English: "RT resistance training, CT concurrent training, n number of studies"

"On the basis of the predetermined criteria, 27 studies that compared effects between concurrent and resistance training only on lower-body 1-repetition maximum (1RM) strength were included. The effect size (ES), calculated as the standardised difference in mean, was extracted from each study, pooled, and analysed with a random-effects model."

"The following inclusion criteria were applied: (1) randomised and nonrandomised original articles, including healthy normal-weight men and women, 18–40 years of age; (2) interventions compared a group performing lower-body resistance and endurance trainings with a group performing identical resistance training only; (3) participants in the intervention and control groups with an equal baseline training status; (4) resistance training programmes performed in at least two sessions per week, including the same exercises as the main outcome measure of the study, with an intensity > 60% of the 1RM or lighter weight to fatigue; (5) endurance training performed as running or cycling at an intensity > 70% of the maximal heart rate in at least 2 sessions per week; and (6) studies reporting changes in maximal strength in leg press or squat exercise."

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"This meta-analysis shows that concurrent resistance and endurance training has a negative effect on lower-body strength development in trained but not in moderately trained or untrained individuals. The impairment observed in the trained category seems to be present only when resistance and endurance exercises were performed within a short time of each other (< 20 min), that is, within the same training session, but not when performed separately (> 2 h). Trained individuals should therefore consider separating endurance from resistance training, with > 2 h, during periods when strength development should be maximised. A concurrent training programme for untrained or moderately trained individuals can be based on more practical considerations or personal preferences rather than trying to keep resistance separated from endurance training. It is important to acknowledge that even though the strength development was impaired in the trained category, the impairment was moderate. Therefore, athletes with limited time may train for resistance and endurance within the same training sessions and still obtain appropriate increases in lower-body maximal dynamic strength."