The Resting Metabolic Rate (RMR) represents the energy requirement (kcal day−1 or kJ day−1) to sustain vital functions, such as breathing or organ functions while lying down quietly and not having exercised for typically 12 h. This in simple terms means that we are using energy (i.e. burning calories) while resting. The RMR is quantitatively the largest component of daily energy expenditure (60–75%) in sedentary humans. Importantly it is proportional to lean body mass (the more muscle mass the higher the RMR) and it decreases with age and loss of muscle mass (i.e. Sarcopenia). Direct and indirect calorimeters are standard and highly accurate tools to assess RMR in research settings. However, these systems are very expensive and other devices, such as body composition analysers can be used in a professional setting to evaluate the RMR. There are also various equations available to predict the RMR. Most, on an individual base, are less accurate (Flack, 2016). However, the Harris & Benedict (1984) equation:
- Male: (Weight (kg) × 13.397) + (Height (cm) × 4.799) - (Age (years) × 5.677) + 88.362 = kcal/day
- Female: (Weight (kg) × 9.247) + (Height (cm) × 3.098) - (Age (years) × 4.33) + 477.593 = kcal/ day
For example, a 45 year old female with a body weight of 68 kg and a height of 172 cm would have a RMR of 1445 kcal/day and a 48 year of male with a body weight of 80 kg and a body height of 180 cm would have a RMR of 1752 kcal/day
and the World Health Organisation equation:
- Male of 30 – 60 years: 11.3× Weight (kg) −16× Height (m) + 901= kcal/d
- Male > 60 years: 8.8× Weight (kg) + 1128× Height (m) −1071= kcal/d
- Female of 30 - 60 years: 8.7× Weight (kg) −25× Height (m) + 865= kcal/d
- Female > 60 years: 9.2× Weight (kg) + 637× Height (m) −302= kcal/d
For example, the 45 year old female with a body weight of 68 kg and a height of 172 cm would have a RMR of 1500 kcal/day and the 48 year of male with a body weight of 80 kg and a body height of 180 cm would have a RMR of 1776 kcal/day are widely used in the prediction of the RMR. Both result in slightly different values for the RMR and both have their limitations (Almajwal & Abulmeaty, 2019) but for simplicity, you can choose either of them and use it consistently to identify changes in your RMR. Please note, that the RMR only proportionally represent your daily energy needs, as it does not include energy required for any daily physical activity. So don’t be surprised if your value comes up with a lesser than expected number.
How can you maintain or even increase your RMR using exercise? Muscle mass decreases approximately 3–8% per decade after the age of 30 and this rate of decline is even higher after the age of 60 (Holloszy, 2000). This means that exercises that preserves muscle mass are crucial in maintaining RMR and exercises which enhances muscle mass consequently increase the RMR. Physical activities promote an increase of the total energetic cost both in an acute and chronic manner. The acuteness refers to the energetic cost itself during exercise and during the recovery phase; while the chronicity refers to the change of the resting metabolic rate RMR, i.e. a longer lasting adjustment (Hill, Johnson and Peters 1995). It is much debated in the scientific literature and the ‘opinions’ range between this acute effect being merely minimal or that it lasts for hours. Either way, this acute effect is not just achieved through endurance type activities but also through resistance training, which consequently with an appropriate regular training will not just maintain but it also might increase your RMR. However, here lies a bit of a gender issue. Lemmer and colleagues (2001) in young and old men and women showed an increase in REM and lean body mass, but it is men who demonstrate much larger increases. Similarly, endurance training mostly sustains the RMR (Man-Gyoon, 2009) rather than it adjusting it to a higher value long term.
So what does this mean? Exercise is much more than just the RMR. However, it is essential to perform regular resistance training to sustain and potentially increase the RMR given the importance of maintaining muscle mass (and hence strength & independency). Depending on factors such as age and gender muscle mass and consequently RMR can be increased. Finally let’s not forget, the stronger we are the ‘easier’ activities of daily life are.
K.D. Flack, L.A. Johnson, J.N. Roemmich (2016) Cross-Validation of Resting Metabolic Rate Prediction Equations Journal of the Academy of Nutrition and Dietetics
A.M. Roza and H.M. Shizgal (1984) The Harris Benedict equation reevaluated: resting energy requirements and the body cellmass. American Journal of Clinical Nutrition
FAO/WHO/UNU (1985) Energy and Protein Requirements: Report of a Joint FAO/WHO/UNU Expert Consultation, World Health Organanisation Technical Report Series, World Health Organanisation, Geneva, Switzerland
A.M. Almajwal & M.A. Abulmeaty (2019) New Predictive Equations for Resting Energy Expenditure inNormal to Overweight and Obese Population. International Journal of Endocrinology
J.O. Holloszy JO (2000) The biology of aging. Mayo Clinical Proceedings
J.A Hill, C. Melby, S.L. Johnson, I.C. Peters (1995) Physical activity and energy requirements. American Journal of Clinical Nutrition
J.T.Lemmer, F.M. Ivey, A.S. Ryan, G.F. Martel, D.E. Hurlbut, J.E. Metter, J.L. Fozward, J.L.Fleg, B.F. Hurley (20021) Effect of strength training on resting metabolic rate and physical activity: age and gender comparisons Medicine & Science in Sports & Exercise;33(4):532-41.
L. Man-Gyonn, D.A. Sedlock, M.G. Flynn, and G.H. Kamimori (2009) Resting Metabolic Rate after EnduranceExercise Training. Medicine & Science in Sports & Exercise
Author: Bettina Karsten (Bettina is a Professor at the European Applied University in Berlin)