WASHINGTON – Active children may have stronger knees as adults, based on data from a long-term follow-up study of approximately 300 children. The findings were presented at the annual meeting of the American College of Rheumatology.
Although physical activity is recommended for children to improve joint health and function, the correlation between childhood exercise and adult bone structure has not been well studied, said Dr. Graeme Jones, who is professor of rheumatology and epidemiology and head of the musculoskeletal unit at the Menzies Research Institute as well as head of the department of rheumatology at Royal Hobart Hospital, both in Hobart, Australia.
Data from previous studies have shown that children who engaged in vigorous activity in childhood had greater cartilage deposition in their knees compared with less active children, said Dr. Jones.
"The idea would be that if you develop more cartilage in childhood and it lasts until adult life, you can prevent the development of osteoarthritis," he said.
In 1985, data were collected on 8,500 Australian children in the population-based Childhood Determinants of Adult Health study. In that study, researchers measured the children’s fitness based on measures of hand strength, leg strength, run times, sit-ups, and physical work capacity at 170 beats per minute (PWC170).
To measure the long-term impact of exercise on knee structure, Dr. Jones and his colleagues reviewed data from 298 study participants at ages 31-41 years. Approximately half of the participants were female.
The researchers assessed tibial bone area (the size of the knee joint) and the amount of cartilage using T1-weighted fat-suppressed magnetic resonance imaging.
All measures of childhood physical activity levels were significantly associated with increased tibial bone area. These associations included 0.48 cm2 per 100 mW (a measure of work) for PWC170, 1.49 cm2 per 100 g of hand muscle strength, 0.29 cm2 per 100 g of leg muscle strength, and 0.28 cm2 per 10 sit-ups.
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Keeping kids active is important; it may help them grow up with stronger knees.
In addition, childhood PWC170 was significantly associated with an increased medial tibial cartilage volume in adulthood (0.1 mm3 per 100 mW). This association was approximately 33% weaker, though still significant, after adjusting for tibial bone area, Dr. Jones said. Hand muscle strength and sit-ups were significantly associated with increased medial tibial cartilage volume before adjusting for bone area, but the association became nonsignificant after adjusting for bone area.
"What this suggests to us is that the response to physical activity in childhood is to increase the size of the bone to adjust for this and to spread the load out, and the cartilage will then expand to cover the bone area or the area of contact," said Dr. Jones.
These associations were independent of fitness performance measures and medial tibial cartilage volume in adulthood, he added.
The findings suggest that childhood exposure to physical activity has a long-term protective effect on knee joint health. Therefore, "we need to get children as active as we can," he said.
The study was funded by the National Health and Medical Research Council of Australia. Dr. Jones had no financial conflicts to disclose.