HIIT before or after weight training? And fasted or fed for optimal fat loss?

HIIT b_a_w

HIIT is a great way to work out if you don’t want to spend hours doing steady pace cardio, and want to reap even more benefits than slow pace cardio. If you have any questions regarding HIIT, be sure to check out the details on HIIT here.

So the question arises – should you do HIIT before or after your weight training session?

And should you do it in a fasted state or after a meal?…

As HIIT is pretty intense, it will require quite some energy from you to perform it.

There is nothing wrong with doing HIIT and weights on the same day, just give a certain amount of time (∼6 hours) between each workout. That recovery time will differ from person to person as well.

HIIT actually enhances the effect of strength training when done apart (separated by a few hours or a day) and not directly after each other (R).

First off, why train fasted anyway?

When I talk about fasted training, I refer to training after ingesting BCAAs or HMB to prevent negative occurrences, such as muscle catabolism.

HMB (β-hydroxy-β-methylbutyrate) is a metabolite of leucine and is even more potent than leucine to be anti-catabolic at a smaller dose. Both HMB and leucine are able to increase muscle protein synthesis –

Very few studies have been done comparing fasted vs fed training, and even fewer studies have been done on its benefits – such as fat loss or hypertrophy.

But, according to the studies that have been done, fasted training does have some more benefits than others. Let’s look at the proven facts.

1) HIIT in a fasted state increases the muscle’s ability to utilize and oxidize fatty acids as energy, therefore it has a glycogen sparing effect. The muscle glycogen can then be used for weight training instead of HIIT or other aerobic exercises.

2) Fasted HIIT also increases resting muscle glycogen stores (supercompensate effect), whereas fed training doesn’t have the same effect. Which means, there will be more glycogen stores in the muscles to be utilized during your weightlifting session.

3) Doing fasted HIIT increases catecholamines such as adrenaline and noradrenaline to a much greater extent than fed training. Adrenaline increases fat mobilization from fat stores and the oxidation thereof in the muscles. Adrenaline also increases contractile strength, blood flow and heart rate, which will enable you to exercise harder with greater catecholamine levels in the blood.

4) Fasted HIIT increases insulin sensitivity. The reason that this is so important, is because your muscles account for up to 80% of your body’s glycogen stores. If you are insulin resistant, muscle glycogen resynthesis can be reduced by up to 60%, meaning your muscles might not replenish completely and that will lead to inadequate recovery as well as a decrease in exercise performance.

Fasted training does have many other potential benefits, though studies are few and mostly theoretical.

HIIT before weights

Studies (R, R, R) show that doing any type of cardio based exercise before your weight training session will negatively influence your strength and hypertrophy adaption from weights. The problem with most of the studies is that they performed the endurance based exercise directly before the weight training session and not a few hours beforehand.

It would be logical to wait a certain amount of hours between a HIIT session and a weight training session in order to allow your body to recover. You don’t want to do weight training while still feeling tired from the HIIT session. The reason being is because HIIT is able to reduce muscle contractile strength for up to 6 hours afterward (R), which means, it can influence your workout negatively by reducing the muscle’s ability to contract at maximal force. Which makes sense, as exercise makes you tired.

Also, doing leg-related endurance exercises – such as running or cycling – directly before your workout, might not affect your total strength, but will decrease the number of reps you will be able to perform with a given weight (R, R).

Doing HIIT before your weight session will affect your weight training negatively by reducing your power output and the number of reps you are able to do, and will alter optimal strength and hypertrophy adaption.

If you want to do HIIT before your workout, keep these 2 things in mind:

  1. The more intense your HIIT session is, the more it will affect your weight training session.
  2. Wait at least 6 hours between each session to minimize the fatigue induced by HIIT so that it has the least impact on your weights session.

My thoughts

It has been proven that doing cardio fasted shows no benefit in terms of fat loss vs doing cardio in a fed state. It’s actually advised to do it in the fed state to prevent muscle breakdown and elevated catabolic hormones.

However, no studies have been done on whether still being fasted after cardio enhances fat loss or not. It’s known that fasted training increases fatty acid oxidation in skeletal muscle by increasing certain fatty acid transport pathways into the muscles and the ability of the mitochondria to oxidize the fat. Exercise, especially HIIT increases beta-oxidation. Eating after cardio will completely abolish the elevated levels of lipolysis. So by staying fasted after doing HIIT, might result in much greater fat loss, than when eating directly after cardio. I prefer to fast an extra 2 hours after HIIT before eating.

Staying fasted after HIIT will increase autophagy and cortisol. Autophagy breaks down non-vital tissue in the body to be converted for energy. Autophagy improves muscle integrity and health. Cortisol is also a catabolic hormone, but is also responsible for fat burning. To prevent muscle breakdown due to autophagy and cortisol after HIIT you can supplement with HMB/BCAAs before and after your cardio session. This will ensure that you maintain all your muscle, while burning only fat.

HIIT after weights

You might feel that by doing HIIT after your weights, that you might not have as much energy for it as before weights, but it eliminates the possibility that it might affect your weight training session negatively.

Doing your HIIT directly after your weight session will also impact your strength and hypertrophy adaption negatively, but not by as much as doing HIIT before weights. The best would be to wait a minimum of 6 hours after weights before doing your HIIT.

One way to still accomplish weight training and then HIIT while being in the fasted state, is to do the following example:

Take your BCAAs/HMB at 10:45am and then do your weights at 11:00am. Eat a large meal post-workout at 12pm and wait ~6hours after the meal for your insulin to return below baseline to re-enter the fasted state around 6:00pm. Once again take your BCAAs/HMB and then do your HIIT session. After your HIIT session, eat your last meal for the day around 7:00pm. This will enable you to do both workouts fasted, keep to your intermittent fasting regiment and consume your total daily calories to reap all the benefits.

Bottom line

Fasted training doesn’t have side effects, and might even be more advantageous than fed training. However, it might lower your energy and impact your adaption negatively if done too close to each other.

The choice about doing HIIT before or after your weights is up to you. Doing HIIT first might result in low energy and altered adaption to weight training, or doing weights first might result in less energy for your HIIT session.

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