Most field-sport athletes need both qualities at once. A midfielder needs the aerobic base to cover ground for ninety minutes and the strength and power to win a duel or accelerate away from one. Training both in the same phase, sometimes the same week, sometimes the same session, is not optional. The question research has spent four decades on is whether doing so quietly caps what either quality can become.
The Original Finding
Hickson (1980) ran the study that started the conversation. Athletes trained strength alone, endurance alone, or both together for ten weeks. Endurance-only and concurrent groups improved aerobic capacity similarly. Strength told a different story. The strength-only group kept gaining through all ten weeks. The concurrent group’s strength gains plateaued around week seven, then declined. Training volume for strength was matched between groups the whole time.
This became known as the interference effect. Endurance training blunts strength and power adaptations when trained alongside it. There’s no matching disruption running the other direction.
Why It Happens
The mechanism sits at the level of cell signaling. Resistance training activates a pathway centered on mTOR, which drives muscle protein synthesis and hypertrophy. Endurance training activates AMPK, which drives mitochondrial biogenesis. Atherton and colleagues (2005) showed these pathways don’t just run in parallel. AMPK activation actively suppresses mTOR signaling.
Train endurance close to a strength session, and the AMPK signal from the aerobic work can blunt the mTOR-driven adaptation. The interference isn’t just competing recovery demand. It runs at the molecular level, inside the same muscle fibers.
Fyfe, Bishop, and Stepto’s 2014 review found the effect isn’t uniform. It depends on endurance volume, modality, and how close in time it sits to the strength session.
Not All Endurance Training Interferes Equally
Wilson and colleagues’ 2012 meta-analysis pooled data across dozens of studies. Running interfered with strength and hypertrophy gains more than cycling did. The likely reason is mechanical, not just metabolic. Running involves a large eccentric loading component that adds muscle damage on top of the signaling conflict. Cycling is largely concentric, producing less of that damage while still delivering an aerobic effect.
Volume and frequency matter too. Low-to-moderate endurance volume shows a smaller interference effect than high-volume, high-frequency conditioning layered on top of a full strength block. The interference effect scales with how much aerobic stress gets added, not just whether any is present.
Managing the Interference, Not Eliminating It
The interference effect is real, but it is not large enough to justify dropping either quality for most field-sport athletes. What the research supports is management, not avoidance.
Session order and spacing help. Robineau and colleagues (2016) found that separating endurance and strength sessions by several hours reduced the interference measured in subsequent adaptation, compared to running them back to back. Same-day training with a real gap outperformed same-session combination.
Strength before endurance, when both happen close together, protects the quality most sensitive to residual fatigue. Choosing lower-eccentric-load modalities, cycling or rowing over running where sport demands allow it, reduces the mechanical contribution to interference. Matching total endurance volume to what the sport genuinely requires, rather than adding conditioning by habit, keeps the AMPK signal from running higher than necessary.
None of these fully remove the effect. Coffey and Hawley’s 2017 review is direct: concurrent training produces smaller strength and hypertrophy gains than resistance training alone, under controlled conditions. For a field-sport athlete, dropping the aerobic base to protect strength gains usually costs more than the interference does.
The Planning Implication
Interference is not constant across a training year. A general prep phase, where near-term strength gains matter less, can tolerate more endurance volume. A max-strength or power phase needs tightly managed endurance volume and careful session spacing, protecting the quality that phase exists to build.
Treating concurrent training as a fixed daily habit, rather than a variable to periodize, is where most avoidable interference comes from. The fix isn’t choosing one quality over the other. It’s sequencing when each gets priority.
Related reading: Deload weeks: why less load can build more strength and Tapering and muscle fibers: what changes before competition.
References
Hickson RC. Interference of strength development by simultaneously training for strength and endurance. Eur J Appl Physiol Occup Physiol. 1980;45(2-3):255-263. DOI: 10.1007/BF00421333. PMID: 7193134
Wilson JM, Marin PJ, Rhea MR, Wilson SM, Loenneke JP, Anderson JC. Concurrent training: a meta-analysis examining interference of aerobic and resistance exercise. J Strength Cond Res. 2012;26(8):2293-2307. DOI: 10.1519/JSC.0b013e31823a3e2d. PMID: 22002517
Fyfe JJ, Bishop DJ, Stepto NK. Interference between concurrent resistance and endurance exercise: molecular bases and the role of individual training variables. Sports Med. 2014;44(6):743-762. DOI: 10.1007/s40279-014-0162-1. PMID: 24549477
Atherton PJ, Babraj J, Smith K, Singh J, Rennie MJ, Wackerhage H. Selective activation of AMPK-PGC-1alpha or PKB-TSC2-mTOR signaling can explain specific adaptive responses to endurance or resistance training-like electrical muscle stimulation. FASEB J. 2005;19(7):786-788. DOI: 10.1096/fj.04-2179fje. PMID: 15716393
Coffey VG, Hawley JA. Concurrent exercise training: do opposites distract? J Physiol. 2017;595(9):2883-2896. DOI: 10.1113/JP272270. PMID: 27581628
Robineau J, Babault N, Piscione J, Lacome M, Bigard AX. Specific training effects of concurrent aerobic and strength exercises depend on recovery time. J Strength Cond Res. 2016;30(3):672-683. DOI: 10.1519/JSC.0000000000000798. PMID: 25546449
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