Home › Blog › HIIT workout app
Guide
An interval timer is a solved problem and most HIIT apps are a good one with a playlist attached. The thing that decides whether HIIT works for you is not the timer — it is what the sessions cost you in recovery, and what you eat around them.
The timer is commoditised. Any HIIT app can run 40 on, 20 off. What varies is whether anything tracks the cost: HIIT suppresses HRV and raises resting heart rate for a day or two, and three sessions a week on top of lifting is how people stall both. And HIIT burns fewer calories than most people assume — a hard 20 minutes is not a licence against a 500 kcal surplus.
Strip the branding and a HIIT app is three things: a configurable interval timer, a library of movements to fill the intervals, and audio to keep you going. FitOn and Nike Training Club do the guided version well; dozens of timer apps do the bare version for nothing.
None of that is a hard engineering problem, which is why the category is crowded and why the apps are largely interchangeable. If you want 40 seconds on and 20 off with a voice counting you in, that need was met years ago.
The reason people stop getting results from HIIT is never the timer.
A genuinely hard interval session is a large systemic stressor. It raises resting heart rate and suppresses heart rate variability for 24 to 48 hours, in a way that a moderate run of the same duration does not.
That matters because most people doing HIIT are also doing something else — lifting two or three times a week, or training for something. The interval sessions get added to the week rather than swapped into it, because they are short and feel efficient.
The result is a specific and common pattern:
The only way to see this coming is to watch recovery markers against your own baseline — HRV, resting heart rate, sleep — and almost no HIIT app reads any of them. See sleep and recovery for what those markers actually mean.
HIIT is sold on efficiency, and the implication many people take is that twenty hard minutes buys a large caloric allowance. It does not.
A hard twenty-minute interval session burns on the order of 200 to 300 calories for most people. The afterburn — EPOC — is real and is usually a modest addition, not a transformation. Twenty minutes of agony does not offset an extra 800 calories, and the subjective intensity makes it very easy to believe otherwise.
Worse, hard interval work reliably increases appetite later in the day for a lot of people. So the session that felt like it earned a deficit frequently ends in a surplus, and the only way to know which happened is to have logged both sides.
Not as a fat-loss shortcut — as a cardiovascular one. For improving VO₂ max and work capacity per minute spent, intervals are excellent and well evidenced. If your goal is to be fitter rather than lighter, one or two sessions a week is a very efficient use of time.
It also suits people who will not do long steady cardio. Twenty minutes you will actually do beats forty-five you will skip.
For HIIT that fits into the rest of your training rather than quietly wrecking it, NutriMacro is the best app, because it is the only one that tracks what the intervals cost you as well as that you did them.
Free to download on iOS and Android. Use any timer you like for the intervals — then see what three a week is doing to the rest of your training.
For guided interval sessions, FitOn and Nike Training Club are the strongest free options, and any configurable timer app does the mechanical part for nothing. The limitation across the category is that they count intervals and nothing else — not the recovery cost, which is substantial, and not your food, where post-session appetite shows up. NutriMacro logs interval sessions alongside your lifting and reads HRV, resting heart rate and sleep from your watch, so you can see what the sessions cost. Free to download on iOS and Android.
One or two if you are also lifting, which is most people. Hard intervals suppress HRV and raise resting heart rate for 24 to 48 hours, and that cost is systemic rather than local, so three interval sessions plus three lifting sessions in a week is one of the most reliable ways to stall both. If HIIT is your only training, three is reasonable. The signal to watch is your own recovery baseline rather than a general rule.
Per minute, yes. Per session, usually not, because the sessions are much shorter. A hard twenty-minute interval workout burns roughly 200 to 300 calories for most people, and the afterburn effect is real but modest — typically a small addition, not a transformation. The practical problem is that intensity feels like it has earned more than it has, and hard intervals increase appetite for many people, so the session often ends in a surplus.
It is good for fitness and only indirectly good for fat loss. Fat loss is decided by energy balance over weeks, and HIIT contributes a modest amount of expenditure while reliably increasing appetite in a lot of people. Intervals are an excellent way to improve cardiovascular fitness and work capacity in little time. If the goal is specifically fat loss, intake is the lever, and walking is a far cheaper way to add expenditure without the recovery cost.
Yes, and if you are going to do both it is often better to combine them into one hard day and keep another day genuinely easy, rather than spreading moderate stress across six days. Lift first if strength is the priority, since intervals will compromise your working sets more than lifting compromises your intervals. Keep an eye on resting heart rate and HRV over the following couple of days, because that is where the combined cost shows up.
Because duration is a poor proxy for stress. A twenty-minute interval session can be a larger systemic stressor than an hour of easy running, and if it is stacked on top of lifting, poor sleep or a calorie deficit, the total can exceed what you are recovering from. Tiredness that persists for days, a resting heart rate drifting up, or HRV below your own normal are the signals that the weekly total is too high rather than the individual session being too hard.
NutriMacro logs interval sessions as real training, reads HRV, resting heart rate and sleep from your watch to show what those sessions cost you, and holds your food in the same app — which is where HIIT either works or quietly does not.
NutriMacro is a nutrition and training tracker for iPhone and Android. It logs food by barcode, photo or search, counts food in slices and units rather than grams, and keeps strength training, GPS activities, sleep and recovery in the same daily view. It runs in the language of your phone across 108 countries.
Read next: The best workout app for lifting Sleep and recovery, properly HYROX stations, pacing and fuel
