What stopping training actually does — over 4 weeks
Four weeks is the shortest horizon the model supports, and the one where error matters most. Expect small movements in every measurement — this is the window where you establish a routine, not where you see a transformed figure. Detraining is the scenario people underestimate, because the scale often stays put while the body composition changes underneath it. This page models that gap.
At four weeks the change is close to the measurement error of the underlying regressions, so read the direction rather than the magnitude.
Your details
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The scale hides this one
In this scenario body weight is held constant, which is exactly why the change is easy to miss in real life. The model raises body fat by around four percentage points across a 24-week horizon, scaled to the horizon you pick, and reduces lean mass by the corresponding amount so that fat plus lean still equals your body weight.
Because waist is estimated from body composition rather than weight, it widens even though nothing changed on the scale. Arm, chest and shoulder circumferences narrow slightly as muscle is lost. Weight staying flat while the waist grows is the whole point of modelling this scenario separately.
How much detraining is reversible
The projection is a description of a direction, not a verdict. The same equations run in reverse when training resumes, and previously trained muscle tends to return faster than it was originally built. The useful question is not whether the change is permanent — it is how much of the horizon you want to spend heading that way.
Where the numbers come from
Every number on this page comes from published sports-science formulas (Mifflin-St Jeor for basal metabolic rate, standard activity multipliers for total daily expenditure, and anthropometric regressions for circumferences). It is a calculation, not an AI-generated image and not a photograph.
Predictions are estimates for motivation, not medical, nutritional, or fitness advice. Circumference values come from anthropometric regressions based on your height, weight and body composition — not measurements.
Common questions
- Why is my weight unchanged but my waist bigger?
- Because the model holds body weight constant in this scenario and moves the composition instead: fat rises, lean mass falls, and the two offset each other on the scale. Waist is derived from composition, so it moves. This is a deliberate feature of the calculation, not a rounding error.
- How quickly does muscle come back?
- This page models the loss direction, not the return. What it can tell you is the magnitude of the change over your chosen horizon, which is the part that is actually calculable from your inputs.
- Is this meant to be a warning?
- No. It is a calculation of a trade-off, shown so you can decide with numbers rather than a vague sense that something is slipping. There is no judgement implied and none in the wording.