title: Immobilization effects on contractile properties of aging rat skeletal muscle.
abstract: The effect of four weeks of ankle immobilization on muscle mass and in situ contractile properties of soleus (SOL), plantaris (PLA), and extensor digitorum longus (EDL) of 31- and 37-month-old (mo) Fisher 344/Brown Norway rats was examined. Following contractile tests, muscles were harvested, weighed, and analyzed for fiber type and fiber cross-sectional area. Body weights (g) were similar in both control (CON) groups (31 mo, 578 +/- 20; 37 mo, 553 +/- 26; mean +/- SE) and both immobilized (IM) groups (31 mo, 496 +/- 6; 37 mo, 461 +/- 15). Immobilization-related differences in peak tetanic tension (g) were less in 37 mo than 31 mo rats (age x treatment, p < 0.05) for SOL (31 mo, CON 156 +/- 11, IM 63 +/- 12; 37 mo, CON 70 +/- 6, IM 46 +/- 8), PLA (31 mo, CON 435 +/- 13, IM 239 +/- 40; 37 mo, CON 155 +/- 14, IM 152 +/- 20) and EDL (31 mo, CON 227 +/- 13, IM 139 +/- 17; 37 mo, CON 117 +/- 16, IM 108 +/- 4). Immobilization-related differences in muscle mass (mg) were smaller in 37 mo rats compared to 31 mo animals for SOL (31 mo, 206 +/- 14 vs 129 +/- 8, 37 mo, 148 +/- 5 vs 114 +/- 2, age x treatment p < 0.06) and PLA (31 mo, 409 +/- 14 vs 257 +/- 22, 37 mo, 234 +/- 17 vs 181 +/- 18, age x treatment p < 0.05), but immobilization-related muscle mass differences were similar in both age groups for EDL (31 mo, 178 +/- 7 vs 134 +/- 9; 37 mo, 157 +/- 10 vs 112 +/- 7). There were no immobilization-related changes in fiber type distribution in any of the three muscles studied in either age group. The results suggest that disuse-related change is diminished when superimposed on muscles that have already undergone marked age-related decline.
authors.affiliation: Program in Physical Therapy, Washington University School of Medicine, St. Louis, Missouri 63108, USA.
authors.forename: J S
authors.initials: JS
authors.lastname: Fisher
authors.forename: M
authors.initials: M
authors.lastname: Brown
mesh_terms: D000375:Aging / Q000502:physiology*; D000818:Animals; D001835:Body Weight; D007103:Immobilization; D008297:Male; D009119:Muscle Contraction / Q000502:physiology*; D018763:Muscle Fatigue / Q000502:physiology; D018482:Muscle, Skeletal / Q000033:anatomy & histology / Q000502:physiology*; D009929:Organ Size; D051381:Rats; D011916:Rats, Inbred F344; D013997:Time Factors