The energy cost of physical activity has been estimated to account for 3-14% of overall energy expenditure in neonates. In order to directly measure energy expenditure of activity, a force platform was developed which lies under the infant mattress and consists of two aluminum plates with straingauge sensors secured between the plates at each corner. Forces from movement on the platform are processed to provide a continuous caloric equivalent measurement. Using precision weights ranging from 20-1000 grams, static calibration of force was determined to be within 1% of expected. A motor driven reciprocating mass was used to simulate dynamic motion on the platform, and using work outputs ranging from 0.3 to 40 kcals/d, recovered work averaged 89.9% for all dynamic trials.

Using this force platform and indirect calorimetry, energy expenditure of activity (EEA) was determined as a percentage of overall energy expenditure(TEE) and for five activity states (i.e. quiet sleep-QS, active sleep-AS, quiet wakefulness-QW, active wakefulness-AW and crying wakefulness-C) in 7 stable, enterally-fed preterm infants with mean gestational age at birth of 28.5 wks and mean chronological age of 3.4 weeks who were studied from 2.2-7.3 hours. Results are shown below: Table

Table 1
Full size table

In conclusion, we have provided the first direct measurement of the contribution of physical activity to TEE. This will allow for the assessment of caloric expenditure from muscle activity in various diseases and for the development of nursing strategies to minimize unnecessary energy loss.