[Regression analysis of the heart rate increase in children during linearly increasing work load on a bicycle ergometer].

E. A. Müller (1950) has introduced a procedure for the measurement of the "Leistungspulsindex" (LPI) based on the determination of a linear regression between heart rate increase and work load. For this purpose the work load on a bicycle ergometer is increased in proportion to time (about 10 W/min) and the heart rate is recorded continuously. We have performed measurements in children (10--11 years of age) and found that the above mentioned regression is markedly nonlinear and can be described best by two overlapping linear regression lines with different slopes (b11 and b12). We propose that under these conditions the regression coefficient b11 of the first part of the relation can be assumed as LPI. In our analysis we found the linear part of the heart rate to increase between the end of min 2 and min 6 (+/- 1.4) of the experiment in boys. In girls we found the linear part of the regression only until min 3.8 (+/- 1.4). One consequence of our results is related to the calculation of the PWC170 by linear extrapolation which appears to be impossible in all cases in which the relation between work load and heart rate is nonlinear. It seems possible to relate that part of the heart rate increase where the slope suddenly changes to the endurance limit.