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.
Funny, my “cardiac drift” goes DOWN as a ride progresses. That’s part of why I don’t bother with a HRM anymore, as I know it’s not giving me an accurate assessment of my efforts.
So, I’m 71 and use an Apple Watch when I ride, paired with Strava. Riding now for more than 50 years continuously. Consider myself very fit. Weigh 132 wringing wet. I don’t race but ride with groups that move along fairly quickly (+ 17 mph over 40 / 50 miles). According to Strava via my watch, my heart rate consistently exceeds what we’d call my max (using 205.8 – age x .685). I have no trouble hitting 170 bpm and higher even. Jamming uphill watch/Strava often tells me I hit 180 bpm.
Before using the watch, I paid no attention to my heart rate with no issues that I know of. I must say this now puzzles me and I wonder if the damn thing is going to explode. Does anyone know if wearing a chest HRM would be more accurate? And is the watch likely to be so far off? Is it possible 180 is an accurate recording, and what are effects of consistently exceeding what would be generally considered my max? Anyone else out there having similar experience? Thanks!
If you’ve stayed fit over the years, it’s likely you’d have a higher heart rate max than a sedentary person or someone who didn’t train very much. A heart rate monitor strop is definitely a lot more accurate, so it’s also possible that the Apple watch is showing a number a little bit off from the real number. Polar and Wahoo both make Bluetooth straps that will sync with your iphone, if you don’t use a Garmin or other bike computer that reads it.
Here’s Joel Friel on max heart rates, where he is skeptical of the formula in general:
https://joefrielsblog.com/max-heart-rate-and-performance/