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 extremely low‐magnitude (<10 microstrain) mechanical signals readily stimulate bone formation if induced at a high frequency. We examined the ability of extremely low‐magnitude, high‐frequency mechanical signals to restore anabolic bone cell activity inhibited by disuse. Adult female rats were randomly assigned to six groups: baseline control, age‐matched control, mechanically stimulated 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 mechanical stimulation. After a 28 day protocol, bone formation rates (BFR) in the proximal tibia of mechanically stimulated rats increased compared with age‐matched control (+97%). Disuse alone reduced BFR (‐92%), a suppression only slightly curbed when disuse was interrupted by 10 min of weight bearing (‐61%). In contrast, disuse interrupted by 10 min per day of low‐level mechanical intervention normalized BFR to values seen in age‐matched controls. This work indicates that this noninvasive, extremelylow‐level stimulus may provide an effective biomechanical intervention for the bone loss that plagues long‐term space flight, bed rest, or immobilization caused by paralysis.—Rubin, C., Xu, G., Judex, S. The anabolic activity of bone tissue, suppressed by disuse, is normalized by brief exposure to extremely low‐magnitude mechanical stimuli. FASEB J. 15, 2225–2229 (2001)