The Chill Bones (Combining High-Intensity Impact Loading and Lifting with Mind-Body Exercise for Optimisation of Nervous System and Skeletal Health) Trial: Protocol for a Parallel-Group, Semi-Randomised Controlled Trial

The CHILL BONES trial aims to determine whether a novel, combined mind-body and osteogenic exercise intervention (Tai Chi + High-intensity Resistance and Impact Training (HiRIT)) improves skeletal health and reduces fracture risk to a greater extent, than Tai Chi or HiRIT alone. Approximately 150 older adults (> 60 years) with low bone mass, will be randomly assigned to one of three exercise interventions – Tai Chi, HiRIT, or Tai Chi + HIRIT for eight months. Volunteers who do not wish to undertake exercise, may opt into a self-selected control group. The primary outcome will be change in hip bone mineral density. Secondary outcomes include changes in other determinants of bone strength (geometric and microarchitectural indices) and falls risk (dynamic balance and functional strength). Autonomic outcomes are also included in this study, as an opportunity to explore the effect of each intervention on sympathetic and parasympathetic activity. We will determine whether changes in these outcomes are associated with the skeletal adaptation to exercise. It is hypothesised that the combined intervention will be an optimal exercise therapy for fracture prevention, as it will achieve the greatest improvements in primary and secondary outcomes by the end of the 8-month intervention period.