Zone 2 Cardio: The Aerobic Workout Everyone Should Be Doing Zone 2 cardio puts the “steady” in “steady-state cardio.” It’s not flashy like high-intensity interval training (HIIT) or dramatic like bonking, yet it deserves just as much attention. Zone 2 cardio is foundational to any fitness routine, whether you’re an endurance athlete who wants to improve their performance or someone who just wants to be a healthy, functional human. So, if you’ve noticed a “trend” around this type of exercise, know this: Low-intensity, steady-state cardio (LISS cardio) has always been around. And if, until now, it hasn’t been part of your exercise routine, it’s time to change that. What Is Zone 2 Cardio? Zone 2 cardio refers to a specific exercise intensity that you can sustain for an extended period, during which your heart rate is about 60 to 70 percent of your max heart rate. (Your max heart rate is the number of times your heart beats in a minute during an all-out effort, like sprinting the final stretch of a 5K. More on how to determine your max heart rate later.) In this zone, you may be slightly breathy, but you’re not gasping for air. There are five heart rate zones, each of which has a target range based on a percentage of your max heart rate (MHR). Below is a general breakdown of heart rate zones, but note that these numbers are estimates and may differ according to your source and from one person to the next. Zone Intensity % of MHR Zone 1 Low–moderate 50%–60% Zone 2 Moderate 60%–70% Zone 3 Moderate–high 70%–80% Zone 4 High 80%–90% Zone 5 Very high 90%–100% Zone 2 Cardio Benefits Like any form of cardio exercise, zone 2 cardio can bolster heart health and reduce the risk of cardiovascular disease. And because it burns calories, steady-state cardio is an effective tool for weight loss and healthy weight management. Zone 2 cardio (and movement, in general) can also positively impact your mood and mental health and improve the quality of your sleep. But cardio that specifically keeps your heart within the zone 2 range also offers some unique benefits, especially for endurance athletes who want to improve their performance. Here are a few: 1. More mitochondria If it’s been a while since you took a biology class, here’s a quick refresher on what mitochondria are and why they’re critical to athletic performance: Mitochondria are a type of organelle found in the body’s cells that use oxygen to produce adenosine triphosphate (ATP), the primary source of energy that fuels physical activity as well as basic biological functions. More mitochondria means more ATP and, therefore, more energy for physical activity. Todd Buckingham, Ph.D. Exercise Physiologist at PTSportsPRO in Grand Rapids, Michigan, explains that zone 2 cardio is “ideal for mitochondria development.” Working out at a sustainable intensity for a longer duration increases your cells’ demand for energy, and the body adapts to this demand by producing more mitochondria. So, for athletes who want to up their endurance (or just feel better during and after a workout), zone 2 cardio is essential. 2. Capillary development Capillaries are small blood vessels that deliver oxygen-rich blood to the muscle cells, where the oxygen is used to manufacture energy by the mitochondria. According to Buckingham, optimal capillary development occurs squarely in zone 2, between 60 and 70 percent of your max heart rate. A more robust network of capillaries allows your body to put more available oxygen to good use during exercise. 3. Longevity Even if you’re not looking to set any new PRs, zone 2 cardio can enhance your everyday life by simply extending it. “Zone 1 and zone 2 exercise has been shown to increase life expectancy,” Buckingham says. “It helps increase your VO2 max, and there’s a direct relationship between your VO2 max and your longevity.” VO2 max is a cardiorespiratory fitness metric that scores how efficiently your body uses oxygen. (The link between VO2 Max and zone 2 cardio makes sense, considering what we know about capillaries and mitochondria.) The number measures milliliters of oxygen per kilogram of body weight per minute (ml/kg/min). 4. Requires less recovery HIIT is popular for multiple reasons: It’s fast, efficient, fun (depending on who you talk to), and offers plenty of its own unique benefits. That said, high-intensity exercise requires more recovery than low or moderate-intensity exercise, and doing too much of it can even negatively impact your health. Because it’s less intense, zone 2 cardio requires less recovery time, which makes it easier to remain consistent with your fitness routine and stay active between workouts. (If you’ve ever been too sore to function after a HIIT session, you get it.) Additionally, steady-state cardio is generally accessible to more people, including those new to fitness, individuals with injuries or mobility issues, and older adults. When Not to Use Zone 2 Cardio While almost anyone will, from a health perspective, benefit from incorporating LISS into their workout routine, focusing on zone 2 cardio won’t help you achieve certain performance goals. If you’re concerned with developing explosiveness and power — maybe you’re a sprinter, a high jumper, or a baseball player — zone 2 cardio should not be your primary focus. Instead, you should prioritize short bouts of intense movement. How Often and Long Do You Need to Train in Zone 2? Along with two days of muscle-strengthening exercise, the Centers for Disease Control recommends the following weekly guidelines for aerobic activity: 150 minutes of moderate-intensity activity (a.k.a. zone 2 cardio) 75 minutes of vigorous-intensity activity An equivalent combination of moderate- and vigorous-intensity activity However, your training should align with your goals, fitness level, and lifestyle. For example, an avid runner training for a marathon needs to log more zone 2 cardio per week than a time-pressed parent who’s just beginning to exercise for the first time. That time can be distributed throughout the week (e.g., five 30-minute workouts) and even throughout the day with exercise “snacks.” For example,
