 0.19 1 . min-1 or 2.9 ml . kg-1 . min-1 per decade of life was found.