For some, cardio is the Holy Grail of fitness. For others, it's a gigantic waste of time.
There are a few reasons for the negativity against cardio, such as overuse injuries, workouts deemed more effective that take less time, and sheer boredom.
However, the elephant in the room is how cardio is thought to affect your resting metabolic rate (RMR), which is the number of calories your body expends when you are at rest. RMR largely depends on muscle mass. The more muscle you have, the more calories your body uses, because there's simply more mass to fuel.
The idea is that building muscle increases the amount of calories you need on a daily basis, making it easier to lose weight or eat more food, which—let's be honest—is always a good thing.
Runners typically have nowhere near the muscle mass of someone who lifts weights. They're lean because they burn a ton of calories from activity, but their RMR is likely lower.
So herein lies the problem. If someone is attempting to lose weight, wouldn't it make more sense to build muscle than to engage in an activity that reduces the size of your engine? That's the logic behind creating long-term sustainable weight loss. There's no way around it.
This caused many folks in the fitness industry, myself included, to devalue cardio as a way to lose weight. In reality, it might not be so bad.
Dr. Jacob Wilson, CEO and director of Applied Science and Performance Institute in Tampa, Florida, recently pointed on his Instagram to a 1992 study on how resistance and cardio training affected RMR after 12 weeks of training on a caloric deficit diet. They found there was minimal decline in RMR for both groups.
The researchers concluded that either resistance training or cardio is appropriate for helping to maintain muscle mass when on a calorie-restricted diet.
That said, you shouldn't go all in on cardio if you want to lose weight. A blend of strength training, high-intensity workouts and cardio is the ideal recipe for success.
But you don't need to fear that a little cardio here and there will cause your muscles to wither away and your RMR to plummet. As Wilson said, "A little cardio never hurt anyone."
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