- Aug 15, 2018
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I've been seeing more people add steady Zone 2 work for heart health and recovery, then immediately worry that it's going to wreck their squat and bench gains. The classic interference story is still floating around, so it's worth looking at what the bigger analyses actually found.
The most comprehensive recent look is the 2021/2022 meta-analysis by Schumann and colleagues in Sports Medicine. They pooled 43 studies and found essentially no difference in maximal strength (standardised mean difference −0.06) or whole-muscle hypertrophy (−0.01) when people combined aerobic and strength training versus strength training alone. Explosive strength took a small hit (SMD −0.28), and that penalty was larger when the two sessions were done in the same workout rather than separated by a few hours. Type of aerobic work (running versus cycling), frequency, age, and training status didn't meaningfully change the strength or hypertrophy outcomes in their analysis.
A follow-up by Lundberg and colleagues in Sports Medicine in 2022 looked specifically at muscle-fibre hypertrophy and found a small overall negative effect (SMD −0.23). It was more noticeable for type I fibres when the cardio was running rather than cycling. Whole-muscle measures still largely held up. Other reviews (including work summarised by Barbell Medicine and Stronger by Science) line up with the idea that any interference is modest, mostly limited to power, and easiest to avoid by keeping total volume recoverable and separating hard sessions when possible.
In short, moderate Zone 2 doesn't appear to cancel strength or size gains for most people. The bigger risks seem to be doing a lot of high-intensity intervals right before or after lifting, or simply accumulating so much total work that recovery suffers. Separating the sessions by at least a few hours, or doing the Zone 2 on easy days, keeps the downside small according to the data we have.
Are you running any Zone 2 right now, and if so are you doing it the same day as lifting or on separate days? Have you noticed any difference in how your strength work progresses compared with periods when you only lifted?
The most comprehensive recent look is the 2021/2022 meta-analysis by Schumann and colleagues in Sports Medicine. They pooled 43 studies and found essentially no difference in maximal strength (standardised mean difference −0.06) or whole-muscle hypertrophy (−0.01) when people combined aerobic and strength training versus strength training alone. Explosive strength took a small hit (SMD −0.28), and that penalty was larger when the two sessions were done in the same workout rather than separated by a few hours. Type of aerobic work (running versus cycling), frequency, age, and training status didn't meaningfully change the strength or hypertrophy outcomes in their analysis.
A follow-up by Lundberg and colleagues in Sports Medicine in 2022 looked specifically at muscle-fibre hypertrophy and found a small overall negative effect (SMD −0.23). It was more noticeable for type I fibres when the cardio was running rather than cycling. Whole-muscle measures still largely held up. Other reviews (including work summarised by Barbell Medicine and Stronger by Science) line up with the idea that any interference is modest, mostly limited to power, and easiest to avoid by keeping total volume recoverable and separating hard sessions when possible.
In short, moderate Zone 2 doesn't appear to cancel strength or size gains for most people. The bigger risks seem to be doing a lot of high-intensity intervals right before or after lifting, or simply accumulating so much total work that recovery suffers. Separating the sessions by at least a few hours, or doing the Zone 2 on easy days, keeps the downside small according to the data we have.
Are you running any Zone 2 right now, and if so are you doing it the same day as lifting or on separate days? Have you noticed any difference in how your strength work progresses compared with periods when you only lifted?