Fitness trends come and go, and it can be hard to separate the signal from the noise. Often even when a trend is scientifically sound it can easily become distorted and misinterpreted. Cardiovascular exercise, one of the major pillars of fitness and health, has been subject to frequent misinterpretation or applied/prescribed inappropriately. In general, when we talk about this type of exercise we are discussing improving “aerobic” fitness, but there are many goals that require different levels of aerobic fitness and subsequently different types of training. You don’t train for a marathon the same way you train for an 800-meter race. Training zones are a convenient way to categorize different types of aerobic training based on intensity, physiological responses, and energy systems. The 5 zones are as follows:
Zone 1 (50-60% max heart rate) Very light intensity. Ideal for warming-up, cooling down, and active recovery.
Zone 2 (60-70% max heart rate) “Aerobic” zone. Improves the body’s ability to utilize fat as an energy substrate and clear lactate. This zone is the foundation for cardiovascular fitness, creating adaptations at the cellular level.
Zone 3 (70-80% max heart rate) Moderate intensity.
Zone 4 (80-90% max heart rate) “Anaerobic” or “Threshold” training zone. The body is now using carbohydrates as the primary fuel source because fatty acid oxidation takes too long, and the muscles need fast fuel. HIIT (high intensity interval training) 30-60 sec.
Zone 5 (90-100 max heart rate) Highest intensity. Can only be done in short bursts. All out effort. SIT (sprint interval training) <30 seconds.
What the experts say
Dr. Inigo San Millán, Director of the Exercise Physiology Lab at the University of Colorado School of Medicine, who has published many studies on Zone 2 training, and worked with many professional athletes including cyclists and triathletes, believes that Zone 2 training is essential for building aerobic capacity. His research supports that theory and practically speaking, almost all elite endurance athletes spend 60-75% of their training time in Zone 2. Dr. Peter Atia, author of the national best seller “Outlive”, recommends Zone 2 training as the foundation for cardiovascular health, a key pillar for longevity. The research supports this assertion as countless studies have correlated higher VO2 max with lower mortality.
A deeper dive into Zone 2
Exercise intensity is correlated with the type of fuel source used and the type of muscle fibers that are primarily active. Zone 2 training utilizes more “slow twitch” or type I fibers and uses fat as the primary fuel source. Zone 4 utilizes more “fast twitch” or type II/IIb fibers and uses glucose for energy. Cellularly, zone 2 training promotes lactate clearance and improves fatty acid oxidation. Lactate, which for years was erroneously labeled as bad and blamed for muscle soreness, is actually an alternate fuel source that can be used by the muscle, brain, and heart. Zone 2 increases a transporter called MCT-1 that lives in type I fibers. MCT-1 grabs the lactate and carries it to the mitochondria to be reused as energy. Fatty acid oxidation (beta-oxidation) is a more efficient way of creating energy and it also spares glucose for harder tasks. Therefore, this type of training improves two key mechanisms for aerobic performance.
How do I incorporate this type of training into my workouts?
It’s actually pretty easy to add this type of training in. Zone 2 can be done walking, jogging, cycling, swimming, rowing or on an elliptical. It’s easier to control the intensity on a stationary, indoor piece of cardio equipment because there are no changes in temperature and you are in complete control of the intensity. Ideally, you would like to do two to three 45-minute sessions of Zone 2 training each week (some people recommend more or less). If you don’t have an HR monitor or just don’t care to get that specific, you can gauge the effort by your ability to breathe and talk. You know you are in Zone 2 if you can talk, but it’s somewhat difficult. If you can breathe entirely through your nose without opening your mouth, you are probably closer to zone 1, and conversely if you can’t really get any words out at all, then you’re encroaching on zone 3-4. The only real barrier for most people is time. If you only have 3 days to workout each week for an hour, then it would be difficult to get any other exercise in, including strength training which is also essential. If that is the case, then even doing 1 session of zone 2 per week is better than none. If you have any questions about this or other types of training please contact Blair at bbradshaw@erjcchouston.org.
