Plan your session.
See your full session and heart-rate targets before you start.
4×4 intervals. Guided by VOTRAIN.
Take your VO₂
to the MAX.
Build your VO₂ max cardio fitness with a research backed workout. 4x4 interval training, guided on your iPhone and Apple Watch.
Coming soon to the App Store
VO₂ max 4 × 4Four focused, four-minute efforts.
Your pace.Heart-rate targets tailored to you.
16 minutes.Of hard effort. Plus warmup, recovery, and cooldown.
A little guidance. A lot of purpose.
Your effort.
Beautifully guided.
Your workout, heart-rate targets, and progress. Together in one clear view, so you can focus on the next four minutes.
Swipe to explore the app
Find your rhythm.
Follow the countdown and your heart rate through every effort and recovery.
See your progress.
Track completed workouts and VO₂ max estimates from Apple Health over time.
Made for the way you train
Tuned to you
Personal by design.
Heart-rate targets for effort and recovery, based on your profile and the Apple Health information you choose to share.
Apple Watch
Right on your wrist.
Follow interval cues and live heart rate from your wrist while your phone stays out of the way.
Keep it going
Every session counts.
Your history and weekly progress make consistency visible—even when your fitness estimate changes slowly.
The 4×4 workout
Simple intervals.
Serious effort.
Four minutes of hard effort. Three minutes of easy movement. Repeat for four efforts. VOTRAIN handles the timing. You bring the effort.
01
5MIN
Warm up
02
4MIN
Work
03
3MIN
Recover
04
×4ROUNDS
Repeat
05
5MIN
Cool down
Build up gradually. The app starts with a 5-minute warmup you can extend; NTNU’s published 4×4 guidance uses 10 minutes. These are sustained hard efforts, not all-out sprints. If you’re returning after inactivity or have a heart condition, check with your clinician before starting high-intensity training. Read NTNU’s guidance ↗
Why work on VO₂ max?
Fitness is about more
than your next workout.
VO₂ max measures how much oxygen your body can use during hard exercise. Think of it as a window into your cardio fitness. Higher fitness is consistently linked to a lower risk of early death.
The reason
to work on it
is personal.
The stairs you want to climb. The trips you want to take. The people you want to keep up with. In your 40s, 50s, 60s—and beyond.
The evidence
Better fitness. Real significance.
The research makes a compelling case for paying attention to your cardio fitness.
Higher risk of death with lower fitness
Below-average fitness was associated with a 41% higher adjusted risk of death over follow-up than above-average fitness in 122,007 patients. Average age: 53.
Read the 2018 study ↗Lower risk of death with better fitness
Each 1-MET higher fitness level—a standard increment in exercise capacity—was associated with 13% lower risk of death from any cause in a review of 33 studies.
Read the JAMA review ↗VO₂ max improvement in 8 weeks
The 4×4 group improved VO₂ max by 7.2% on average with three sessions a week in a small randomized trial of 40 healthy, moderately trained young men across four groups.
Read the 4×4 trial ↗*The mortality figures compare groups; they do not prove that a workout prevents death or predict your personal risk. The 4×4 result comes from a training study, not a trial of VOTRAIN, and is not a promised result for every age or fitness level. The evidence supports improving fitness; it does not establish that this app extends lifespan.
Learn the method
Understand the why.
A few minutes of learning. A clearer picture of your fitness. Explore VO₂ max and the 4×4 method with independent educators.
01 / Watch & learn
What VO₂ max measures
Corporis · YouTube
02 / Watch & learn
Why aerobic capacity matters
Institute of Human Anatomy · YouTube
03 / Watch & learn
How the 4 × 4 session works
Dr. Stacy Sims Official · YouTube
04 / Watch & learn
What the research shows
Physionic · YouTube
These independent educational videos are shown through YouTube’s official privacy-enhanced player and remain controlled by their respective creators. Their inclusion does not imply an endorsement or partnership. Content is for general education, not medical advice.
Your privacy matters
Your health data stays yours.
VOTRAIN reads only the Apple Health metrics you allow. Health information is processed on your device and is never used for advertising or tracking.
Start with your next workout
Your next chapter.
Start with four minutes.
Make 4×4 interval training part of your fitness routine.
VOTRAIN is coming soon to iPhone and Apple Watch.