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Exp Gerontol. 2018 Jun;106:116-124. doi: 10.1016/j.exger.2018.02.023. Epub 2018 Feb 24.

Human neuromuscular aging: Sex differences revealed at the myocellular level.

Author information

1
UAB Center for Exercise Medicine, University of Alabama at Birmingham, Birmingham, AL 35294, United States; Department of Cell, Developmental, and Integrative Biology, University of Alabama at Birmingham, Birmingham, AL 35294, United States.
2
UAB Center for Exercise Medicine, University of Alabama at Birmingham, Birmingham, AL 35294, United States; Department of Physical Therapy, University of Alabama at Birmingham, Birmingham, AL 35294, United States; Department of Physical Therapy, Samford University, Birmingham, AL 35229, United States.
3
Department of Surgery, University of Alabama at Birmingham, Birmingham, AL 35294, United States.
4
UAB Center for Exercise Medicine, University of Alabama at Birmingham, Birmingham, AL 35294, United States.
5
Department of Kinesiology, Samford University, Birmingham, AL 35229, United States.
6
Geriatric Research, Education, and Clinical Center, VA Medical Center, Birmingham, AL, 35233, United States; UAB Center for Exercise Medicine, University of Alabama at Birmingham, Birmingham, AL 35294, United States; Division of Geriatrics, Gerontology, and Palliative Care, University of Alabama at Birmingham, Birmingham, AL 35294, United States.
7
UAB Center for Exercise Medicine, University of Alabama at Birmingham, Birmingham, AL 35294, United States; Department of Human Studies, University of Alabama at Birmingham, Birmingham, AL 35294, United States.
8
UAB Center for Exercise Medicine, University of Alabama at Birmingham, Birmingham, AL 35294, United States; Department of Surgery, University of Alabama at Birmingham, Birmingham, AL 35294, United States.
9
Geriatric Research, Education, and Clinical Center, VA Medical Center, Birmingham, AL, 35233, United States; UAB Center for Exercise Medicine, University of Alabama at Birmingham, Birmingham, AL 35294, United States; Department of Cell, Developmental, and Integrative Biology, University of Alabama at Birmingham, Birmingham, AL 35294, United States; Division of Geriatrics, Gerontology, and Palliative Care, University of Alabama at Birmingham, Birmingham, AL 35294, United States. Electronic address: mbamman@uab.edu.

Abstract

Age-related muscle loss (sarcopenia) is a major clinical problem affecting both men and women - accompanied by muscle weakness, dysfunction, disability, and impaired quality of life. Current definitions of sarcopenia do not fully encompass the age-related changes in skeletal muscle. We therefore examined the influence of aging and sex on elements of skeletal muscle health using a thorough histopathological analysis of myocellular aging and assessments of neuromuscular performance. Two-hundred and twenty-one untrained males and females were separated into four age cohorts [mean age 25 y (n = 47), 37 y (n = 79), 61 y (n = 51), and 72 y (n = 44)]. Total (-12%), leg (-17%), and arm (-21%) lean mass were lower in both 61 y and 72 y than in 25 y or 37 y (P < 0.05). Knee extensor strength (-34%) and power (-43%) were lower (P < 0.05) in the older two groups, and explosive sit-to-stand power was lower by 37 y (P < 0.05). At the histological/myocellular level, type IIx atrophy was noted by 37 y and type IIa atrophy by 61 y (P < 0.05). These effects were driven by females, noted by substantial and progressive type IIa and IIx atrophy across age. Aged female muscle displayed greater within-type myofiber size heterogeneity and marked type I myofiber grouping (~5-fold greater) compared to males. These findings suggest the predominant mechanisms leading to whole muscle atrophy differ between aging males and females: myofiber atrophy in females vs. myofiber loss in males. Future studies will be important to better understand the mechanisms underlying sex differences in myocellular aging and optimize exercise prescriptions and adjunctive treatments to mitigate or reverse age-related changes.

KEYWORDS:

Aging; Atrophy; Lean mass; Muscle power; Myofiber; Sarcopenia; Strength

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