Purpose <p>The primary concerning outcome in early onset scoliosis (EOS), pulmonary function, is challenging to measure in children. Surrogate measures, including thoracic length and curve magnitude, poorly predict patient outcomes. Activity capacity as determined by Metabolic Equivalents of Task (MET) is a potentially useful alternative or adjunct since it more directly reflects the tasks being performed. The objective of this pilot study was to assess MET values for varying intensity activities in children with EOS and explore their relationship to pulmonary function indices, scoliosis characteristics, and patient-reported outcome measures.</p> Methods <p>For this pilot study, basal metabolic rate and physical activity MET values were measured using indirect calorimetry. MET values were assessed while performing video games representing low (bowling), moderate (boxing), and high intensity (active running) activities, and treadmill walking at low, moderate, and high intensity. MET values were compared to age-matched standardized energy expenditure values in youth (METy) for similar tasks. Pulmonary function testing was assessed using spirometry with percent predicted values based on arm span. Patient outcomes were obtained for each participant through the 24-question Early-Onset Scoliosis Questionnaire (EOSQ-24) and select assessments from the Patient-Reported Outcomes Measurement Information System (PROMIS). A linear mixed model assessed differences between groups. Spearman correlation coefficients assessed relationships between variables.</p> Results <p>Eight children (ages 6-16y, 50% female) completed testing. Etiologies for scoliosis were congenital (<i>n</i> = 3), syndromic (<i>n</i> = 3), and idiopathic (<i>n</i> = 2). Five had spirometry suggestive of severe restriction (FVC and FEV₁ &lt; 50% predicted). Children with EOS had a 0.6 lower mean MET video game value compared to published METy values (<i>p</i> &lt; 0.001). Increased intensity corresponded with increased MET values comparing hard to moderate and low intensities (<i>P</i> &lt; 0.001). Average percent predicted MET values across all tasks revealed a negative correlation with FEV₁/FVC (<i>R</i> = −&#xa0;0.927, <i>p</i> = 0.024). All eight children completed the low-intensity treadmill and low and moderate-intensity videogames; seven completed the moderate-intensity treadmill and high intensity videogame. Only five completed the high-intensity treadmill.</p> Conclusion <p>MET values in children with EOS were directionally similar to values in normal children. Children unable to generate higher MET values appear to self-limit their activity. The relationship between MET and pulmonary function is complex and requires further exploration. Children with EOS and pulmonary impairment appear unable to generate the energy required for more vigorous activities. This could be due to poor pulmonary function, deconditioning from their underlying condition, or limitations in the tested video games.</p> Level of evidence <p>II.</p>