RECOVERY OF SKELETAL-MUSCLE AFTER IMMOBILIZATION OF RABBIT HINDLIMB -A LIGHT-MICROSCOPIC STUDY

The histopathology of the deep portion of the vastus intermedius (VIP) muscle from 13 rabbit hindlimbs immobilized in shortened position for 2-2.5 (n=4), 3 (n=3), 14 (n=3) and 28 (n=3) days and VIP muscles from 13 rabbit hindlimbs immobilized for the same time periods and subsequ ently remobilized for 4 weeks were compared. After 3 days of immobiliz ation the VIP muscles displayed a 15% (p<0.004) decline in muscle fibr e diameter. By 2 weeks of immobilization fatty change was prominent an d muscle fibre diameters had decreased to 56% (p<0.0001) of control va lues. By 4 weeks of immobilization severe fibrotic damage of myofibres was observed and fibre diameters had decreased to 47% (p<0.0001) of c ontrol values. Three days of immobilization followed by 4 weeks of rem obilization led to marked fatty change as well as an increase in conne ctive tissue in the affected VIP muscles. The muscle fibre diameter in these muscles was 71% (p<0.0001) compared to the VIP immobilized for 3 days and 61% (p<0.0001) compared to the control muscles. By 2-4 week s of immobilization the subsequent remobilization did not aggravate th e initial damage. We conclude that the morphology of VIP muscle immobi lized for 3 days suffers more during a subsequent remobilization perio d than those immobilized for 14-28 days. These findings focus attentio n on the mechanisms operating at the onset of disuse muscle atrophy.