Objective To examine relationships among daily activity levels, body composition and bone outcomes in children aged 6.7 years who were born at term with birth weights <20th centile.

Methods Activity data collected using accelerometers were correlated with body composition and bone outcome z-scores from dual-energy X-ray absorptiometry in 36 children.

Results Activity levels were related to body composition outcomes; for example, lean mass index (lean mass/height²) was positively associated with time spent in moderate activity (r=0.40, p=0.02) and negatively with time spent in sedentary activity (r=−0.50, p=0.002). Per cent time spent in sedentary activity correlated negatively with whole body bone mineral density z-score (r=−0.44, p=0.01) and hip bone mineral content (r=−0.38, p=0.03).

Conclusions Moderate and vigorous activity levels were associated with increased lean and bone mass in this population but not with conventional measures of adiposity such as weight and body mass index z-scores. Standard measures of adiposity may mask potential benefits of regular activity.