Riven - Your Apple Watch knows when you've truly hit muscle failure
by•
Riven turns your Apple Watch into a muscle failure tracker. It auto-detects your exercise, counts reps hands-free, and measures rep speed loss — the science-backed signal of true muscle fatigue — to tell you if you actually trained to failure or stopped reps short. Built for hypertrophy and strength training: no camera, no bar sensor, no extra hardware — just the watch you already own. Get a 0–100 failure score after every set, so every workout drives real muscle growth.
Replies
@baraa_bilal Congrats on the launch Bilal. This is a really cool use case. For heavy weights, what is the safety margin? I don't want to be benching "just.one.more" and then have to wiggleslide under the bar (yes, it's happened. anyone who lifts heavy has one of these). Are notifications audio?
@zolani_matebese
Such a great point — thanks, Zolani!
Right now Riven shows your failure score after you finish the set, not during it — so nothing interrupts you while you're suffering under the bar 😂 It tells you how close you got, and you use that to decide how hard to push the next set. So there's no "just one more" prompt mid-set, and no safety margin to worry about — the app never asks you to grind a rep you weren't already going to try.
That said, a live mode is definitely on the radar. If we build it, it'd be a watch vibration (not audio), and deliberately conservative — nudging you to stop, never to push past what's safe.
@baraa_bilal Watch vibration definitely works
minimalist phone: reduce your screentime
Is it "pairable" with any smart device, like rings or watches?
@busmark_w_nika Hi Nika! For now, it supports Apple Watch only, and the workout data is synced with your Apple Health app.
Fun! Congrats on the launch :) Does it work best for upper body vs lower body given the wrist-movement-based tracking?
@ferdi_sigona Great question! Currently, the app supports exercises that involve upper-body or wrist movement, as well as some lower-body movements like squats (since your body moves up and down). However, exercises where your wrists remain stationary—such as the leg curl machine—cannot be tracked automatically. You can still log these exercises manually to ensure your entire workout is recorded!
Do I have to have a ceratin routine programmed in?
@st1100 Nope, you go to the gym, do whatever you want, and it shall detect it. You can still manually input what you want to do, or build a program if you want. But usually I go to the gym with a program only in my head; I don't need to write it down in an app - and sometimes my plan changes based on what machines are available if the gym is busy.
The science behind rep speed loss is solid. What was the biggest challenge in getting reliable failure detection from just an Apple Watch?
@keren_dona Thanks! Honestly, the biggest challenge was noise — separating real reps from everything that isn't a rep. There are two kinds:
Sensor noise. The watch IMU doesn't give you clean signals. Raw accelerometer and gyroscope data is jittery, and any attempt to compute velocity from it drifts fast. A lot of the work was filtering the signal down to something you can actually trust rep-to-rep.
Movement noise. This was the harder one. Unracking the bar, adjusting your grip, setting the weight down — on the wrist, these can look almost identical to a rep. And it gets worse near failure, because grinding reps get slow and irregular, which is exactly when you can't afford to miscount. Telling "ugly real rep" apart from "setup motion" reliably was where most of the iteration went.
@baraa_bilal The fact that the hardest part was separating real reps from "everything else" wasn't what I expected. That's a much more interesting engineering problem than simple rep counting. Thanks for sharing the behind-the-scenes details.
Wish there was something like this for Android.
@ankur_jeswani Thanks, Ankur! For sure, something we have in our minds. Other wearables (other than the Apple Watch) should be able to produce close IMU signals that we can use for Riven.