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High Intensity Cardio for Weight Loss

Updated: Aug 27, 2020

Firstly, what does cardiovascular (cardio) training mean? Cardio basically means any activity that raises your heart rate above its resting rate and works to improve the efficiency and function of your heart and lungs. How much your heart rate increases depends on the intensity of the training session. So today, we will talk about high intensity.

What is meant by high intensity Cardio training? High intensity training is often referred to as HIIT (High Intensity Interval Training). The reason it is called HIIT is because it is performed by high intensity bursts of max effort followed by rest or active recovery. This is known as what is called an interval, for example, 30 seconds sprinting at max effort followed by 60 seconds walk or slow jog, then repeat for a number of times. This can be performed with many different exercises from cycling and running to circuits that incorporate exercises like burpees, mountain climbers and kettlebell swings etc. As long as it is a short time at max effort followed by rest or active recovery, it is considered HIIT.


HIIT uses more glucose and ATP* as energy as it is shorter bursts and it is a lot more demanding on the body. Glucose is more energy dense than fat which is why HIIT uses more glucose and ATP. HIIT being such high intensity, means that we expend much more calories in a workout compared to steady state. The overall calorie loss will be significantly higher even though HIIT workouts are shorter. This is because of the high demand on your body to continually produce energy for your active muscles to work burst after burst.

Another benefit of HIIT training is that your body adapts by increasing its speed and power. This means your muscles adapt to become stronger and more resistant to fatigue. The way our muscles increase in strength and power is that our muscles will learn to produce ATP from glucose at a higher rate. It provokes adaptations on the cardiorespiratory system (heart and lungs), the metabolic system (to produce ATP) and buffering systems that are needed to control acid. This is the body's way of adapting to such high intensity demands on your body. To keep up, it starts to learn to produce energy faster and more efficiently. This way our muscles get stronger, more powerful and efficient. The higher the intensity of exercise, the more our body needs to adapt to the stress being put on it. This goes for all muscles including the heart.

The oxygen uptake in HIIT is significantly higher over a short period of time. It increases very quickly and sharply during the high intensity bursts and slowly drops during the rest periods. A great adaption the heart has to this is it will increase the hearts MAX VO2. MAX VO2 refers to the body's maximum ability to consume oxygen during intense exercise, so increasing MAX VO2 means that the heart will be stronger and more efficient at consuming and pumping oxygenated blood to muscles quicker. A stronger heart is always better. As we might already know from previous blogs, our bodies need oxygen to burn fat, so increasing the efficiency of our heart to consume and pump oxygenated blood around the body will help us burn more fat during steady state cardio and at rest. A good pay off.

A great benefit from HIIT is the post exercise effect called EPOC (Excess Post-exercise Oxygen Consumption). This means that your metabolic level remains elevated even after exercise. After such high intensity exercise your body will need time to return to resting levels. We are in what’s called ‘oxygen deficit’, where our bodies still need to work at a higher rate to get the oxygen and blood back to our bodies as we should be at rest. This is because the high intensity forced a temporary overload on our bodies, our bodies were forced into a high state of stress. After the workout, our bodies are still trying to 'catch up' with what just happened. So, this means that our bodies will continue to work harder to get the body back to the normal state of rest prior to workout. Oxygen consumption can be elevated for hours after HIIT has been completed, depending of fitness level. So even after we exercise and we are resting, our metabolic rate is still increased for hours. Which can be very helpful in terms of weight loss as it means our bodies are still uptaking and using elevated levels of oxygen.

Another benefit is that it takes a short amount of time to complete. With such great benefits, it only takes anywhere from 15 mins to 30 mins to complete a full HIIT workout. It really is a bang for your buck. If you are someone that doesn't have a large amount of time a day to dedicate to exercise, HIIT will work a treat.


For people that are looking for muscle hypertrophy (muscle gain in size), regular HIIT will have a negative effect on the muscle growth. This is because of the ATP breakdown during HIIT. As mentioned above, HIIT prefers glucose as energy instead of fat, this means that HIIT does not preserve muscle mass as well as steady state does. When we are using glucose continuously, we keep taking away from our muscles and it will interfere with the muscles growth. This is different for steady state as steady state uses more fat. Doing HIIT once or twice a week will not have much effect if you're consistently doing resistance training, it is only when high amounts of HIIT training is done regularly that you might see an effect on muscle hypertrophy.

HIIT is also high impact. HIIT training consists of high impact activities as we need to increase the stress on our bodies so that we force it to adapt. This might not be the best idea for beginners in exercise as our bodies are not accustomed to these sorts of intensities. It may be a problem for people with poor joints or previous injury restrictions also. Definitely get professional clearance before you start doing HIIT if you have been injured or if you're just beginning in exercise.

I hope this clears up any confusion you may have when it comes to what type of cardio you should do and what the benefits are. The most important thing to know is that any exercise will have benefit if done correctly, so it would be wise to add variety as each type of cardio will have different benefits. There will be a separate blog post on Steady State (low intensity) training for weight loss.

Click here to see how Steady State Training affects weight loss.

*Read energy systems blog if you want to know more about what ATP is.