“Swimsuit season” is almost here and there’s been a lot of posting about cardio on Reddit, Instagram, and anywhere else people discuss fitness and aesthetics. There is a lot of information out there… we’ve got the quick and dirty for you. Very nerdy chat about cardio, HIIT, and metcons coming your way! Shall we?


  1. Cardio by definition is “cardiovascular exercise” – per dictionary.com it’s “any type of exercise that gets your heart rate up and keeps it up for a prolonged period of time. Your respiratory system will start working harder as you begin to breathe faster and more deeply.”
  2. What makes cardio different from strength training is that it relies on your body’s ability to use oxygen during your session. A person’s cardio capacity can vary based on a few factors: genetics, sex, age, body composition, and fitness level. 
  3. Cardio training has advantages and disadvantages… so let’s start with the benefits, yeah?
    • Burns fat and calories, making it easier to lose weight.
    • Enhances your sleep quality.
    • Expands your lung capacity.
    • Improves your sex life. Hellooooo.
    • Helps you feel good about how you look and feel.
    • Reduces your risk of heart attack, high cholesterol, high blood pressure, diabetes, and some forms of cancer.
    • Strengthens the heart so it doesn’t have to work as hard to pump your blood.
    • Too much cardio can lead to overtraining in certain situations.
    • It can promote muscle loss by being in a constant calorie deficit.
    • If you do too much cardio, your body adapts to it and can retain fat even though you’re running and swimming every day.
  1. When people pick their cardio, they get to pick between steady state and interval training.
    • Steady state: Maintains a consistent speed, level of intensity and rate of work during a session.
    • Training intensity can be measured by keeping a consistent work rate/level at a certain percentage of max heart rate or VO2 max. If you wanna get really nerdy, you can work with RPE (ratings of perceived exertion) that gives you a scale of 1-10 to judge the level of difficulty.
    • Interval training: Alternates between periods of high-intensty exertion and lower intensity recovery.
    • Both the high and low intensity intervals can be measured as a percentage of max heart rate, VO2 max, or RPE.

There tends to be some confusion regarding HIIT on message boards, so let’s break it down.


  1. First, let’s talk about the advantages.
    • HIIT can be super effective at improving your aerobic capacity and/or calorie burning in less time than when compared to steady state training.
    • Interval training can be an effective strategy for people who get easily distracted or bored during workouts.
    • Can improve the efficiency of type-II (fast twitch) muscles.

Fast twitch muscle fibers are broken down into two types, type-IIx and type-IIa.

IIx: produce the most force, but are really inefficient based on their ATP activity, low oxidative capacity, and heavy reliance on anaerobic metabolism.

IIa: AKA intermediate muscle fibers. They’re a mix of type-I (slow twitch) and type IIx. They’re able to use both aerobic and anaerobic energy systems, and have a higher oxidative capacity and fatigue more slowly than type-IIx.

  • HIIT can help you train above your lactate threshold which can help stimulate production of muscle-building, fat-burning hormones like testosterone and growth hormone.

2. Now, the disadvantages.

  • HIIT increases mechanical damage to muscle tissue, which can lead to increased soreness and the perception of “painful” exercise in people who aren’t used to this type of training yet.
    • Anaerobic metabolism gives you an accumulation of metabolic stress, and that can limit a muscle’s ability to function.
    • High mechanical stress of HIIT can lead to increased risk of muscle strain.
    • Too much HIIT can diminish your glycogen stores and put you in gluco-neo-genesis… which we’ve talked about before on “Carbs are your friend” This limist the amount of protein available to repair muscle tissue after training.

3. We don’t want to forget about HIIT’s “less sexy cousin” LISS

  •  LISS: Low intensity steady state – Instead of short bursts, you’re aiming for longer, low levels of exertion over a period of time. LISS would be walking, hiking or cycling
    • LISS also has a ton of benefits: you’re burning fat, it’s great for cardiovascular capacity, and is also scalable and accessible to all fitness levels

Another question we see often, “Are HIIT and metcons interchangeable?” Let’s find out. 


1. Metcon is short for “metabolic conditioning” – a type of workout that will test your cardiovascular system to the max and will get your heart rate up while building muscle. Pros, cons, is HIIT a metcon? Is metcon HIIT? Here we go. First, the pros.

  • First and foremost, it helps you improve lean muscle mass. Hello. Isn’t that what we’re all searching for? Research has shown that both moderate and high intensity metcons can reduce body fat percentage. And regular weight training metcons can help you build muscle while working on your cardio fitness. Double win!
    • Muscles burn more calories than fat, we’ve talked about that quite a bit… and using metcons helps you add muscle tone to your body while improving your metabolism.
  1. Now, the cons.
    • As with anything, you can leave yourself open for injury if you’re not used to metcons, if you are interested in working conditioning into your training plan, please talk to a pro. They’ll steer you in the right direction.
    • It may require some equipment. This is where HIIT and steady state cardio have the advantage… especially if you’re in a budget or space crunch.
  2. So is HIIT a metcon? Is a metcon HIIT? What’s the difference? 
    • Metcons are high intensity, have fixed or variable rest that can depend on when the individual is ready to do the next set with good form and range of motion. Metcons can be done as weighted circuits, single activities (swimming, running, rowing, biking), gymnastic movements, or a combination of all of those.
    • On the other hand; HIIT is high intensity… 80% or more max heart rate or 8-10 RPE. HIIT has periods of rest or active recovery but they’re usually very specific, fixed periods of time. HIIT is often done in single modality activities like running, rowing, biking, swimming.. but there aren’t any set rules that these types of workouts have to just be one type… you can do bodyweight HIIT circuits too.
  3. So the answer is yes and no. HIIT can be a metcon but a metcon isn’t always necessarily HIIT. You know, how a square is a rectangle but a rectangle isn’t a square. 


Ease yourself into any cardio training plan to avoid injury and so you don’t hate your life. If it sucks, you’re not gonna wanna do the thing, right?

Find a good timer app or wall timer. There are all kinds of solutions for all kinds of budgets, if you need some ideas, we will have them in the show notes at meathead test kitchen dot com.

Want some metcon ideas? We gotchoo there too, find them in this week’s show notes.







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