HIIT is an interval based training format.
It stand for 'High Intensity Interval Training' meaning that the work periods are high intensity,
then you recover in a low intensity state and repeat.
The Science Behind HIIT
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.
Post HIIT Fat Burning
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.
Outdoor HIIT Sprints
+ Jog 200m. (Every 50m perform 20 but kicks). That's 1 set. Do 3 sets.
+ Walking lunge 20m, walk back. That's 1 set. Do 3 sets
+ Sprint 20 metres, jog back. Do 12 sets
+ Sprint 50 metres, jog very slowy back. Do 12 sets
+ Sprint 20 metres, jog backwards to the start. Do 12 sets
+ Walking lunge 20 metres, turn and do the same back. That's 1 set. Do 5 sets
+ Sprint 50 yards and jog back. Do 15 sprints.
+ 20 press ups, sprint to 15 metres line and back. Do 10 sets.
+ Sprint 50 yards, immediately turn and sprint back. Do 5 sets.