Slowing things down to train in zone 2 will benefit your cardiovascular system, mitochondrial health, mood, and more. Here’s a primer on why zone 2 is so beneficial and how to incorporate it into your training—whether you’re an elite athlete or an occasional fitness class junkie. Typically, Niren explains, your heart rate can be divided into the following five zones. These are also the zones that most fitness companies like Polar, MyZone, and Garmin use to program their devices: So to determine whether you’re in zone 2, you can go off perceived exertion or calculate your maximum heart rate and work backward from there. With that said, a 2020 JMIR Health study found that devices like MiBand and Garmin “generally produce accurate heart rate readings” compared to the Polar H7 chest strap, so it’s largely a matter of preference. Once you’ve got your heart rate measuring device, you can identify your MHR using a field test—a practical way to perform an all-out, maximal-endurance effort that will get you to your highest possible heart rate. Lazauskas says that depending on your fitness level, the Cooper Run Test (run as far as you can in 12 minutes), the George Jog Test (a shorter jog), and the Rockport Walk Test (walk as fast as you can for 1 mile) are “great MHR field tests due to their minimal use of equipment.” Most doctors will tell you that your maximum heart rate is found using the equation: 220 - your age = MHR. So, the average 30-year-old would have an MHR of 190 beats per minute (BPM). However, a newer formula used among trainers is 208 - (0.7 x your age) = MHR This would put a 30-year-old at a MHR of 187. A recent study of recreational marathon runners3 compared both of these equations to the Polar chest strap and found that, for women, both equations overestimate MHR by about 5 BPM. For men, the 220 - age equation underestimates MHR by about 3 BPM, but the 208 - 70% of age equation is similar to the chest strap. The heart is our main pumping mechanism, circulating oxygenated blood throughout the body to the working tissues. As the body begins to exercise, the heart must pump more blood to meet this increased demand. Stroke volume is the volume of blood being pumped out with each beat. The heart pumps out approximately 70 ml of blood each beat. Stroke volume and heart rate together determine cardiac output, which is the volume of blood being pumped through the heart in a given time. The training effect of zone 2 is that stroke volume increases while exercise heart rate decreases, signaling greater cardiorespiratory endurance. That’s the long-term magic of taking things slow in your training. “Zone 2 cardio makes your heart stronger, and it will require fewer pumps to pump blood, making it more efficient,” says Niren. “Your body also expands its vascular system, better enabling it to deliver oxygenated blood to different parts of the body.” VO2 max is the greatest rate at which oxygen can be taken in and used during exercise. Normal VO2 max for most college athletes would be 45 to 60 mL/kg/min whereas a world-class marathon runner would be 70 to 80 mL/kg/min. “Zone 2 is the level at which you’re stimulating your mitochondria the most to create ATP,” says Niren. “Zone 2 training improves mitochondrial efficiency since the more you train in this zone, the better your body gets at burning fat for energy.” “The minimum effective dose of zone 2 cardio to get the mitochondrial benefits seems to be 45 minutes,” says Niren. She recommends 80% of all cardiovascular exercise to be in zone 2, with a small amount of high-intensity interval training thrown in, maybe one session per week. Though, Lazauskas says, there is no clear consensus on the amount of time one should spend on one zone versus the others. Everyone is different, so find what works for you. It’s worth noting that chronic zone 2 training without resistance exercise can lead to muscle loss7. This is why variety in training is essential for people looking to maintain strength and muscle mass too. Check out this guide to resistance training to get started. “To make my zone 2 cardio something I look forward to rather than avoid, I watch movies and TV shows while I work out,” Niren adds. Here are some light cardio workouts that can help you get into zone 2 and reap all the benefits of staying there: A former editor of Muscle & Fitness, Barroso earned a B.A. in Journalism/Professional Writing from The College of New Jersey and has been featured in several health and fitness publications as both an author and expert. Barroso would eventually trade editing in a cubicle for training clients at gyms including Snap Fitness, 24 Hour Fitness and Blink Fitness. Most recently, Barroso earned his Master of Science in Athletic Training at Montclair State University and looks to continue his career in Sports Medicine.
