The rate and patterns of longitudinal bone growth are affected by many different local and systemic factors; however, uncompromised growth is usually considered to be smoothly continuous, with predictable accelerations and decelerations over periods of months to years. The authors used implanted microtransducers to document bone growth in immature lambs. Bone length measurements were sampled every 167 seconds for 21 to 25 days. The authors show that at least 90% of bone elongation occurs during recumbency and almost no growth occurs during standing or locomotion. The authors hypothesize that growth may also occur in children during rest or sleep, thus supporting the concept of nocturnal growth and perhaps a relationship to growing pains.