The science
When you start an Adaptive ride, Derny suggests a target heart rate. Here’s exactly where that number comes from, what’s backed by research, and what’s an honest rule of thumb. A target you understand is one you’ll trust.
One number, one job
With a usable heart-rate profile, the suggested target starts from a steady aerobic range designed for continuous riding. It’s an adjustable starting estimate built from three things.
Heart-rate reserve
Two riders can share the same max heart rate while having different resting rates. The reserve between resting and max gives the estimate another individual anchor; it does not measure fitness or identify a metabolic threshold. So Derny targets a percentage of that reserve (the Karvonen method), not a flat percentage of your max.
This isn’t a stylistic choice. In incremental maximal-test studies, a given percentage of heart-rate reserve tracks the same percentage of oxygen-uptake reserve much better than a percentage of max heart rate does. That makes it a better-grounded personal-range anchor, not validation of this continuous-hold curve or a promise that every rider shares the same metabolic boundary.
Haven’t set a resting heart rate? Derny translates the same curve through a reference rider and applies that percentage to your max. Adding resting HR replaces that assumption with your measured range, while the result remains an estimate you can adjust.
Your maximum
If you haven’t entered a max heart rate, we estimate it from your age with the best-fitting formula from a meta-analysis of nearly 19,000 people, not the old “220 minus age,” which was never based on real research and runs low for older riders.
But be honest with any age estimate: it can be off by 10–12 beats for an individual. That’s the biggest source of slack in the whole calculation, far bigger than anything the reserve math adds. So the best number is a measured one.
Time on the bike
With usable resting and max heart-rate values, the underlying fraction slides down as the ride gets longer: 72% of heart-rate reserve at 20 minutes, tapering to 62% at two hours. As you ride on, your heart rate can also drift upward at the same effort, so a target that made sense at minute 10 may be too hard at minute 90.
The principle is textbook. The exact curve is our best judgment: a sensible rule of thumb, not a number pulled from a study.
We’d rather say that plainly than dress a rule of thumb up as precision. The target is always yours to move.
How it holds
Once you have a target, ours or your own, it becomes the goal the whole ride is organized around. As you pedal, Derny watches your actual heart rate and changes the trainer’s resistance to keep you there: easing when you drift above, pushing when you’re below. You never touch a dial.
So the target genuinely matters: it is the ride’s intensity. The suggestion is a starting estimate, and it’s yours to change. If the effort doesn’t feel right, nudge it up or down and the ride re-centers on the new number.
No fixed percentage lands every rider in exactly the same metabolic place. The controller adapts the trainer power needed to hold your selected heart rate; it can’t prove that the selected number is the right boundary for your body. You stay in charge of that judgment.
Responsive pacing, with the rider still in charge.
References