Introduction: The role of muscle forces in determining bone micro-architecture and strength in children is poorly understood as limited evidence relies on surrogate measures of muscle force such as muscle size. The objective of this thesis was to explore the role of muscle area, peak forces from neuromuscular performance tests and physical activity in determining bone properties at the radius and tibia in children.
Methods: 37 boys and 42 girls (mean age 10.5; SD 1.6y) had their dominant forearm and lower leg imaged using peripheral quantitative computed tomography (pQCT) and high resolution pQCT (HR-pQCT). Bone mass, density, area and estimated strength were assessed. Muscle area was determined from the pQCT scans and grip strength measured via a handheld dynamometer. Peak force from a single maximal push-up performed on force platforms and the number of standard push-ups completed in a single attempt were recorded. Countermovement and standing long jump maximal forces were recorded, impulse and power were calculated, and average standing long jump distance was measured. Physical activity was measured using the Physical Activity Questionnaire for Children. Sex, maturation (estimated age from peak height velocity), weight and limb length (ulna and tibia) were controlled in the linear regression models. Variance predicted (R²) by models using muscle area, neuromuscular performance measures as independent predictors (squared partial r) of bone properties are reported.
Results: Grip strength and muscle area independently predicted 14-18% of the variance in bone area at the distal radius and 9-22% of the variance in bone strength at the distal and shaft sites of radius. Peak push-up force predicted 10% of the variance in trabecular number at the distal radius. Muscle area independently predicted 5-28% and countermovement and standing long jump forces and impulses predicted 6-10% of the variance in bone area, cortical content or density at the tibia shaft. Standing long jump power predicted 5-8% of the variance in bone area and cortical density at the tibia shaft. Physical activity predicted 9% of the variance in trabecular number at the distal tibia.
Discussion: Thesis findings support the use of muscle area as a surrogate for muscle forces and identified neuromuscular performance measures that will guide targeted exercise interventions aiming to optimize bone strength development in children.