The anabolic activity of bone tissue, suppressed by disuse, is normalized by brief exposure to extremely low-magnitude mechanical stimuli

It is generally believed that mechanical signals must be large in order to be anabolic to bone tissue. Recent evidence indicates, however, that extrem ely low-magnitude (<10 microstrain) mechanical signals readily stimulate bo ne formation if induced at a high frequency. We examined the ability of ext remely low-magnitude, high-frequency mechanical signals to restore anabolic bone cell activity inhibited by disuse. Adult female rats were randomly as signed to six groups: baseline control, age-matched control, mechanically s timulated for 10 min/day, disuse (hind limb suspension), disuse interrupted by 10 min/day of weight bearing, and disuse interrupted by 10 min/day of m echanical stimulation. After a 28 day protocol, bone formation rates (BFR) in the proximal tibia of mechanically stimulated rats increased compared wi th age-matched control (+97%). Disuse alone reduced BFR (-92%), a suppressi on only slightly curbed when disuse was interrupted by 10 min of weight bea ring (-61%). In contrast, disuse interrupted by 10 min per day of low-level mechanical intervention normalized BFR to values seen in age-matched contr ols. This work indicates that this noninvasive, extremely low-level stimulu s may provide an effective biomechanical intervention for the bone loss tha t plagues long-term space flight, bed rest, or immobilization caused by par alysis.