Concurrent training interference

The interference effect describes the attenuation of resistance-training adaptations - strength, power, and especially hypertrophy - when endurance training is performed concurrently in the same training cycle. The proposed molecular mechanism centres on AMP-activated protein kinase (AMPK), which is activated by endurance exercise and inhibits mTORC1, the master regulator of muscle protein synthesis. Wilson and colleagues' meta-analysis (J Strength Cond Res, 2012) pooled 21 studies and 422 effect sizes: hypertrophy and power were significantly blunted by concurrent endurance, with running producing larger interference than cycling, and longer or more frequent endurance sessions worsening the effect. Strength was less affected. The magnitude is modest, typically around 10-15 percent. Practical mitigations: separate modalities by at least 6-24 hours, cap endurance volume, prefer cycling for lifters, and prioritise the goal-relevant modality first.