I’m still getting caught up with work and life in general having just returned from 2 weeks in Switzerland and the UK. So this is just going to be a quicky. It has to do with a study I came across addressing the issue of max heart rate variation with changes in fitness.
Over the years I’ve noticed that as athletes’ aerobic fitness changes their max heart rate (MHR) also changes. A review of the literature by Zavorsky of the University of British Columbia in Vancouver showed that MHR declines as aerobic capacity (VO2max) increases (Zavorsky, G.S. 2000. Endurance and possible mechanisms of altered maximum heart rate with endurance training and tapering. Sports Med 29(1):13-26).
So as you become more fit in the lead-up to your race you might expect to see lower heart rates at the high end. The reverse of this is also true. As fitness declines MHR increases. The review reported 3% to 7% shifts with training and detraining. So, for example, someone with a MHR of 200 at the start of the Base period may expect to see their MHR decline to 186 to 194 by the time of their first race.
Both of these changes probably have to do with variations in cardiac stroke volume – how much blood the heart pumps per beat. As fitness increases the heart becomes more efficient at pumping. More blood goes out for each beat satisfying the body’s need for oxygen and fuel and so the heart can use fewer beats per minute to accomplish its mission. As fitness declines the opposite occurs.
This is yet another good reason not to use MHR as the standard by which heart rate zones are established. Lactate (or anaerobic) threshold seems to be much more stable with changes in fitness.