What is the interference effect in concurrent training?

• A. Concurrent endurance and strength training can attenuate maximal gains in either modality due to competing signaling pathways.
• B. Endurance training does not affect strength gains.
• C. Strength training inhibits endurance completely.
• D. There is no interference between modalities.

Answer: (A)

When you train endurance and strength together, the body faces competing demands for adaptation. Endurance exercise activates signaling like AMPK and PGC-1α, which promote mitochondrial biogenesis and oxidative capacity. These endurance-driven signals can dampen the mTOR pathway and the muscle-protein-synthesis processes that drive hypertrophy from resistance training. Because these pathways can antagonize each other, the maximal gains you could achieve from either modality in isolation are often attenuated when both are trained concurrently. This doesn’t mean you can’t improve in both areas, but the peak improvements tend to be smaller unless programming carefully manages volume, intensity, and recovery. Endurance doesn’t leave strength gains completely untouched, nor does strength completely erase endurance adaptations, and the idea that there’s no interference contradicts a substantial body of evidence showing concurrent training effects.