Objective: To characterize specific musculoskeletal contractile property changes that occur during inactivity and intermittent weight bearing in aged muscle. Design: Randomized control trial. Setting: A controlled laboratory environment. Subjects: Fifteen aged rats were randomly assigned to control (CON), hindlimb unweighted (HU), and bindlimb unweighted with intermittent weight bearing (HU-IWB) groups. Interventions: The HU and HU-IWB rats were suspended for 1 week. The HU-IWB animals were unsuspended four times daily allowing 15 minutes of weight-bearing. Main Outcome Measures: Muscle weights, muscle fiber diameter, peak absolute force, peak specific tension (P(o)), and maximal shortening velocity (V(o)). Results: In comparison to CON animals, the sulcus (SOL) wet weight was significantly (p ≤ .05) reduced by 19% and 6% in HU and HU-IWB animals, respectively. SOL single fiber analysis showed no difference in fiber diameter between the three groups. However, peak absolute force and P(o) of SOL type I fibers were significantly (p ≤ .05) reduced in the HU group compared to CON values, V(o) of SOL fibers increased with HU. In comparison to CON animals, the gastrocnemius (GAS) wet weight was significantly reduced by 9% and 8% in HU and HU-IWB animals, respectively. Conclusions: Inactivity significantly altered the contractile properties of single fibers isolated from aged mammalian SOL skeletal muscle. Furthermore, minimal weight bearing attenuated these detrimental effects induced by inactivity in the SOL. However, this weight-bearing protocol did not attenuate the inactivity-induced alterations in aged mammalian GAS skeletal muscle.
Bibliographical noteFunding Information:
From the Master of Physical Therapy Program, The College of St. Catherine (Ms. Alley), and the Program in Physical Therapy, Department of Medicine and Rehabilitation, School of Medicine, University of Minnesota (Dr. Thompson), Minneapolis. Submitted for publication January 15, 1996. Accepted in revised form June 12, 1996. Supported by American Heart Association-MN Affiliate. Minnesota Medical Foundation, Grant-In-Aid University of Minnesota Graduate School. No commercial party having a direct financial interest in the results of the research supporting this article has or will confer a benefit upon the autbor~ or upon any organization with which the authors are associated. Reprint requests to LaDora V. Thompson, PhD, PT, Department of Physical Medicine and Rehabilitation, Program in Physical Therapy, University of Minnesota, UMHC Box 388, Minneapolis, MN 55455. 0 1997 by the American Congress of Rehabilitation Medicine and the American Academy of Physical Medicine and Rehabilitation 0003-9993/97/7801-3838$3.00/O
Acknowledgment: The authors thank .I. Kehler and The College of St. Catherine’s Master of Physical Therapy faculty for their collaborative efforts. We also thank J. Shoeman, B. Carlson, 5. Schwengler, and B. Snyder for their technical assistance. This work was supported by funds from American Heart Association-MN Affiliate. Minnesota Medical Foundation, and Grant-In-Aid University of Minnesota Graduate School.
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