I have heard a lot about benefits of HIIT; however, nobody seems to address when is the best time for such activities. I got this question when watching "The secret life of your body clock" (BBC Horizon 2009). I intend to do HIIT in the early morning to kick start my metabolism and also to have a boost of endorphins for my day. However, the BBC documentary suggests that the best time for exercise in general is afternoon and it might not be safe to exercise heavily in the morning!

Do you know of any scientific study addressing this issue? If not, what is your personal opinion (i.e. would you do HIIT in the morning)?

  • Take a look at this question and some of the answers on what is the best time to exercise.
    – user241
    Commented May 29, 2012 at 13:28
  • Guess you'll have to do more research but I don't think you're in any real danger as long as you warm up and such. On another note, few (if any) sports that involve high intensity intervals (in their training or for competition) have competitions in the early morning. 9am would be the earliest, and thus the athlete would be awake by 7am, to be able to eat prior to competition.
    – VISQL
    Commented May 29, 2012 at 16:19
  • I'd experiment with various times of the day, and see what feels best. If a scientific study recommends doing it in the morning but you're not a morning person, it doesn't work out well for you anyway.
    – Robin Ashe
    Commented Aug 29, 2012 at 9:38

5 Answers 5


If you are training outdoors, when you train is largely dependant on the weather. For example, I'm from Dallas so in the summer I have to weigh lower temperatures and higher humidity in the morning versus higher temperations and lower humidity in the late afternoon/evening. In a more temperate climate, you may not have that issue.

When I run sprints or a quick pace tabata session, normally it's about an hour from sunset to take advantage of my night-owl tendancies while having some daylight to run it. Plus there is less danger of heat exhaustion at that time.

In regards to morning training, I rowed in college so practices started around 6-7am. Tough to wake up for, but doable.


Many will tell you the best time to do HIT is first thing in the morning on an empty stomach. The theory being that a lack of readily available carbohydrates will ‘force’ your body to burn fat.

A secondary benefit is the metabolic boost that comes with HIT (or any exercise for that matter). Doing HIT in the morning means you’ll experience your ‘boost’ throughout the entire day.

This is the main reason why HIT (or any other exercise) is best not done late evening or night time as the metabolic boost and general rush in all sorts of post exercise hormones that you experience, may affect your ability to fall asleep.

The big problem with early morning HIT is …, who’s got the physical or mental energy to do exercise after just waking up? Not I. If you’re one of those people that wake as bright as a button then go for it. For the rest of us, early morning HIT is a hard slog. If something is a hard slog, you’re less likely to give it 100% and less likely to stick to it.

Some research does point to afternoon as being the best time for any physical exercise, based on your body’s biological rhythms. However, when it comes to scientific research, bear in mind that the tests are usually performed on a bunch of people in a controlled environment. All research can only ever be an indication.

Whatever the results of these tests, that doesn’t necessarily mean they will apply to you. Your best approach is always to give something a try see how it goes then try changing it a little and compare your own results.

IMO, the best time to do HIT is when your lifestyle allows. Whether that be early morning, lunchtime, mid-afternoon or after work. If you choose a time based on research or the word of others and you find it a struggleand then it’s not going be effective.

Finding a time that suits you, a time that you can stick to and find most convenient will probably mean you’ll stick to it long term.

The best time of the day for HIT training is the time of day that you can stick to.


First of all, there is no wrong time in doing HIIT training. But if you want to do it in the morning, you have to mind some important aspects. DON'T do HIIT on a empty stomach in the morning and right after waking up. Let your body wake up for 30 Minutes, and take a Proteinshake or a small breakfast an hour or an half hour before workout. If you don't eat, and you do HIIT training in morning, your body will get the energy for your workout from your muscles. This will end in up in muscle loss (it won't be so serious muscle loss but you will loose some muscle mass..). Low intensity Cardio in the morning on a empty stomach won't have the same negative impact on your muscles as HIIT.

To make it clearer we compare HIIT in the Morning and HIIT in the late night (before going to bed): In the morning: The warm up BEFORE training, and the state of your body and blood pressure after waking up is the most important thing for the results of your workout. At night: The cool down of your body AFTER the workout is the emost important thing for the results of your workout.

My personal experience: Doing Cardio Training in the morning is a very good start in the day. You just have to take enough time so you dont start doing cardio while you are half a sleep. I'm not a morning person so i have a lot of trouble with that.

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    There's glycogen in the liver, HIIT can use that on an empty stomach.
    – chila
    Commented Aug 9, 2014 at 19:09

I did a search on Google Scholar "best time of day to exercise", the most relevant article seems to be Time of day and exercise. In short, you seem to perform a little better in the afternoon.

My own experience regarding high intensity training is that 1) it is needed in an all-round training program, so sometimes you have to exercise in the morning to meet all other requirements. 2) If I can choose, I exercise on afternoons in the weekend.


There’s no escaping the benefits from an early morning cardio workout. Both from a physiological and an emotional perspective, early morning exercising is the kick start your body needs. It promotes positive circulation whilst releasing a rush of endorphins. But, and it’s a big but…. It is exceptionally dangerous, particularly if you are relatively new to exercising or are generally unfit.

Yes there will be those who suggest this is nonsense and that they have exercised every morning for many years without issue, and that’s fine as it’s personal choice. But please be aware of the actual facts, particularly with HIT training. Why is it dangerous, it’s rather simple and very well documented. This is because when you first wake up of a morning, your body, heart in particular is under an enormous amount of stress adjusting to the needs of the body. Whist sleeping the body gently slows down, in some cases stops executing non essential functions with the body’s natural healing and rebuilding process occurring. However as you wake up there is a surge of activity which lasts around 45 minutes and as a result, your heart becomes vulnerable to over stressing. Normally a person would expect a low blood pressure relative to a their base line at this time.

Statistically, most heart attacks which occur of natural causes occurs between the hours of 7am and 8:30am. When a person wakes up, it is essential they allow their body to naturally adjust for a minimum of 1 hour. From a medical perspective, you would normally allow your body 2-2.5 hours before participating in any form of HIT training. However there’s no denying, early morning exercise sets you up for the day as well as kick starting the bodies metabolism. But ask yourself, are the benefits significant enough to warrant risking a heart attack or stroke. Remember, exercising in general regardless of of the day improves your overall health.

Good luck, just weigh up all of the the pluses and negatives.

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