Zone 2 cardio training  is often overlooked as a modality of training best for endurance athletes, but it has enormous benefits for anyone, regardless of their fitness level or goals.

With Zone 2 training you will build your aerobic base, enhancing your endurance, and optimize your fitness. Training in this zone makes oxygen the primary driver of energy production, in turn increasing aerobic capacity. Zone 2 training not only increases the number of your mitochondria, but improves their efficiency as well. The more you exercise in Zone 2, the better your body gets at burning fat for energy. 

Zone 2 training also helps you improve your body’s energy efficiency, prevent injury, improve recovery, and is quite helpful with weight management. It improves heart rate variability (HRV) and resting heart rate (RHR). It increases HRV over time by decreasing the sympathetic response, and increases parasympathetic activation.

Why not Zone 3? Training in Zone 3 can be detrimental to your fitness goals. Zone 3 training is above aerobic pace and has some lactate response, which means that it isn’t hard enough to elicit a desirable physical adaptation, and yet it’s too hard to allow for day-to-day recovery.

When easy runs are run in heart rate Zone 3, your body is having to work too hard, and you are not actually facilitating any type of recovery. In contrast, you are further stressing the body and digging yourself into a deeper hole in terms of how much recovery will be needed to get yourself back to 100% for your next hard workout.

In summary, Zone 3 training can lead to overtraining, injury, and burnout. It is important to balance your training intensity and volume to avoid the negative effects of Zone 3 training.