Combining endurance and strength training blunts explosive strength gains more than maximal strength or muscle growth, mainly when both are in the same session
Interpretation
Schumann et al. 2022 (43 studies, mostly untrained or active adults) found no meaningful blunting of maximal strength (SMD −0.06) or hypertrophy (−0.01) but a significant reduction in explosive strength (−0.28), larger in same-session training than with ≥3 h between. Petré et al. 2021 (27 studies) found lower-body 1RM gains blunted in trained people (ES −0.35), mainly in same-session designs (−0.66 vs −0.10 separate). Wilson et al. 2012 (21 studies) linked running, more frequent and longer endurance work with smaller gains. Graded moderate: consistent direction on explosive strength and session timing from several meta-analyses, but they partly disagree on maximal strength in trained people, sex splits aren't reported, and no study involved triathletes training three sports.
Practical implication
Triathletes can lift and train endurance in the same week. Separate the two by at least 3 hours where possible, place lifting on easy days, and if combining in one session lift first only when strength is the block's priority. The interference concerns strength gains, not endurance performance.
Sources
6 sources, independently verified.
Concurrent vs strength-only training: maximal strength SMD −0.06 (95% CI −0.20 to 0.09, p=0.446), hypertrophy −0.01 (−0.16 to 0.18, p=0.919), explosive strength −0.28 (−0.48 to −0.08, p=0.007). Attenuation larger when both were in the same session (p=0.043) than when separated by ≥3 h (p>0.05). No moderation by cycling vs running, frequency (>5 vs <5 sessions/week), training status (untrained vs active) or age (<40 vs >40). Online 2021.
Lower-body 1RM: untrained ES +0.03 (p=0.87), moderately trained −0.20 (p=0.08), trained −0.35 (p<0.01). In trained individuals the reduction appeared when both modes were in the same session (ES −0.66, p<0.01) but not in separate sessions (−0.10, p=0.55). Abstract read via Europe PMC; metadata via OpenAlex.
Mean ES for strength: strength-only 1.76, concurrent 1.44, endurance-only 0.78; hypertrophy 1.23, 0.85, 0.27; power 0.91, 0.55, 0.11. Combining strength training with running, but not cycling, significantly reduced hypertrophy and strength gains. Endurance frequency (r −0.26 to −0.35) and duration (r −0.29 to −0.75) correlated negatively with hypertrophy, strength and power gains. Running vs cycling inferred across studies, not tested head to head.
Strength-then-endurance order improved lower-body dynamic strength more than the reverse (weighted mean difference 6.91% change, 95% CI 1.96 to 11.87, p=0.006). No effect of order on hypertrophy (1.15%, p=0.40), lower-body static strength (−0.04%, p=0.98), maximal aerobic capacity or other outcomes. Online 2017.
Both groups did heavy strength training twice a week for 12 weeks. Both increased 1RM, thigh muscle CSA and squat jump performance, but relative improvements were greater in the strength-only group; peak rate of force development improved only in the strength-only group. Non-randomised comparison of different populations; abstract read on SPONET, metadata on OpenAlex.
Adding heavy or explosive strength training improves running economy; heavy strength training is recommended for cycling economy; the most compelling evidence for an additive effect on cycling performance comes from heavy strength training. Proposed mechanisms: delayed recruitment of less efficient type II fibres, improved neuromuscular efficiency, IIX-to-IIA fibre conversion and greater musculo-tendinous stiffness. Online 2013; issue 2014;24(4):603–612.