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Quantitative and qualitative adaptations of muscle fibers to glucocorticoids

Introduction: The aim of this study was to understand the effects of short‐term glucocorticoid administration in healthy subjects. Methods: Five healthy men received dexamethasone (8 mg/day) for 7 days. Vastus lateralis muscle biopsy and knee extension torque measurement were performed before and after administration. A large number of individual muscle fibers were dissected from the biopsy samples (pre‐administration: n = 165, post‐administration: n = 177). Results: Maximal knee extension torque increased after administration (∼13%), whereas both type 1 and type 2A fibers had decreased cross‐sectional area (type 1: ∼11%, type 2A: ∼17%), myosin loss (type 1: ∼18%, type 2A: ∼32%), and loss of specific force (type 1: ∼24%, type 2A: ∼33%), which were preferential for fast fibers. Conclusion: Short‐term dexamethasone administration in healthy subjects elicits quantitative and qualitative adaptations of muscle fibers that precede (and may predict) the clinical appearance of myopathy in glucocorticoid‐treated subjects. Muscle Nerve 52: 631–639, 2015