Figure 1. Force output and activity measures in adult and old rats. In vivo isometric force production at frequencies ranging from 20-125 Hz was measured in (A) adult (9 mo) and (B) old (29 mo) rats prior to hindlimb unloading (HU) (baseline, open squares), after 14 days of HU (open circles), and then after 7 (open triangles) and 13 days of reloading (open diamonds). n=6/group. Values are mean ± SEM, *p<0.05 vs old baseline value, #p<0.05 for old 14d HU value vs old baseline value at 40 Hz. (C) Normal cage activity of adult (open squares, n=4) and old (filled squares, n=5) rats was recorded during the dark cycle for six days prior to HU and for the first five days of reloading following 14 days of HU. Values are mean ± SEM, #p<0.05 vs old control.