Osteoporosis, through its association with age-related fracture, is a major public health concern worldwide. Although osteoporosis was once considered a disease of the elderly, it is now recognized as a condition that has childhood antecedents. The capacity of bone to adapt is the greatest before puberty because of a higher rate of modeling and remodeling. Therefore, the amount of bone gained during childhood and adolescence has the potential to impact lifetime skeletal health. Children who participate in greater amounts of physical activity have greater bone mineral accrual in adolescence as well as a greater peak bone mass in young adulthood. Structured impact loading during growth also positively influences bone parameters. However, the intensity, duration and frequency of loading that is required to elicit skeletal benefits are not well established. Furthermore, although structured physical activity during growth has been hypothesized to delay or prevent the risk of osteoporosis and related fracture later in life there is no clear evidence of a persisting benefit once the loading stimulus has been removed. Therefore, the objective of this thesis was to investigate low-level impact loading during growth and skeletal development as well as to determine the influence of the withdrawal of the loading stimulus on adult bone parameters. Two studies were necessary to realize this objective. The findings should help to determine whether adolescent and adult bone health benefits from structured physical activity during growth. If this is found to be the case then structured gymnastic activity could be promoted as an effective means to optimize adult bone mass, structure and estimated strength.
Study 1: The purpose of study one was to investigate whether the differences previously reported in the skeleton of competitive female gymnasts (high level gymnastics exposure) are also demonstrated in young children with a current or past participation history in recreational or precompetitive gymnastics (low level gymnastics exposure). One hundred and sixty three children (30 gymnasts, 61 ex-gymnasts, and 72 non-gymnasts) between 4 and 6 years of age were recruited and measured annually for four years. Total body (TB), lumbar spine (LS) and femoral neck (FN) bone mineral content (BMC) was measured by dual energy x-ray absorptiometry (DXA) at each measurement occasion. Bone mass, density, structure and estimated strength was determined using peripheral quantitative computed tomography (pQCT) at the radius and tibia during the third measurement occasion. Multilevel random effects models were constructed and used to predict differences in TB, LS and FN BMC between groups while controlling for differences in body size, physical activity and diet. Analysis of covariance (covariates of sex, age and height) was used to investigate differences in bone content, density, area, and estimated strength at the radius and tibia. Gymnasts had 3% more TB and 7% more FN BMC than children participating in other recreational sports at the fourth measurement occasion (
