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.