On a smart trainer, a treadmill or an elliptical, Derny reads your heart rate as you go and moves the target when your body asks for it. Watts on the bike, belt speed on the run. The workout follows you.
When your heart rate climbs past its ceiling, Derny lowers the intensity and brings you back. As you recover, it builds again. You never touch a button.
Most people never touch a setting. Pick a ready-made adaptive workout, press start, and Derny adjusts to your body as you go. If you like control, open the editor and write your own rules, trigger by trigger.
“If my heart rate goes above 160 for 10 seconds, drop the target by 5 watts, then hold for 30.”
That’s a rule you write yourself, in plain fields. Or let the presets do the writing.
Effort holds no matter what. Your heart rate redlines and the workout never notices.
Effort eases as you tire, so your heart rate settles right where it should.
Every beta rider gets the whole app: every workout, every adaptive rule, nothing held back.
FTMS is the open Bluetooth standard nearly every modern smart trainer and many treadmills and ellipticals speak, whatever badge is on them. Derny drives a trainer’s or elliptical’s power and resistance, or a treadmill’s belt speed, never above the max speed you set. Screen locked, all workout. Pair any Bluetooth heart-rate strap alongside.
Connect your account once. Every finished workout uploads itself: rides with power, heart rate, and cadence, treadmill sessions as runs or walks. There’s nothing to export and nothing to remember afterward.
Build and edit workouts by chatting with your own Claude or ChatGPT. The connection is OAuth-secured. Ask for a 60-minute sweet-spot workout that backs off when your heart rate climbs, and it lands in your library. How it works →
Derny works fully signed-out. Sign in only if you want your workouts and rides synced across devices. During the beta, the rides you record, how you use the app and diagnostics about your machines are shared with the developer under a random ID, not your name, to find bugs. There are no ads, and your data is never sold. Read the privacy policy.
Any treadmill that speaks FTMS. If it accepts speed control from an app, Derny sets the belt speed, leaves the incline to you, and never goes above the max auto speed you choose. If it doesn’t, Derny tells you the speed to run and you set it. Treadmills →
EllipticalsAny elliptical that speaks FTMS. Derny sets the target power when the elliptical takes one, and otherwise shows you the target while you set the resistance. Ellipticals →
Rowers coming soonFTMS is the open Bluetooth standard for smart trainers, treadmills and ellipticals, and it’s what Derny talks. Every machine that supports it is driven the same way, with no partnership and no per-brand hacks. Using something that isn’t listed? If it pairs as a controllable machine over Bluetooth, it almost certainly works.
See full compatibility →Pair your Bluetooth trainer or treadmill and a heart-rate monitor, then train with your numbers and the adaptation in view. Afterward, the recorded stream becomes a detailed analysis.
The beta is live on iPhone via TestFlight and on Android through Google Play. Pick your phone, connect your trainer, treadmill or elliptical, and feel a workout adapt to you for the first time.
Talk to the developer, share how your workouts went, and hear what’s shipping first. Rowers are next, so come help shape them.