Zone 2 Heart Rate Training

The second heart rate training zone, often referred to as the “gold zone” or the foundation of all endurance training, is Zone 2. Many argue that this zone makes up most of one’s training—up to 80 or even 90 percent of the total volume—but why is this zone so important?

This zone is determined by heart rate, roughly between 60% and 70% of your maximum heart rate (see the first blog post in this series). It’s more intense than Zone 1 (see the second blog post), but still relatively easy. You can also judge if you're in Zone 2 using the “talk test”: you should be able to speak short, complete sentences without gasping or struggling to breathe. Monitoring heart rate with an external monitor and using the “talk test,” which typically corresponds to RPE (rate of perceived exertion) 2-3 on a 10-point scale, indicates a light effort and means you are training the right metabolic pathways and systems.

The physiological changes in this zone mirror those in Zone 1—such as increased mitochondrial size and number, higher capillary density, and overall cardiovascular improvements. However, Zone 2 specifically trains the oxidative phosphorylation pathway in a way that favors developing an aerobic base, promoting fat oxidation (using fat as fuel) and reducing dependence on carbohydrates as heart rate and workload increase. This zone is ideal for building a base and developing long-duration endurance.

How often you train in Zone 2 depends on your fitness and goals, but it is typically recommended to do it 3-4 times a week for 30-60 minutes. Activities include brisk walking, jogging, cycling, and swimming. Even if your main focus is on one discipline, training in other disciplines within the same zone, known as “cross-training,” provides similar cardiovascular benefits. Different activities add variety, and some, like swimming, may have a less significant impact on your body compared to running, aiding recovery after intense sessions. The key is to stay in the correct zone and avoid slipping into Zone 3 when your goal is Zone 2.

Is Zone 2 the “gold standard”? That depends on your perspective, but it certainly has its place and should constitute a significant portion of your training volume. While it won’t make you faster directly, it enhances your body’s ability to utilize fats for energy, reducing reliance on carbohydrates—a critical factor for endurance events such as half and full marathons. Training in this zone also reduces stress on the cardiovascular and central nervous systems, allowing consistent training without negatively affecting future threshold, tempo, and VO2max sessions, which are essential for improving speed.

- PRC Founder, William C. Howerton, M.S. Exercise Science