High Intensity Interval Training (HIIT), and other acronyms/names for interval workouts (tabatas, anyone?), have become de rigueur among fitness enthusiasts and trainers lately, and no wonder. The workouts, which include brief periods of a burst of high intensity exercise, followed by a set period of lower intensity “recovery” exercise, or even complete rest, are shown to be quick, efficient, and they leave those doing the workouts feeling like they’ve really killed themselves (in that way that fitness fiends and athletes love).
The benefits of interval training are pretty attractive, too. The high intensities push your heart rate up, helping to improve your cardiovascular fitness (in some cases, even doubling your aerobic endurance capacity); you can accomplish higher training levels (i.e. run farther at higher intensities) because you allow your body to recover a bit in between bouts; and it’s been shown in studies to improve time-trial performances (in other words, can help you hit that PR you’re aiming for in a race).
Chemically/metabolically, it’s helped improve muscle oxidative potential, muscle buffering capacity, and muscle glycogen content–fancy ways of saying it helps delay fatigue by getting the muscles to store/use energy more efficiently.
The trick to intervals is knowing what you're training for, since the intensity/rest ratios can be manipulated to target very specific energy systems. Are you a 100-m dash specialist looking to gain an edge (in the form of maybe a tenth of a second shaved off your time) for your upcoming meet? Are you looking to improve your endurance for your next soccer season? Or are you looking to improve your time in an upcoming marathon? Knowing your goals is the first step. The next is knowing how intervals impact the energy systems in the body. There are three major energy systems that we use:
- Phosphagen System
- Oxidative System
Knowing how long to let the body recover so that the energy sources being used can “re-up” and be fully taxed again means the difference between training that particular system and having another energy source “step in." (All three systems are at work at any given point in time, but one is more dominant depending on the energy sources available).
So what are some good interval-to-rest ratios?
If you want to increase power/strength--needed in short sprints and Olympic/heavy lifting--tax the phosphagen system. The phosphagen system is mainly responsible for very short-duration, high-intensity exercise. You'll want a 1:12 or even a 1:20 work interval to rest interval ratio. That means 10 seconds of hard, very high intensity work to 120 seconds of rest. This kind of interval is best used by elite athletes training for a very specific power improvement, and typically done under supervision of a trainer.
For more moderate intensities--good for improving performances in sports, like soccer, where you need short bursts of speed and power (a sprint down the field) followed by longer duration exercise (field positioning)--try working on the glycolytic system. Those intervals, which can last from 15 seconds to three minutes, are best targeted by intervals with a 1:3 or 1:5 ratio...a minute of moderate-to-high intensity work and three to five minutes of lower intensity recovery. If you have a solid aerobic base already, this is a good interval system to try, but it's suggested to have a fitness test done before you start doing these.
If you're looking to improve your time for long races and endurance levels in general--good for beginners, and for endurance athletes like marathoners--working with your oxidative system is your best bet. Use 1:1 or 1:3 low-to-moderate intervals of work, followed by low intensity recovery intervals. If you're new to running, try jogging for a minute and then walking for a minute.
Blog post by Ashley Crosby.