Research
Mixed
Aging is associated with a fast-to-slow muscle fiber type transformation (specifically IIx to I) and a reduction in type II fiber number and size, contributing to loss of power and strength.
Your muscles naturally shift towards slower, endurance-oriented fibers and lose fast-twitch fibers as you age, reducing your power. High-intensity resistance training can help counteract this shift and preserve fast-twitch fiber characteristics.
GoodSupportsHIGH confidence
Aging is associated with a fast-to-slow fiber type shift, affecting mostly IIx fibers... The decline in muscle mass, most prominent in the lower limbs, is accompanied by a 30% to 40% decrease in muscle fiber number... reduction in muscle fiber size is fiber type specific, with 10%–40% smaller type II fibers observed in muscle tissue collected from elderly compared with young controls.
Why this rating
Review article citing multiple primary studies.
Source
Aging of Skeletal Muscle Fibers
Nataša Miljković et al. · Annals of Rehabilitation Medicine · 2015
DOI 10.5535/arm.2015.39.2.155
narrative_reviewCited 302×
Read the paper DOI resolved against Crossref · corpus check 2026-06-10
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