Scientific Approach to Cardio: Is it Helping or Hurting?

Cardio is the one saving grace we can rely on to keep us lean, drop a couple pounds before summer, and cancel out that brownie (or 5) I just ate right?? … or wrong?

A funny thing happened when I started researching cardio- the more I learned, the less I did.

There is so much information that is thrown at us on the internet, social media, and in the magazines that catch our eye while we’re just trying to check out of the grocery store with our bottle of wine and chocolate in peace!! It is important that we apply science and research to these “facts” before we start throwing them into our training regimen.  Let’s ask some questions that will allow us to filter through some myths and truths about cardio:

1. How much food are you eating daily?

Your daily caloric intake will play a huge role in the effectiveness of your cardio.  God made our bodies to fight against harsh environments.  Eating less than our bodies, lifestyles, and activities demand is considered a harsh environment.  With survival as a priority, our bodies respond in the following ways (just to name a few):

  • Lowers basal metabolic rate (the majority of calories burned throughout the day)
  • Lowers calories burned during exercise
  • Lowers thermic effect of food (calories burned while we process food)
  • Increases fat storage
  • Disruptions hormone production
  • Decreases sex drive
  • Decreases energy in everyday activities

By introducing excessive amounts of cardio on top of a low calorie diet, we are magnifying the negative effects on our metabolisms.  Food is fuel.  In order to be fat-burning, sculpted, lean muscle-building machines, we need to eat.

2. What type of cardio are you performing?

Now that we’ve covered our diets… the type of cardio we are performing is the most important influencer of it’s effectiveness in weight loss.  Let’s break down the two most common forms of cardio:

High Intensity Interval Training [HIIT]:

  • Short bursts of all-out anaerobic work, followed by rest periods
  • Large fluctuations in heart rate
  • Creates metabolic adaptions (increases your metabolism), as long as you are reaching your anaerobic and lactate thresholds
  • Induces a 24 hour energy expenditure (the “after-burn” of calories)
  • Taps into abdominal fat storage
  • Increases mitochondrial capacity (where ATP is produced and fat is burned)
  • Allows retention and even increases in muscle mass, as long as cardio mimics multi-joint exercises with plenty of hip flexion

Low Intensity Steady State [LISS]:

  • Consistent period of work at a low to moderate intensity
  • No fluctuations in heart rate
  • Creates no metabolic adaptions, and even tends to slow the metabolism
  • Burns calories only in the given period of cardio, as opposed to the HIIT “after-burn”

Considering the major contrast between the two, choose your cardio based on your goals.  If your goals are to burn fat and build/maintain lean muscle mass, HIIT wins 10/10 in my book.  If you just want to lose a little short-term weight, enjoy the social aspect of going for a jog with your buddy, or find the idea of your face turning 50 shades of red while feeling like your lungs are going to explode (after running only the first sprint) a little unappealing, LISS might be the cardio for you!

3. Are you progressing your cardio week by week?

The body amazes me in many ways, and one of its most mind-blowing functions is its adaptability.  The body adapts rapidly to the environments to which we introduce them.  What does this have to do with cardio you might ask? E V E R Y T H I N G.  When you introduce LISS cardio into your program, your metabolism adjusts to the energy expended.  This means that the calories burned last week from cardio become the new baseline of calories you need to burn the next week to maintain your bodyweight.  Yes, you read that correctly.  I’m telling you that if you ran a mile every single day for 7 days and burned 100 calories each time, you might eventually burn as little as 0 calories running that same amount in the future.  LIGHTBULB MOMENT.  This is why we see initial weight drops from cardio, then complete plateaus after a few weeks.  So how do we ensure that we are benefiting from cardio?

Start with a minimal amount of cardio, then progress each week by only 1-2 intervals of HIIT or a few minutes of LISS.  Studies have shown that as little as 6 sprint intervals per week are enough to make adaptions in metabolic health.

4. How often are you performing cardio?

There is an inverse relationship between muscle gains and cardio volume, meaning the more cardio that you perform, the more your muscles will suffer.  Considering this point in combination with what we now know about adaptability- if you are performing cardio 5-6 days a week and are not losing any weight… you might be doing too much.  Less is more.  The key is to start with a minimal amount, and increase slowly week by week… or in my case, just retire cardio all together;)


Sources: Hoff J, Gran A, and Helgerud J. Maximal strength training improves aerobic endurance performance. Scandinavian Journal of Medicine & Science in Sports. 12: 288-295, 2002 MacLean, Paul S. et al. “Biology’s Response to Dieting: The Impetus for Weight Regain.” American Journal of Physiology – Regulatory, Integrative and Comparative Physiology 301.3 (2011): R581–R600. PMC. Web. 10 May 2017.


  1. Katie

    Hey Kori,
    I just watched your video and you said to email with questions so I will! One of my goals in 2018 is to focus on my health but I just don’t know where to start. My overall goal would be to loose 10-15 lbs and build lean muscle. I’m a pretty clean eater but have not been great about working out the last 2 Years and don’t feel like I know what to do at the gym. Also, I would love to know the some basics about what you recommend for protein intake and limiting sugar intake.

    I have thought about working with a personal trainer for a few months to get started but don’t know if that is necessary.

    Also, I know your sister-in-law, Courtney, from Baylor, which is how I found your site.

    Katie Holden

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