Cardio and Lifting at the Same Time: Why it’s a Bad Idea

So, is doing cardio and resistance training concurrently really that bad of an idea? In truthfulness, it depends. In general, most people at your gym are there to look and feel better, and, in order to achieve this, they are likely trying to burn fat and build lean muscle mass in hopes of achieving an attractive physique.

In order to achieve this, these folks are probably lifting weights to build the muscle and doing some form of cardio to burn the fat. While the concept is correct, the application, from my perspective, is wrong and hurting these folks from achieving their goals.

When a person is lifting weights, an enzyme known as mTOR (short for “mammalian target of rapamycin”-- don’t worry, you don’t have to memorize that) is released to tell the muscle fibers that they will need to grow larger in order to adequately perform the lifts in the future.

Additionally, when that same person is doing cardio, his muscle cells realize that the energy factory in the muscle fibers, known as the mitochondria, must be larger to complete the endurance workout. The enzyme released that lets the muscle fibers know that mitochondria has to increase in size is AMPK (5’ AMP-activated protein kinase).

The reason why performing cardio immediately before or after a resistance training session is that the AMPK acts as a barrier to several mTOR receptors, therefore, the signal that tells the muscles fibers to grow in size is not being received as efficiently as it could have.

In other words, imagine that you are trying to receive a message through a CB radio during a blizzard; chances are, the static will interfere with your ability to hear what the other person is saying.

Fun Fact: While endurance training may negatively affect muscle strength and size gains,

resistance training does not appear to have the same effects upon endurance training gains.

Does this mean that you should avoid cardio? ABSOLUTELY NOT!!! However, some planning is required, so you don’t repeat the mistakes that so many continue to make.

Dr. Andy Galpin, tenured Professor in the Center for Sport Performance at CSU Fullerton, has a list of 5 approaches that you can adopt if you want to do both cardiovascular training and resistance training:

  1. Reducing the number of endurance training sessions to 1-2 times a week

  2. Reduce the time/mileage

  3. Perform endurance training on non-resistance training days

  4. If doing both resistance and endurance training on the same day, give yourself more than 4 hours between the two

  5. If there is no way any of the above can be done, leave the endurance training for last.

So, there you have it-- gym bros were actually right...to a certain extent. Hopefully, this will give you a better idea on training without killing your gains.

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