Cardio. You either love it, or you hate it; there’s really no gray area. I find this dichotomy very amusing.
Bodybuilders and strength athletes avoid cardio like the plague; endurance athletes obviously view it as their vehicle to optimal performance. While it’s clear that your view should be heavily influenced by your goals, there are certain truths about cardio and endurance exercise that should answer the question of how applicable it may be to you.
One of these truths is hard for many people to grasp: if long-term fat loss and improved body composition is what you want (and there’s about a 99% chance that it is), then cardio isn’t going to be the best tool to get you there.
Yeah, I said it.
This should be simple enough. Cardio can be defined as endurance-type exercises of varying intensities, generally low to moderate, that rely mostly on aerobic (requiring oxygen) metabolism. The endurance distinction is crucial, as we’ll discuss in detail later. Typical forms of cardio include jogging, long-distance running, swimming, cycling, etc.
Cardio, as you could probably assume by the name, is commonly utilized to improve parameters of cardiovascular health. This is all well and good, though research has shown strength training to improve cardiovascular health to some extent as well . But last I checked, your heart is pretty important.
As opposed to anaerobic (absence of oxygen) exercises that can only be performed for short bursts at a time, endurance-based activities can generally be carried out for much longer lengths.
An easy comparison is the time it takes to run a marathon (global average: 4 hr, 20 min) versus the time it takes to run a 40-yard dash (generally <5 seconds for NFL athletes). You simply can’t sustain the maximal output and intensity required to cover those 40 yards for very long.
Cardio also has “unique ability” to burn (oxidize) more fat during a given time frame compared to other modalities of exercise. This is vetted by research: in the immediate timeframe of your cardio workout, fatty acid oxidation (a.k.a. “fat burning”) increases in most populations [2, 3].
The inaccurate extrapolation of these two observations is the genesis of most misguided exercise recommendations centered around cardio.
“Wait, more fat burning for longer is better, right?”
This is the easy conclusion to jump to; many trainers and trainees have made that leap of faith in the past and haven’t stopped spreading the message since, resulting in generation after generation of cardio-first exercisers.
But this conclusion is overly simplistic and basically misses the entire point of why we use exercise in the first place. Outside of the people who absolutely love to do cardio and the people who require endurance training for their specific sport or goal, you need to take a step back and reanalyze your goal.
As I mentioned earlier: if long-term fat loss and improved body composition is what you want (and there’s about a 99% chance that it is), then cardio isn’t going to be the best tool to get you there.
This is because when it comes to long-term fat loss and improved body composition, energy balance is NOT the only factor at play. These goals can only be achieved by enhancing your metabolism, improving nutrient partitioning, improving hormonal profile and, by definition, increasing lean (muscle) mass.
And I’m sorry to say, but cardio doesn’t check any of those boxes.
Let’s use an example:
John, a 220 lb male, wants to do an hour of exercise. He does a little research and finds out that jogging can burn roughly .12 kcal/kg/minute spent exercising, while strength training generally burns .1 kcal/kg/minute spent exercising [4, 5].
John rightly figures that this would give cardio the upper hand in terms of calories burned: you can burn more energy per minute while jogging, and you can also basically go the whole hour straight. Strength training requires rest intervals between high intensity efforts.
John grabs his calculator and finds that a full hour of jogging would burn 720 kcal, whereas strength training for 40 minutes within the hour (to account for rest) would burn 400 kcal.
Furthermore, John has also heard about the majestic “fat burning zone”; a range of intensity of exercise that will allow him to burn a higher proportion of fat during exercise. While keeping his heart rate between 65-75%, he can burn anywhere from 50-60% of his energy while jogging as fat. While strength training, his heart rate will go much higher and the preferred energy source for his body will switch to carbohydrate and ATP. That means only about 10-20% of energy burned while strength training will be in the form of fat.
To recap for John:
- An hour of jogging = 720 kcal burned with 360-432 kcal coming from fat
- An hour of strength training = 400 kcal burned, 40-80 kcal coming from fat
Case closed, right?
The truisms that a) cardio/endurance exercise burns more calories than strength-based training and b) cardio/endurance exercise burns more fat are only true in the acute sense and only takes energy balance into account.
Cardio/endurance exercise has little to no lasting effects on your metabolism. When you stop your cardio routine, any energy deficit you may have been creating will disappear.
In fact, studies have found that whether you’re creating your energy deficit with less food or more cardio, you will lose the same amount of weight over time [6, 7]. This literally means that the hour John was about to spend on the treadmill can provide a similar effect on your energy balance as just leaving that other half of the sandwich on the table instead of eating it (remember this for later).
Moreover, the actual amount of fat burned during the time you spent exercising is pretty minuscule . In that study, it took 15 weeks to burn roughly one kilogram of body fat. For reference, one pound of body fat carries about 400 grams of fat, meaning one kilogram would ~880 grams. 880/15 weeks = roughly 59 grams of fat burned per week. Chipotle burritos have more fat than that.
In our example, even if we figure John will burn the maximum amount of fat while jogging, that adds up to whopping 48 grams per hour. More favorable than the study above would show, sure, but you’d have to do about eight hours of cardio to burn one pound of body fat. Kinda puts things in perspective, doesn’t it?
And this is solely viewing exercise from the perspective of energy balance; again, it means nothing if you can’t keep your diet in check.
The Little-Known Danger of Cardio for Strength Athletes
Furthermore, this speaks nothing of the training adaptations and hormonal implications of doing that much cardio.
All exercise can be viewed on a spectrum: the Endurance/Strength Spectrum. All exercise falls somewhere on this spectrum: marathon running is entirely endurance-based; power lifting is entirely strength-based.
Everything else falls somewhere in between, and where an exercise lands explains what adaptations your body will go through in order to adapt to it and perform better at it over time. This follows the Specific Adaptations to Imposed Demands (SAID) Principle to a T.
Adaptations to the endurance end of the spectrum include increasing VO2 Max, improving Mitochondrial Density and boosting AMPk gene transcription . These are all fancy ways to describe internal mechanisms behind improved endurance performance. If endurance performance is your goal, then you should stick to these adaptations and therefore the endurance end of the spectrum.
Activities on the strength end of the spectrum illicit entirely different adaptations: increased muscular cross-sectional area, increased Myofibrilar Protein Synthesis and, in the long term, improving mTOR gene transcription .
These changes are so different that they have been shown in research to be mutually exclusive. Interestingly, studies show that during a bout of resistance training, AMPk actually increases, which causes mTOR activity to decrease . Following training, this inverts and favors mTOR activation, which is how resistance training stimulates mTOR in the long term.
This strongly illustrates the point: your body cannot adapt maximally in both directions at exact the same time. By training on both ends of the spectrum, you’re essentially asking your muscles, cardiovascular system and genes to become better at long, low intensity efforts and short, high intensity efforts at the same time.
As visionary wordsmith T.I. once said, “It Ain’t Both.”
This phenomena is called the “Interference Effect.” Research has repeatedly shown that cardio training alongside strength training diminishes your strength gains and growth in a near dose-dependent manner [12, 13, 14]. This means the more cardio you do, the less adaptations will be made following strength training. If you do this without having any endurance-based goals, you’re self-sabotaging your efforts in the gym, and THOSE are the efforts that are much more likely to get you to your goal. More on that in a second.
First, we need to figure out what really needs to be done in order to achieve fat loss and improved body comp. We know that an energy deficit is permissive (not a necessity, though) for fat loss, and improved body composition depends on the ratio of fat mass to lean mass that you are carrying.
With cardio and endurance training, you’re essentially only relying on an energy deficit to do the job. You’re also severely limited by time with this approach. Remember earlier when we ran some numbers to find our example friend John would need eight hours of jogging to create a deficit big enough to burn one extra pound of body fat? That’s for a relatively large male; this amount of time commitment for a similar calorie burn would scale upwards for gender (females burn less energy per minute) and weight (you burn less energy at a lower weight).
If you take this route, I hope you have a lot of Ebooks and Podcasts on hand.
If a lack of a lasting effect on metabolism, major time commitment and the “Interference Effect” sabotaging your efforts in the gym weren’t enough to scare you away, then maybe the detrimental effect to your hormone profile and increased injury risk might do the trick.
Excessive (and yes, I’d qualify eight hours a week to be VERY excessive) cardio can really do a number on many hormones, namely cortisol and testosterone. Exhaustive endurance exercise has been shown to increase cortisol by more then double while simultaneously decreasing testosterone by over 30% .
You may be familiar with cortisol, coined the “stress hormone” by society. Elevating cortisol via endurance exercise is not all that dissimilar from elevating cortisol by any other means. While it may not be a form of psychological stress (although I would definitely feel stressed out if I was trapped on a treadmill for eight or more hours a week), your body still responds to it all the same by putting your body in a predominantly catabolic (tissue break down) state.
This has a number of negative outcomes over time, including but not limited to: increased appetite/carb cravings, reducing insulin sensitivity, reduced strength and muscle gain, reduced recovery and higher risk of injury .
All of these things strongly contradict the goal of losing fat and improving body composition, in case you’re wondering. Some of them, namely increased appetite, can literally nullify any benefits you’re seeing from cardio in the first place by re-filling the energy deficit you’re trying to create.
And let’s not neglect the reduced testosterone side of this equation. Testosterone is vital for tissue anabolism, a.k.a. muscle growth. By simultaneously reducing testosterone and increasing cortisol, you greatly distort the ratio and double down on the effects listed above. And guys, this could also lead to a “feminizing” effect over time if left unchecked. Just sayin’.
“Okay, but what makes strength training so great then?”
I’m glad you asked. Keeping the goal of improved body composition in mind, there are myriad ways that proper strength training can get you there.
Instead of having an acute impact on metabolism like cardio, strength training has lasting effects on your metabolism for multiple reasons. For starters, muscle is a “metabolically expensive” tissue, meaning your body requires more energy to maintain your lean mass than it does your fat mass. You can expend up to five times as many calories preserving a pound of muscle versus a pound of fat . While the difference may seem trivial (10 kcal/lb vs 2 kcal/lb), this adds up.
Using our 220-pound friend John as an example again, let’s say he has about 10% body fat. Quick math gives us 22 lbs of fat mass and 198 lbs of everything that’s not fat. This includes muscle, but also organ tissue, which is much more calorically expensive than muscle and makes up the majority of your metabolic rate.
A conservative estimate tells us that John would need 44 kcal to “preserve” his fat mass and (at least) 1980 kcal to preserve his lean mass. As such, 2024 kcal may be a VERY rough estimate for his Basal Metabolic Rate (BMR, or amount of energy burned while sitting around all day).
Now let’s imagine if John was fatter; say 40%, obese. That’s 88 lbs of fat, needing 176 kcal, and 132 lbs of everything else, needing 1320 kcal. His BMR starting point may be closer to 1496 kcal thanks to his sub-par body composition.
These numbers are highly theoretical, and more accurate BMR formulas such as the Katch-McArdle Equation (which is based around lean body mass measurements) would show that the lean version of John would have a BMR close to 2314 kcal while the obese John would have a BMR closer to 1666 kcal. But this only strengthens my point: the more lean body mass you have, the higher your BMR.
You literally have a higher ceiling on your metabolism by carrying more muscle mass, and this is even before factoring in things like exercise and Thermic Effect of Food (which, go figure, also increase with muscle mass and body composition).
This is part of the reason why people with a lower body fat percentage and a good deal of muscle (a.k.a. strength or physique athletes) can eat a seemingly disproportional amount of food and stay lean.
Secondly, creating new lean tissue costs a lot of energy; that new muscle didn’t just appear out of thin air . Therefore, when gaining muscle mass, your metabolism will increase to accommodate this higher rate of energy being expended via tissue creation (anabolism).
Strength training also greatly improves nutrient partitioning, which means that the calories you do consume are more likely to be burned or go towards muscle building rather than being stored as fat [19, 20]. Not to mention strength training’s long-term benefits on testosterone (it increases) and inflammation levels (it decreases). Oh, and the reduced time commitment.
And these are not acute benefits; these are lasting benefits.
It should be more clear by now why cardio or endurance training shouldn’t be the cornerstone of your training regimen if you want to lose fat and improve body composition. The costs highly outweigh the benefits across the board; you’re actually more likely to negatively impact your body composition, hormone profile and inflammation levels while increasing injury risk.
On the other hand, strength training offers a much more viable tool to reach your goal. Improvements in muscle mass, testosterone (this is good for both sexes, by the way), nutrient partitioning and inflammatory profile will all drastically improve your body composition and ability to lose body fat, provided you know what you’re doing in the gym, which requires another article (or nine).
Oh, and remember at the start when I talked about cardio being used to improve cardiovascular health? Improving body composition will do just that.
However, this is not to say cardio has no application. But before we consider who it may be useful for and how, we need to redefine what we mean when we refer to cardio.
By now, it should be pretty clear that cardio’s utility is basically limited to an impact on energy balance in the acute sense.
From this point on, unless you’re a competitive endurance athlete, you should basically view cardio as a temporary tool that can help increase an energy deficit.
When Cardio is Appropriate
At the beginning of this article, I spoke of four populations that would find value in consistent cardio training. Here they are:
The first two should be obvious. I’m not trying to tell competitive cyclists to stop doing cardio, nor am I brushing off your love for jogging/biking/rowing/hiking/etc. If endurance exercise is absolutely vital to your performance or wellbeing, then keep on keepin’ on.
If you’re in group two, though, be honest with yourself about why you’re doing it in the first place. After reading this, you should see right through the idea that cardio is “ideal” for fat loss and body comp change. If this truly is your goal, then you should really be looking elsewhere (i.e. the squat rack) to help you reach it.
If you still love it no matter what anyone tells you, there’s a way to implement it intelligently. Just don’t be doing it because someone told you it’s the secret to fat loss. It’s not (see: everything to this point).
The third group of people comes with a lot of contingencies, but the premise remains the same. In this scenario, carrying so much extra weight is inherently more unhealthy than trying to “crash diet” and create a huge energy deficit via caloric restriction and exercise. While this is clearly not advisable for someone who is already relatively lean, the rules change when you find yourself above ~25% body fat as a male or ~35% body fat as a female.
Your extra fat mass is destroying your inflammation levels, hormonal profile and nutrient partitioning all by itself. In this case, losing weight as fast as possible is the most advisable route. This route could include cardio to create a larger energy deficit.
Overweight/obese people respond differently to more drastic deficits because they simply have more tissue to lose. If you send your body the signal to get rid of bodily tissue, and you have plenty of one type of tissue (in this case, fat) to lose, you’re going to preferentially lose that tissue. The story changes when body composition improves, so crash dieting should only be done in truly overweight populations with very supervised conditions and a defined cut off to avoid running into any of the issues I mentioned above relating to chronically elevated cortisol.
Cardio is also relatively more beneficial if these overweight/obese individuals happen to be female and/or untrained individuals. Females tend to have an “endurance-based” muscle fiber type profile, and this study found that females are able to oxidize more fat during cardio over a broad range of intensities when compared to males . This doesn’t mean women should only do cardio; the rationale above still hold for both sexes. It just may be a slightly less risky decision to make if you’re a female.
Untrained people will receive a positive growth stimulus even from cardio. At the very beginning stages of exercise, any trainee will experience very broad adaptations to most any form . Within a few weeks or months, these adaptations start to become more specific based on where the exercise lands on the Endurance/Strength Spectrum.
And for the fourth group of people, cardio literally embodies the lesser of two evils. Navigating weight loss as a competitive physique athlete is a whole different ball game. You’re often trying to finesse your way from insanely low body fat to freakishly low body fat in order to be stage-ready.
To get to this point in the first place, you’re likely going to want to withhold cardio as long as possible and create your energy deficit via caloric restriction. But this method has a limit; at a certain point, you risk lowering your calories to the point where your recovery from exercise is greatly compromised, as well as risking the development of nutrient deficiencies thanks to an unreasonably restricted diet.
In this scenario, you need to continue to increase your deficit to continue progressing, and any further caloric reductions pose a greater risk than an equivalent deficit created by cardio. As a rough barometer, most males shouldn’t go below 2000 kcal per training day; most females shouldn’t go below 1500 kcal. When you’re approaching these values, it’s time to consider cardio.
When Cardio is Not Appropriate
Essentially any scenario that’s not listed above. Sorry, not sorry.
How to Implement Cardio
If you’re in group one, the “how to” of implementing a successful cardio regimen for high-level endurance athletes is way beyond the scope of this article.
If you find yourselves in groups two through four, there are some simple guidelines to follow. Keep in mind our new definition of cardio: solely a means to increase your energy deficit.
A Word on HIIT
You may think you’ve circumvented all of this logic by utilizing High Intensity Interval Training (HIIT) training. This is a style of cardio that intersperses bursts of high intensity efforts with longer periods of rest, creating a peak and valley effect of effort. It also drastically reduces the amount of time you have to spend per workout, which is a huge plus logistically.
Not too long ago, the media caught wind of some research pertaining to HIIT training. You may have heard the stories along the lines of “Blast Fast in 5 Minutes a Day” or “Less Exercise; More Results.”
If these stories piqued your interest, you may have done some searching on the trusty interwebz for more about HIIT, where you surely found out about the epic benefits it has on something called EPOC, or excess post-exercise oxygen consumption. HIIT does boost this marker to a greater extent and for longer than regular cardio, which made many people think HIIT training was closer to weight training in terms of metabolic adaptations.
And of course, those online articles included picture diagrams of sprinters vs marathon runners, often with the question “who would you rather look like?” plastered underneath. Since many Olympic-and-elite level sprinters look like they could make a cameo on a bodybuilding stage while the marathon runners look… um… frail, you’re probably going to pick the sprinters.
So to look like sprinters, we gotta train like sprinters, right? And sprinters are using HIIT!
Allow me to channel my inner Donald Trump for a second (and it’s frightening that that’s a real sentence)…
While HIIT does save you time, the EPOC benefits were blown way out of proportion. I remember reading articles stating a session of HIIT can “boost your metabolism by 100-200 calories for a number of days.” With that rate of return, you’d be stupid NOT to do HIIT.
Meanwhile, in the real world…
“EPOC comprises only 6-15% of the net total oxygen cost of the exercise.” That’s a direct quote from this study . 6% of energy burned during a HIIT session totals in the tens of calories at best, not the hundreds. Oh, and if you actually read that abstract, you’d find that those benefits seem to last from 3-24 hours, not “a number of days.”
And yes, this lack of lasting effect on metabolism means it’s actually not much different from regular cardio in terms of impact on energy balance. Not to mention the exponentially higher muscle damage you’ll accumulate from the much higher intensities of HIIT training, which would enhance the interference effect.
But what about the model-esq sprinters?
Newflash: they don't use HIIT training.
HIIT protocols commonly employ bursts of 20-60 seconds of all out effort, followed by rest periods of anywhere from 10 seconds to four minutes. Ask any high level sprinter and they will laugh in your face if you were to ask them to run multiple 100-meter dashes with only 30 seconds of rest.
Real sprint training is more like: all out 100 meters (~10 seconds), rest five to 10 minutes, repeat. Specific goals require specific training routines; HIIT does not represent the activities of a sprinter .
You simply can’t sustain that type of output without ample rest periods. Repeated sprint efforts transition you from anaerobic (without oxygen) to aerobic (fueled by oxygen, a.k.a. regular cardio) metabolism, since your force output can decrease by nearly 75% after 10 sprints .
At this point, since you’re basically accomplishing the same goal with HIIT or regular cardio, you’re better off using regular cardio to avoid the excess muscle damage. And even though some people might say “HIIT keeps me more motivated than boring steady-state cardio,” research finds that to be false as well: people just dread HIIT more .
This also comes with an easy solution: shorten your cardio time. You shouldn’t be doing a ton of it anyway.
So next time some trainer at the gym tries to tell you HIIT cycling or HIIT group classes will turn your metabolism “into a furnace,” you reserve the right to HIIT them square in the jaw. If you’re going to do cardio at all, short and sweet steady-state sessions are better for fat loss than HIIT can ever hope to be .
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