High-intensity interval training (HIIT) is not only effective for burning calories, but it can also help improve aerobic capacity. At higher intensities, the body will use ATP from anaerobic sources, but will rely on aerobic metabolism during the lower-intensity recovery intervals to help replace the energy spent during the high-intensity work periods. The downside is that while HIIT is effective, too much of it could cause overtraining. For best results, limit your clients to no more than three HIIT workouts per week.
Low-intensity steady state (LISS) training, also known as long slow distance (LSD) training, is the ability to maintain a steady work-rate over an extended period of time. LISS relies on aerobic energy pathways for energy and can supply fuel muscle activity for extended durations like endurance races. Compared to HIIT, LISS is a lower-stress way to improve aerobic capacity, but it is not as effective for burning calories (for a specific comparison between HIIT and LISS, click here). The upside, however, is that LIIS can be performed almost every day, especially for those who can walk or ride a bike to work.