What Is HIIT

HIIT is an acronym for High Intensity Interval training and involves the performance of short bouts of difficult cardiovascular work with rest in between bouts. These bouts can be as short as 20 seconds and go all the way up to 4 minutes with varying rest periods. This training is performed both to improve the cardiovascular system (mitochondria density, stroke volume etc) and to burn calories for weight loss. It has been shown to be effective at both of these goals , but also that frequency of training can have an impact on adaptations.

Guidelines

One session of HIIT per week has been shown to have an impact on cardiovascular health. I recommend beginner perform 1 HIIT session per week while advanced individuals 1-3 sessions per week. Please read on for more details about how you can chose the correct intensity for you.

How Many Times Should I Do HIIT Per Week?

The dose of HIIT training really depends on a number of factors that you will need to read through and make your decision based on these factors. Everyone is an individual, and although there can be some guidelines for everyone, you will need to make your own decisions on how many HIIT sessions you want to perform in a week. Personally I take all of these factors into consideration when designing my own and my clients programmes, especially because performing too much HIIT can have negative impacts that we will discuss later.

Variables to Consider

Training Age

Training age is how long you have been doing physical activity, it doesn’t just consider how long you have been doing HIIT workouts or how long you have been going to the gym. It takes into account your athletic background, how athletic you are and many other factors. The higher your training age, the more you will be adapted to recovering from certain activities. The high your training age, the more likely you will be able to handle more volume in the gym and therefor take on more HIIT workouts in your week.

Goals

Your goals will also play a key role in how many HIIT workouts you perform in a week. If your training for a marathon, you may only want to do 1 running based HIIT workout a week, also known as an interval training session. If you want to be a competitive weightlifting, it’s likely you will do no HIIT workouts in your week as it will take to much away from your weightlifting training. I your goal is too be very healthy you may perform 1-2 HIIT sessions per week and put emphasis on other areas of fitness in your other sessions.

Life Stress

This factor cannot be forgotten, stress from life will play a substantial role in your selection of how many times you perform HIIT workouts you perform a week. When your life is already causing a lot of stress, this could be job, relationships or any other area of life, you need your exercise routine to reflect this and be a source of energy rather than something that beats you down. I have a client that is a doctor with long hours and two young children, getting enough sleep is already difficult enough and the last thing I want to do is add load to an already stressful timetable, my aim is to create enough stress to cause adaptations through resistance training while allowing the client to leave the session full of energy. I discussed this at length in my article about reasons to avoid HIIT (life stress being one of them)

Training Economy

Training economy is a fancy way of saying how much time you have to train. This is absolutely crucial to how many times you do HIIT in the week. If you only have 3 x 45’ to exercise in the week then doing HIIT three times a week would be a very poor use of your training economy if you’re aiming for health. You would be far better off doing 1 HIIT and two strength training sessions, or 1 HIIT, 1 LISS and 1 Strength. You can see how training economy has an impact on your decision making here.

Sample Week with HIIT Session

In this example I am going to give an example of someone who already has an active lifestyle, but just needs some guidance on tying it all together. The goal of the individual is to be in excellent health and have high levels of vitality.

Monday - Full Body Resistance Training

Tuesday - HIIT

Wednesday - Rest Day

Thursday - Full Body Resistance Training

Friday - Off

Saturday - LISS

Sunday - Walk

In this example I only put HIIT in once, but twice would also be fine. Doing a stand alone HIIT session is great as it means you can be in and out of the gym in under 20’, but also adding HIIT onto the end of Full Body Resistance Training can be a great way to use your time if you have 60’ of time to allocate to exercise. Performing a week like this, mixed with good sleep and good nutrition for over 6 months will result in being in excellent physical health.

What’s the Difference Between HIIT and LISS

I discussed HIIT vs LISS at length in my article HIIT vs LISS: Is It Really a Debate , but wanted to mention it again here because I feel its such an important part of the health puzzle that a lot of people are missing out on. LISS stands for low intensity interval training and is also known as steady state, but steady state could also be confused with tempo training so I prefer the term LISS as it puts emphasis on the low intensity aspect of it. LISS is much more approachable (other than the time required) than HIIT, causes a lot less fatigue but has similar adaptation and is great to add into your training routine if you have the time available.

Not All HIIT Is Equal

HIIT is often bucketed into one group of sessions, but some HIIT sessions can be excruciating and cause a lot more fatigue than other types of HIIT. This is especially true of mixed model HIIT where you perform a CrossFit style workout with heavy loads and complex movement under fatigue. This compared to an interval session on a rowing machine is substantially more difficult, meaning how you programme the details of your HIIT sessions is important to how much fatigue they will generate.

HIIT Can Lead to Overtraining

Performing too much HIIT can be one of the best ways to suffer from symptoms of overtraining which include, general fatigue, poor sleep, decreased physical performance, irritability, muscle soreness, increased risk of injury and re-occurring illness. None of this is very fun, that is why making sensible decisions about how much you training, especially how many HIIT sessions you perform in a week is important. If your currently performing 4 or more HIIT sessions a week and are experiencing any of these symptoms, I would highly advice reducing your HIIT frequency and put more emphasis on your recover.

References