Low-level mechanical signals and their potential as a non-pharmacological intervention for osteoporosis

Background: exercise is recognised as a critical regulatory signal to the skeletal system, but which specific aspects of exercise are responsible for influencing bone mass and morphology and resisting fractures remains unknown. Recent data indicate that extremely low-level mechanical signals are anabolic to bone, and thus may be used, non-invasively, as a form of 'passive' exercise to positively influence skeletal status. Objective: to summarise recent experimental studies on the effect of low-level mechanical signals (hypothesised to serve as a surrogate for the spectral content of muscle contractility) as a potential non-pharmacological intervention for osteoporosis. Results: low magnitude mechanical signals are anabolic to bone if applied at a high frequency (15-90 Hz). Long-term animal studies (1 year) show that these low-magnitude mechanical signals can increase cancellous bone volume fraction, trabecular thickness, trabecular number and enhance bone stiffness and strength. Studies in the mouse have shown that these low-level signals will stimulate bone formation rate and labelled surface in cortical and cancellous bone, but the molecular and genetic regulation of this mechanosensitivity is extremely complex. Preliminary studies in children with disabling conditions and post-menopausal women indicate that such signals can be efficacious in reversing and/or preventing bone loss. Conclusions: considering that the strains (deformations) that result from these low-level vibrations are far below (< 1/1000th) those which may cause damage to the bone, we believe they represent a unique, non-pharmacological prophylaxis for osteoporosis. Given that so many physiologic systems are tuned to specific frequencies, such as sight, hearing and touch, it should not be entirely surprising that the musculoskeletal system would be responsive to frequency as well.