Calorie estimates are useful but run high

Standard activity charts give a workable estimate of the calories a workout burns. But they tend to run 15 to 20 percent high next to lab measurements, and fitness watches often overstate the burn too.

Why it works

A MET measures how hard you are working as a multiple of resting metabolic rate (the energy your body uses just sitting still). Multiply that by your body weight and how long you exercise, and you get a calorie estimate. Its accuracy depends on whether the standard MET value matches how hard you actually worked.

The evidence

• Herrmann, S.D., Willis, E.A., Ainsworth, B.E. et al. (2024). 2024 Adult Compendium of Physical Activities: A Third Update of the Energy Costs of Human Activities. Journal of Sport and Health Science.

  This is a reference update, not an experiment. It catalogs the energy cost (in METs, a multiple of resting metabolism) of 1,114 physical activities across categories like leisure, sport, transportation, home, and work. The authors screened 32,173 abstracts and 1,507 full papers, then pulled 2,356 measured energy-expenditure values from 701 studies to build it. Compared with the prior version it adds 303 new activity codes and modifies 176 existing ones, giving more entries backed by directly measured (rather than estimated) values.

• Klass, M., Faoro, V., Carpentier, A. (2019). Assessment of Energy Expenditure during High Intensity Cycling and Running Using a Heart Rate and Activity Monitor in Young Active Adults. PLOS ONE.

  In 18 active young adults (4 women, 14 men, average age 25), a heart-rate-plus-motion monitor (Actiheart) was compared against indirect calorimetry (the lab reference) during cycling and running at 60%, 75%, and 85% of maximal oxygen uptake. Using a one-size-fits-all group calibration, the monitor underestimated activity energy expenditure by 3% to 20% depending on intensity. Calibrating the heart-rate-to-energy relationship for each person cut the underestimation to under 5% and raised agreement with the reference (intraclass correlation 0.79 to 0.93, up from 0.64 to 0.79). The takeaway: individual calibration matters a lot for accuracy at higher intensities.

• Ainsworth, B.E., Haskell, W.L., Herrmann, S.D. et al. (2011). 2011 Compendium of Physical Activities: A Second Update of Codes and MET Values. Medicine and Science in Sports and Exercise.

  This is a reference update, not an experiment. It lists the energy cost (in METs) of specific physical activities so studies can compare self-reported activity on a common scale. The 2011 version contains 821 activity codes, including 217 new ones, and 68% (561 of 821) carry directly measured MET values rather than estimates. About half of the codes from the 2000 edition were revised to sharpen definitions or update values, with updated MET values accounting for 73% of those changes.

Why we call confidence medium

The Compendium of Physical Activities (updated 2024) is the standard reference, so the method rests on solid ground. But its MET values are population averages, so your own burn can run ±15-20% off. That gap grows when your fitness, technique, or the weather differ from the study populations.

Where it applies

Healthy adults