In a 40-year old person, physiological HRmax will be:

Physiological hea rate maximum is the hea rate up to which, increasing hea rates can cause an increase or maintain the cardiac output. Beyond this hea rate, cardiac output will decrease. By Karvonen formula: HRmax = (220 - age in years). Thus, in 40- year old person, the hea rate maximum will be 180 beats per minute. Beyond this hea, cardiac cycle duration will be very sho and hence, diastole duration and ventricular filling will be very less. Consequently, stroke volume will decrease drastically (Frank-Starling law: Less the filling, low is the stroke volume). Hence, cardiac output will decrease, beyond this hea rate.