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Kristi L. Storoschuk, Andres Moran-MacDonald, Martin J. Gibala | Sports Medicine | (2025)
Key Takeaways
Plain English Takeaway
Working out at a moderate pace is not the best way to improve your heart health or how your body uses energy. Exercising harder, even for less time, can give better results.
Study Aim
The paper aims to evaluate whether Zone 2 training (exercise at a moderate intensity just below the lactate threshold, where the body can still clear lactic acid efficiently) is the most effective way to improve mitochondrial capacity (the ability of cells to produce energy) and cardiorespiratory fitness (how well the heart and lungs supply oxygen during exercise) in the general population.
Simply put: The study asks if working out at a steady, moderate pace is the best way to boost energy use and heart health.
Study Design
This research is a narrative review, meaning the authors analyzed and summarized existing studies on Zone 2 training. They compared the effects of Zone 2 exercise with higher-intensity workouts, focusing on outcomes like mitochondrial function, fat burning, and overall heart and lung fitness. The review included studies from the general population, not just athletes.
Simply put: The authors looked at many past studies to see if moderate exercise is better than harder workouts for most people.
Findings
The review demonstrates that current evidence does not support Zone 2 training as the best way to improve mitochondrial capacity or the body's ability to burn fat. The authors argue that higher-intensity exercise, even if done for shorter periods, is more effective for improving heart health and energy use, especially when people have limited time to exercise. They recommend prioritizing higher-intensity workouts over moderate, steady-state exercise to maximize health benefits.
Simply put: The study found that harder workouts are better than moderate ones for getting fitter and healthier, especially if you don't have much time.
Abstract
No abstract available
Referenced In
May 23, 2026 10:34 AM
The other point the study highlights is 'what exactly does zone 2 mean?'. It seems the technical definition is:
"Zone 2 corresponds to exercise below the first lactate threshold, i.e., a blood lactate concentration below ~2.0 mmol/L"
(according to the sci-sports article summary)
And this corresponds to a certain heart rate threshold ("zone 2"). So I imagine heart rate would be a good proxy.
But I've also heard "easy runs, can hold a conversation" (especially by the hardcore runners) and "rate of perceived effort" being used as measures.
I personally use zone 2 heart rate as a guide.
I imagine they're all more or less the same for practical purposes, but would be interesting to learn more.
Hm interesting! This is the study reviewed in the article. Key takeaway makes sense:
Most of the "influencer" stuff I see, I think, is targeted at people who aim to be semi-intense i.e. combine "hard runs" with "easy runs" (which more or less means zone 2).