Clinical Medicine & Physiology
Cunningham RMR Formula (1980 & 1991): Fat-Free Mass Athlete Metabolic Rate Calculator
Calculate athletic Resting Metabolic Rate from body-composition Fat-Free Mass FFM = Weight * (1 - BodyFat% / 100) using John J. Cunningham’s classic 1980 athlete equation (500 + 22 * FFM_kg) and 1991 general LBM equation (370 + 21.6 * FFM_kg).
Why sports dietitians use Cunningham’s Fat-Free Mass equations instead of BMI/weight equations in athletes!
Height-weight-age equations (Mifflin-St Jeor, Harris-Benedict) systematically underpredict Resting Metabolic Rate in muscular strength and endurance athletes because metabolically active skeletal muscle is lumped together with adipose tissue — AND they apply arbitrary sex offsets that vanish once Fat-Free Mass (FFM) is measured via DXA, BodPod, or skinfolds! John J. Cunningham demonstrated in 1980 (Am J Clin Nutr: RMR_1980 = 500 + 22 * FFM_kg,endorsed by the American College of Sports Medicine ACSM for lean athletes) and refined in 1991 across general body-composition cohorts (RMR_1991 = 370 + 21.6 * FFM_kg) that FFM alone explains ~70%–80% of human RMR variance independent of sex!
Computing FFM_kg = Body_Mass_kg * (1 - Body_Fat_% / 100) also enables immediate screening for Low Energy Availability (LEA / RED-S) when Dietary_Intake - Exercise_kcal divided by FFM_kg drops below 30 kcal / kg FFM / day!
| Cunningham Equation Variant (80 kg Athlete at 12.5% Body Fat -> FFM = 70.0 kg) | Formula | Evaluated Daily kcal |
|---|---|---|
| Fat-Free Mass FFM (kg) | Weight_kg * (1 - BodyFat_% / 100) | 70.00 kg |
| Cunningham (1980) Athlete RMR (ACSM Preferred) | 500 + 22 * FFM_kg | 2,040 kcal/day |
| Cunningham (1991) General FFM RMR | 370 + 21.6 * FFM_kg | 1,882 kcal/day |
| Total Daily Energy Expenditure (PAL = 1.75x RMR_1980) | RMR_1980 * PAL | 3,570 kcal/day |
Cunningham (1980) Athlete Resting Metabolic Rate: 500 + 22 * FFM_kg (kcal/day)
Derives FFM = B2 * (1 - B3 / 100) from body mass B2 (kg) and body-fat percentage B3 (2%..65%), returning ROUND(500 + 22 * FFM, 0).
=IF(OR(B2 < 30, B2 > 250, B3 < 2, B3 > 65), "Invalid Body Mass or Body-Fat Percentage", ROUND(500 + 22 * (B2 * (1 - B3 / 100)), 0))Cunningham (1991) General Fat-Free Mass RMR: 370 + 21.6 * FFM_kg (kcal/day)
Evaluates Cunningham’s 1991 review equation 370 + 21.6 * FFM_kg (often called the Katch-McArdle / Cunningham 1991 equation).
=IF(OR(B2 < 30, B2 > 250, B3 < 2, B3 > 65), "Invalid Body Mass or Body-Fat Percentage", ROUND(370 + 21.6 * (B2 * (1 - B3 / 100)), 0))Try the example
Use the original values or change them to test your understanding.