Any time you move your ass you’re doing cardio.

Weightlifting works your heart and lungs too, duh. A better term for what people refer to as “doing cardio” is “aerobic training.” But since I’m not totally anal, I’ll mostly stick with the common vernacular.

This is all about weights vs. cardio, like you only have one choice, and no one has ever decided that maybe they could do both, or something.

Each has its own merits, but a lot of the debate has to do with body composition, so in any analysis that compares the two it is critical to also analyze the effect these two forms of exercise have on diet.

I will link to many of my own articles throughout to reinforce specific points, but first a quick analysis of …

Anaerobic vs. Aerobic Exercise

Anaerobic processes do not require oxygen, and aerobic processes do. Generally speaking, anaerobic activities are the ones that are short in duration and requiring a lot of power, and aerobic ones are longer duration of a sustained effort. These processes are broken down into three different types of energy systems:

  • The Phosphagen System (Anaerobic) – This is the short-burst, high-intensity power stuff like weightlifting and sprinting. It is an all-out effort that lasts only seconds. The phosphagen system uses adenosine triphosphate (ATP) by breaking down creatine phosphate (CP), the latter of which is stored only in very small quantities. When the CP runs out, so does your body’s ability to use this energy system until CP is replenished via a rest interval. As an example, when you sprint you can only go all out for just a few seconds, and then your cells run out of stored CP and you have to slow down and switch over to a slower energy system, such as …
  • Glycolysis (Still Anaerobic) – Glycolysis is the breakdown of either glycogen stored in the muscle or glucose delivered in the blood as fuel which serves to resynthesize ATP (instead of CP). It doesn’t do it nearly as quickly as the phosaphagen system does, but it has a much higher capacity so this type of exertion can last longer. An example of using the glycolysis system would be something like basketball, hockey or intense downhill skiing.
  • Oxidative System (Aerobic) – This is the lower-intensity, prolonged exertion energy system that relies primarily on carbohydrates and fat as fuel, although protein can be used as well in sustained efforts that last longer than 90 minutes. Things like sustained running (not sprinting), cycling, swimming and couch rugby all use the oxidative system. These are your traditional “cardio” activities.

Duration and Intensity of Energy Systems

These systems don’t work as though one just shuts off and instantly transitions to the next if you switch from sprinting to fast running. Instead, there can be some overlap.

Here is a breakdown of exercise duration, the respective intensity, and the energy system(s) used:

Duration of Activity Intensity of Activity Primary Energy System(s)
0-6 seconds Extremely high Phosphagen
6-30 seconds Very high Phosphagen and glycolysis
30 seconds to 2 minutes High Glycolysis
2-3 minutes Moderate Glycolysis and oxidative
>3 minutes Low Oxidative

Adapted from Essentials of Strength Training and Conditioning, 3rd Edition

Now that the primer on energy systems is done, let’s compare the pros and cons of weights and cardio.


Lifting heavy shit is cool. Nothing beats it. Were you to say you could only possibly do one exercise, and you asked me what to do, I would recommend weights. And I have objective street cred, because I qualified for and ran the Boston Marathon. This isn’t some cardio-hating meathead telling you this.

Weights give and they give. Here are the …


  • Gaining of strength and size, duh.
  • Easier for obese people to integrate. They are often quite strong and get positive reinforcement from early success. Also, weights allow for rest breaks for beginners who have a low threshold for sustained exercise. It is especially valuable for obese children.
  • Great for improving bone strength, which can be very protective for the elderly.
  • Another benefit for the elderly is how it helps them sustain their independence; they can continue to look after themselves because they’ve not become frail.
  • This is a big one: From a weight loss perspective there is a strong argument to be made that regular weight training has a major psychological benefit in terms of making the necessary dietary changes that lead to fat loss.
  • Weightlifting is protective; it strengthens / hardens your body against injury in other activities. It also has a low rate of injury when done properly.
  • Nutrient partitioning: You require approximately 2,500 calories of ingested food to build one pound of muscle. If you’re looking to lose fat while gaining muscle (which is totally possible), this assists by creating a greater overall energy deficit requiring additionally tapping into fat stores.
  • It can be done under the guidance of a trainer. This can be a con, but when you find a great trainer they can change your life for the better.
  • A gym can become a home away from home, where you embrace the culture and leave the stress of the day behind. Lifting weights is a fun and often a social endeavor. I’ve made many friends in the weight room.


  • Caloric burn is not nearly as high for weightlifting as it is for (intense) aerobic activity. What’s more, the stories you’ve heard about added muscle mass having a profound effect on resting metabolism is a myth.
  • From a physiological perspective, weightlifting does not bestow the same level of benefits for appetite control that cardio does.
  • Gym memberships can be expensive, and while travelling it can be difficult to find a place to workout.
  • There is a great deal of corruption in personal training, with trainers often being prized at their gyms for their ability to sell training packages over their ability to train clients well. They may also engage in creating learned helplessness, where they teach their clients in such a way that creates dependence upon the trainer. They don’t want their clients to graduate out of not needing them because it cuts into future income.
  • There is a lot of bad information about weightlifting permeating the Internet. The basics haven’t changed, but market forces keep creating newfangled bullshit ways to lift weights better, or something, because that’s what sells. It is even worse on the nutrition and supplement side.
  • It can be intimidating for some, especially if the gym they choose is full of douchebags.
  • There is a limit to how much you can do. If you have the time and inclination, you can’t lift weights for hours at a time, day after day – your body just can’t handle it. While this may sound silly, I get a lot of enjoyment from a four-hour bike ride or a long day of downhill skiing.
  • It can lead to obsessive / unhealthy behaviors, such as disordered eating or use of unsafe supplements / pharmaceuticals, especially for those interested in physique competitions.

Overall, the pros far outweigh the cons, and the cons are quite easily managed or avoided once one accepts and understands them.

Now let’s move on to …


There are many forms of cardio, but the big three would be those that make up the triathlon: swimming, cycling and running. Running is one of the most popular, although cycling gives it a good … run … in terms of popularity. Fuck swimming though. I hate doing lengths.

You have likely heard a lot of negative stuff about cardio. It is time to whip out Occam’s Razor and use it to cut through the bullshit. And the bullshit. And the bullshit. And the bullshit. And the bullshit


  • Wide variety of training possibilities. You can run, swim, cycle, do fitness classes, play a variety of sports, martial arts, hike, walk, engage in non-exercise activity
  • Caloric burn, while variable depending upon type and intensity of aerobic exercise, is generally significantly higher than that achieved with weightlifting, especially if you’re comparing something like running.
  • Ability to build up endurance for lengthier sessions beyond what would ever be possible with weights. This can be beneficial both in terms of adding to caloric burn as well as for pure enjoyment of a nice, long bike ride or a hike.
  • Significant health benefits especially in terms of internal organ function and promoting of longevity and compressed morbidity.
  • More profound physiological benefits than weights in terms of ability to suppress appetite and make wiser eating choices.
  • Can be used as a form of transportation, such as bicycle commuting.
  • Can be done socially, by running / walking / hiking with friends.
  • Can be easily integrated into travel, especially running / walking. I’ve seen cities all over the world by running through them.
  • Hiking allows for exploration of the outdoors.
  • For running especially, there are lots of opportunities to engage in competition at a variety of distances to suit your capabilities.
  • While my bike was damn expensive, you can buy an inexpensive one. Running doesn’t cost too much, as long as you don’t get carried away with the clothes or you’re not forking out a fortune to go run Boston.
  • Allows for thoughtful reflection and can boost creative thinking ability.
  • Ability to integrate anaerobic components such as interval training, which can be of great benefit to enhancing weightlifting ability.


  • Runners are idiots and manage pain and injury badly. Running injury clinics are a thing. They exist for a reason. It doesn’t have to be this way, but yeah, we’re dumb.
  • Stupidity about food. While cardio can give great physiological benefit in regards to eating behavior, psychologically we’re often stupid about food, using aerobic exercise sessions as an excuse to eat. Again, it doesn’t have to be this way. Use your brain.
  • On the above note, there is also potentially a problem with ego depletion, which is when cardio sessions become so lengthy that it drains the willpower resources necessary to control food intake. This is not enhanced appetite so much as it is a tired brain (from all the cardio) that simply can’t resist the tasty treats that are available to us 24/7. When I was training to qualify for Boston I actually gained fat, even though I was doing the hardest running of my life. Hell, my alcohol intake doubled because I just couldn’t resist beer.
  • Harder for obese people to begin except at low intensity. They often have low aerobic thresholds and can become exhausted quickly.
  • Endless. Fucking. Laundry.
  • The area next to my balls are permanently red. Good thing I’m married, as any new love interest would surely think I had some kind of horribly infectious disease.
  • Cost, especially if you travel for races or buy expensive bikes.
  • Needing a pool to swim in. That just sucks.
  • Lowered metabolic rate during exercise. While caloric restriction and weight loss will lower your resting metabolic rate, there is little evidence to show that lots of cardio has a negative effect on resting metabolism. However, you will become more efficient at aerobic exercise. A new runner will want to barf up his toenails after running a mile, with a high heart and breathing rate and extensive EPOC (caloric after burn). A well-trained runner has greater running economy (efficiency of movement) as well as an “in shape” body that can run that same mile at the same pace and have lowered heart and breathing rate, and minimal EPOC, and so fewer calories will be burned for the same amount of work. Because I am well trained I have a lowered metabolic rate than untrained James during exercise, but I also have the capacity to engage in a lot more activity and burn additional calories. I just have to do the work in order to compensate.

Conclusion: What about how cardio kills gainz, bro?

Nowhere is Occam’s razor more useful in the cardio vs. weights debate than in this area.

Lots of cardio can have an inhibitory influence on muscle growth. Inhibit, not stop. It is generally quite small, however, and is only an issue with those who engage in many hours of aerobic activity each week.

The silly memes of the scrawny marathoner next to the muscular sprinter are just that: silly. Competitive athletes drift towards what they are genetically best at. People who have an inherited tendency to short burst power will train for that sport and excel at it, as well as avoid anything aerobic. Same goes for those who are top marathoners, it is the genetically skinny folks who have bodies built for marathons that are top in this field. Also, they don’t want the extra muscle mass weighing them down, so they’ll avoid resistance training.

For the average person there is plenty of room to do both.

But cardio can inhibit muscular growth potential for one important reason: BECAUSE YOU’RE FUCKING TIRED!

I have a three-hour bike ride planned for today because it’s sunny out and tomorrow it’s supposed to rain, so guess how many weights will be lifted today. Answer: None! I’ll be too damn tired.

Engaging in a lot of cardio wipes you out, and makes it harder for you to get to the gym and lift those weights, or work as hard when you do go to lift. What’s more, an intense lifting regimen is also quite tiring, and is going to inhibit your ability to do a lot of cardio. I mean, unless you don’t have a life and can train your endurance to high levels in both areas, but your body and your schedule can only take so much, so it often comes down to priorities.

For the average person, I think there is room for a good amount of both, and at least you now have the knowledge you need to make informed decisions about your exercise choices and don’t have to rely upon some bullshit click-bait article to give you excuses not to do something.

If you’re having trouble managing your weight, be sure to check out my Caloric Deficit Cheat Sheet.

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James S. Fell is an internationally syndicated fitness columnist for the Chicago Tribune and author of Lose it Right: A Brutally Honest 3-Stage Program to Help You Get Fit and Lose Weight Without Losing Your Mind, published by Random House Canada. He also interviews celebrities about their fitness stories for the Los Angeles Times, and is head fitness columnist for and a regular contributor to Men’s Health.