An estimate of V̇O max is based on maximum and resting heart rates. In the Uth et al. (2004) formulation, it is given by:
This equation uses the ratio of maximum heart rate (HR) to resting heart rate (HR) to predict V̇O max. The researchers cautioned that the conversion rule was based on measurements on well-trained men aged 21 to 51 only, and may not be reliable when applied to other sub-groups. They also advised that the formula is most reliable when based on actual measurement of maximum heart rate, rather than an age-related estimate.
The Uth constant factor of 15.3 is given for well-trained men. Later studies have revised the constant factor for different populations. According to Voutilainen et al. 2020, the constant factor should be 14 in around 40-year-old normal weight never-smoking men with no cardiovascular diseases, bronchial asthma, or cancer.
Every 10 years of age reduces the coefficient by one, as well as does the change in body weight from normal weight to obese or the change from never-smoker to current smoker. Consequently, V̇O max of 60-year-old obese current smoker men should be estimated by multiplying the HR to HR ratio by 10.