• physical activity
• exercise
• cartilage
• joints
• development

Physical activity in childhood has many health benefits. In the musculoskeletal area, physical activity leads to substantial gains in bone mass, at least some of which are maintained into later life.¹ The most opportune time for intervention appears to be the prepubertal and early pubertal years.^1–4 However, much less is known about joint development. Recently, advances in magnetic resonance imaging have allowed an accurate in vivo assessment of hyaline cartilage in joints. Most studies have been of the knee, but methods for hip and hand assessment have also been validated. Magnetic resonance imaging is accurate and highly reproducible with coefficients of variation of 2–3%.^5,6

Development of articular hyaline cartilage in the knee appears to be a very dynamic process.⁶ Physical activity has been shown to be associated with cartilage development both cross sectionally and longitudinally in randomly selected healthy children without knee pain or injury.^5,6 Cross sectionally, physical activity was a significant explanatory factor for cartilage volume at all knee sites (R² 7–14%).⁵ The most striking association was with vigorous activity in the …