Question: After warming up and beginning to push, my heart rate climbs to 85% of max and I breathe hard. It’s uncomfortable and I’m hurting. In about 15 minutes, my heart rate climbs even higher, to 90% of max –but I’m not breathing as hard and the effort is more comfortable. What’s going on? — Don H.
Coach Fred Matheny Replies: What you’re experiencing is a warm-up effect. As heart rate climbs, your rating of perceived exertion (RPE) usually climbs, too.
The exception is early in a ride when breathing hasn’t “caught up” yet. You’ll breathe heavily at moderate heart rates. Later in the ride when all systems are fully functioning, you can ride at about 90% of max without breathing quite as hard, although your leg muscles may burn.
But heart rate is really a red herring. It can vary for a given power output depending on many factors, including glycogen supplies, humidity and even your psychological state. So while heart rate is an important gauge of intensity, it isn’t infallible. This is why some riders choose to base training intensity on wattage from their power meters, combined with RPE.
I contend it’s better to base training intensity on RPE. Use heart rate as a secondary check if you’d like. Soon you’ll get a better feel for what heart rate is doing at various exertion levels. You’ll be able to adjust for its inconsistency so it’s a more useful tool. Using RPE effectively also will help you avoid overtraining and aid recovery.
Bottom line: Heart rate can mislead you about how hard you’re actually working.