METs: the universal currency of exercise energy
Nearly every calorie-burn estimate in sports rests on the metabolic equivalent of task (MET) system. One MET is defined as the resting metabolic rate — roughly 3.5 mL of oxygen per kilogram of body mass per minute, or about 1 kcal per kg per hour for an average adult. Activities carry published MET values compiled in the Compendium of Physical Activities: gentle walking sits near 3 METs, brisk walking around 4-6, jogging around 7-9, and hard running 10-12, while cycling cost tracks power output and speed rather than a single fixed value.
The estimate chain is then simple multiplication: energy (kcal) ≈ MET × body mass (kg) × duration (hours). Worked example: a 70 kg runner jogging for 45 minutes at 8 METs burns roughly 8 × 70 × 0.75 = 420 kcal. Pacing calculators and calorie calculators are two views of the same model — one divides time by distance, the other prices that time in energy.
Three honest caveats:
- METs are population averages. Two 70 kg runners at the same pace can differ by 15-20% in energy cost because of running economy, terrain and efficiency.
- Intensity is priced nonlinearly. Doubling speed does not double kcal/hour; uphill work costs far more than flat, and wind is invisible to the table.
- Body mass scales everything linearly in the formula — which is true in broad strokes (carrying more mass costs more) and wrong in detail (composition matters: fat and muscle are not metabolically identical loads).
For planning — weekly energy budgets, fuel needs, rough weight trends — MET arithmetic is genuinely useful. For precise individual accounting it is not, and no consumer calculator can make it so without individual calibration data.