Research
Mixed
Retraining after long-term detraining (30-32 weeks) induces rapid hypertrophy of fast-twitch muscle fibers (Type IIa and IIab+IIb) and a shift in fiber type composition from IIb to IIa, occurring faster than in untrained individuals.
When returning to lifting after a long break, your fast-twitch muscle fibers will grow quickly, and your muscle fibers will shift towards more oxidative (IIa) profiles. This structural change happens rapidly, contributing to the speed at which you regain strength.
GoodSupportsHIGH confidence
Retraining increases in the cross-sectional areas of both fast fiber types (IIa and IIab + IIb) compared with detraining values and a decrease in the percentage of type IIb fibers.
Why this rating
Small sample size but confirmed via muscle biopsies.
Source
Strength and skeletal muscle adaptations in heavy-resistance-trained women after detraining and retraining
Robert S. Staron et al. · Journal of Applied Physiology · 1991
DOI 10.1152/jappl.1991.70.2.631
crossover · n=13Cited 397×
Read the paper DOI resolved against Crossref · corpus check 2026-06-10
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