Concurrent Strength and Endurance Training: A Systematic Review and Meta-Analysis on the Impact of Sex and Training Status

Background Many sports require maximal strength and endurance performance. Concurrent strength and endurance training can lead to suboptimal training adaptations. However, how adaptations differ between males and females is currently unknown. Additionally, current training status may affect training adaptations. Objective We aimed to assess sex-specific differences in adaptations in strength, power, muscle hypertrophy, and maximal oxygen consumption (\documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$\dot{V}$$\end{document}V˙O2max) to concurrent strength and endurance training in healthy adults. Second, we investigated how training adaptations are influenced by strength and endurance training status. Methods A systematic review and meta-analysis was conducted according to PRISMA (Preferred Reporting Items for Systematic Reviews and Meta-Analyses) guidelines, and a Cochrane risk of bias was evaluated. ISI Web of science, PubMed/MEDLINE, and SPORTDiscus databases were searched using the following inclusion criteria: healthy adults aged 18–50 years, intervention period of ≥ 4 weeks, and outcome measures were defined as upper- and lower-body strength, power, hypertrophy, and/or \documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$\dot{V}$$\end{document}V˙O2max. A meta-analysis was performed using a random-effects model and reported in standardized mean differences. Results In total, 59 studies with 1346 participants were included. Concurrent training showed blunted lower-body strength adaptations in males, but not in females (male: − 0.43, 95% confidence interval [− 0.64 to − 0.22], female: 0.08 [− 0.34 to 0.49], group difference: P = 0.03). No sex differences were observed for changes in upper-body strength (P = 0.67), power (P = 0.37), or \documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$\dot{V}$$\end{document}V˙O2max (P = 0.13). Data on muscle hypertrophy were insufficient to draw any conclusions. For training status, untrained but not trained or highly trained endurance athletes displayed lower \documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$\dot{V}$$\end{document}V˙O2max gains with concurrent training (P = 0.04). For other outcomes, no differences were found between untrained and trained individuals, both for strength and endurance training status. Conclusions Concurrent training results in small interference for lower-body strength adaptations in males, but not in females. Untrained, but not trained or highly trained endurance athletes demonstrated impaired improvements in \documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$\dot{V}$$\end{document}V˙O2max following concurrent training. More studies on females and highly strength-trained and endurance-trained athletes are warranted. Clinical Trial Registration PROSPERO: CRD42022370894. Supplementary Information The online version contains supplementary material available at 10.1007/s40279-023-01943-9.


Figure S1 .
Figure S1.Forest plot of studies comparing differences in adaptations in lower-body strength with concurrent training between males and females.

Figure S2 .
Figure S2.Forest plot of studies comparing differences in adaptations in upper-body strength with concurrent training between males and females.

Figure S3 .
Figure S3.Forest plot of studies comparing differences in adaptations in power with concurrent training between males and females.

Figure S4 .
Figure S4.Forest plot of studies comparing differences in adaptations in muscle hypertrophy with concurrent training between males and females.

Figure S5 .
Figure S5.Forest plot of studies comparing differences in adaptations in V ̇O2max with concurrent training between males and females.

Figure S6 .
Figure S6.Forest plot of studies comparing differences in adaptations in lower-body strength with concurrent training between untrained and endurance-trained participants.

Figure S7 .
Figure S7.Forest plot of studies comparing differences in adaptations in upper-body strength with concurrent training between untrained and endurance-trained participants.

Figure S8 .
Figure S8.Forest plot of studies comparing differences in adaptations in power with concurrent training between untrained and endurance-trained participants.

Figure S9 .
Figure S9.Forest plot of studies comparing differences in adaptations in muscle hypertrophy with concurrent training between untrained and endurance-trained participants.

Figure S10 .
Figure S10.Forest plot of studies comparing differences in adaptations in V ̇O2max with concurrent training between untrained, trained and highly-trained endurance athletes.

Figure S11 .
Figure S11.Forest plot of studies comparing differences in adaptations in lower-body strength with concurrent training between untrained and strength-trained participants.

Figure S12 .
Figure S12.Forest plot of studies comparing differences in adaptations in upper-body strength with concurrent training between untrained and strength-trained participants.

Figure S13 .
Figure S13.Forest plot of studies comparing differences in adaptations in power with concurrent training between untrained and strength-trained participants.

Figure S14 .
Figure S14.Forest plot of studies comparing differences in adaptations in muscle hypertrophy with concurrent training between untrained and strength-trained participants.

Figure S15 .
Figure S15.Forest plot of studies comparing differences in adaptations in V ̇O2max with concurrent training between untrained and strength-trained participants.

Figure S16 .
Figure S16.Funnel plots for outcome measures maximal lower-body and upper-body strength, power, muscle hypertrophy and V ̇O2max with comparisons related to sex (left panels), endurance training status (middle panels) and strength training status (right panels).Egger's regression tests showed no funnel plot asymmetries indicative for a publication bias (P>0.05),except for lower-body strength with levels of strength training status (P=0.033).

Figure S17 .
Figure S17.Risk of bias assessment of all included studies according to the Cochrane guidelines.

Table S4 .
Characteristics of the participants, training and reported outcomes for the studies included in the meta-analysis.

Table S5 .
Differences in training status and training regimen between males and females for comparisons related to lower-body strength.