Age-dependent effects of treadmill exercise during a period of inactivity

The objective of this study was to investigate the effect of a treadmill exercise protocol to prevent muscle weakness, atrophy and alterations in calcium regulation in adult, old and very old rats. Adult (7–12 months), old (29–30 months) and very old (34–36 months) F344BNF 1 rats were randomly assigned to weight bearing (WB), weight bearing exercise (WBX), non-weight bearing (NWB) and non-weight bearing exercise (NWBX) groups. The WB group was considered the sedentary-control animals. NWB rats were hindlimb unweighted for 14 days. WBX and NWBX groups were exercised on a treadmill for approximately 15 min four times daily. The contractile properties [diameter, peak active force ( P 0), specific tension ( P 0/CSA)] of single myosin heavy chain type II fibers and Ca regulation [Ca 2+ dependent ATPase activity] were determined. Fiber diameter reduced by 24% in the very old rats with NWB. P 0 and P 0/CSA declined in the young adult and very old rats with NWB. NWBX attenuated these changes in the young and very old rats. Ca 2+ dependent ATPase activity increased with treadmill exercise during non-weight bearing in the young animals. In conclusion, the treadmill exercise is beneficial in attenuating the non-weight bearing-induced changes in the individual MHC type II muscle fibers of the gastrocnemius muscle.