Abstract <p>The purpose of the work is to determine the interrelationships of parameters approximation equations of heart rate (HR) dynamics during work and recovery with various performance characteristics in maximal incremental test (MIT). The study analyzed 87 HR dynamics of subjects who performed the maximal incremental running test with a second-by-second recording of HR dynamics during the test and recovery. The HR approximation was performed using the least squares method. For each case, the maximal working time in test was recorded and six parameters of the approximation equations were determined (<i>R</i> ² 0.986 ± 0.010). A quantitative indicator for estimating the curvature of the HR dynamics in maximal incremental test is proposed. We have identified two variants of acute adaptation to physical work with increasing power, which are reflected in the form of the working HR dynamics. The relationships between the parameters of the equations approximating HR dynamics during exercise and recovery are demonstrated with HR cost of work, specific intensity of physiological costs, the relative contribution of anaerobic energy supply, and the maximal working time in a maximal incremental test. An analogy is noted between exponential dependences describing the HR dynamics and transition processes in electrical <i>RC</i> circuits.</p>