Improving Bone Health with Physical Activity: The Power PE Study and Development of the Bone-specific Physical Activity Questionnaire (BPAQ)

Abstract

The bone response to mechanical loading is not yet fully understood. Optimal doses of skeletal loading throughout life may reduce the risk of osteoporosis in the later years. There remains a need to determine what form and amount of mechanical loading comprises an optimal dose. Weight-bearing exercise is an obvious method of exposing the skeleton to mechanical strain, however, issues of practicality and compliance often mar its effectiveness. The aim of this project was to further explore the effect of physical activity on bone. In particular, we set out to determine the effectiveness of an exercise intervention applying previously identified relevant load parameters that could be simply implemented on a community level in order to deliver the greatest widespread impact on osteoporosis incidence. Measuring bone-relevant physical activity Current methods of measuring physical activity tend to reflect cardiovascular or metabolic load rather than osteogenic potential. Thus, the first initiative of the project was to develop a physical activity measurement tool of particular relevance to bone. The bone-specific physical activity questionnaire (BPAQ) was constructed and tested for its ability to predict parameters of bone strength in 40 healthy adults in comparison to several common measures of physical activity (e.g. questionnaires, diaries and pedometers) (Chapter 3). In analysing the BPAQ, particular emphasis was placed on biomechanical components of the loads imposed on the skeleton by physical activity. For this reason, we measured the ground reaction forces produced during a large variety of exercises to incorporate into algorithms used to score the BPAQ. We found that the BPAQ was capable of predicting parameters of bone strength at clinically relevant regions of the skeleton in healthy men and women, while other common measures were not. Influence of physical activity and maturity on bone strength Current research suggests that the most efficacious approach to reducing the risk of osteoporotic fracture in later life may be to maximise peak bone mass; a state that is largely achieved by the age of 20. Thus, early exercise intervention has become a target in the prevention of osteoporosis. Knowledge of the salient factors that influence bone integrity during childhood and more specifically the adolescent years, however, is lacking. For this reason, we studied the relationship of physical activity, sedentary behaviour, and maturational status with bone strength parameters in 99 adolescent boys and girls (Chapter 4). We observed sex-specific differences in bone strength characteristics and discovered, that in this age group, level of participation in physical activity predicted bone strength strongly for boys, while maturational status was a better predictor of bone strength in girls.