Guide
What 12 weeks can change
Over 12 weeks, your waist moves first. Shoulder bone doesn't move at all, and muscle builds over several cycles.
What published research says one 12-week cycle can change in each part of your V, in plain numbers, with the sources. The studies are of adult men, and no coach has checked these numbers yet.
No coach has checked these numbers yet
The numbers
What published studies found. They studied adult men, so read them as a rough guide, not a promise.
Shoulder bone
No change
Biacromial width is bone. Adults don't change it with training.
Delts
About ±0.3 cm
In the one direct trial, trained lifters doing lateral raises added about 0.5 to 1 mm of side-delt thickness per side in 8 weeks. Fat over the delt shrinks as you lean out, so shoulder width nets out near ±0.3 cm. That's smaller than a photo scan can see.
Larsen 2025, Front Physiol · Poland 1997, JAMA
Waist
1.0 to 1.2 cm per kg
The part that moves. Average and heavier men lost about 1.0 to 1.2 cm of waist for each kg of fat they lost.
Hunt 2014, Lancet · Foulis 2023, Front Physiol
Neck, with neck work
About +0.4 cm
In a 12-week trial, neck extension training grew neck muscle by 12.8 %, roughly 0.4 cm of circumference. Lifting without neck work didn't grow the neck at all.
Conley 1997, Eur J Appl Physiol
Lats and traps
No study yet
We found no completed training study that measured lat or upper-trap growth, so there's no honest number to give you.
Week to week
About ±1.2 cm
In a study of 3-D phone scans, the waist repeated within about 1.2 cm, and a waist varies about 3 % from day to day on its own. One week's change is mostly noise.
Nácher-Fernández 2026, J Int Soc Sports Nutr · Nordhamn 2000, Int J Obes
So over 12 weeks, your taper ratio moves mostly through your waist. Shoulders build over several cycles.
If you're 16 or 17, the app sets no calorie deficit and shows no projections.
Can you make your shoulders wider?
Partly, and slowly. Your shoulder width is bone plus the muscle on the outside of it. The bone (biacromial width) is set: adults don't change it with training. The delts on top of it are the part you can build.
In 12 weeks, that's millimetres. The one direct trial of lateral raises found about 0.5 to 1 mm more side-delt thickness per side in 8 weeks, in lifters who had trained for years. If you lose fat at the same time, the fat over the delt shrinks by about as much, so the width you'd measure can stay about the same.
Over several cycles, the millimetres add up. And your shoulders look wider next to a smaller waist, which is the part that moves sooner.
What the app does with this
The app never promises visible shoulder growth in 12 weeks. It shows shoulder width as an estimate, and your plan keeps building it, cycle after cycle.
Shoulder guideWhy your waist moves first
Your taper ratio is shoulder width over waist width. Fat loss changes the bottom of that fraction far faster than training changes the top.
In a 12-week program for overweight men, the average loss was about 5.8 kg, and their waists came down by about 1.0 to 1.2 cm for each kg. A research review puts the pace that best keeps muscle at about 0.5 to 1 % of body weight a week. For average and heavier men at a moderate pace, that comes to roughly 3 to 11 cm of waist over 12 weeks, depending on body size and how closely they stuck to it.
There's no study of men who were already lean, so if that's you, expect less per kg. If you're 16 or 17, none of this applies: the app sets no calorie deficit and shows no projections.
Core training and your waist
Planks, carries and Pallof presses make your middle stronger and steadier. They don't burn fat from your waist. Losing fat does that.
Waist guideYour neck needs direct work
In the one trial that measured it, 12 weeks of neck extension training grew neck muscle by 12.8 %. The group that lifted without neck work had no neck growth at all, even though their legs grew.
Converted to a tape measure, that's about 0.4 cm. Fat loss takes a little back, about 0.15 cm per kg of fat. So the change is real, but small next to the noise of a photo scan.
Under 18, neck work in the app is holds and chin tucks only.
Start with holds
The app's neck block starts with holds at about half effort, builds slowly, and pauses if you report pain or a warning sign.
Neck guideWhy one week means nothing
Every measurement has noise. In a study of 3-D phone scans, the waist repeated within about 1.2 cm and the shoulders within about 0.6 cm. Your waist also varies about 3 % from day to day with food, water and breathing. A photo scan like the app's has no published repeatability numbers yet.
So a single week's change is mostly noise. The research model behind the app puts a clear waist trend at about 7 to 9 weekly scans for a typical adult losing fat. Shoulder and neck changes are too small to confirm within 12 weekly scans.
What the app shows
Your waist trend appears at 6 scans, counting your sign-up scan, so at your 5th weekly check-in. Until then, one week's change is never treated as meaningful. Shoulder and neck changes stay estimates.
What this means for your plan
Judge your waist by the trend over several weeks, not by one scan.
Keep training shoulders and back. Width builds over cycles, not weeks.
If you want a thicker neck, it takes direct neck work. Start with holds.
For exact numbers, use a tape, and measure the same way each week.
If you're 16 or 17: no deficit and no projections. Train, eat enough to fuel it, and let the trend come.
General guidance, not medical advice.
Sources
Hunt K et al. 2014. Football Fans in Training. Lancet 383:1211–21.
Foulis SA, Friedl KE et al. 2023. Front Physiol 14:1183836.
Larsen S et al. 2025. Front Physiol 16:1611468.
Poland GA et al. 1997. JAMA 277:1709–11.
Conley MS, Stone MH, Nimmons M, Dudley GA 1997. Eur J Appl Physiol 75:443–8.
Helms ER, Aragon AA, Fitschen PJ 2014. J Int Soc Sports Nutr 11:20.
Nácher-Fernández B et al. 2026. J Int Soc Sports Nutr 23:2724094.
Nordhamn K et al. 2000. Int J Obes 24:652–7.
Find your weakest zone in the app
Three photos measure your shoulders, waist and posture. Your 12-week plan starts with the zone that needs it most.
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iPhone · Ages 16+ · Scores are an AI estimate, not medical advice.