The maximal oxygen uptake (V̇O2max), by definition, is related to aerobic work capacity since integrates responses from three different systems: cardiovascular, respiratory, and muscular [

Nowadays, the best way to measure V̇O2max is by a treadmill or a cycle ergometer lab test with equipments that analyze the exhaled air composition during a bout of exercise until volitional exhaustion [

A low-cost option is the V̇O2max estimated by equation, which do not require direct gas analysis of exhaled air during the test. Through the last few years, several equations looking for estimated V̇O2max during exercise stress test without the direct gas measure. Those equations could use as variables data from the test (treadmill speed, slope grade) and/or individual characteristics (age, gender, body mass index, physical activity level). However, even the most used equation shows limitations which compromise the extrapolation of the results to other populations. The main reason for this came from the wide range of ages of the studied populations, types of ergometers and exercise protocol [

The American College of Sports Medicine (ACSM) [

The objective of the present study is to analyze the agreement of the V̇O2max values estimated by ACSM and Foster equations with direct measure gas analyze in young Brazilian males.

This was an experimental study which involved a maximal incremental exercise test using a treadmill and simultaneous V̇O2max measuring by an ergospirometric device based on breath-by-breath gas exchange analyzing system.

Forty-one healthy young male volunteers aged from 19 to 26 years-old (21.4 ±2.2 years) took part in this study. All participants had a minimum of 3 aerobic training sessions per week during last six months. The study was in agreement with the good clinical practice requirements, ethical principles of Declaration of Helsinki and informed written consent was obtained from each participant before data collection. The research protocol was approved by Human Research Ethics Committee of Campos de Andrade University Center under number 28901414.3.0000.5218.

All participants were screened by independent physician for their healthiness to participate in the study and none of them had any detected medical issue.

Anthropometric assessment was performed by Whole-body dual X-ray absorptiometry (DEXA) scans (Lunar iDXA; GE Medical Systems, Wisconsin, USA), which acquired signal at T0 and T1 to quantify total lean mass and fat mass [

All volunteers performed a maximal incremental exercise test using a treadmill (SuperATL, Inbramed, Brazil). Participants exercised to exhaustion using a Ramp protocol without handrails support. The treadmill gradient was constant at 1% through the test. The speed of the treadmill was adjusted for each individual in order that the test should be completed within 8–12 min. The initial speed of the belt ranged from 8 to 10 kmh-1 and raised 0.1 kmh-1 every each 6 or 7 seconds. Both the initial speed and the incremental interval were determined based on the physical fitness of each participant. Heart rate was monitored continuously during the test (RS800, Polar, Finland). The V̇O2max was measured by an ergospirometric device based on breath-by-breath gas exchange analyzing system (Ultima Series, MedGraphics, USA). The following exercise test criteria were used for the achievement of V̇O2max: leveling off (plateau) of oxygen uptake with an increase of work rate; respiratory exchange ratio (VCO2/VO2) greater than 1.10; achievement of 90% of the age-adjusted estimate of maximal heart rate. They were asked to avoid any alcoholic and caffeinated beverage or ergogenic aids 48 hours prior to the test [

To estimate VO2 through equations was used the variables obtained in the cardiopulmonary exercise test. The equation proposed by ACSM 5 as the sum of 3.5 + (0.2 * speed) + (0.9 * speed * grade), with speed in m.min-1 and grade expressed in decimal format (eg. 10% = 0:10). Foster equation [4] was (0.869 * VO2 ACSM) – 0.07, where VO2 ACSM corresponds to the value VO2 previous obtained through the ACSM equation.

All volunteers’ physical variables were expressed by average and standard deviation (SD) values. Kolmogorov-Smirnov test was performed to assess the normality assumption of the sample, Pearson (r) correlation coefficient was used for evaluation of the association among the measured and estimated values. The Student T test was used to compare the values of V̇O2max measured (mean) and V̇O2max estimated using equations. Bland and Altman analysis [

Participant’s anthropometric characteristics and cardiorespiratory data during maximal exercise test are presented in

Correlations between the measured V̇O2max and each equation (ACSM, Foster’s equation) were strong [

* Correlation is significant at the p<0.01

Comparing the values of measured V̇O2max (mean) and estimated V̇O2max using ACSM equation by the Student T test, it was observed a statistical difference (p<0,001). The estimated V̇O2max by the Foster’s equation was different from the measured V̇O2max. (p=0.025), as well, but the difference between the measured V̇O2max and the estimated V̇O2max by the ACSM equation (9.40±3.67) was approximately 7,5 times greater than the difference between the measured V̇O2max and estimated V̇O2max by the Foster’s equation (1.25±3.46), as presented in

SD – standard deviation; IC – interval confidence

Analyzing the bias for each estimated equation by Bland Altman graph (

Considering the results obtained in this study, the Foster equation [

These findings were similar to other studies, but in the elderly and athletes, where the ACSM equation showed a tendency to overestimate the values of V̇O2max.

Koutlianos et al. [

Analyzing Bland-Altman plot (Figures 1 and 2) was observed, in both equations, a tendency to over- and underestimation of V̇O2max compared to measured values at the low and high ends of the fitness spectrum, respectively. This systematic bias has previously been reported, whereby others V̇O2max estimation equations overestimates the V̇O2max of the least fit people and underestimates values for the most fit [

Other studies have showed physical activity level, gender, age, BMI, treadmill speed, treadmill grade as independent predictors of V̇O2max [

A practical implication is that coaches and young physically active adults should use the Foster equation instead of the ACMS equation. This is recommended because, based on the normative values of maximal aerobic power from ACSM’s Guidelines for Exercising Test and Prescription, the mean measured V̇O2max of the participants was 52.3 ml.kg-1.min-1 classifying them between percentiles 80 and 85, described, therefore, as excellent. In the meantime, the same volunteers when assessed by an estimating equation as ACMS equation, the mean difference of 9.40 ml.kg-1.min-1 ensures a superior classification, as the estimated values are above percentile 99. Those discrepancies don’t occur with Foster’s equation since the smaller difference from the directly measured value did not affect the maximal aerobic power classification.

As a limitation of this study, although it was observed the same phenomenon described by Petersen and coworkers [17], the magnitude of these events cannot be precisely stratified, mainly because the characteristics of the sample, which was composed basically by young physically active adults with a narrow age range which would rank them above the 85th percentile according to the ACSM. For the same reason, extrapolation of current results is not possible for other populations, such as women, sedentary individuals or people with coronary heart disease or heart failure.

The ACSM equation, although the most widely used prediction equation in clinical settings, is not appropriate for during treadmill stress testing young adults in a ramp protocol. Foster equation is more accurate estimator of V̇O2max for this population, besides showed a bias along the aerobic capacity, trending to overestimates and underestimates V̇O2max of least and most fit people, respectively.