A systematic review and meta-analysis examining if hyperplasia occurs in humans in response to resistance exercise

While it is understood that resistance exercise in humans induces muscle growth primarily via muscle hypertrophy, there is some debate as to whether muscle hyperplasia also occurs. The purpose of this meta-analysis was to quantitively assess whether the presence of muscle hyperplasia occurs in humans performing resistance training.

Medline, Scopus, and Web of Science were searched on May 17, 2024. Studies that measured or reported sufficient data to estimate muscle fiber number before and after resistance training were included in a three-level random effects model. Fiber number was estimated from the ratio of muscle cross-sectional area to fiber cross-sectional area.

A total of 11 studies met the inclusion criteria. Changes in fiber number were estimated in the biceps brachii or vastus lateralis muscles. Meta-analysis results indicated that resistance exercise did not significantly alter the estimated number of muscle fibers (ES: 4086; 95% CI: -6430, 14,604; P=0.419). Additionally, the presence of muscle hyperplasia was not moderated by prior training status, training duration, or the muscle group analyzed (all P>0.05).

These findings suggest that meaningful changes in muscle fiber number are unlikely to occur in humans following resistance training interventions lasting up to 6 months. While muscle hyperplasia was not evident, it may be difficult to detect due to the relatively short duration of the included training interventions and/or difficulties in estimating muscle fiber number, which resulted in a wide range of estimates across studies.