In one sentence
A range of weights for your height and sex given by four old formulas, shown because people ask for it, and shown as a range because the formulas disagree and none of them knows your muscle.
Where it comes from
The "ideal" weight equations were never derived from health outcomes directly. They descend from mid-twentieth-century life-insurance height-and-weight tables, which recorded the weights at which policyholders lived longest; over time those weights were called desirable, then ideal, and were turned into simple rules of thumb for clinical use, mostly for dosing medicines (Pai 2000). The four Vitality Tracker shows are Hamwi (1964), Devine (1974), Robinson (1983) and Miller (1983); they are so similar because they come from the same tables, and the review that traced their history concluded that any one of them may be used.
Why a range and not a number
Because the formulas see only height and sex. A muscular person's healthy weight sits above every one of them; an older person's can sit inside the range at a body fat that is not healthy at all. The range is historical context, not a target, and VT's own measures of composition (body fat and its percentile, waist-to-height) are the ones that describe you.
How Vitality Tracker uses it
Displayed as the span between the lowest and highest of the four, on the profile page, with this explanation beside it. Nothing scores on it, and no plan in VT uses it as a goal.
How far to trust the number
Exact arithmetic on a basis that was never about you.
Sources
- Pai MP, Paloucek FP. The origin of the "ideal" body weight equations. Ann Pharmacother 2000;34:1066–9. doi:10.1345/aph.19381.