Target Heart Rate Zones Explained - How To Use Them Correctly

Zone 1

Zone 1 refers to a target heart rate of 50-60%. As such, it is considered a light exercise that can be comfortably maintained for nearly as long as you like. Due to its low intensity, it will not provide you with the same cardiorespiratory benefits as slightly higher intensity exercises. In most situations, exercises in heart rate zone 1 are used for recovery purposes. 

Zone 2

Although all target heart rate zones are needed in a well-balanced training block, zone 2 should form the core of your overall training program. This refers to a training intensity of 60-70% of your maximum heart rate, which is essential for building a solid base level of fitness to improve upon.

Following multiple studies, trainers and athletes often spend 60-75% of all training time in zone 2 depending on their sport. This is especially important for endurance athletes, who should incorporate three to four zone 2 training days per week during preseason. The closer you get to competitive season, the more you should move from high volume training to more high-intensity training. Similar results have been found in numerous different sports.

Training at zone 2 specifically focuses on utilizing slow-twitch muscle fibers, which stimulates mitochondrial growth and function. Increased mitochondrial content helps your body use fat as a fuel source during longer activities. Increased fat oxidation preserves your muscle’s glycogen stores which can provide a significant performance advantage especially in longer endurance events. After all, the leftover glycogen can be used for your last sprint at the end of a race.

Type I fibers are also responsible for clearing lactate, which are mainly produced by type II with poor oxidative capacity. To prevent a dangerous accumulation of acidity in the muscle, lactate must be delivered to well-oxygenated type I muscle fibers. There, lactate can be transported to the mitochondria where it is used to produce more ATP.

Zone 3

Heart rate zone 3 is performed at a moderate intensity of 70-80% of your maximum heart rate, which can also be seen as a slight increase in blood lactate. Because of this, zone 3 is considered too hard for recovery or building an aerobic base, while also not hard enough to improve lactate tolerance or speed endurance. In fact, there is little benefit from training in heart rate zone 3 when compared to the increased aerobic capacity and fatty acid utilization of zone 2 or the VO2max and lactate threshold improvements of zones 4 and 5. This is why heart rate zone 3 is sometimes called the ”grey zone”.

A common mistake for recreational athletes is to consistently run on zone 3. There are numerous reasons for this. For example, trying to consistently run at your ”average pace” or trying to get the most out of your training when time is of the essence. The best advice we can give is to clearly divide your easy and hard days.

Zone 4

Heart rate zone 4 refers to training at 80-90% of your maximal heart rate, also known as your anaerobic threshold or “threshold pace”. At this intensity, most of the energy is produced anaerobically (without oxygen) from glucose, which also produces lactate at a faster rate than it can be removed. This leads to shortness of breath, a burning sensation in the muscles, and fatigue. 

Consistent training in zone 4 improves your anaerobic capacity (the total amount of energy produced from the anaerobic energy systems) lactate threshold, lactate tolerance, and maximal oxygen uptake (VO₂max). Essentially this means that you are able to produce ATP with oxygen at higher intensities and maintain performance for longer in high-lactate situations. This is especially useful in medium-distance events that rely heavily on speed endurance.

Zone 5

Heart rate zone 5 refers to all-out efforts at 90-100% of your maximum heart rate. Because of this, most people are only able to maintain this intensity for less than a minute. This makes it suitable for only a few different sports, such as a 100m or 400m sprints.

Zone 5 relies on two energy systems to produce ATP; the ATP-phosphocreatine system (ATP-PC) and anaerobic glycolysis. The ATP-PC system uses stored ATP and creatine phosphate for immediate energy production. However, these stores are fully used up in as little as 10-30 seconds. After this, anaerobic glycolysis starts taking over as the main energy system. 

These training sessions are often reserved for athletes and very fit individuals who want to improve their speed or speed endurance in quick, very intense bursts of exercise. High-intensity interval training (HIIT) is one example of this type of exercise.

Final thoughts

As you can see, all target heart rate zones have their own specific physiological effects and training implications. Being able to utilize them in the best way possible can provide you with significant improvements in performance.

Heart rate zones can be used in a wide variety of endurance activities such as running, rowing, cycling, and cross-country skiing. For swimming however, it is important to remember that heart rate is approximately 10-15 bpm lower in the water than on land. This is due to hydrostatic pressure that increases the amount of blood that is pumped to the extremities. Thus, heart rate zones should be adjusted accordingly.

In addition to using your maximum heart rate to gauge training intensity, some people also use perceived effort or a threshold-based percentages to determine optimal training effort. Whichever method you end up using, it is important to choose the right zone for your own goals. This will lead to consistent progression in your performance. 

Did you learn anything new about heart rate zones? Let us know in the comments.