# Accuracy of estimating VO₂ max from submaximal treadmill exercise

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This study examined the sources of error in predicting VO2 max from submaximal treadmill exercise using a single stage model. It involved the identification and quantification of the sources of error of estimated VO2 max. Subjects consisted of 602 male employees of NASA/Johnson Space Center, Houston, Texas. Each subject was administered a maximal treadmill exercise test as part of their yearly physical. The Bruce treadmill protocol was followed with VO2 and heart rate measured continuously. Four VO2 max prediction models were evaluated. Two of the models were developed by Astrand and Ryhming (1954) and the others were modifications of then- equations. Of the four submaximal prediction models examined, two used an estimate of maximal heart rate (i.e., 220 - age) and two of the models used true maximal heart rate in the estimation of VO2 max. The zero order product-moment correlation between measured and estimated VO2 max from each model was used to estimate the model's validity. The validity coefficients for all models ranged from 0.69 to 0.74, which was consistent with published research. The mean difference between measured and estimated VO2 max was calculated to determine if the models significantly overestimated or underestimated average VO2 max. The two original Astrand models significantly underestimated measured VO2 max, which is generally consistent with the literature. The two Modified Astrand models yielded a mean estimate of VO2 max which was not different from the true mean. The standard error of estimate (SEE) was calculated for each model to quantify the measurement error in the prediction of VO2 max in actual score units (ml/kg/min). The models which employed true maximal heart rate were more accurate than the models which used estimated maximal heart rate to predict VO2 max. The Modified Astrand equations were more accurate in both cases than the original models and easier to use. The least accurate was the Astrand-Age Factor model, the SEE was 8.23 ml/kg/min. The most accurate model used true maximal heart rate in the equation and had a SEE of 5.96 ml/kg/min. Substitution of estimated maximal heart rate (i.e., 220 - age) for true maximal heart rate in the prediction equation only increased the SEE by about 1 ml/kg/min (6.99 ml/kg/min for the Modified Astrand-Age model).