Effects of High Intensity Interval Training

High Intensity Interval Training or HIIT has become an increasingly popular mode of exercise over the past few years primarily due to its effects on exercise capacity, the small amount of time requirements and its exponential increase of weight loss. 

In today’s world people are wanting to get results the fastest way. Would someone rather do 60 to 90 minutes on a treadmill or 30 to 40 minutes of different intervals that burn the same amount of calories if not more and also keep you more engaged throughout. One of the appeals of HIIT training is that it represents a more time efficient way to accomplish the adaptive goals of exercise training. 

My first question is what do people really know about high intensity interval training (HIIT)? They know it takes less time to complete, they can lose fat at a faster rate and it’s a little more fun than jogging on a treadmill or riding a stationary bike. So this article is going to dig a little deeper and truly explore what adaptations there are with high intensity interval training. We are going to be looking at 3 physiological adaptations that can happen with consistent and structured HIIT. 

 1. Fat Oxidation: 

Fat Oxidation can be associated with increased mitochondrial (muscle) volume which can be assessed by citrate synthesis activities which improves the potential for muscle to utilize lipids as a substrate for energy, but is also associated with improved insulin sensitivity (the same as intermittent fasting). Improvement of skeletal muscle fatty acid oxidation is a key factor in someone trying to increase fat oxidation during exercise and is also very important for athletes attempting to spare carbohydrates during competition. This statement is acknowledging that through higher intensity workouts your body can use fat as a direct energy source instead of carbohydrates which is a primary energy source for muscles and Glycogen Synthesis. 

2. V02 Max and Blood Cholesterol panels

People are very concerned with the changes that they can physically see like added muscle definition and fat loss, but with High Intensity Interval Training we are going to see a lot of acute and chronic changes to the body like an increase in somebody’s V02 max or the volume of oxygen their body can supply their muscles during exercise; Up to 13-18% in some studies. We can also see an Increase with HDL (High Density Lipoproteins aka the good cholesterol), Decrease in Triglycerides and Body Fat, etc. We may not be able to see all of the changes that are happening to our bodies, but your body and physicians will compliment and thank you later. 

3. Aerobic and Anaerobic Capacity Changes 

Aerobic capacity is the ability of the heart and lungs to get oxygen to the muscles. An example of aerobic capacity is the body’s ability to take in and use oxygen to improve aerobic performance. On the other side we have anaerobic capacity which is the total amount of energy from the anaerobic (without oxygen) energy systems, that is the combined amount of output for the ATP, phospho-creatine and lactic acid systems.

As an individual completes a consistent and structured HIIT protocol they should see aerobic and anaerobic changes due to the increase in the body’s ability to use oxygen more effectively and efficiently throughout a workout. With High Intensity Interval Training we are combining both forms of aerobic durations and exercises with anaerobic movements like sprinting, strength and plyometric movements, etc. 

My last question is How much is too much? 

Just like any other mode of exercise your body needs time to recover and rest. During a HIIT session you are working at a much higher energy level; your muscles are going to need time to reabsorb nutrients, recover and make those necessary adaptations to keep you progressing, so how much time do you need? I would say give yourself 24-36 hours of rest or active recovery. This will allow someone to complete 2-3 true HIIT sessions per week which will decrease the chance of injury and increase the productivity and legitimacy of each session. Good luck and lets get after those goals.

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