title: Prolonged performance of a high repetition low force task induces bone adaptation in young adult rats, but loss in mature rats.
abstract: We have shown that prolonged repetitive reaching and grasping tasks lead to exposure-dependent changes in bone microarchitecture and inflammatory cytokines in young adult rats. Since aging mammals show increased tissue inflammatory cytokines, we sought here to determine if aging, combined with prolonged performance of a repetitive upper extremity task, enhances bone loss. We examined the radius, forearm flexor muscles, and serum from 16 mature (14-18 months of age) and 14 young adult (2.5-6.5 months of age) female rats after performance of a high repetition low force (HRLF) reaching and grasping task for 12 weeks. Young adult HRLF rats showed enhanced radial bone growth (e.g., increased trabecular bone volume, osteoblast numbers, bone formation rate, and mid-diaphyseal periosteal perimeter), compared to age-matched controls. Mature HRLF rats showed several indices of radial bone loss (e.g., decreased trabecular bone volume, and increased cortical bone thinning, porosity, resorptive spaces and woven bone formation), increased osteoclast numbers and inflammatory cytokines, compared to age-matched controls and young adult HRLF rats. Mature rats weighed more yet had lower maximum reflexive grip strength, than young adult rats, although each age group was able to pull at the required reach rate (4 reaches/min) and required submaximal pulling force (30 force-grams) for a food reward. Serum estrogen levels and flexor digitorum muscle size were similar in each age group. Thus, mature rats had increased bone degradative changes than in young adult rats performing the same repetitive task for 12 weeks, with increased inflammatory cytokine responses and osteoclast activity as possible causes.
authors.affiliation: Department of Anatomy and Cell Biology, Temple University School of Medicine, 3500 North Broad St., Philadelphia, PA 19140, USA.
authors.forename: Vicky S
authors.initials: VS
authors.lastname: Massicotte
authors.affiliation: Department of Anatomy and Cell Biology, Temple University School of Medicine, 3500 North Broad St., Philadelphia, PA 19140, USA.
authors.forename: Nagat
authors.initials: N
authors.lastname: Frara
authors.affiliation: Department of Anatomy and Cell Biology, Temple University School of Medicine, 3500 North Broad St., Philadelphia, PA 19140, USA.
authors.forename: Michele Y
authors.initials: MY
authors.lastname: Harris
authors.affiliation: Department of Anatomy and Cell Biology, Temple University School of Medicine, 3500 North Broad St., Philadelphia, PA 19140, USA.
authors.forename: Mamta
authors.initials: M
authors.lastname: Amin
authors.affiliation: Department of Physical Therapy, Thomas Jefferson University, Philadelphia, PA 19107, USA.
authors.forename: Christine K
authors.initials: CK
authors.lastname: Wade
authors.affiliation: Department of Anatomy and Cell Biology, Temple University School of Medicine, 3500 North Broad St., Philadelphia, PA 19140, USA.
authors.forename: Steven N
authors.initials: SN
authors.lastname: Popoff
authors.affiliation: Department of Anatomy and Cell Biology, Temple University School of Medicine, 3500 North Broad St., Philadelphia, PA 19140, USA; Department of Physical Therapy, Temple University, Philadelphia, PA 19140, USA. Electronic address: mary.barbe@temple.edu.
authors.forename: Mary F
authors.initials: MF
authors.lastname: Barbe
mesh_terms: D000375:Aging / Q000473:pathology*; D000818:Animals; D001842:Bone and Bones / Q000473:pathology*; D012090:Cumulative Trauma Disorders / Q000503:physiopathology*; D016207:Cytokines / Q000097:blood*; D004195:Disease Models, Animal; D004967:Estrogens / Q000097:blood; D005260:Female; D009140:Musculoskeletal Diseases / Q000503:physiopathology*; D010006:Osteoblasts / Q000166:cytology; D010010:Osteoclasts / Q000166:cytology; D051381:Rats; D017207:Rats, Sprague-Dawley; D055114:X-Ray Microtomography
chemical_list: D016207:Cytokines; D004967:Estrogens
keywords: Aging; Bone; Inflammation; MicroCT; Musculoskeletal; Radius; Repetitive strain injury