Effects of Concurrent Resistance and Endurance Training Using Continuous or Intermittent Protocols on Muscle Hypertrophy: Systematic Review With Meta-Analysis.
Level 1 - systematic review of randomized trials
Systematic review and meta-analysis of comparative trials
PubMed 36508686 · doi:10.1519/JSC.0000000000004304
What was done
A systematic review and random-effects meta-analysis evaluated the effects of concurrent resistance and endurance training (CT) versus resistance training alone (RT) on whole-muscle and type I/type II muscle fiber cross-sectional area. Database searches were conducted across Web of Science, PubMed, Scopus, SPORTDiscus, and CINAHL for randomized and nonrandomized studies comparing RT to CT incorporating continuous endurance training, high-intensity interval training (HIIT), or combined protocols.
What was found
Twenty-five studies were analyzed: - At the whole-muscle level, no significant differences were observed between RT and CT for any endurance protocol comparison (SMD < 0.03). - At the muscle fiber level, RT elicited significantly greater type I and type II hypertrophy than CT when HIIT was incorporated alone (SMD > 0.33) or combined with continuous endurance training (SMD > 0.27). - CT incorporating only continuous endurance training did not significantly compromise muscle fiber hypertrophy relative to RT (SMD < 0.16).
Why it matters
This review clarifies the interference effect in concurrent training, showing that while macroscopic muscle growth appears unaffected by concurrent endurance exercise, microscopic fiber-level hypertrophy is blunted specifically when HIIT is combined with resistance training.
Limits
The review pooled both randomized and nonrandomized designs. The abstract does not report exact confidence intervals, p-values, participant demographics (e.g., sex, age, baseline training status), or training volume/frequency controls, which can heavily moderate the magnitude of training interference.
Cited by
- supports Higher levels of concurrent aerobic training may negatively affect muscle fiber hypertrophy specifically in type I muscle fibers.