How long should Zone 2 runs be?

Zone 2 runs need to be long enough to generate a meaningful aerobic stimulus, which generally means at least 45 minutes and ideally 60 to 90 minutes or more. Shorter sessions do not give mitochondria enough time to adapt. Elite athletes and serious amateurs often spend 70 to 80 percent of their total weekly training volume in Zone 2, spread across multiple sessions. If you are new to structured training, two 60-minute Zone 2 runs per week is a solid starting point. As your aerobic fitness improves, you can extend individual sessions or add a third weekly run before increasing intensity elsewhere.