REF-1682 · Zhao, Zhang & Wang, 2026 · Journal of Sports Sciences, · Paper · PubMed

Adding resistance training to endurance training showed no significant difference in the VO2max gain overall (SMD −0.12, 95% CI −0.28 to 0.05) or in athletes, nor in muscle mitochondrial markers, in a meta-analysis of concurrent versus endurance-only training; when the concurrent group's endurance load was reduced, VO2max rose less in untrained people (SMD −0.32) and over 16-week programmes (SMD −0.63). The number of studies and participants is not in the abstract

Main caveat: From the abstract: the authors' own limitations are not stated.
moderate evidenceMeasured on non-athletes to trained athletesRead from the abstract only

Zhao and colleagues pooled studies comparing concurrent training, resistance and endurance training combined, with endurance training alone, and asked whether the combination changes the rise in maximal oxygen uptake and in skeletal-muscle mitochondrial adaptation. They searched three English-language and three Chinese databases.

Overall, VO2max gains did not differ significantly between concurrent and endurance-only training (SMD −0.12, 95% CI −0.28 to 0.05), and the abstract reports the same for athletes, without a figure.

In subgroups where the concurrent group's endurance load was reduced, VO2max rose less with concurrent training in untrained people (SMD −0.32, −0.62 to −0.02) and in 16-week interventions (SMD −0.63, −1.21 to −0.06).

None of the four mitochondrial markers (PGC-1α mRNA, citrate synthase activity, state 3 respiration and protein synthesis rate) differed significantly between the two approaches.

The authors conclude that concurrent and endurance training change VO2max and muscle adaptation alike overall and in athletes, but that cutting the endurance load within concurrent training goes with smaller VO2max gains in untrained people or over 16 weeks.

Participants

Number of studies and participants, sex, age and training status: not in the abstract.
Subgroups named in the abstract: untrained individuals and an "athletic population".

Protocol

Search: PubMed, Embase, Cochrane Library, CNKI, Wanfang and CBM, following PRISMA; search dates not in the abstract.
Comparison: concurrent training (resistance plus endurance) against endurance training alone.
Outcomes: VO2max; muscle mitochondrial markers (citrate synthase activity, state 3 respiration, protein synthesis rate, PGC-1α mRNA).
Analysis: standardised mean differences with 95% CIs; subgroups by training status, intervention length and whether the concurrent group's endurance load was reduced.
Not in the abstract: study designs (randomised or not), the endurance mode, the resistance dose, session order, the risk-of-bias tool and findings, heterogeneity, the number of studies in each subgroup, and registration.

Key Results

Outcome (concurrent vs endurance-only training)SMD (95% CI)Significant
VO2max, overall−0.12 (−0.28 to 0.05)no (p > 0.05)
VO2max, athletesnot givenno (per the abstract)
VO2max, untrained, concurrent with reduced endurance load−0.32 (−0.62 to −0.02)yes (p < 0.05)
VO2max, 16-week interventions, concurrent with reduced endurance load−0.63 (−1.21 to −0.06)yes (p < 0.05)
Citrate synthase activity, state 3 respiration, protein synthesis rate, PGC-1α mRNAnot givenno (p > 0.05)
Negative values mean a smaller VO2max gain with concurrent training.
The abstract's wording leaves unclear whether the 16-week subgroup is limited to untrained people; it is stated alongside the untrained subgroup, both "involving reduced ET load".

Practical Application

Adding strength training to endurance training showed no significant difference in the VO2max gain overall (SMD −0.12, CI −0.28 to 0.05) or in athletes; smaller VO2max gains were reported where the concurrent group's endurance load was reduced, in untrained people (−0.32) and in 16-week programmes (−0.63). No endurance performance outcome is reported.
Inference, not tested here: add the lifting rather than taking it out of the endurance volume. The smaller VO2max gains appeared in the subgroups where the concurrent group did less endurance work than the endurance-only group. Inference, not tested here: for an athlete whose goal is endurance, strength sessions belong on top of a protected endurance load, or replace only easy volume, rather than replacing key aerobic sessions.
This supports what [SYNTH-21] and [SYNTH-105] assume. SYNTH-21 says the interference poolings in the base did not measure the endurance outcome and rests the "endurance is not harmed" claim on the strength-for-endurance literature (REF-071, REF-149); this review supplies a VO2max comparison against endurance-only training that points the same way. SYNTH-105 notes that no source measured endurance athletes for its strength-dose rows; this review does not test a strength dose, and its athletes' level is not given.
Muscle mitochondrial markers did not differ either, but these are markers, not performance, and the abstract gives no effect sizes for them.

Limitations

From the abstract: the authors' own limitations are not stated.
Not in the abstract: how many studies and participants were pooled, their designs, sex, age and training status, the endurance mode and resistance dose, risk of bias, heterogeneity and registration.
The reduced-load findings are subgroup results between studies, not a randomised comparison of endurance volumes; the number of studies in each subgroup is not given.
VO2max is a capacity measure; whether endurance performance (time trial, economy) changed is not reported.
The mitochondrial outcomes are markers and their effect sizes are not given.
Written from the abstract and the PubMed record; full text not read.
How this entry was checked and changed
Why this level

a meta-analysis comparing training groups, capped because the risk of bias is not reported: risk of bias not read (abstract only); VO2max is a capacity outcome, so the main claim takes no marker step, while the mitochondrial results are markers and weigh less (B by rule 3)