Page L¹, Ojala B¹, Moore M¹, Thompson L²; College of St. Catherine¹, Minneapolis MN, USA. University of Minnesota², Minneapolis, MN, USA. mamoore@stkate.ed.

PURPOSE: To determine the effects of aging and inactivity on glycolytic enzymes in single skeletal muscle fibers of the gastrocnemius muscle. SUBJECTS: Eleven 12-month (adult) and thirteen 30-month (aged) rats were randomly assigned to control (C), one week of hindlimb unweighting (HU1), or two weeks of hindlimb unweighting (HU2). The HU1 and HU2 rats were suspended, using a tail harness to unweight the hindlimbs. METHODS: After the experiment, the calf muscles were removed, quick-frozen, and freeze-dried. 379 single skeletal muscle fibers were dissected from the soleus and white gastrocnemius muscles. Half of each fiber was used to determine muscle fibers type, via myosin heavy-chain (MHC) analysis on sodium dodecyl sulphate-polyacrimide gel electrophorosis (SDS-PAGE) method. Another portion of each fiber was tested for glycolytic enzyme activity. Results reported here are for lactate deydrogenase (LDH). RESULTS: With aging, a 29.1% decrease (p < 0.05) in LDH activity occurred in single gastrocnemius type IIB muscle fibers of aged versus adult control animals. With inactivity, the single gastrocnemius fibers of the aged animals showed a 30% increase in glycolytic/anaerobic activity after HU2 (p < 0.05), while the 12-month adult animals showed no increase in anaerobic activity following HU1 or HU2. CCONCLUSIONS: Both aging and inactivity lead to changes in muscle enzyme activity. With aging, a decrease in glycolytic activity in a phasic muscle may lead to a loss of strength and speed. But with inactivity, there is an increase in glycolytic activity, which may help compensate for these changes. This change is age-dependent, occurring in aged muscle, but not in adult inactive muscle. Clinically, it is likely that aged patients will exhibit more rapid declines in muscle strength than young patients. Therefore, it is important that PTs treat aged inactive patients more aggressively to prevent functional decline. FUNDING SOURCE: American Heart Assoc. & the Fesler-Lampert Chair in Aging Studies at Univ. MN.

Copyright 2004 by the American Physical Therapy Association

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