How to get better results from HIIT training

I see a lot of "Internet wisdom" (there's an oxymoron if I've ever seen one) these days that suggests all you have to do get fit is beat the crap out of yourself with HIIT workouts and conversely I also see a lot of people suggesting that you just have beat yourself up with cardio. Sure those methods work but they both have drawbacks which a smart trainer/coach can avoid and get even better results than either method alone.

I really want to make a long in depth post to spell out all the intricacies but not many people have the time or the attention span to read long posts any more so I'll make it as brief as possible.

The cardio I'm referring to is steady state cardio or long slow distance (LSD) in a moderate heart rate range 120 - 150 bpm depending on age and condition etc.
This is also known as anti-glycolytic or Cardiac Output training.

When we train in a balls to the wall HIIT fashion we achieve a few things.

1 We switch on our parasympathetic nervous system (fight or flight mechanism)
2 We push our heart rate very high and cause our left ventricle to expand and contract very rapidly. Our heart tries to get the blood to the muscles/lungs as fast as possible and doesn't have time to completely fill our left ventricle.
3 We burn a lot of calories or Kilo calories to be more precise.
4 We elicit a beneficial hormonal response which gives us a surge in HGH and boost our insulin sensitivity.

When we train steady state cardio which I'll refer to as cardiac output (CO) training from now on, we achieve a few different things.

1 We switch to a more parasympathetic (relax and repair) dominant state.
2 Our left ventricle has time to fill completely and pump a large volume of blood on each beat, our ventricle wall actually stretches to allow it to pump a larger volume of blood.
3 We burn Kilo calories but much less than a HIIT jedi

So now we've had a bit of a primer on what happens to our bodies with these two styles of training let's examine the effects.

If we train in a predominant HIIT style our left ventricle adapts to the rapid heart rate and becomes more efficient at pumping a relatively small volume of blood very quickly, so as a result the muscle tissue on the ventricle wall thickens reducing the inner volume of the ventricle and reducing the volume of blood pumped per beat. People who train like this typically have fairly high resting heart rates as the heart needs to pump slightly faster to pump the same volume of blood as someone with with a normal heart.

If we train for cardiac output (CO) our hearts become more efficient and can pump more blood on each stroke without the ventricle walls thickening like a HIIT trainers heart. At rest the heart rate typically falls below that of a non trained person and much lower than that of a HIIT jedi - this is a good indication that the person is operating predominately on the parasympathetic system (low resting heart rate that is) and recovering well.

If you're still with me then let's look at our bodies energy systems, they all rely on adenosine triphosphate (ATP) to produce energy but they are refuelled by different systems.

For the sake of this discussion we have three basic energy systems.

1 The aerobic energy system
2 The anearobic energy system
3 The phosphate energy system also known as the ATP-PCr system

The aerobic system is used for long sustained efforts at moderate heart rates approx 120-150, less if you're old, out of shape or if you've been sick. This system (in a trained athlete) is super efficient at producing sustained amounts of available ATP. Fat is the primary fuel source for this system*.

The Anaerobic energy system (also known as the glcolytic energy system) is used for intense exercise that can be sustained for fairly short durations, in bursts like a HIIT style program. This system burns ATP like a jet engine and replaces it at a medium rate but it's not highly efficient. Glycogen (from carbs) is the main fuel source used here*.

The Phosphate energy system is typically what's used in strength training, it lasts for 6-10 seconds (slightly more in some cases) before it's fully depleted and takes several minutes to replenish. This is our fastest energy system. The fuel for this system is produced both aerobically an anaerobically from different sources*

So now we understand the energy systems a bit better let's look at what happens when we just train the one system like a HIIT jedi.

1 Our glycolytic fuel system gets much more efficient
2 Our left ventricle wall thickens reducing the volume of blood pumped on each beat.
3 We place ourselves in a sympathetic state (fight or flight) and can suffer from slow recovery and sleep problems.
4 We have not trained the other enegy systems effectively so we have limited endurance and tend to gas out fast in sporting events.
5 We haven't trained the ATP-PCr system efficiently and never develop maximum strength levels because we have never exploited this system properly.

So if we train in a predominantly HIIT fashion we are relying on the glycolytic system to refuel our ATP supplies. With the glycolytic system not being being very efficient at replenishing ATP we fatigue fairly fast and gas out fairly quick if we undertake an endurance event.

If we cut back a bit on the HIIT training and add some CO training we gain several benefits.

We gain some endurance
We recover faster, both after excerise and between bursts of exercise (during HIIT on cycles).
We start to place ourselves in a parasympathetic state and as a result we sleep better, are more relaxed, recover better both after exercise and between glycolytic efforts.
We have a lower resting heart rate because our heart becomes more efficient at pumping larger volumes of blood.
We favour the development of a better capillary blood supply system.
We increase the production of mitochondria (which is the part of the cell that produces energy)

A well designed training schedule will include a split between the time spent training each different energy system based on the needs of the athlete and sport they are training for. HIIT training can replace other training methods in some instances, it's especially good for getting fast results but it's mentally tough and (I believe) not optimal for long term use as a sole training method.

So how do I incorporate CO (Cardiac Output) training to my HIIT schedule ?

Only do 2 or 3 HIIT seesions each week - HIIT is very intense and your body needs to fully recover, adapt and overcompensate from the training to get the most from HIIT

Do 3 - 5 sessions of steady state cardio or CO training each week. Unless you are training for a distance event keep these sessions between 20 minutes to an hour. Longer sessions will start to favour the production of stress hormones like cortisol and negatively impact on your recovery and can lead to inflammation. Long sessions can also put you into a catabolic state and cause your body to use your muscle tissue as fuel.

Keep the heart rate in a relatively low range - Maffettone guidelines are excellent but a rough guide is between 120 - 150 BPM depending on age, fitness levels and outstanding circumstances like if you've recently been sick or injured. 140 BPM is a good starting point for almost everyone. If you push your heart rate just a little bit too far you switch to glycolitic state and put yourself back into a different training zone, which is not the goal with CO training. Once you get into a glycolytic state you may as well just do HIIT and get it over and done with fast.

So next time you see a picture of Connor McGreggor hitting the road on his bike you will understand why he does it. He didn't get to where he is by accident, to achieve that level of success you need to work smart and not just beat the crap out yourself and believe you are doing the best you can.

Is there a place for HIIT ?

Yes without doubt, it's an excellent tool in the right hands but if you believe you can rely solely on HIIT to make the most out of your training you are selling yourself short. No doubt cross fit trainers will have a different opinion and maybe even want to argue about all this, but I really couldn't give a shit, I make a living from fixing broken cross fitters. tell uncle rhabdo.I'm sure he'll listen.

*These energy production systems are a lot more complex than the brief overview I've outlined here, to explain them properly would require a long boring technical post that only a few people would be interested in. So I've generalised about the fuel sources used for these energy systems. Our bodies can produce energy from multiple fuel sources in different cases so my explanation is just a guide.

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