What this means in real training
Why the claim sounds convincing
Direct conflict between traditional strength training and endurance participation.
The mistake is turning a possible mechanism, average association, or useful option into a universal rule.
What the evidence supports
No. Well-programmed strength training can support running economy and performance without automatically creating excessive bulk. The relevant evidence needs to match the exact population, intervention, comparison, and real-world outcome instead of borrowing certainty from a mechanism, acute response, or marketing label.
What do running economy, performance, body mass, fatigue, and concurrent-programming outcomes show?
Mechanisms, short-term measurements, and anecdotes can explain interest, but they do not automatically establish long-term benefit or safety.
The useful verdict depends on dose, training status, baseline habits, adherence, and whether the measured outcome matches the promise.
How to use the answer
Keep strength work progressive but recoverable, and place demanding lifting so it does not sabotage key running sessions.
Study populations, protocols, outcome definitions, and follow-up periods vary.
Averages do not guarantee the same response for an individual reader.
Pain, illness, pregnancy, medication use, or medical exercise restrictions can change the practical decision.