A workout app for Mike Mentzer-style Heavy Duty training.

Heavy Duty, briefly

One working set per exercise, taken very hard. Several days of rest between sessions, often more as you get stronger. Add weight or reps only when the last session earned it. For the routine itself, read our guide to the Mike Mentzer workout and Mentzer's own books.

Heavy Duty is not the Big Five

Intense Fit's default session is a six-exercise machine Full Body routine based on the Body by Science Big Five — seated row, chest press, pulldown, overhead press, leg extension, leg press. Mentzer's routines differ: for example, a two-workout split with exercises such as squats or leg presses, pullovers, dips and deadlifts. To run those, build a custom workout in the app.

What the app records per set

• Load and reps, compared with your last session of the same exercise.
• Time under load from a set timer, with spoken cadence cues and beeps for a steady tempo.
• Optional camera estimates of reps and cadence. They are estimates and can miss reps; without the camera, reps are marked "not captured" or entered by hand.
• A next-load suggestion and a short recovery check-in before you train.

The app does not measure bar speed or detect failure. You decide when a set ends and how hard to push.

Common questions

Is this an official Mike Mentzer app?

No. Intense Fit is independent and is not affiliated with, or endorsed by, Mike Mentzer, his estate or any Heavy Duty brand.

How is it different from a regular workout log?

General logs centre on many sets, rest timers and weekly volume. Intense Fit centres on one timed set per exercise, its cadence and its load. See how the time-under-load tracker works.

Is Heavy Duty the same as HIIT?

No. HIIT is interval cardio. Heavy Duty is brief, hard resistance training.

Where can I use it?

In your phone's browser at intensefit.co/app. A native Android app is in closed beta: request Android beta access.