title: The effects of non-weight bearing on skeletal muscle in older rats: an interrupted bout versus an uninterrupted bout.
abstract: Age-related changes in skeletal muscle, in combination with bed rest, may result in a poorer rehabilitation potential for an elderly patient. The purpose of this study was to determine the effects of non-weight bearing (hind limb unweighting [HU]) on the soleus and extensor digitorum longus (EDL) in older rats. Two non-weight bearing conditions were used: an uninterrupted bout of HU and an interrupted bout of HU. Twenty-one rats were randomly placed into 1 of 3 groups: control, interrupted HU (2 phases of 7 days of HU, separated by a 4-day weight-bearing phase) and an uninterrupted HU (18 uninterrupted days of HU). Following non-weight bearing, the soleus and EDL muscles were removed. Fiber type identification was performed by myofibrillar ATPase and cross-sectional area was determined. The findings suggest that any period of non-weight bearing leads to a decrease in muscle wet weight (19%-45%). Both type I and type II fibers of the soleus showed atrophy (decrease in cross-sectional area, 35%-44%) with an uninterrupted bout of non-weight bearing. Only the type II fibers of the soleus showed recovery with an interrupted bout of weight bearing. In the EDL, type II fibers were more affected by an uninterrupted bout of non-weight bearing (15% decrease in fiber size) compared to the type I fibers. EDL type II fibers showed more atrophy with interrupted bouts of non-weight bearing than with a single bout (a 40% compared to a 15% decrease). This study shows that initial weight bearing after an episode of non-weight bearing may be damaging to type II fibers of the EDL.
authors.affiliation: Program in Physical Therapy, University of Minnesota, Minneapolis, MN 55455, USA.
authors.forename: Alissa Guildner
authors.initials: AG
authors.lastname: Gehrke
authors.forename: Margaret Sheie
authors.initials: MS
authors.lastname: Krull
authors.forename: Robin Shotwell
authors.initials: RS
authors.lastname: McDonald
authors.forename: Tracy
authors.initials: T
authors.lastname: Sparby
authors.forename: Jessica
authors.initials: J
authors.lastname: Thoele
authors.forename: Sara Willen
authors.initials: SW
authors.lastname: Troje
authors.forename: Jaime
authors.initials: J
authors.lastname: ZumBerge
authors.forename: LaDora V
authors.initials: LV
authors.lastname: Thompson
mesh_terms: D000251:Adenosine Triphosphatases / Q000032:analysis; D000367:Age Factors; D000704:Analysis of Variance; D000818:Animals; D001510:Bed Rest / Q000009:adverse effects*; D001835:Body Weight; D004195:Disease Models, Animal; D019417:Hindlimb Suspension / Q000009:adverse effects*; D018485:Muscle Fibers, Skeletal / Q000201:enzymology / Q000473:pathology; D018482:Muscle, Skeletal; D009133:Muscular Atrophy / Q000209:etiology* / Q000473:pathology / Q000517:prevention & control* / Q000534:rehabilitation; D011897:Random Allocation; D051381:Rats; D011916:Rats, Inbred F344; D013997:Time Factors; D016474:Weight-Bearing
chemical_list: D000251:Adenosine Triphosphatases