Direct measurement of the energy expenditure of physical activity in preterm infants

The energy cost of physical activity (EEA) has been estimated toaccount for 5-17% of total energy expenditure (TEE) in neonates. To directly measure EEA, a force plate was developed and validated tomeasure work outputs ranging from 0.3 to 40 kcal · kg¹ · day¹.By use of this force plate plus indirect calorimetry, TEE and EEA weremeasured and correlated with five activity states in 24 infants withgestational age of 31.6 ± 0.5 (SE) wk and postnatal age of 24.8 ± 3.7 days. TEE and EEA were 69.2 ± 1.5 and 2.4 ± 0.2 kcal · kg¹ · day¹,respectively. EEA per state was 0.5 ± 0.0 (quiet sleep), 2.4 ± 0.2 (active sleep), 2.8 ± 0.4 (quiet awake), 7.5 ± 0.8 (active awake), and 15.1 ± 2.3 (crying)kcal · kg¹ · day¹.This provides the first direct measurement of the contribution ofphysical activity to TEE in preterm infants and will enable measurementof caloric expenditure from muscle activity in various diseaseconditions and development of nursing strategies to minimize unnecessary energy losses.