Cardiorespiratory response to absolute and relative work intensity in untrained men

Summary

Twenty young, untrained men performed two tests on cycle ergometer in order to verify whether the kinetics of the cardiorespiratory reactions exhibit any relation to maximal oxygen uptake ($\dot V_{O_{2\max } }$) in the untrained state. On the 1st day, the subjects exercised at work intensities of 50 and 100 W, the increase as a step function, for periods of 10 min each. The next day, they performed exercise at a relative intensity of 50%$\dot V_{O_{2\max } }$ for 10 min. Respiratory frequency, tidal volume, minute ventilation ($\dot V_E$), heart rate (HR), stroke volume (SV), and cardiac output ($\dot Q$) were measured continuously. The SV was measured by impedance plethysmography. All the cardiorespiratory variables increased rapidly at the onset of both absolute and relative intensity of work, with a faster response for$\dot Q$ than for$\dot V_E$. The increase in absolute intensity of work from 50 to 100 W caused a significantly slower cardiorespiratory reaction than at the beginning of exercise. The SV increased by 20 ml during first 20 s of both absolute and relative intensities of work and then began to decrease after 6 and 4 min of the exercise, respectively. The decrease in SV was associated with an increase in HR and a stable value of$\dot Q$. Acceleration at the beginning of, and deceleration during recovery from, the relative intensity of work for$\dot V_E$, HR, and$\dot Q$ were well correlated with individual levels of$\dot V_{O_{2\max } }$ in the tested men. It is concluded that the kinetics of cardiorespiratory reaction to a constant, relative intensity of work is related to$\dot V_{O_{2\max } }$ in untrained men, and that the kinetics probably constitute a physiological feature of an individual.