We’re in a sad time of Fitness shaming.

It’s impossible to log onto Twitter, Instagram, or any fitness site without a post vilifying steady state cardio (hereafter referred to as cardiac output training), or trashing someone who does steady state cardio in their training.

We hear every excuse under the sun as to why you should not engage in cardiac output training.

It’s catabolic.

It zaps your power.

You risk converting precious type II muscle fibers to slow, type I muscle fibers, leaving you weak and puny.

The truth is, cardiac output training has huge advantages, and if programmed correctly, will supplement your training regardless of your primary goals.

I know what you’re thinking, “doesn’t HIIT provide with me all of the benefits of cardiac output training?” Simply put, nope!

steady state cardio vs h.i.i.t.

There are distinct differences between HIIT and cardiac output training concerning the exercise response, as well as the adaptations that occur. We will discuss shortly.

First, lets get to the basics.

Our body has three main energy systems that work in concert to provide us with the energy (i.e. ATP) necessary for our daily activities, including exercise.

• ATP-PCr: Provides energy for very high intensity, short duration activities (6 – 10 seconds) without the use of oxygen (1 ATP per reaction)
• Anaerobic Glycolysis: Provides energy for high intensity, short-to-moderate duration activities (10-90 seconds) without the use of oxygen (2 ATP per anaerobic cycle)
• Oxidative Phosphorylation (Aerobic): Provides energy for low-to-moderate intensity activities lasting more than 2 minutes (36-38 ATP’s per cycle)

Now I won’t kill you with every detail of these pathways, but the first two pathways provide very little ATP for energy, which is why these pathways can only support short duration, explosive activities like a brief sprint or heavy lift.

Moving on, the third pathway is extremely efficient and can provide 36-38 ATP’s per cycle. The catch- it is slower at producing energy than the first two pathways, therefore it supports sustained low-to-moderate exercise intensities.

That said, the power-infused, hypertrophy driven lifter has no interest in low-to moderate activity exercise, right?

Wrong. These energy pathways are not turned on, or off. Instead, they’re “turned on” all of the time. The aerobic system lays the foundation for developing the anaerobic pathways.

Gasp, cringe, I can hear it already.

 

Now that you have the basic energy pathways, let’s discuss the benefits associated with both HIIT and CO (1, 2)!

• Increased activity of mitochondrial enzymes (i.e. citrate synthase, succinate dehydrogenase, and cytochrome C oxidase)
• Increased exercise capacity (i.e. increased VO2peak and VO2max)
• Increased markers of mitochondrial biogenesis (i.e. increased mitochondrial volume)
• Improved endothelial function
• Increased insulin sensitivity

These are all great benefits to overall health and performance that everyone benefits from.

These are just some of the major benefits associated with both HIIT and CO training. Now let’s discuss the potential pit-falls with using ONLY HIIT.

• Requires very high intensity workouts that need to be programmed carefully to allow effective recovery to take place.
• Requires increased sympathetic drive, as required with strength training, which can ultimately effect resting heart rate and recovery (read on!)
• Initiates left ventricular concentric hypertrophy (i.e. thickening of the heart wall), which needs to be balanced out by left ventricular eccentric hypertrophy in order maximize cardiac function.

Let’s break this down further…

• Recovery: As with any form of high intensity training, we must allow our body time to recover. If you primarily run, cycle, or swim at low-to-moderate intensities, then this will not apply to you in the same fashion. However, if you consistently exercise at higher intensities (i.e. strength training), then this applies to you.

High intensity exercise bouts require the body to maximally exert itself, which in turn results in exercise-induced muscle damage and an increase of sympathetic stimulation.

When training for adaptations, it is critical to intersperse high intensity training sessions with lower-to-moderate training sessions, which facilitate active recovery without initiating excess muscle damage. Remember, it’s not how hard you train, it’s how well you recover from your training that determines the overall adaption and gains you make.

• Increased Sympathetic Drive: As mentioned above, high intensity exercise bouts require increased sympathetic stimulation, which ultimately result in a higher sympathetic drive. The great Mike Robertson refers to this as being sympathetic dominant versus parasympathetic dominant.

A sympathetic dominant person will tend to have a higher resting heart rate, as well as a higher resting heart rate at sub-maximal intensities. Lower-to-moderate intensity training sessions facilitate a reduced resting heart rate and a lower sub-maximal heart rate at any given exercise intensity (i.e. relaxes you by decreasing your sympathetic drive).

Ultimately, this “balances out” a sympathetically dominant person, which specifically improves most recovery parameters to help you get stronger, shredded, and more athletic.

• Left Ventricular Concentric Hypertrophy: Okay, let’s make this simple. There are vast differences between pathological and physiological ventricular hypertrophy, however there are also differences between types of physiological hypertrophy. Now let’s be clear, there is nothing wrong with producing this type of physiological hypertrophy, but there is another type (discussed later) that can provide you with a multitude of benefits.

Left ventricular concentric hypertrophy increases the thickness of the heart wall, as opposed to making the left ventricle larger and wider.

This is because high intensity training results in an increase in pressure work, and does not allow the left ventricle to completely fill and stretch before needing to eject the blood to your body.

This is the blood that your heart ejects to all parts of your body, otherwise known as your stroke volume (SV). To us nerdy scientists this is creates a large increase in mean arterial pressure (MAP) due to a dramatic increase in afterload, or the amount of pressure against which the heart has to pump in order to eject the blood. No bueno, my friends.

Does this mean that I should no longer do HIIT? No- absolutely not. HIIT has numerous benefits to your health, performance, and physique:

• It allows you to work at higher relative intensities, which elicit peripheral adaptations associated with aerobic AND anaerobic metabolism (i.e. improves function of ALL three energy pathways). This means wham, you’ll be able to work harder to facilitate greater gains in the gym.

• Allows you to obtain/maintain peripheral adaptations associated with aerobic training in a low volume manner

• Allows you to burn more calories when compared to low-to-moderate intensity exercise during a given period of time, making your exercise more efficient.

So, what will cardiac output training (CO) do for you? Well, let’s break it down and compare to some of the problems associated with HIIT. 

• Recovery Tool: CO training can be used as a tool to facilitate proper recovery. As we discussed, CO training will provide you with a robust aerobic energy system, which will assist your body in repairing itself in between bouts of high intensity exercise.

Additionally, CO training assists in balancing your autonomic nervous system (i.e. parasympathetic vs. sympathetic dominant), which can lead to better sleep and improved neural efficiency for more strength, power, and speed in your training.

• Aerobic Efficiency: As mentioned above, CO training provides you with a robust aerobic system. And as we discussed earlier, the aerobic energy system provides us with the majority of our energy throughout the day. Therefore, the more efficient we become in producing energy oxidatively (i.e. aerobically) we become more efficient in all of our activities throughout the day.

Essentially, you’ll improve your performance for the 23 hours you’re not in the gym.

• Left Ventricular Eccentric Hypertrophy: We touched on physiological hypertrophy when we discussed HIIT. When you engage in cardiac output training (i.e. CO training), you allow a maximum amount of blood to enter the left ventricle of your heart. This allows your left ventricle to fully expand and stretch, which results in an increased amount of blood to eject, known as an increased preload.

As blood gets forced into the left ventricle, it stretches the muscle fibers. Over time your heart adapts, which results in an increased amount of initial muscular tension placing your heart in an improved contractile state. This results in an increased maximum volume of blood the heart can eject, or an increased maximum SV.

When paired with adaptations previously mentioned, this ultimately makes your heart more efficient (i.e. your heart does not have to work as hard at given relative intensities).

Not impressed? Think about if you make your car engine more efficient- it’s not only efficient at slow speeds, but at all speeds 0-100!

So this begs the question- why does cardiac training get a bad rap? Let’s face the two biggest myths head on. 

“Steady state cardio will make you slow”

This is simply not true. Engaging in well-planned and strategic CO training will not turn you into a 140 pound marathoner that can run all day, but has virtually no power or sprinting ability.

Remember- your adaptations are a product of ALL of your training collectively, and you will adapt according to the focus of your program.

Just as a marathon runner who strength trains a couple of times a week isn’t going to turn into the Incredible Hulk, you will not dwindle away to a stick-figure just by implementing some CO training into your program.

Now here’s an important point- you do not need to implement an extensive amount of CO training into your program wreap the health promoting, high performance benefits.

Additionally, these adaptations are maintained through a concerted effort to intersperse BOTH HIIT and CO training into your program. That you means you get the best of both worlds with HIIT and CO training.

“Steady state cardio kills your gains”

Again, this is simply not true.

Can excessive steady state aerobic training significantly alter skeletal muscle hypertrophy, strength, and power parameters- absolutely! Can a well-planned, strategically structured aerobic training plan including CO training significantly alter these parameters- simply put, no (3, 4)!

 

A meta-analysis by Wilson et al. (2012) suggested that concurrent resistance and endurance training only significantly altered muscular power, as opposed to strength and hypertrophy (3). However, the threshold of endurance training they outlined was >20-30 minutes of continuous aerobic exercise >3 days per week (3). Therefore, if you want to maximize muscular strength, power, and hypertrophy do not engage in concurrent aerobic training >3 days per week.

 

Strategically placing CO training into your program coupled with HIIT will protect your “gains” in muscular strength, power, and hypertrophy, while simultaneously improving recovery and cardiac function!

Wrapping Up:

How would a program with a muscular strength, power, and hypertrophy focus look with HIIT and CO training strategically placed in it?

 

Sunday	Monday	Tuesday	Wednesday	Thursday	Friday	Saturday
HIIT 60s sprint intervals @ max effort w/75s rest periods	Upper Body HT	Lower Body ST	COTrainingCycling @40-60% MHR for 30 minutes	Upper Body ST	Lower Body HT	Rest

HT- Hypertrophy Focus

ST- Strength Focus

MHR- Max Heart Rate  

Regardless of your goals, implementing strategically planned CO training provides numerous benefits. Keep your program focused on your primary goals, but understand that CO training can assist in ultimately making you stronger and more powerful.

About the Author: Marc Lewis M.S.(c), CSCS, ACSM-CPT is a sports performance coach at the United States Performance Center in Charlotte, North Carolina, as well as a graduate teaching/research assistant at the University of South Carolina.

 

1.) Little JP, Safdar A., Wilkin GP, Tarnopolsky MA & Gibala MJ. A practical model of low-volume high-intensity interval training induces mitochondrial biogensis in human skeletal muscle: potential mechanisms. Journal of Applied Physiology. 588(6): 1011- 1022. 2010.

 

2.) Haram PM, Kemi OJ, Lee SJ, Bendheim MO, Al-Share QY, Waldum HL, Gilligan LJ, Koch LG, Britton SL, Najiar SM & Wisloff U. Aerobic interval training vs. continuous moderate exercise in the metabolic syndrome of rats artificially selected for low aerobic capacity. Cardiovascular Research. 81: 723-732. 2008.

 

3.) Wilson JM, Marin PJ, Rhea MR, Wilson SM, Loenneke JP & Anderson JC. Concurrent Training: A meta analysis examining interference of aerobic and resistance exercise. Journal of Strength and Conditioning Research. 2012.

 

4.) Lundberg TR, Fernandez-Gonzalo R & Gustafsson T. Aerobic exercise does not compromise muscle hypertrophy response to short-term resistance training. Journal of Applied Physiology. 114(1): 81-89. 2012.