The Vitality Collective Podcast is a health and fitness podcast focused on strength, longevity, and real-world performance, bridging the gap between health and performance. Hosted by Dr. Jeremy Bettle, PhD—an internationally recognized expert in Human Performance with over 20 years of experience working with elite athletes and high performers—this podcast brings world-class expertise straight to you. Built from elite sport and applied to real life, it breaks down what actually drives resilience, health, performance, and long-term capability. Designed for high performers, professionals, and anyone who wants to stay strong, capable, and injury-free while balancing real life. This health and wellness podcast explores how to build strength, prevent injury, improve cardiovascular fitness, optimize sleep and nutrition, support cognitive performance and brain health, and maintain emotional and social well-being through expert interviews, applied breakdowns, and proactive, real-world strategies. Whether you're training, recovering from injury, or trying to stay consistent while balancing work, family, and life, this podcast gives you a clear, practical path forward. Most people treat cardio and strength training as competing priorities. This episode makes the case that they are the same investment.This episode with Dr. Mike Axler, who holds a PhD in Kinesiology and Applied Physiology and has completed nearly 70 marathons while building a research career in cardiovascular health, breaks down why the aerobic system is not optional for anyone who wants to stay strong, move well, and avoid the slow decline that passes for normal aging.If you have been asking yourself whether you actually need cardio if you already lift, this is the episode for you. What's inside: How the three energy systems work in sequence during any exercise -- and why what happens during your rest intervals matters more than most people realize Why building mitochondrial density through cardio makes you recover faster between strength sets, not just between running workouts The difference between burning fat and burning carbohydrates during exercise -- and why aerobically trained athletes can keep going long after glycogen-dependent athletes hit the wall Why zone two training is not just for endurance athletes: how it strengthens left ventricular contraction and reduces resting heart rate over time, with implications for decades of cardiovascular health If you are a strength-focused athlete, a recreational lifter, or someone who has written off cardio as unnecessary, this episode will help you understand exactly what your aerobic system is doing for you and give you a practical place to start. Listen to the full episode of The Vitality Collective Podcast with Dr. Jeremy Bettle. Guest Bio Dr. Mike Axler is an Assistant Professor of Exercise Science with a PhD in Kinesiology and Applied Physiology. He brings a unique blend of academic expertise and real-world performance experience, having worked as a Division I strength and conditioning coach while also competing in nearly 70 marathons and 20 ultramarathons. Mike is the founder of Axler Concierge Coaching and the host of the Simple Science Podcast, where he breaks down complex topics in exercise, nutrition, and human performance into practical, actionable insights. His research focuses on nutritional epidemiology and applied physiology, with ongoing collaborations spanning wearable technology companies and clinical settings. Driven by both curiosity and personal challenge, he is currently pursuing the goal of running marathons in all 50 U.S. states and on every continent. Links Simple Science Podcast: YouTube Spotify Instagram: @mikeaxler.phd Three Actionable Takeaways Do something physically challenging today that is slightly harder than yesterday. It does not have to be dramatic. If you walked 4,000 steps yesterday, walk 4,050 today. If you ran a six-minute mile, try for 5:59. Progress is the direction, not the distance. Challenge your mind with something new and unfamiliar every day. Ask an AI for a random fact, learn how to say a word in another language, or try a physical skill you have not done before. Neuroplasticity requires novelty and effort. Every time you sit down to eat, put a protein source and a fruit or vegetable on your plate alongside whatever else you are having. You do not have to overhaul your diet. Just anchor every meal to those two things. Key Insights The ATP-PC (phospholytic) system powers the first roughly 10 seconds of any maximal effort. After that, the glycolytic system takes over. The aerobic system becomes dominant when intensity drops to a level the body can sustain -- and it is the only system that runs on stored fat. Aerobic training builds mitochondrial density and capillary density inside muscle fibers. More and healthier mitochondria mean faster ATP regeneration during rest intervals, which translates directly to shorter recovery time between strength sets. Cardiac output equals heart rate multiplied by stroke volume. Consistent zone two training increases left ventricular stroke volume, meaning the heart pumps more blood per beat and does not need to beat as fast. A lower resting heart rate is evidence of this adaptation -- and it compounds over decades. During aerobic exercise, the body draws on both stored glycogen and stored triglycerides (fat). During anaerobic exercise, it burns only carbohydrates. Because the body carries a finite supply of glycogen and a very large supply of stored fat, aerobic efficiency is the key variable that determines how long someone can sustain meaningful output. BDNF (brain-derived neurotrophic factor) rises with cardiovascular exercise and remains elevated for days after consistent training. It correlates with increased neuronal growth, protection of existing neurons, and improved mood. The effects of BDNF outlast the post-workout endorphin window by a significant margin. Exercise-induced neuroplasticity helps build redundancy in the brain. Research on aging populations suggests that high cognitive and physical engagement can allow people to maintain strong cognitive function even when early markers of neurodegeneration are present in brain tissue. Running is approximately 1,000 single-leg plyometric impacts per mile, each generating three to six times body weight through the kinetic chain. Endurance athletes who skip strength training -- particularly ankle, knee, and hip stability work -- are systematically underprepared for that load and set themselves up for overuse injury. Hybrid and concurrent training is gaining traction precisely because high-level athletes in events like HYROX and CrossFit are demonstrating that building aerobic capacity does not require sacrificing lean mass or power output. The old tradeoff framework is eroding in practice. Injury is not just a performance setback. A single significant injury can produce a stepwise decline across all physical capacities -- muscle mass, bone density, cardiovascular fitness -- that takes months to recover and, in older adults, may never fully reverse. Avoiding injury is itself a longevity strategy. The principle of progressive overload applies identically to the cardiovascular system and the musculoskeletal system. Applying consistent, incremental stress to the aerobic system creates structural adaptations -- stronger heart muscle, more mitochondria, denser capillary networks -- just as progressive loading creates stronger muscles and denser bones.