The Pros and Cons of High Intensity Training

By: Coach J

First lets start by defining the term Intensity with regards to fitness.

  • Greg Glassman, the founder of CrossFit, defines Intensity as Power Output (force x distance / time). The higher the power output, the higher the intensity.
  • Others look at heart rate to determine intensity, where anything over 80% of max heart rate would be considered high intensity.
  • Lastly, some will use a Rate of Perceived Exertion scale to measure intensity. This is usually a 1-10 scale of how hard someone ‘feels’ they worked and anything 8 or higher would be considered high intensity.

For this discussion, lets use the RPE model – I believe its easier to relate to as most people don’t measure their heart rate or use their TI-83 calculator to determine their power output for each workout. Soooo, you know you’re doing high intensity training if you’re breathing very heavy, you feel burning in your muscles, your thoughts are less focused on your movement and more focused on your output, and your effort is not sustainable. With that said, lets talk Pros and Cons:


  • Improvement in work capacity (ability to do more work faster)
  • Faster workouts – you can get more work done in a shorter time which can be beneficial for busy people
  • You push yourself to do things you probably didn’t think were possible – thats kinda cool!
  • Could promote faster results (results usually slow as training age increases)


  • High Intensity training puts a lot of stress on your body (especially your heart and nervous system). If you live a generally high stress life (from work, family, relationships, etc) and you add high stress from your workout, you may be burning the candle at both ends – this could result in poor progress, high blood pressure, injury, poor sleep, fat gain, etc.
  • In order to reach a high intensity in a workout, you must try really hard, and when you try really hard, it is very challenging to focus on the actual movement you’re performing – so unless you’re performing movements / loads that you’re really, really good at, you could hurt yourself. That’s why its important to focus on your movement first and intensity second.

In closing, if you enjoy pushing yourself to a high intensity, you’re best off doing movements at loads that you can perform well with very little thought when you’re breathing heavy and tired. For some, the best exercises for high intensity training are biking, rowing, ski erg, etc. Remember, movements themselves are not good or bad for high intensity training – its all relative to the persons ability to perform the movement when fatigued.

Lastly, if you are chronically stressed from work, family, etc. you will get more out of low intensity training even though it doesn’t ‘feel’ like you’re doing as much work. Remember, stress is stress, and too much stress, too often, can wreak havoc on long term health and fitness.