Most rest timers count down from a number you typed in once and never changed. Ninety seconds for everything. Ninety seconds after a light curl, ninety seconds after a near-max squat. The number is the same because the timer has no idea what you just did.
Valen's Smart Rest timer decides how long to rest after each set, based on the set you just finished.
SHORT ANSWER
- Smart Rest sets the rest time from three things: how demanding the exercise is, how heavy the set was compared with your own best, and how many sets you have already done.
- Heavy compound lifts get up to 5:00. Isolation lifts are capped at 2:00. Nothing goes below 0:30.
- It runs in the background with a live notification, so you can put the phone down.
- Smart Rest is a Pro feature. The standard timer with fixed durations and notifications is free.
Why a fixed rest time is a blunt tool
Rest between sets exists so that the next set can be done well. What "well" costs depends on the lift. A near-maximal barbell squat drains far more than a lateral raise, and the same lift late in a session costs more than early on.
The research here is more nuanced than gym folklore. A widely cited 2016 study from Schoenfeld and colleagues found that trained men who rested three minutes between sets gained more strength and more quadriceps thickness than those who rested one minute, on the same programme. Reviews of rest intervals for strength, such as Grgic and colleagues in 2018, generally favour rests of two minutes or longer for heavy sets. For hypertrophy specifically, a 2024 Bayesian meta-analysis (Singer and colleagues) found the difference between medium and long rests to be small, and very short rests looked like the weaker option. So the honest summary is: heavy work benefits from longer rests, lighter isolation work does not need them, and the evidence for muscle size is mixed.
How Smart Rest actually works
The calculation lives in one small function. Every time you log a set, it runs these steps in order:
| Step | What it does | Effect |
|---|---|---|
| 1. Base time | 30 seconds plus 15 seconds per point of exercise fatigue cost (1 to 10) | A cost-8 bench press starts at 2:30. A cost-3 curl starts at 1:15. |
| 2. Intensity | Compares this set's weight with your heaviest logged set on that exercise | Over 85% of your best: x1.2. Over 95%: x1.5. |
| 3. Set number | Adds 10% per set already done, capped at x1.4 | Late sets earn a longer rest. |
| 4. Ceiling | Isolation exercises cap at 2:00, everything else at 5:00 | Curls never get a 5 minute wait. |
| 5. Floor | Never shorter than 0:30, never longer than 5:00 | Always a sane number. |
| 6. Fallback | If anything is missing, use 1:30 | It fails quiet, not loud. |
Fatigue cost is a 1 to 10 value stored for every exercise in Valen's library.
Look at the bench press bars. Set one at 70% of your best gets 2:30. Set four at 92% gets almost four minutes. By set five, at 96% of your best, the timer asks for 4:52 and the last set hits the 5:00 ceiling. The cable curl, on light and steady work, never needs more than about 1:45 and never goes above two minutes.
A worked example
| Set | Rest suggested |
|---|---|
| Bench, set 1, 70% of best | 2:30 (150 s) |
| Bench, set 3, 90% of best | 3:36 (216 s) |
| Bench, set 4, 96% of best | 4:52 (292 s) |
| Cable curl, set 3, 90% of best | 1:48 (108 s) |
| Cable curl, set 1, 60% of best | 1:15 (75 s) |
Every value here is computed from the formula above, not estimated.
Using it in the gym
Start a set, log it, and the timer starts on its own with the duration already chosen. You get a live notification with the countdown, so you can lock the phone. You can nudge the time by 30 seconds either way if a set felt easier or harder than the numbers say, or skip it. Rest timers also work in the background, so switching apps does not lose your place.
Two caveats worth saying. Smart Rest is a decision aid, not a rule. If you are pressed for time, cut it. And the rest-interval literature is not settled on every point, so if your experience says 90 seconds works for you, the fixed timer is still there.
Smart Rest is part of Valen Pro, alongside the adaptive weekly planner, deep muscle insights, encrypted cloud backup and home-screen widgets. If you are curious how the rest of the training loop fits together, the adaptive-weekly-planning.html and the pricing.html cover it.
Frequently Asked Questions
How long should I rest between sets?
It depends on the lift. Heavy compound lifts usually benefit from two to five minutes, while lighter isolation exercises often need about one to two minutes. Research on rest intervals and muscle growth is mixed, but for heavy strength work longer rests generally perform better.
What is a smart rest timer?
A smart rest timer chooses your rest time automatically instead of using one fixed number. Valen's Smart Rest uses the exercise's fatigue cost, how heavy your set was compared with your best, and how many sets you have done, to set a rest between 30 seconds and 5 minutes.
How does Valen calculate rest time?
Valen starts from 30 seconds plus 15 seconds for each point of exercise fatigue cost, multiplies by 1.2 or 1.5 when the load is above 85% or 95% of your best, adds 10% per set already done up to 1.4 times, then caps isolation exercises at 2 minutes and everything else at 5 minutes.
Is the Valen rest timer free?
The standard rest timer with fixed durations and notifications is free. Smart Rest, which adapts the duration to each set, is part of Valen Pro.
Does the rest timer work when my phone is locked?
Yes. Valen runs a live rest notification with the countdown, so the timer keeps going while the screen is off or another app is open.
Keep reading: adaptive-weekly-planning.html. unlimited-workout-routines.html. ad-free-workout-app.html.
Valen is free on Android. Get it on Google Play or see valenapp.tech.