QUESTION: I’m 58 and don’t understand what’s happening to my heart during longer road rides. After about 90 minutes of steady riding at around 80% of my max heart rate, it gradually climbs to 90% even though my speed, cadence and energy output remain constant. Why? — Len M.
RBR REPLIES: I suspect you’re experiencing a common phenomenon known as “cardiac drift.” This is a gradual rise in heart rate after about an hour of steady aerobic work, even though power output isn’t increased. It’s caused by dehydration and other factors, although physiologists haven’t figured out all of them. Merely staying hydrated won’t eliminate cardiac drift, but it helps delay it.
So, use plenty of sports drink, and continue training to gradually extend the time before your heart rate drifts higher.
Another approach is to vary your workouts so you aren’t always doing the steady rides you’ve implied are your habit. Instead, each week do a couple of rides quite easily at about 60-70% of your max heart rate. Do two longer rides at 80% like you’ve described. And add an interval or climbing day that raises your heart rate to 90% or higher for short periods, alternated with easy cruising for recovery.