High Intensity Interval Training (HIIT)–alternating between periods of higher and lower intensity exertion during a workout–yields significant health benefits over and above those obtained by exercising at a steady level. Studies comparing the two regimens have repeatedly demonstrated the superiority of HIIT with respect to key cardiovascular parameters, muscular uptake of oxygen, and even insulin sensitivity (diabetes and pre-diabetes). And the bonus: HIIT achieves these benefits with less time than traditional, continuous exercise, making it a more efficient method of exercise. In other words, cramming more workout into less time can have big payoffs if intervals are used.
Don’t let the hard-core name intimidate you.”High intensity” merely refers to a level of exercise which raises your heart rate to at least 80% of your maximal heart rate…whatever your personal maximum heart rate might be [208- (0.7 x age) is the most accurate formula to determine that]. So, what constitutes high intensity exercise for a 24 year old, professional tennis player will be different than for a 64 year old professional couch potato. However they can both reap similar health improvements by alternating low intensity exercise with their respective high intensity zones.
High/low intervals should generally be done in a 1:2-ish ratio. So a typical cycle would include anywhere from 15 seconds to 4 minutes of high intensity followed by a period of low intensity lasting up to twice that long. And you would simply repeat that cycle throughout your workout.
Functional Health workouts are a natural fit for HIIT since they mix more intense whole body movements together with less-rigorous-but-still-demanding core exercises like planks, bridges, and swiss ball work. Done properly, (brief!) rest periods and regular transition times between the various exercises also allow for fluctuations in heart rate without dropping it all the way back to baseline.
TIP: For greater general, cardiovascular, and Functional Health benefits, use High Intensity Interval Training.