I am a big fan of HIIT training. I always feel great after a hard session and a good cool down,stretch,and cold shower. Studies show an increase in growth hormone(HGH) as much as 450% after a good HIIT workout.I am here to tell you that I believe it because I feel incredible after pushing myself hard for 20-30 minutes. HIIT crushes conventional cardio as the most effective and efficient form of exercise. It is also much less time consuming and you don't need any equipment to do it. Can do it almost anywhere with NO GYM needed.
Benefit of HIIT training physiologically include the substantial post workout boost of HGH that I mentioned above and the benefit of burning more fat at a standstill for the 24hrs to come due to the increase in both HGH and your metabolic rate increase. Studies have shown that 12 weeks of HIIT had participants show significant reductions in abdominal,trunk, and visceral fat while increasing fat free mass and aerobic power. There is also an immediate,measurable change in DNA after a good HIIT routine.
A basic breakdown of our bodies energy systems goes like this. The energy for all physical activity comes from the conversion of high energy phosphates(adenosine triphosphate-ATP) to lower energy phosphates(adenosine diphosphate-ADP). Since our muscles don't store much ATP,we must constantly re-synthesize it. The three energy systems are;
1. Phosphagen System-ATP+CP(creatine phosphate). This is predominant system used in all exercise lasting up to about 10 seconds.
2. Glycolysis System-Predominant energy system used for all out exercise lasting from about 30 seconds to 2 minutes and is 2nd fastest way to re-synthesize ATP. Glycolysis uses glucose(sugar) in the blood and glycogen witch is stored form of sugar,present in the muscles and liver for fuel.
3. Aerobic System-Uses oxygen and is slowest system to re-synthesize ATP. Uses blood glucose,glycogen,and fats as fuel to re-synthesize ATP in the mitochondria.
Phosphagen System-About 10-30sec
Glycolysis System-About 30sec-2min
Aerobic System-Approximately after 2min mark when glycogen stores are low. Switches to oxygen and fats as energy.
We should train all these systems on a regular basis to be well rounded,but since we are talking about HIIT training,we are primarily using the phosphagen and glycolysis systems.
Example of a basic HIIT routine;
-Warm up 3 minutes
-Exercise as hard as you can for 30sec and take 60-90sec rest. you should be spent after the 30sec. Shoot for 90% max heart rate if you are healthy enough for this type of activity of coarse.
-Repeat this 8-10 times
-20min is ideal for total interval time
-Cool down and stretch
-Cold shower and food LOL
I personally like doing HIIT using all different exercises to make it more fun and more challenging. The reality is that you can sprint in place and get the benefits as long as you are pushing hard enough,but trying all different movements makes it well rounded and more fun. If you are in good shape and want to go for it, try the fun HIIT routine I put up on Youtube. It's a bit longer than 20min and very challenging,but good fun! Please do not attempt until you build up to that level.
In conclusion,HIIT is a time efficient ,challenging,and body/mind altering tool you should add to your routine if you are healthy enough for that level of exercise.