The science behind HIIT is complex, but I will try my best to break it down. When you train in the presence of enough oxygen (such as walking, light jog etc), the body will use the aerobic pathway to provide the energy it requires. When your body can no longer receive enough oxygen it then switches to a different pathway called the anaerobic pathway. In terms of HIIT training (and for fat burning) this concept is key. When you work in the anaerobic pathway, such as during sprints, you begin to increase your ‘resting metabolic rate’. Your RMR is the amount of energy you use at rest, therefore the higher this is the better. This occurs by an increase in the EPOC effect (Excess Post Exercise Oxygen Consumption). Think of this as the afterburn from an intense exercise session.
Boosting the EPOC effect of exercise also has the added ability that it heightens our V02 Max. This is the amount of oxygen our body can use (ml) in one minute, per kilogram of body weight (ml/lg/min). Increasing the VO2 Max, you can therefore intake and process more oxygen, leading to enhanced performance.
HIIT training doesn’t use much fat for fuel during the session (prodominantly glycogen), however afterwards, the metabolism remains high as the body begins to use fat as fuel. Post HIIT, the body tries to revert back to its pre-workout state of using both glucose and fat as energy sources; however, to restore the now depleted glycogen stores, the body must conserve whatever glucose/ glycogen that remain, and to do this it means that the energy source must come from fat. This can lead to an elevated caloric expenditure for around 14-15 hours AFTER you have finished training. With LISS (low intensity steady state) cardio, you lose this affect almost as soon as you are done.
When it comes to HIIT, my preferred choice is to get outside, onto the football pitch and do sprints. I have included several workouts below.
These are outdoors workout, so you’ll need to find yourself a football pitch. This is the easiest way to gauge distances. Parts 1 and 2 are the active warm ups before moving into the High Intensity portions of the workout. After the session, always spend a few minutes stretching to cool down and to help minimise the risk of DOMS, because believe me, this does hurt.
Workout 1.
Workout 2. You’ll need a speed ladder, or at least a set of cones that can be placed at intervals for this one
Workout 3.
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