MET (Metabolic Equivalent of Task) measures exercise intensity relative to rest. A MET of 1 is sitting quietly; running is ~8–11 METs. Calories burned = MET × weight(kg) × duration(hours).

Population-averaged METs produce estimates within ±10–15% for most people. Fitter individuals burn fewer calories at a given intensity because their bodies are more efficient.

Heavier bodies require more energy to move. A 90 kg person burns roughly 35% more calories running at the same pace as a 65 kg person, all else being equal.

Partially. Most nutrition plans already factor in a moderate activity level. Eating back 50–75% of exercise calories is a safe strategy to avoid over-compensating, which is a common cause of stalled progress.