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How to Use Cardio to Maximize Your Muscle – The Essential Guide

What are the first thoughts through your head when I say you NEED some low-intensity cardio to maximize your strength performance?
You probably think I am the devil, an idiot, or both. You do not want to hear that because like almost all people you despise cardio. You just want to lift some heavy weights.

This article will cover:

  1. A basic description of the body’s energy systems.  
  2. The energy system used during certain exercises like strength training and LISS (Low Intensity Steady State Cardio).  
  3. The adaptations of LISS that cannot be derived from strength training.
  4. The negative aspects of cardio.  
  5. A recommendation for LISS that will allow you to accelerate your strength training (it is not as much as you think).

A Brief Overview of the Energy Systems

Your body mostly uses one form of energy to drive cellular processes, like muscle contractions.  

Adenosine triphosphate (ATP) is the cell’s high energy molecule, and it is in constant turnover. The body has three different ways to produce ATP:

  1. ATP-PCr
  2. Glycolysis (anaerobic)
  3. Oxidative phosphorylation (aerobic)

The fastest method to produce ATP is to transfer a phosphate molecule from PCr to ADP.  The only problem with this reaction is the lack of substrate, so energy production only lasts 8-12 seconds. Glycolysis can anaerobically (without oxygen) produce ATP for 2 minutes, but it is less efficient with glucose. Glycolysis cannot produce as many ATP per glucose molecule as aerobic respiration, and it produces muscular failure faster. The longest-lasting producer of ATP is oxidative phosphorylation, which requires oxygen for the oxidation of glucose.  Oxidative phosphorylation produces 36 ATP per glucose molecule versus 2 with anaerobic glycolysis.

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Your body mostly uses one form of energy to drive cellular processes, like muscle contractions. Adenosine triphosphate (ATP) is the cell’s high energy molecule, and it is in constant turnover. Image courtesy of:

When are the Energy Systems Used

Each energy system is specifically adapted to be used as needed for exercise.

They work together and simultaneously.  Heavy lifting will start off with the ATP-PCr system. If the set extends past 12s glycolysis will have to take some of the workload.

If you do not consider anything except for the sets of lifting, you might come to the conclusion that there is no need to have a strong aerobic engine.  Thinking in that way is common, but that thinking also misses recovery between sets and recovery between workouts. The aerobic system will even be in use during repeated bouts of exercise durations of 30s. That means building up a stronger aerobic system will help you perform repeated sets better and recover between sets and workouts better. This will increase overall lifting performance.

A great study (3) looked at sprinting duration and the energy system the body used. During a 200m sprint, 20% of the energy was produced by the aerobic system. A 200m sprint will be 23-26s. Even with the short duration, the aerobic system was providing 1/5th of the energy.  When the distance increased to 400m and 800m, highly anaerobic intervals, the aerobic system was producing almost 50% of the energy demands. As you repeat effort through a workout from set 1 to set 3 or 4+, the energy demands slowly shift. They become more aerobically dominant even though the duration of work is not changing. If you want to have the best chance to perform well through your whole workout, you need to have a high-functioning aerobic system.

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That means building up a stronger aerobic system will help you perform repeated sets better and recover between sets and workouts better. Image courtesy of:

The Benefits of LISS

Already, I have discussed the advantages of recovery during sets of short durations as well as performance through a workout.

But, the benefits extend beyond those. The aerobic system is also used to clear metabolic waste, like lactate, after anaerobic glycolysis.  

The AS will also replete levels of PCr, so those stores are full for the next exercise bout.  The aerobic system helps keep the body ready to perform again at a high level. LISS will provide cardiac benefits that you cannot get from lifting weights or even HIIT.  There are two primary ways the heart can adapt to the stresses of exercise. When we weight train or do a high-intensity activity the heart is only trying to put out more volume of blood as fast as it can. It does not have time to fill fully. To accomplish moving more blood (cardiac output), the heart gets thicker so it can create more force.  The heart growing thicker is called concentric hypertrophy. In contrast, low-intensity activity (HR 120-150) allows the heart to fill fully before each beat. The heart adapts by stretching further to allow more blood before each beat. That means each beat will move more blood and making each beat more efficient.  Adaptation by stretching is called eccentric hypertrophy.

Many lifters are sympathetic tone dominant.  The sympathetic nervous system is the fight or flight system. When you are sympathetic dominant, it means your body is ready to fight or run all the time. The opposite system is the parasympathetic nervous system. The PNS is the rest and digest portion of the nervous system. An excellent way to determine if you are sympathetic dominant is to take a morning resting heart rate. If you are an active individual, but your resting HR is not below 60, there is a good chance your SNS is a bit keyed up. LISS will help your body switch to a more PNS dominant state.

Muscles need blood to function. Blood carries nutrients in and wastes away. LISS will increase the capillary density in the muscles being used. The increase in blood flow will allow better oxygen delivery and further enhance recovery of those muscles.

So That’s Great, but What About the Adverse Effects of Cardio?

I am sure you have heard that cardio will make you slow and look like a marathon runner.

The meme pictures across the internet are abundant that you do not want to look like a marathon runner. You want to look like a sprinter.

The argument that you immediately become a slow-moving “skinny fat” person if you do LISS is overstated. The adaptations taking place in your body address the cumulative total of the stress placed across it. So, if you continue to lift heavy and perform enough LISS to make your aerobic system perform in top shape, you will not all of a sudden become weak and slow. A meta analysis (4) showed the adaptations from cycling do not hinder strength to a significant degree.  Running creates more eccentric stress and has a great possibility to slow strength gains. Another problem that crops up with LISS vs. HIIT is how much time it takes to perform LISS. Time is a not a major concern since the goal is not to run marathons but to just build a good aerobic base. This can be done with 1-2 hrs of LISS a week.

What about HIIT?

High intensity interval training creates a similar stress to weight training.

The body and the heart will adapt in similar ways through concentric hypertrophy of the heart as well as using the sympathetic nervous system.  The adaptations gained from HIIT are completely different than adaptations from LISS.

Doing HIIT as the only form of cardio will cause you to miss out on many of the beneficial adaptations that I discussed in the article. HIIT consists of sprinting all out as fast as you can for 10-30s, and then active rest for 50s to 4 minutes.  HIIT does increase VO2 max but it misses out on some of the key adaptations of LISS.  HIIT also has some issues when it comes to programming it into a lifting program. HIIT is more taxing to the body and nervous system than low intensity cardio. Performing 6 rounds of 20s sprints will affect your workout performance the next day, while cycling at 130 BPM will likely not. I am not saying you cannot use HIIT. HIIT can be used but it has to be properly structured. It will not lead to the same adaptations as longer duration low intensity work.

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High intensity cardio stimulates a similar response to weight training. Image courtesy of:

Recommendations for LISS

Now, you have a good foundation of knowledge of the energy systems as well as a list of reasons that cardio will help you in your quest for strength and size.

The fundamental concept for any approach to LISS is to keep your HR above 120, and no higher than 150, for 30+ minutes. Honestly, any activity that keeps your HR in that target range for the proper duration can be used.

You can use sled pushes, dynamic mobility drills, cycling, jogging, or incline to walk. The heart is just dumb muscle, therefore what you do does not matter all that much. My recommendation is cycling or elliptical for 30min 2x a week to start.  Keep your heart rate in the target zone.   Track your resting HR and notice any downward trend. Only increase time/intensity if you need to.  Once you reach a resting HR in the 50s, find the minimum dose of LISS that allows you to maintain that resting HR. I recommend cycling or elliptical because they have less impact on your body, and they will hinder recovery the least. Sled pushing, tire flipping, and similar activities can create more local fatigue. This carries the possibility of hindering lifting performance.  You want to use something with the least interference that allows for the target goals. If you want an in-depth look at cardio training for strength athletes I recommend picking up The Hybrid Athlete by Alex Viada.

About the Author

maximize muscle - jmax fitnessMy name is Ryan Bergren, a soon to graduate medical student pursuing psychiatry. I have been a fitness enthusiast and coach for 7 years and I have experimented with many as many diet and workouts as I can find. I help people learn how to avoid mistakes and accelerate their growth and development.

1:  Kohn, T. A., Essén-Gustavsson, B., & Myburgh, K. H. (2010). Specific muscle adaptations in type II fibers after high-intensity interval training of well-trained runners. Scandinavian Journal of Medicine & Science in Sports, 21(6), 765-772.
2:   McArdle, W. D., Katch, F. I., & Katch, V. L. (2001). Exercise physiology: Energy, nutrition, and human performance. Philadelphia: Lippincott Williams & Wilkins.
3:  Spencer, M. R., & Gastin, P. B. (2001). Energy system contribution during 200- to 1500-m running in highly trained athletes. Medicine and Science in Sports and Exercise, 157-162.
4:  Wilson, J. M., Marin, P. J., Rhea, M. R., Wilson, S. M., Loenneke, J. P., & Anderson, J. C. (2012). Concurrent training. Journal of Strength and Conditioning Research 26 (8): 2293-307.