Background Both athletes and recreational exercisers often perform relatively high volumes of aerobic and strength training simultaneously. However, the compatibility of these two distinct training modes remains unclear. Objective This systematic review assessed the compatibility of concurrent aerobic and strength training compared with strength training alone, in terms of adaptations in muscle function (maximal and explosive strength) and muscle mass. Subgroup analyses were conducted to examine the influence of training modality, training type, exercise order, training frequency, age, and training status. Methods A systematic literature search was conducted according to the PRISMA (Preferred Reporting Items for Systematic Reviews and Meta-Analyses) guidelines. PubMed/MEDLINE, ISI Web of Science, Embase, CINAHL, SPORTDiscus, and Scopus were systematically searched (12 August 2020, updated on 15 March 2021). Eligibility criteria were as follows. Population: healthy adults of any sex and age; Intervention: supervised concurrent aerobic and strength training for at least 4 weeks; Comparison: identical strength training prescription, with no aerobic training; Outcome: maximal strength, explosive strength, and muscle hypertrophy. Results A total of 43 studies were included. The estimated standardised mean differences (SMD) based on the random-effects model were − 0.06 (95% confidence interval [CI] − 0.20 to 0.09; p = 0.446), − 0.28 (95% CI − 0.48 to − 0.08; p = 0.007), and − 0.01 (95% CI − 0.16 to 0.18; p = 0.919) for maximal strength, explosive strength, and muscle hypertrophy, respectively. Attenuation of explosive strength was more pronounced when concurrent training was performed within the same session (p = 0.043) than when sessions were separated by at least 3 h (p > 0.05). No significant effects were found for the other moderators, i.e. type of aerobic training (cycling vs. running), frequency of concurrent training (> 5 vs. < 5 weekly sessions), training status (untrained vs. active), and mean age (< 40 vs. > 40 years). Conclusion Concurrent aerobic and strength training does not compromise muscle hypertrophy and maximal strength development. However, explosive strength gains may be attenuated, especially when aerobic and strength training are performed in the same session. These results appeared to be independent of the type of aerobic training, frequency of concurrent training, training status, and age. PROSPERO: CRD42020203777.

Background Whole muscle hypertrophy does not appear to be negatively affected by concurrent aerobic and strength training compared to strength training alone. However, there are contradictions in the literature regarding the effects of concurrent training on hypertrophy at the myofiber level. Objective The current study aimed to systematically examine the extent to which concurrent aerobic and strength training, compared with strength training alone, influences type I and type II muscle fiber size adaptations. We also conducted subgroup analyses to examine the effects of the type of aerobic training, training modality, exercise order, training frequency, age, and training status. Design A systematic literature search was conducted according to the Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) [PROSPERO: CRD42020203777]. The registered protocol was modified to include only muscle fiber hypertrophy as an outcome. Data Sources PubMed/MEDLINE, ISI Web of Science, Embase, CINAHL, SPORTDiscus, and Scopus were systematically searched on 12 August, 2020, and updated on 15 March, 2021. Eligibility Criteria Population: healthy adults of any sex and age; intervention: supervised, concurrent aerobic and strength training of at least 4 weeks; comparison: identical strength training prescription, with no aerobic training; and outcome: muscle fiber hypertrophy. Results A total of 15 studies were included. The estimated standardized mean difference based on the random-effects model was − 0.23 (95% confidence interval [CI] − 0.46 to − 0.00, p = 0.050) for overall muscle fiber hypertrophy. The standardized mean differences were − 0.34 (95% CI − 0.72 to 0.04, p = 0.078) and − 0.13 (95% CI − 0.39 to 0.12, p = 0.315) for type I and type II fiber hypertrophy, respectively. A negative effect of concurrent training was observed for type I fibers when aerobic training was performed by running but not cycling (standardized mean difference − 0.81, 95% CI − 1.26 to − 0.36). None of the other subgroup analyses (i.e., based on concurrent training frequency, training status, training modality, and training order of same-session training) revealed any differences between groups. Conclusions In contrast to previous findings on whole muscle hypertrophy, the present results suggest that concurrent aerobic and strength training may have a small negative effect on fiber hypertrophy compared with strength training alone. Preliminary evidence suggests that this interference effect may be more pronounced when aerobic training is performed by running compared with cycling, at least for type I fibers.

ObjectiveThis systematic review assessed the compatibility of concurrent aerobic and strength training compared to sole strength training regarding adaptations in muscle function (maximal and explosive strength) and muscle mass. Subgroup analyses were conducted to examine the impact of training modality, exercise type, exercise order, training frequency, age, and training status.DesignA systematic literature search was conducted according to the Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA). PROSPERO: CRD42020203777Data sourcesPubMed/MEDLINE, ISI Web of Science, Embase, CINAHL, SPORTDiscus and Scopus were systematically searched (12th of August 2020, updated on the 15th of March 2021).Eligibility criteriaPopulation: Healthy adults of any sex and age; Intervention: Supervised, concurrent aerobic and strength training of at least 4 weeks; Comparison: Sole strength training with matched strength training volume; Outcome: maximal strength, explosive strength and muscle hypertrophy. ResultsA total of 43 studies were included. The estimated average standardised mean differences (SMD) based on the random-effects model were -0.06 (95% CI: -0.20, 0.09, p=0.446), -0.28 (95% CI: -0.48, - 0.08, p=0.007) and -0.01 (95% CI: -0.16, 0.18, p=0.919) for maximal strength, explosive strength and muscle hypertrophy, respectively. The attenuation in explosive strength was more pronounced when concurrent training was performed within the same session (p=0.043) compared with separating the sessions by at least 3 h (p&gt;0.05). Summary/ConclusionConcurrent aerobic and strength training does not compromise muscle hypertrophy and maximal strength development. However, explosive strength gains may be attenuated, especially when aerobic and strength training are performed within the same session.