Do you want to know how and why you can lose six times more body fat from a 20 minute workout than 40 minutes of steady state cardio? Excess post oxygen consumption for more than 24 hours which equals more calories burned. Increase your VO2max to be able to work longer and burn more calories. Fat mass loss greater than ten percent during a 15 week study versus steady state. Improved insulin sensitivity and muscle strength. High Intensity Interval Training (HIIT) is your answer!
HIIT training at its most basic level is elevating a person’s heart rate to the point of muscle failure and allowing a rest period to try to recover.
Here’s a quick overview of how and what energy sources will be used, how VO2max will lead to more calories burned, and how excess post oxygen consumption helps burns fat calories after high intensity interval training.
The “work” and “rest” periods will be varied depending on the person’s cardiovascular levels. Our bodies run off of mainly two types of energy sources… carbohydrates, glucose and/or fats, triglycerides. Majority of us use carbohydrates as our primary energy source. They require less oxygen to produce energy and because of our access to a lot of carbohydrate dense foods, the body prioritizes them as fuel first over fats.
While we workout, the muscle will receive energy in two ways
Either intramuscular or by blood peripherally. Initially the phosphagen system is used but can only last for 10-15 seconds Glycolysis is then the energy method used to break down carbs, glucose and glycogen which is found in the muscles and liver. This energy method can last near 30 seconds to 3 min. The last method for energy usage is the Aerobic system which will use either fats (aerobic lipolysis) or carbs (aerobic glycolysis) in combination with oxygen. Fats do require more oxygen than carbs to produce energy therefore carbs will be the primary source of energy when intensity rises. This system allows for a great amount of total energy but takes longer to do so.
Lipolysis is the process of fats being released into the bloodstream
There are a few factors to keep in mind when the body is exercising to determine the energy source a muscle will use. Intensity and the duration of the exercise activity, training status of the specific muscles being used, general diet, specifically the amount of carbs versus fats, and the last factor is the time interval from the last meal.
As we exercise and intensity increases, blood flow moves to the surface of the skin to try to be cooled down and blood flow goes to the muscles that are being used. This leaves less blood in areas where the muscles are not being used and so fat from peripheral areas will be limited. Even tho fat from the blood will be limited the muscle will still burn fat as exercise is being continued. This is where intramuscular fat storage will be converted for energy. During low levels of intensities the body does not have to revert to intramuscular fat stores.
A way to help improve the usage of fat for energy is through diet
Eating less carbohydrates and more fats will have an impact on this outcome. Ketogenic diet, eating less than 50g of carbs per day, has become more and more popular over the past few years. Dom D’Agostino or Rhonda Patrick are very good sources for more information on the Ketogenic diet. Also, eating carbohydrates before exercise will produce insulin and that leads to the inability of fat utilization
Now for some quick math. While walking the body typically is burning 85% of fat for energy and the remainder are carbs. The largest problem being that on the high end of walking per min the body may burn up to 6 calories per min. If a person walks for 60 min times 6 calories per min that would be a total 360 calories for one hour of walking. If walking for that full hour and 85% of those calories are burned from fat we get a total of 306 fat calories burned. Now take into consideration the fact that one pound of fat is equal to 3500 calories. This then means to burn one pound of fat by merely walking a person would need to walk over 11 hours.
VO2Max is the maximum amount of oxygen that the body can intake during intense exercise. Reaching this point also results in the heart rate being maxed out for an individual. As the body is reaching this point the muscles are being broken down and more acidic and leading to muscle failure and a need to rest. During the rest periods the body is trying to clear the muscle up and allow for more oxygen to exercise again. This can be improved with HIIT training because as you train at or near your VO2max the body will adapt to try to become more efficient. If you have a greater VO2Max that allows for a greater caloric expenditure because the body can work for longer periods at a high level.
Excess Post Oxygen Consumption (EPOC) is the key to HIIT training
During intense or longer durations of exercise the body will burn the intramuscular energy (carbs or fats) and because of that the body is instantly trying to get those pre exercise levels of energy back into the muscles in case you gotta run for your life because a tiger is chasing you. This creates a prioritizing of the body to get more carbs back into the muscle from blood sugar before fats. Glycogen replacement requires energy and the energy found is fat that is circulating from peripheral areas that couldn’t be used at the high intensities during exercise. This indicates why people tend to lose more body fat from peripheral body fat stores while doing HIIT. EPOC does not always happen after exercise but will occur after high intensity workouts or long durations. EPOC can last longer than 24 hours.
There are many ways to set up a personalized HIIT training
Some ratios can be as 10 seconds of sprinting to 60 seconds of walking, all the way up to 10 seconds of sprinting to 10 seconds of rest. It doesn’t only have to be sprinting or biking, there are endless ways to perform HIIT training. Some examples would be a series of jumping jacks, push ups, jump squats for an interval period working at full exertion. Remember though form over output. Do not sacrifice good form to be able to do more reps. If a break is required then take a break in the middle of the interval and then get back to it with good form.
HIIT is a great way to lose body fat percentage in a small amount of time although strenuous. You can improve insulin sensitivity and burn more calories, specifically fat calories, even when you are not working out due to EPOC. VO2max will increase allowing for more work at a higher intensity to be performed and capable of more calories being burned. I believe this is one of the best ways to decrease body fat percentage without doing boring steady state exercise.