Can I Do HIIT Every Day?

“I lift weights for two hours and do 30 minutes of HIIT every day,” wrote one Muscle Evo reader.

“Are there any negative issues that might result? Will I lose muscle gains by doing this?”

There are indeed a few negative issues with your current training routine.

Firstly, lifting weights for two hours every day comes to 14 hours of training a week.

That’s way more than most people need, or can even recover from.

I know guys on the juice who are doing less than that.

In the majority of cases, 3-5 hours of strength training per week is plenty. That’s more than enough to get the job done.

Second, it says to me that you’re not entirely clear on what you’re trying to achieve.

Do you want to build muscle? Burn fat? Improve your conditioning?

It’s my opinion that you’re better off having one clear goal (i.e. fat loss or muscle growth), and focusing on that goal to the exclusion of everything else.

Trying to go in several different directions all at the same time almost always leads to a frustrating lack of progress.

If your main goal is to build muscle, some light cardio two or three times a week for 20-30 minutes is plenty. And by light, I’m talking about something that gets your heart rate up to around 60-70% of its maximum. A brisk walk in the fresh air first thing in the morning will do the job just fine.

You certainly don’t need to do HIIT every day.

The Metabolism-Boosting Benefits of HIIT are Exaggerated

HIIT is often promoted as the best form of exercise for getting rid of body fat, mainly on the basis that it raises your metabolism in the hours after exercise to a greater extent than moderate or low-intensity activity.

However, the size of the post-exercise calorie burn after an intense workout (known in scientific circles as EPOC, or excess post-exercise oxygen consumption) just isn’t as great as some people seem to think.

A review paper synthesizing all the research comparing moderate-intensity continuous training with HIIT does conclude that HIIT provides a greater reduction in total absolute body fat than steady-state cardio [1].

However, while the difference between HIIT and steady-state cardio was statistically significantly, the real world difference isn’t worth getting excited about.

After 30-35 workouts, the average amount of fat loss with HIIT was 3.5 pounds (1.58kg), compared to 2.5 pounds (1.13kg) with steady-state cardio. That’s not much of a difference. Nobody’s getting out of bed for an extra pound of fat loss over a 10-12 week period.

Third, HIIT is a very demanding form of training.

Doing high-intensity interval training every day on top of a daily strength training routine (which, if you’re doing it properly, is not entirely unlike HIIT in that it involves short bursts of intense exercise) will seriously impair your ability to recover and grow.

Here’s what Greyskull Barbell Club owner John Sheaffer has to say on the subject:

“Once the base of strength is established the decision is then made as to what is appropriate in terms of ‘conditioning’ work. If something is going to be added to a program then one must understand that total recovery ability will be spread thinner than it previously had been.

“If someone was formerly lifting weights three days per week and resting on the other days, then they are in for a rude awakening if they attempt to add three high intensity conditioning workouts on the days in between. Often times, the simple addition of a single stress outside of a regimented program can bring progress in the program to a halt, or at the least slow it down considerably.”

Let me repeat that last sentence:

Often times, the simple addition of a single stress outside of a regimented program can bring progress in the program to a halt, or at the least slow it down considerably.

In other words, doing high-intensity interval training every day alongside a training routine designed to make your muscles bigger and stronger has the potential to put the brakes on muscle growth.

Martin Berkhan, high priest of intermittent fasting, makes a similar point here:

“Even though you burn more calories in less than half the amount of time compared to, for example, brisk walking, HIIT is very draining on the central nervous system. In stark contrast to lower intensity cardio, which you can do for a much longer time, with much greater frequency. For someone interested in fat loss and strength maintenance, and not metabolic conditioning primarily, including HIIT too frequently is playing with fire.”

Elliot Hulse talks about some of the problems he encountered when trying to combine interval training with bodybuilding-style workouts in the video below:

Back in the day when I was an interval training “fundamentalist,” the only cardio I did was 20 minutes of HIIT first thing in the morning three times a week. I considered anything other than HIIT as nothing more than a wasted opportunity for progress.

Given the superiority of HIIT over steady-state cardio, I thought to myself, why spend time doing something that takes longer and is less effective?

What I learned the hard way is that high-intensity interval training is very tough on the body, especially if you combine it with three days a week of heavy strength training and a calorie-restricted diet.

While HIIT training helped me drop fat as well as maintain a reasonably high level of conditioning, I noticed that it had an adverse effect on my strength levels in the gym. And I would often feel burned out, tired and irritable.

Why Daily HIIT Workouts Aren’t a Good Idea

If you want to do exercise every day, rather than daily HIIT workouts you’re far better off with some kind of low-intensity exercise, such as walking, or even riding a bike.

Cycling is often the ideal form of exercise to pair with resistance training, mainly because it’s a lot easier on your joints than running or sprinting.

Daily HIIT workouts will quickly lead to a physiological state of overreaching, a term used to describe temporary overtraining. You just end up digging yourself into a hole that can take weeks to recover from.

In summary, lifting weights and doing HIIT every day is not a great idea. If you want to do HIIT while you focus on building muscle, limit it to a couple of short HIIT sessions a week.

You can also program HIIT after lifting, doing sprint interval cycling immediately after training your legs [2].

Done in this way, HIIT serves as a finisher for your quads, helping to improve your cardiovascular fitness without interfering with muscle growth.