Eighty women from the age group of 50 to 65 years and having knee pain on most days of the month were enrolled into the study and randomly assigned to either a training group or a control group. Prior the intervention, radiographs were taken to prove that each participant had mild knee osteoarthritis. The training group exercised according a supervised progressive exercise program three times a week for 12 months, while the control group continued their normal physical activity. The effect of exercise on the femoral neck bone mineral mass was measured by DXA, and the effect on the biochemical composition of knee cartilage was measured by dGEMRIC -- a MRI method specifically designed to measure the proteoglycan content of cartilage.

"The loss of proteoglycans from the articular cartilage is considered to represent the onset of the degenerative process of osteoarthritis, and if this loss of proteoglycans can be hindered, for example, via physical activity, it might slow down the disease progression," says Doctoral Student Juhani Multanen from the Department of Health Sciences.

Jumping exercise and rapid direction changes for strong bones

The most efficient exercise to improve bone strength includes high-impact loading (jumping exercises), as well as rapid change of directions. Previously, this type of exercise has been thought to be harmful for the integrity of articular cartilage, although it has never been scientifically proven.

This study showed that training increased femoral neck bone mineral mass and improved physical function such as cardiorespiratory fitness, muscle strength and dynamic balance. The most important finding was that high-impact jumping exercise did not have negative effects on the biochemical composition of cartilage as investigated by MRI in persons with mild knee osteoarthritis. In addition, the 12-month training was very well tolerated -- it did not induce knee pain or stiffness, and the general training compliance was high. For postmenopausal women, the clinical significance of this study is that, despite of mild knee osteoarthritis, progressive high-impact loading exercises are allowed and even recommended to maintain and improve their bone health and functional ability.

The results of this study will be published early in 2014 in the Journal of Bone and Mineral Research.