Heart Rate-Derived Markers of Mechanical Work and Blood Lactate Concentration in Cyclic Exercises of Varying Power Output

The aim of this study was to identify heart rate-derived markers reflecting both the volume of mechanical work performed and the contribution of anaerobic processes to energy supply during high-intensity cyclic activity. Eighteen trained cyclists specializing in BMX (Bicycle MotoX) and road cycling (age, 21.3 ± 3.4 years; body mass, 71.3 ± 8.5 kg; maximum oxygen consumption, 56.8 ± 12.9 mL/min/kg; maximum power in a ramp test, 4.64 ± 0.5 W/kg) performed, on different days, an incremental test to exhaustion and a series of maximal bicycle ergometer exercises of fixed duration, 10, 30, 60, 120, and 360 s. Average exercise power, oxygen consumption, heart rate (HR), and maximum lactate concentration were recorded. The exercises were performed on a bicycle ergometer. Gas exchange and HR were recorded using a gas analyzer, and lactate concentration was determined with a stationary automatic analyzer. Based on pulse sums during exercise and recovery—namely, the cumulative number of heartbeats during exercise (pulse arrival, PA) and during five-minute recovery (pulse debt, PD)—the following indicators of physical load were calculated: the specific physiological intensity, SPIHR = (PA + PD)/(t × ΔHRmax), where ΔHRmax = HRmax – HRpre; the relative contribution of anaerobic processes to the total energy supply of exercise, AnCHR = PD/(PA + PD); and load exposure, LEHR = t × SPIHR. Based on these parameters, the anaerobic component of load exposure was calculated (LEanHR = LEHR × AnCHR). Corresponding indicators were also calculated from oxygen consumption. SPIHR and AnCHR are closely related to the corresponding oxygen-based indicators, as well as to exercise power and the rate of maximum lactate accumulation. The exercise load exposure indicators, LE_O₂ and LEHR, are strongly correlated with each other (R2 = 0.87) and with external mechanical work, A (R2 = 0.81 and R2 = 0.91, respectively). The indicator of the anaerobic component of load exposure, LEanHR, calculated from SPIHR and AnCHR, is closely related to the maximum lactate concentration (maxLa) (R2 = 0.71). The results indicate that the heart rate-derived indicators LEHR and LEanHR are suitable for the indirect assessment of mechanical work performed and lactate accumulation during exercise, respectively.