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Effects of exercise on bone mineral density

What is the background to this research?
Among the elderly, bone mineral density (BMD) is an ever increasing health concern. In 1990, the number of hip fractures occurring each year was estimated at approximately 1.25 million world wide with females being three times more likely to suffer from an incident (reference). In the same publication, Gilbert (1990) estimated a significant increase of up to 310% the fracture numbers by 2025. Aging is linked to a decreased osteoblast activity and an increase in osteoclast activity (reference). This is attributed to a relative decline in hormones favouring local expression of molecules such as interleukins and TNF-α (reference). The result is a decrease in skeletal tissue, causing bones to become weaker and commonly leading to osteoporosis (reference). Hip and vertebral fractures cause serious complication in the form of a decreased quality of life, disability, chronic pain and premature death. Hip fractures caused by falls increases women mortality by 12-20% within the first year post incident (reference*). Additionally, there is an economic burden due to the injuries suffered from falls. Between 2006 and 2007, the estimated cost of falls related injuries New South Wales healthcare system has been calculated at over $558 million. Due to the impact fractures has on the public and economy, significant research has been conducted in an attempt to find ways of increasing bone mineral density. The effects of exercise on BMD has been extensively studied as repeted mechanical loading has been theorised to increase the cross sectional area of certain bones. This lead to researchers reviewing the literature and summarising the results of the relevant articles (reference).

Where is the research from?
The review of the literature was conducted by researchers from the University of Porto's Research Centre in Physical Activity, Health and Leisure in Portugal. The project was funded by grants from the Portuguese Foundation of Science and Technology along with other independent grants. The article was was reviewed and published online by The American Ageing Association in 2011.

What kind of research was this?
The research was conducted as a meta-analysis of randomised control trials with a specific range of acceptable criteria. The review was specifically looking at randomised control trials that investigated the effects of exercise interventions on femoral neck and lumbar spine BMD (reference).

What did the research involve?
The aim of the review was to assess the effects of exercise interventions with different impact loading characteristics on lumbar spine and femoral neck bone mineral density in older adults (in this instance defined as over 60 years old) (reference). The study narrowed their focus to weight bearing exercises such as aerobics, resistance training, endurance training, circuit training, jogging, jumping and any other modalities that create an impact on the skeleton (reference). Studies that included pharmacudical interventions or treatments known to improve BMD were excluded.

The review had seven specific inclusion creator that each study needed to comply with; the criteria included (1) be exclusivly RCT's, (2) exercise was the only intervention applied, (3) older adults aged ≥60 years or whose mean age is ≥65 years, (4) data for one or more of the following variables provided: lumbar spine BMD and femoral neck BMD, (5) studies were published in English language journals, (6) a control group was assigned for comparative purposes, and (7) the exercise intervention lasted a minimum of 16 weeks. The data was extracted using a coding framework that screaned for multiple variables including but not limited too sample size, attrition, follow up length and compliance (reference).

What were the basic results?
Out of the 19 acceptable studies, researchers found a significant increase in mean BMD of 0.011g/cm2 for the lumbar spine, and 0.016g/cm2 at femoral neck (reference). Results relating to combined loading strategies on FN were moderately inconsistent, conversely, LS data remained consistent throughout the review. Studies which consisted of resistance exercise as the intervention resulted in consistent data, however their results were not significant.

References (including the primary reference that this fact sheet relates to)
Gender Differences in Mortality After Hip Fracture: The Role of Infection* http://www.health.nsw.gov.au/falls/Publications/incidence-cost-of-falls.pdf