DIFFERENTIAL-EFFECTS OF REDUCED MUSCLE USE (HINDLIMB UNWEIGHTING) ON SKELETAL-MUSCLE WITH AGING

The changes in hindlimb muscle mass, fiber area and contractile tensio n that occurred with two weeks of reduced weight-bearing (HU) were of greater magnitude in 6-month-old as opposed to 36-month-old rats. The pattern of change following HU for young and old animals differed, whi ch may indicate that multiple mechanisms are responsible for the obser ved changes. The majority of old rats had difficulty with ambulation f ollowing unweighting suggesting that the functional consequences of re duced weight-bearing are greater in old than in young animals. One hou r of weight-bearing during HU attenuated the decline in SOL fiber atro phy, muscle mass and P-0, but had no apparent effect on the GAST, PL o r EDL. The reduction in P-0 with HU was not due, except for the old FL , to changes at the neuromuscular junction.