We attempted to fit heart rate (HR) changes induced by constant exercise lo
ads of different intensities to an exponential hyperbolic sine curve by the
least-squares method, and we compared the results with the fitting of the
changes to exponential curves. Seven healthy male volunteers performed thre
e different intensities of constant-load exercise on a bicycle ergometer. T
he exponential hyperbolic sine function adequately fitted the HR responses
induced by all three different intensities of loads: low (30 W, correlation
coefficient, r=0.68+/-0.13, mean+/-SD), moderate (75 W, r=0.93+/-0.07) and
high (125 W: r=0.97+/-0.02). The first-order exponential curve fitted only
the moderate load response. Although the second-order exponential equation
fitted the HR response for both the moderate and high loads, the equation
did not fit the low-load response (r=0.43+/-0.26). In low-load exercise, th
e sum of the power of the residuals for the exponential hyperbolic sine cur
ve fitting was significantly smaller than that for the first- or second-ord
er exponential curve fitting. In conclusion, the exponential hyperbolic sin
e function is useful for quantitative analyses of the HR response to exerci
se loads of various intensities.