In this episode of the Flex Diet Podcast, I sit down with my friend Kristi Storoschuk, a PhD candidate in exercise physiology, to unpack her review paper on zone 2 cardio and what the evidence actually shows. We dig into what “zone 2” really means (including lactate thresholds and why common proxies like heart rate and the talk test can miss the mark), where the 80/20 endurance model came from, and why messaging around zone 2 for mitochondrial function, fat oxidation, metabolic flexibility, and health may be overstated, especially for the general population.  Kristi explains why higher intensities often produce equal or better mitochondrial and performance-related adaptations, how training volume and population context change the conversation, and where low-intensity work like walking may still fit. Sponsors: Flex 4:  Kristi's Top 4 tips for improving aerobic fitness as a recreational lifter: https://flex-diet.kit.com/17ac1beade Daily Fitness Insider Newsletter: https://flex-diet.kit.com/bfa1510fa8 Coming up: ISSN 2026: https://www.sportsnutritionsociety.org/ Available now: Grab a copy of the Triphasic Training II book I co-wrote with Cal Deitz here. Episode Chapters: 04:04 Why Zone Two Went Viral 09:40 Defining Zone Two Lactate 14:15 Talk Test and Practical Limits 16:43 Does Zone Two Even Matter 21:08 The 80/20 Misapplied 26:14 Origins of Base Training 32:06 Mitochondria Volume vs Intensity 40:08 How Myths Persist Online 44:16 Zone Three Over Zone Two 44:46 Why Some Recover Faster 45:37 Overtraining Study Lessons 49:59 Listen To Output Signals 52:20 How Often To Train 54:42 Short Daily Progressives 57:46 Tabata Reality Check 01:00:19 Walking And Health Outcomes 01:05:23 Mitochondria Versus Performance 01:08:04 Lactate Threshold Beats VO2 01:12:43 Fueling And Final Wrap 01:14:33 Podcast Outro And Disclaimer Flex Diet Podcasts you may enjoy: Episode 360: Exploring Aerobic Development & Concurrent Training with Jason Brown YouTube: https://www.youtube.com/watch?v=lkqim0EDfec&t=4s Episode 269: From Mitochondria to Metabolic Health Insights with PhD Candidate Kristi Storoschuk YouTube: https://www.youtube.com/watch?v=T9EFRluKt6Q Connect with : Instagram: https://www.instagram.com/krististoroschuk/ Website: https://krististoroschuk.com/ Get In Touch with Dr Mike: Instagram: Drmiketnelson YouTube: @flexdietcert Email: Miketnelson.com/contact-us