Revisiting the calculation of PAL from physical activity data

The physical activity level (PAL), defined as the ratio of total daily energy expenditure to resting metabolic rate, is widely used to assess energy requirements in both clinical and research settings. PAL is often not estimated directly-via measurements of total energy expenditure and resting metabolic rate-but rather indirectly using self-reported or objectively recorded physical activity data interpreted through the metabolic equivalent of task (MET) system. However, exercise physiology research consistently shows that the conventional value of 1 MET (set at 1 kcal/kg·hour, corresponding to a resting oxygen consumption of 3.5 mL/kg·min) overestimates true resting metabolic rate by 10%-30%. This systematic bias can lead to inaccurate PAL and energy expenditure estimates when relying solely on physical activity data. To address this problem, a simple correction formula is proposed for adjusting PAL values when individual resting metabolic rate is available or can be predicted from demographic and anthropometric data.