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1 Physiology and Biophysics, University of Alabama at Birmingham, Birmingham, United States
2 Surgery, University of Alabama at Birmingham, Birmingham, United States
* To whom correspondence should be addressed. E-mail: mbamman{at}physiology.uab.edu.
Resistance training (RT) has shown the most promise in reducing/reversing effects of sarcopenia, although the optimum regime specific for older adults remains unclear. We hypothesized myofiber hypertrophy resulting from frequent (3 d/wk, 16 wk) RT would be impaired in older (O; 60-75 yr 12 women, 13 men), sarcopenic adults compared to young (Y; 20-35 yr; 11 women, 13 men) due to slowed repair/regeneration processes. Myofiber type distribution and cross sectional area (CSA) were determined at 0 and 16 wk. Transcript and protein levels of myogenic regulatory factors (MRFs) were assessed as markers of regeneration at 0, 24 h post-exercise, and after 16 wk. Only Y increased type I CSA 18% (P<0.001). O showed smaller type IIa (-16%) and type IIx (-24%) myofibers prior to training (P<0.05) with differences most notable in women. Both age groups increased type IIa (O, 16%; Y, 25%) and mean type II (O, 23%; Y, 32%) size (P<0.05). Growth was generally most favorable in young men. Percent change scores on fiber size revealed an age x gender interaction for type I fibers (P<0.05) as growth among Y (25%) exceeded that of O (4%) men. Myogenin and MyoD mRNAs increased (P<0.05) in Y and O, while myf-5 mRNA increased in Y only (P<0.05). Myf-6 protein increased (P<0.05) in both Y and O. The results generally support our hypothesis as 3d/wk training led to more robust hypertrophy in Y vs. O, particularly among men. However, this differential hypertrophy adaptation was not explained by age variation in MRF expression.
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