Frequently asked questions about WimFIT and beat-locked interval training

Music, tempo and locking

How do I sync my music to my HIIT intervals?

Make every interval last a whole number of bars. In 4/4, one bar lasts 240 ÷ BPM seconds: 2.5 s at 96 BPM, 1.875 s at 128 BPM. A 30-second effort is therefore exactly 12 bars at 96 BPM, or 16 bars at 128 BPM. The second condition is less obvious: the countdown has to read its position from the audio stream instead of running on an independent system timer, because two separate clocks drift apart and the gap becomes audible before the session ends. WimFIT does both — it snaps every phase to the nearest bar, and the timer is driven by the audio engine's clock.

What is beat-locked interval training?

Beat-locked interval training is HIIT where each work and rest phase lasts a whole number of musical bars instead of a round number of seconds. The practical consequence: phase changes land on a downbeat, never in the middle of a bar. In WimFIT the requested duration is snapped to the nearest bar, with a minimum of one bar, and it is that snapped duration which is displayed and counted down on screen — not the value you asked for. At 96 BPM the gap between the two is never more than 1.25 seconds.

Why does my workout timer always cut the song mid-bar?

Because the timer and the music player are two independent systems that never talk to each other. The timer counts round seconds — 30, 45, 60 — while the track moves in bars of 1.8 to 2.7 seconds, so unless the numbers happen to line up, the end of an interval falls in the middle of a bar. Drift makes it worse: two separate clocks do not stay aligned over twenty minutes. The only fix is to derive the countdown from the audio playback position and to change phase with a pre-scheduled crossfade — about 400 milliseconds in WimFIT — rather than with a hard cut.

What BPM should I use for HIIT music?

There is no proven optimal BPM. Studies on synchronous music mostly work between 120 and 140 BPM — Bacon, Myers and Karageorghis (2012) tested 123, 130 and 137 BPM — but the useful tempo depends mainly on the cadence of the movement, not on a universal number. What matters more is that the BPM is constant and known, since that is what makes bar-accurate intervals possible. Worth noting: the faster the tempo, the shorter the bar and the finer the rounding. The largest possible gap between the requested and the played duration is 1.25 s at 96 BPM, against 0.75 s at 160 BPM.

Can I use my own music, Spotify or Apple Music?

No, and that is a deliberate limitation: WimFIT only plays tracks from its own built-in catalogue. Locking a timer to the bar requires two things an imported track cannot provide: a constant, known BPM, and a track cut into loopable segments — intro, work loop, rest loop, outro — aligned to the rhythmic grid. The Spotify and Apple Music APIs do not give an app access to the audio file itself, which makes that editing impossible on the client side. Every track in the catalogue is produced for this; tracks are included in the subscription or can be bought individually for €1.99.

What the research says

Does music actually improve exercise performance?

Yes, but the effect is modest and worth stating precisely. The meta-analysis by Terry, Karageorghis, Curran, Martin and Parsons-Smith (2020), published in Psychological Bulletin and covering 139 studies, 598 effect sizes and 3,599 participants, reports significant benefits for physical performance (g = 0.31, 95% CI [0.25–0.36]), perceived exertion (g = 0.22 [0.14–0.30]) and, most of all, affective valence — how good the effort feels (g = 0.48 [0.39–0.56]). These are small to moderate effects: music makes hard work more bearable and slightly more productive; it does not replace training. DOI: 10.1037/bul0000216

Does moving exactly in time with the beat do anything, or does it just feel good?

Synchronising to the tempo, rather than merely listening to it, has been measured. Bacon, Myers and Karageorghis (2012) found oxygen consumption 7.4% lower on a cycle ergometer when movement was synchronised with the music rather than offset, at equal intensity. On time to exhaustion, two independent studies converge: Bood, Nijssen, van der Kamp and Roerdink (2013) measured +17.5% with synchronous music in recreational runners (624 s without music, 733 s with), and Terry et al. (2012) +18.1% in eleven elite triathletes. That mechanism is what WimFIT is built to make usable in a workout; the app itself has never been studied.

Is HIIT really better than long steady cardio?

Not better: equally effective, in less time. The meta-analysis by Wewege, van den Berg, Ward and Keech (2017), published in Obesity Reviews and pooling 13 studies of overweight and obese adults aged 18 to 45 over roughly 10 weeks, found no statistically significant difference between HIIT and moderate-intensity continuous training on any body-composition measure — both reduced fat mass and waist circumference. The difference is training time: about 40% less for HIIT. That result applies to that population and those protocols; it is not a personal promise. DOI: 10.1111/obr.12532

How long should a HIIT workout be?

Shorter than most people assume, and the research sets no ideal length. Studied protocols are brief: the Tabata format described in 1996 fits in 4 minutes (8 rounds of 20 s work and 10 s rest), and the trials pooled by Wewege et al. (2017) typically ran 3 sessions a week for about 10 weeks. The arithmetic is simple: duration = rounds × (work + rest), plus warm-up and cool-down. Eight rounds of 30 s / 30 s is 8 minutes of actual work. In WimFIT that total is computed from the bar-snapped durations and shown before you start.

Which work-to-rest ratio should I use: 30/30, 40/20 or Tabata?

It depends on the goal, and no ratio is universally superior. Three common reference points: 1:1 (30 s work, 30 s rest), the most forgiving and the sensible place to start; 2:1 (40 s / 20 s), where recovery is incomplete and intensity drops faster over the final rounds; and 20 s / 10 s repeated 8 times, the Tabata protocol — only 4 minutes, but designed for near-maximal intensity rather than daily use. In WimFIT each of these is snapped to the bar: at 96 BPM a 30/30 becomes 12 bars plus 12 bars, which is exactly 30 s and 30 s.

WimFIT in practice

Can I download WimFIT yet?

Not yet. WimFIT is pre-launch: the app is not published on the App Store or on Google Play at this time. The only thing wimfit.coach offers today is a waitlist, which triggers a single email at launch. iOS ships first. No public date is announced until Apple review has been cleared — announcing a date and missing it would be worse than saying nothing. WimFIT is published by DirtyLab, in France.

Will there be an Android version?

Yes, but after iOS. The Android port is in development and has no announced release date. Publishing a first app on Google Play also requires a closed test of at least 14 consecutive days with 12 testers before production access can even be requested, which mechanically adds several weeks after the iOS release. Joining the waitlist on wimfit.coach is the way to be notified for both platforms.

How much does WimFIT cost?

WimFIT PRO costs €9.99 per month or €79.99 per year, which works out at €6.67 a month — about 33% less than monthly. Tracks can also be bought individually for €1.99, with no subscription, and are kept for good. This is not the cheapest HIIT app available: free interval timers exist. What you pay for here is a catalogue of tracks produced and cut to loop on the bar, plus a voice coach recorded by real human voices.

Do I need an account to use the app?

No. WimFIT works straight away, with no sign-up and no email address: sessions done without an account are stored locally on the device, history and progress included. An account only matters if you want that history on a second device or after a reinstall. Purchases are tied to your App Store or Google Play ID rather than to a WimFIT account, so they restore without signing up.

Does WimFIT work offline?

Yes, once the content is downloaded. Tracks, guided sessions, exercise demos and the coach's voice files are stored on the device, so a full session runs with no network request at all — on a plane, in a basement, abroad. That follows directly from the audio engine, which decodes files locally before playing them; streaming would make bar-accurate timing impossible. A connection is only needed to download new tracks.

Is there a voice coach, and which languages does it speak?

Yes, in English and French, recorded by real human voices rather than text-to-speech. The cues call out phase changes, the countdown and form reminders, so you can train without looking at the screen — the actual use case for HIIT, where you are rarely facing your phone. The coach follows the app's language setting.

Does WimFIT work with Apple Watch, a heart-rate strap or Apple Health?

No, none of the three. WimFIT does not measure heart rate, does not sync with Apple Health or Google Fit, and has no watch app. That is a scope decision: the product solves one precise problem — locking the timer to the music — and does not claim to replace an activity tracker. If heart-rate tracking is essential to you, WimFIT is not the right app.

What does WimFIT add over a free Tabata timer?

A free timer counts seconds; WimFIT builds the session on the music. Three concrete differences: intervals are snapped to the bar and the countdown is driven by the audio clock, so nothing drifts over twenty minutes; work-to-rest changes happen through a crossfade of about 400 ms, with no cut and no silence; and the app ships 29 exercise demos, guided sessions and an EN/FR voice coach. In exchange it costs €9.99 a month and will not play your own music. For a plain 20/10 countdown in silence, a free timer is entirely enough.