[On the validity of W170 as a measure of physical performance capacity in the assessment of children with heart disease (author's transl)].

W170, i.e., the work rate at a heart frequency of 170 beats per minute, and maximal oxygen uptake were determined in one performance in 20 boys and 23 girls from 6 to 16 years of age on a bicycle ergometer. The results were related to normal values according to age and height. In different age and sex groups correlation coefficients between W170 and maximal oxygen uptake amounted to values between 0.36 and 0.66. Accordingly only 13--44% of the variance of maximal oxygen uptake were covered by W170. The imperfect conformity between indirectly and directly measured cardiovascular performance capacity was due to the considerable variability of the maximal heart rate. Accordingly we found correlation coefficients from 0.28 to 0.69 for the relations between maximal heart rate on the one hand and the difference between percentage values of maximal oxygen uptake and W170 on the other hand. That means that the error of an indirect determination by means of the W170 is mostly higher, the more the maximal heart rate differs from the mean value of the group. The estimation of cardiovascular performance capacity by means of the W170 yielded higher relative values than by means of maximal oxygen uptake. The reason for this is probably that in our present investigations we used another type of ergometer than that we had used earlier for determination of normal values of W170, to which we referred in our present investigations. We suggest that the different gyrating mass of different types of ergometers in spite of identical calibration may influence the results via a different mechanical efficiency.