Using the monitors on the equipment at the gym for many years now has given me a pretty good ability to guestimate my heart rate and it’s never as high when I’m biking. Even a long steep climb doesn’t have the same effect on my heart rate as intervals on the elliptical, pushing hard on a rowing machine, or running on an incline. I’ll keel over in the gym long before I will on a bike, which is what passes for “comforting” at my age.