Natural variability of daily physical activity measured by accelerometry in children with a mitochondrial disease.

In this exploratory study we aimed to select the most valid and feasible accelerometer to measure daily physical activity at home in 10 children with mitochondrial disease. Using the experimentally-selected GENEActiv, good to excellent short- and long-term test-retest reliability of daily physical activity was found. Especially in children with more severe limitations daily physical activity seemed more stable and less susceptible to weather conditions. Moreover, small standard errors of measurement were found, indicating high precision of this measuring method. We conclude that measuring daily physical activity using accelerometry is a promising outcome measure for future studies in this unique population.