High Intensity Interval Training (HIIT) a specialized type of training involving brief periods of maximum effort couple with longer periods of low to moderate effort in-between. Because of the intensity, you can get a more effective workout in less time.
Because of both the high and low-to-moderate intensity, it is a good routine to work both your aerobic and anaerobic energy systems. Before continuing, let’s explain the difference.
Aerobic activity can be sustained for long periods of time. You are breathing heavily, but at the rate at which you are exercising, you are able to provide enough oxygen to your cells and remove the carbon dioxide produced, thus preventing the buildup of lactic acid – the cause of muscle soreness the day after exercising. With aerobic activity, your muscles are metabolizing glycogen and fat into energy, so it is good for weight reduction.
With anaerobic activity, you are exercising at a much higher level of intensity – so high in fact that your muscles are not able to get enough oxygen or remove enough carbon dioxide to prevent the build-up of lactic acid. With anaerobic activity, your muscles are metabolizing strictly glycogen into energy. Anaerobic activity is better for keeping off the weight due to its ability to develop lean muscles mass better. More muscle mass requires more calories to sustain.
So HIIT involves short periods of anaerobic training interspersed with longer periods of aerobic activity. For example a good, but simple, HIIT routine would be running at a moderate pace with short periods of all out sprinting in-between. By keeping the high intensity periods short, lactic acid buildup is kept to a minimum.
Everyone has a metabolic threshold. This is the point where your body moves from aerobic to anaerobic. While there isn’t an exact way of knowing what that point is, you will know when you have made the switch because your muscles will start to feel fatigued. Continue on and they will eventually quit functioning.
Not everyone has the same metabolic threshold. For example, two people at different fitness levels are climbing flights of stairs. The person at the lower fitness level will go into his/her anaerobic zone much sooner than the more fit person. Some activities lend themselves to anaerobic do to just the nature of the activity; for example, weightlifting is almost all anaerobic.
Generally speaking, HIIT is practiced by athletes training for a competitive event, however, non-competing athletes can also gain some fitness benefits when HIIT is practiced safely and with common sense.