Efficacy of 3 days/wk resistance training on myofiber hypertrophy and myogenic mechanisms in young vs. older adults.

Abstract

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 days/wk, 16 wk) RT would be impaired in older (O; 60-75 yr; 12 women, 13 men), sarcopenic adults compared with 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 and 24 h postexercise, 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 before 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 myogenic differentiation factor D (MyoD) mRNAs increased (P < 0.05) in Y and O, whereas myogenic factor (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 3 days/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.

• Authors: David J Kosek, Jeong-Su Kim, John K Petrella, James M Cross, Marcas M Bamman
• Journal: Journal of applied physiology (Bethesda, Md. : 1985) (J Appl Physiol (1985)) Vol. 101 Issue 2 Pg. 531-44 (Aug 2006) ISSN: 8750-7587 [Print] United States
• PMID: 16614355 (Publication Type: Clinical Trial, Comparative Study, Journal Article, Research Support, N.I.H., Extramural, Research Support, U.S. Gov't, Non-P.H.S.)

Chemical References

• MYF5 protein, human
• MyoD Protein
• Myogenic Regulatory Factor 5
• Myogenic Regulatory Factors
• Myogenin
• RNA, Messenger
• myogenic factor 6

Topics

• Adult
• Aged
• Aging (physiology)
• Exercise (physiology)
• Female
• Humans
• Hypertrophy (pathology, physiopathology)
• Male
• Middle Aged
• Muscle Development (physiology)
• MyoD Protein (genetics, physiology)
• Myofibrils (pathology, physiology)
• Myogenic Regulatory Factor 5 (genetics, physiology)
• Myogenic Regulatory Factors (genetics, physiology)
• Myogenin (genetics, physiology)
• RNA, Messenger (analysis)
• Sex Characteristics
• Time Factors
• Weight Lifting