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Norsk Epidemiologi, 2011; 20(2): 173-178

Physical activity and bone: The importance of the various
mechanical stimuli for bone mineral density. A review

Year: 2011

Bente Morseth, Nina Emaus and Lone Jørgensen
Department of Community Medicine, University of Tromsø, Tromsø, Norway


Numerous studies have reported benefits of regular physical activity on bone mineral density (BMD). The
effects of physical activity on BMD are primarily linked to the mechanisms of mechanical loading, but the
understanding of the precise mechanism behind the association is incomplete. The aim of this paper was to
review the main findings concerning sources and types of mechanical stimuli in relation to BMD. Mechanical
forces that act on bone are generated from impact with the ground (ground-reaction forces) and from skeletal
muscle contractions (muscle forces or muscle-joint forces), but the relative importance of these two sources
has not been elucidated. Both muscle-joint forces and gravitational forces seem to be able to induce bone adaptation
independently, and there may be differences in the importance of loading sources at different skeletal
sites. The nature of the stimuli is affected by the type, intensity, frequency, and duration of the activity. The
activity should be dynamic, not static, and the magnitude and rate of the stimuli should be high. In accordance
with this, cross-sectional studies report highest BMD in athletes of high-impact activities such as dancing,
soccer, volleyball, basketball, squash, speed skating, gymnastics, hockey, and step-aerobics. Endurance activities
such as orienteering, skiing, and triathlon seem to be beneficial to a lesser degree, whereas low-impact
activities such as swimming and cycling are associated with lower BMD than controls. Both the intensity and
frequency of the activity should be varied and increased beyond the habitual level. Duration of the activity
seems to be less important, and a few loading cycles seem to be sufficient.

GID: 3339; Last update: 15.10.2013