The effects of training and/or ageing upon maximal oxygen uptake ( VO(2max)) and heart rate values at rest (HR(rest)) and maximal exercise (HR(max)), respectively, suggest a relationship between VO(2max) and the HR(max)-to-HR(rest) ratio which may be of use for indirect testing of VO(2max). Fick principle calculations supplemented by literature data on maximum-to-rest ratios for stroke volume and the arterio-venous O(2) difference suggest that the conversion factor between mass-specific VO(2max) (ml.min(-1).kg(-1)) and HR(max).HR(rest)(-1) is approximately 15. In the study we experimentally examined this relationship and evaluated its potential for prediction of VO(2max). VO(2max) was measured in 46 well-trained men (age 21-51 years) during a treadmill protocol. A subgroup ( n=10) demonstrated that the proportionality factor between HR(max).HR(rest)(-1) and mass-specific VO(2max) was 15.3 (0.7) ml.min(-1).kg(-1). Using this value, VO(2max) in the remaining 36 individuals could be estimated with an SEE of 0.21 l.min(-1) or 2.7 ml.min(-1).kg(-1) (approximately 4.5%). This compares favourably with other common indirect tests. When replacing measured HR(max) with an age-predicted one, SEE was 0.37 l.min(-1) and 4.7 ml.min(-1).kg(-1) (approximately 7.8%), which is still comparable with other indirect tests. We conclude that the HR(max)-to-HR(rest) ratio may provide a tool for estimation of VO(2max) in well-trained men. The applicability of the test principle in relation to other groups will have to await direct validation. VO(2max) can be estimated indirectly from the measured HR(max)-to-HR(rest) ratio with an accuracy that compares favourably with that of other common indirect tests. The results also suggest that the test may be of use for VO(2max) estimation based on resting measurements alone.

Derivation of an equation for a relationship between _ V O 2max and the ratio between HR max and HR rest According to the Fick principle, _ V O 2 may be expressed as the product of cardiac output ð _ QÞand the arterio-venous O 2 difference (CaO 2 ÀC" vO 2 ).Thus, since _ Q is the product of HR and stroke volume (SV), _ V O 2 can be expressed as:When applied to rest _ V O 2 can be expressed as:implying that:During maximal exercise the Fick equation reads:By multiplying the right side of Eq. 5 with 1 in the form of Eq. 4 it follows that:This implies that _ V O 2max may be calculated as the product of _ V O 2rest and the ratios of maximal versus resting values of, respectively, HR, SV, and (CaO 2 ÀC" vO 2 ). _ V O 2rest is dependent on and increases with the individual's body mass. Å strand and Rodahl (1986) suggest that, relative to body mass (BM), resting _ V O 2 equals about 3.5 mlAEmin À1 AEkg À1 (one MET), but slightly lower values were reported by McCann and Adams (2002) (3.3 for men and 3.1 for women, respectively). As a compromise we chose 3.4 mlAEmin À1 AEkgÀ1 to represent the massspecific resting _ V O 2 . Accordingly, _ V O 2rest (mlAEmin À1 ) may be expressed as 3.4 mlAEmin À1 AEkg À1 times BM in kg.From a test perspective only the HR max -to-HR rest ratio is readily obtainable. The other two ratios in the equation involve complicated measurements, in factThe online version of the original article can be found at http:// dx

The maximal rate of oxygen uptake uptake (VO2max) is an important determinant of cardiorespiratory fitness and aerobic performance. Estimation of VO2max from body mass (BM), maximal heart rate (HR (max)) and resting heart rate (HR(rest)) has recently been conducted in a group of well-trained men using the equation: dot VO2max = BM.PF.(HR(max)/HR(rest)), where PF denotes the proportionality factor between HR(max)/HR(rest) and the mass specific VO2max. Fick principle calculations show that PF is given as the product of the mass specific resting oxygen uptake (VO2rest) and the maximum-to-resting ratios for stroke volume and the arterio-venous O2 difference. Due to women's lower mass specific VO2rest, a gender PF difference was hypothesised. In the present study PF was examined in a sample of 27 trained female subjects, and compared with a similar study conducted in men. Significant gender difference was observed in PF, but there was no gender difference when lean BM replaced BM in the PF calculation. Accordingly, VO2max could be estimated indirectly by the following equation: dot VO2max = BM.PF.(HR(max)/HR(rest)), where PF is 14.5 ml.min(-1).kg(-1) for women and 15.3 ml.min(-1).kg(-1) for men. Cross validation showed that the SEE was 0.22 l/min (approximately 6.8 %).