Could cardio be the key to unlocking new muscle growth? Or does it burn muscle faster than you can put it on? Spoiler alert: bros need cardio too, and it's good for hypertrophy.
I was a skinny kid—not quite the iconic “90-pound weakling” from the comic books, but definitely more Steve Rogers than Captain America. As a result, I was always a little gun-shy when it came to cardio. I was in the gym to build muscle, not stay skinny! I worried that cardio would burn muscle, or at the least, limit muscle growth.
It turns out I was missing out on one of the most underrated ingredients in the quest for more muscle: a well-developed aerobic system.
To simplify a fairly complex issue, let’s divide “cardio” into two types: low intensity work and high intensity work. We’re skipping over a lot of detail there, but if your primary goal is to build muscle, that distinction should suffice. In part one, we'll take a look at low level work. Come back for part two and a look at how higher level work can help build muscle.
Low Level Cardio
While it’s been overlooked in recent years, “steady state” cardio—so called for the steady, maintainable pace of work—is a tremendous way to develop the aerobic energy system. Aside from being the most efficient of the body’s three energy systems, the one with the greatest potential to produce energy, and the only one that can burn fat (in case that’s not enough of an upside), developing the aerobic energy system can have a startlingly direct positive impact on muscle growth via a number of different mechanisms.
Intraworkout Recovery
All recovery is aerobic. That’s true of a basketball player panting during a timeout, a fighter getting ready for the next round, and a lifter between heavy sets. No matter the energy system involved in the effort, the aerobic energy system drives the recovery.
Better recovery during a workout means more sets in less time, a concept sometimes referred to as “work density”. If lifter A does a total of 12 sets and lifts a combined total of 20,000 in an hour his work density is 20,000 pounds per hour. If lifter B does the same 12 sets and lifts the same combined 20,000 pounds, but does so in half the time, his work density is 40,000 pounds per hour. Guess who’s putting on more muscle? In addition to increasing volume (total weight lifted), upping your work density may be one of the most effective ways for an experienced lifter to trigger new muscle growth.
Interworkout Recovery
All recovery is aerobic. It was true a minute ago, and it’s still true. All the recovery gadgets in the world aren’t worth squat if you can’t get your body back to homeostasis (a resting state of balance) across the board. Good training should mess you up a bit, and good recovery—built around a solid aerobic energy system—should get you right for the next day.
Muscle growth doesn’t happen in the gym—it happens at home or at the office as your body repairs the damage you’ve done and tries to come back stronger. How you recover depends in large part on the aerobic energy system, and being ready to go again day after day, month after month brings much better results than needing more time on the sidelines.
Delivery and Removal
Take a moment to imagine an even more all-powerful version of Amazon; let’s call it “Super-Amazon”. They deliver everything, and also offer waste removal as well. And to ensure their services are uninterrupted, they’ve built a bigger, better distribution center in your area and even upgraded all the roads in town.
Now imagine you’re doing some home remodeling: you need some lumber, some nails, sheetrock and the like, and you’re also accumulating a fair amount of garbage as the work goes on. You call on Super-Amazon, who promises to be there ASAP, and sure enough, within a few hours they stop by, drop off your supplies, haul away the trash, and you’re back to work. As they leave, you notice trucks pulling up to all of your neighbor’s houses doing the same thing; apparently everyone’s remodeling this week.
You may see where this is going: swap Super-Amazon out for your cardiovascular system, the distribution center out for your heart, trucks for blood, roads for blood vessels, the building supplies for protein and other nutrients, garbage for metabolic waste, and your neighbors’s houses for nearby muscle cells and you get the idea. Better delivery and removal isn’t very sexy, but it keeps things running.
Increased Parasympathetic Tone
Ok, big words here that really just mean a shift away from “fight or flight” and towards “rest and digest”. The autonomic nervous system subconsciously regulates all the invisible processes that keep us alive, and it shifts, depending on the demands of the moment, between sympathetic and parasympathetic dominance. A more active sympathetic nervous system is a good thing, provided you’re in the midst of a demanding situation. That could be a workout, running from a bear, or even taking a test. In each of these cases your autonomic nervous system shifts towards a more sympathetic state to mobilize the energy you need to succeed. As things calm down, a more parasympathetic state sets in, and we move from mobilizing resources to conserving them.
If that doesn’t immediately register in regards to building muscle, consider this: mobilizing energy and resources is inherently catabolic, while conserving those resources in inherently anabolic. Those two words might ring a bell. Catabolic refers to the act of breaking molecules down into smaller pieces, while anabolic refers to the opposite; to building bigger molecules out of smaller ones. If we’re trying to build muscle, guess where we’d like to spend most of our time? #Beastmode is a catabolic state, and a helpful one, but once we’ve finished training we need to be able to hit the brakes and start rebuilding what we’ve torn down. A well-developed aerobic energy system helps us do just that by essentially moving the needle on our autonomic dial a little farther towards the anabolic end of the spectrum.
(Want more on this? Here you go!)
That shift is important on its own, but it has two subsequent, cascading effects that are worth individual discussion.
Better Sleep
Sleep may be the ultimate embodiment of a parasympathetic shift; the body’s daytime systems go offline (or close to it) and systems charged with restoring everything from the immune system to consolidating memory to repairing cells (hey, muscle is made of cells!) are ramped up. Good sleep relies on a lot of things, and a reasonable level of cardiovascular conditioning is foundational to better, more restorative sleep.
Happier Hormones
Hormones can’t really be happy—they might make us happy, but… in this case, “happier hormones” simply refers to a hormonal balance that supports muscle growth. To simplify yet another complex topic, we’d like to see more of hormones like testosterone and human growth hormone and less of hormones like cortisol and epinephrine. As we sleep (see above), the body restores this hormonal balance. See? Happy.
Bottom Line/Summary
Here it is: more energy to do more work in less time. Better delivery of the good stuff, better removal or the bad stuff, and a hormonal environment more suited to building muscle.
If that’s not enough, come back for part 2. We’ll take a look at higher intensity training methods and how they can positively impact muscle growth.
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