Compatibility of Concurrent Aerobic and Strength Training for Skeletal Muscle Size and Function: An Updated Systematic Review and Meta-Analysis.
Level 1 - systematic review of randomized trials
Systematic review and meta-analysis of intervention studies
PubMed 34757594 · doi:10.1007/s40279-021-01587-7
What was done
A systematic review and random-effects meta-analysis following PRISMA guidelines was conducted across six databases (PubMed/MEDLINE, Web of Science, Embase, CINAHL, SPORTDiscus, Scopus) through March 2021. Eligible studies evaluated healthy adults undergoing supervised concurrent aerobic and strength training for at least 4 weeks compared with identical strength training alone. Outcomes assessed were maximal strength, explosive strength, and muscle hypertrophy. Subgroup analyses examined aerobic modality (cycling vs. running), exercise order/timing, weekly frequency, age (<40 vs. >40 years), and training status (untrained vs. active).
What was found
Across 43 included studies, concurrent training compared to strength training alone showed: - Maximal strength: SMD -0.06 (95% CI -0.20 to 0.09; p = 0.446) - Explosive strength: SMD -0.28 (95% CI -0.48 to -0.08; p = 0.007) - Muscle hypertrophy: SMD -0.01 (95% CI -0.16 to 0.18; p = 0.919) Explosive strength attenuation was significantly greater when both modes occurred in the same session (p = 0.043), whereas separating sessions by at least 3 hours showed no significant impairment (p > 0.05). Aerobic training type, training frequency (>5 vs. <5 sessions/week), training status, and age did not significantly moderate outcomes.
Why it matters
This clarifies the "interference effect": adding aerobic conditioning does not hinder muscle growth or maximal force production, but power-dependent athletes should separate endurance and strength bouts by at least 3 hours to preserve explosive strength gains.
Limits
The total participant count and sex distribution are not reported in the abstract. Interventions were required to last only 4 weeks, leaving long-term compatibility over multi-year periods uncertain. Training intensity, volume distribution, and dietary controls across the included trials are not described in the abstract.