HIIT – High Intensity Interval Training

Our previous blog was on fat burning. If you want to burn loads of fat HIIT training will do that for you. And fast!
A recent study in the U.S. showed huge gains in fitness level and fat burning with HIIT in a much shorter period of time compared to long distance training at a moderate level.

In test subjects, performing only 1.5 hours of high-intensity interval training per week resulted in the same increase in the amount of fat burned and glucose consumed by the muscles as 5 hours of long-distance training per week after six weeks. In only 2.5 hours of intervals over 2 weeks, the participants increased enzyme (fat burning) activity in the muscles; the group that did the long distance training took upward of 10 weeks to show the same level of improvement.

It makes sense to assume that the harder exercise consumes more calories because of the increased demand on the muscles. The energy expended in a single exercise session is dependent on the duration and intensity of the activity. Here are some examples of caloric expenditure for 30 minutes of activity:
Badminton 220
Marathon running 496
Basketball 400
Skiing (Nordic) 540
Cycling, moderate 150
Squash 325
Swimming 300
Walking 160
Jogging 300
Intense exercise is just that: It’s hard. It is something that you couldn’t continue for long periods of time. For it to be effective the exercise must be more challenging than you are used to. The intense exercise must put you in an anaerobic state working above your VO2 max (the capacity of the cell to take in oxygen). Since you can’t do this for very long, it must be interspersed with periods of rest (or active rest – slower movement). Intense exercise (above 85 percent of your heart rate maximum) should only be done if you have the functional capacity to do it. In other words, if you aren’t fit to begin with you should ease into the intensity of the exercise.

One of the benefits of intense exercise is that you spend less time training, and the results you achieve in the shorter amount of time are worth the extra effort you expend. An intense bout of cardio exercise can last anywhere from 10–30 minutes, or more if you are up to it: You get more work done in a lot less time. Intense training should be done no more than three times a
High-intensity interval training (HIIT) is excellent in raising the lactate threshold (the point at which you switch to anaerobic energy production) and increasing the body’s ability to work aerobically during intense exercises. In other words, you can do more intense work without it
becoming anaerobic. During HIIT, metabolism increases due to the high demands of the exercise. Shorter, intense workouts burn as much fat at the end of the day as longer, milder workouts done more often. Long distance or prolonged aerobic workouts are still great ways to burn fat as fuel during exercise. However, you need to work out for at least 20 minutes
to start burning lots of fat. It may not make sense to say that intense exercise burns more fat, but it does...just not while you are working out. HIIT increases the After Burn (amount of fuel burned after exercise). When you exercise at an intense level, your body requires lots of fuel (fat and carbohydrates) and oxygen to burn the fuels. During exercise other parts of the body slow down and do not require as much oxygen.

Digestion, for example, will practically stop since energy is needed to fuel the muscle cells during exercises. If you work out intensely – harder than your body is used to – your breathing and blood circulation can’t keep up with the muscles’ demands for oxygen. The muscles will “borrow” oxygen from other parts of the body (organs and other cells). This creates an “oxygen debt” in the body.

When the body goes into oxygen debt, it needs to “pay back” the oxygen after exercise. This is why your heart rate and breathing rate may stay elevated for extended periods after exercise. An elevated heart rate for more than three or four minutes after exercise is a good indicator that you required more oxygen to the working muscles than your body was capable of taking in.

After exercise, your body goes through Excess Post Exercise Oxygen Consumption (EPEOC); this is also called the “afterburn.” EPEOC is the process that returns the body to its resting state. The body wants to be in homeostasis, the tendency of a system to maintain internal stability. A good example of this is when you are cold, you shiver. The shivering creates heat in the
muscles, which warms you up. Conversely, if you are warm, you sweat. The sweat takes heat from the body, which cools you down. EPEOC is the body’s attempt to return to homeostasis.

EPEOC has several repercussions. After exercise, your metabolism increases and the body needs to consume extra fuel to return to its pre-exercise state. More oxygen will be consumed in response to the exercise, which is directly related to the intensity of the exercise. Fat will be broken down in the body to free fatty acids which are released into the bloodstream. These fatty acids now fuel your increased metabolism. A person’s metabolism can be elevated for up to two days post-exercise. After exercise the body’s hormones, fuel stores, and oxygen stores all need to return to pre-exercise levels. The body will try to repair itself by making you hungry, so you eat to get the carbohydrates and protein to fuel and repair the muscles. It will also cause you to consume more oxygen, and together the oxygen and fuel consumption equates to ATP (energy) levels being restored. Add to this that your muscles have accumulated lactic acid during the exercise, so the body will consume more oxygen in an attempt to return the
pH of the blood to a normal level. With EPEOC you consume more oxygen throughout
the rest of the day than if you had done a long, steady run. This translates to more fat burning while you are resting later on in the day.