Continuous training and high-intensity interval training (HIIT) could not be more different, and yet they both use cardio to improve endurance performance. Continuous training involves semi-intense, longer-duration workouts below the lactic (anaerobic) threshold (typically 60-75% VO2 Max), while HIIT involves shorter, highly-intense (approximately 90-100% VO2 Max) durations of faster, harder exercise. Many fitness experts and some scientists are now beginning to argue against the traditional view that continuous training alone is the best way to improve endurance performance, now recognizing that HIIT is also a critical aspect of the mix.

It’s often said that athletes who only work with continuous training stop seeing results after some time. Once they hit this “wall,” athletes can train for many hours each week without observing any changes to their performance levels. This is because metabolism gradually adjusts to the lower-intensity exercise and does not increase the caloric burn rate, explains Simply Shredded.

Additionally, when practiced without some form of strength-enhancing exercise such as HIIT, continuous training can often lead to muscle loss. According to Jamcore Training, high-intensity interval training builds muscle, as the workouts focus on muscle fibers that use anaerobic energy and are not used in continuous training.

Ironically, the shorter but more intense nature of HIIT workouts are useful for elite athletes trying to boost their endurance performance as well as recreational athletes with less time to exercise.

These points may lead the reader to the conclusion that continuous training is therefore unimportant; this is far from the case. While HIIT can be a very efficient way to achieve peak performance levels, it is not possible to exercise at high intensities with any kind of frequency. Practiced alone, HIIT can be too exhausting and eventually begin to negatively impact endurance performance or lead to injury.

In fact, the latest research suggests that HIIT can be most effective when it is performed as little as 1-2 times per week.

Continuous training below lactate threshold not only provides athletes with an easier workout on days between HIIT workouts, it also helps to build the aerobically-used muscles that are essential to improving endurance performance.

A balance of both continuous training and HIIT should therefore be practiced, with the balance of time spent on the former.