Every superhero has their strengths. Some are strong, quick, witty; some can fly, and some are just plain fast- like The Flash. Why is The Flash so fast? Let’s let physics answer that for us:

Intensity is power per unit of area (basically). When measured, it’s usually watts per square meter (watts/meter2).

Power is essentially the rate of work, or the amount of energy used over time (force x velocity).

The Flash has superhuman speed. By applying high amounts of power (lots of force at a very high speed), and balancing the intensity in the right manner, he gets to places exceptionally fast. But if he didn’t apply his intensity appropriately through the ground, he might end up as inefficient as a windstorm. Power without control is useless.

What is the lesson in beginning with physics and superheros? Because a lot of runners waste energy when they run, and run with a higher intensity than they need to. High intensity running isn’t a bad thing, but it comes at a cost…energy. When it comes down to running, your goals are going to help guide you in this department. Avoiding intensity during running isn’t the goal, but finding the best balance and discerning the when & how much of intensity is how to help gauge running wellness and performance.

Running intensity is fairly complex. It encompasses multiple factors, that go beyond simple biomechanics of running, namely: Heart rate (HR), VO2 Max capacity, Respiratory Exchange Ratio (RER), Personal training history, MET’s (Metabolic Equivalents), Power output (watts), Rating of Perceived Exertion (RPE), and multiple others that can be measured. For the purposes of the STRIDE Running self-assesment, I want to focus on just three things that are pretty tangible for the runner:

  • Target Heart Rate
  • Rate of Perceived Exertion
  • Power Output

Target HR:

In common running training there’s something called the 80/20 Rule: 80% of training occurs at low intensity, while 20% occurs at higher intensity. The benefits in the long term reduce overall demands on your body, and help maximize the capacity to exert high amounts of energy during more important runs (races, etc.) The saying goes like this:

“Train slow to run fast.”

Adjusting for your heart rate, and having a good idea of where it is during a run will give you a good idea of how long you might be able to safely and consistently sustain a certain speed of movement. Finding yours is pretty simple, but takes just a little bit of leg work. Lot’s of resources exist to help you do so. The moral of the story in this regard is that your ability to take in oxygen, and apply it to fuel for your run is going to largely be done by your heart. Finding an optimal rate will assist in you maximizing your capacity to run at a high or desirable level.

Rate of Perceived Exertion (RPE):

This is a great way of self-assessment. The RPE began with Dr. Gunnar Borg, and ranges on a scale of 6-20. By multiplying 10 to someone’s perception of how hard they’re working, a fairly (and surprisingly) accurate heart rate at a given time can be given. It looks something like this (and has a modified version):



Power Output:

As speed increases, contact time on the ground decreases. To maintain the demands of your rate, a higher limb stiffness is required to prevent your body from breaking down. This happens with a well developed training plan (explosive and heavy lifting), and a highly trained neuromuscular system. Last week’s post detailed the perfect pendulum in rhythm- and this is a major factor you have control of in order to maximize power output during running. There are a few devices out there to try and accurately measure power output, called running power meters. As your body uses the right tissues in the right way (i.e. elastic recoil), you can maximize this by increasing the tolerance of the tissue to the demands of your running goals.

Not leaving out a great treasure of other tests- especially for the VO2max (Cooper 12-Minute, 1.5 M run, etc.)- lots of resources exist to help you discover a more wholesome understanding of how you’re made to run. (An exercise physiologist, appropriate Physical Therapist, or MD would be able to walk you through the details of these tests and/or how to obtain one.)

So your rate of work (power) applied over the best possible area of space, is going to dictate how efficient your intensity is during running. As you’re out putting in miles, assessing and re-adjusting for optimal intensity is a valuable way to ensure you aren’t wasting energy (internally or externally) where it doesn’t need to be applied. Additionally, using this factor in combination with some of the biomechanical considerations (strike pattern, contact placement, etc.) allows you to dictate more of the “how much” and “when” to generate more or less force during a run, whether training or race-pace. These “hows”, “whens”, and general judgement, or discernment will be covered in the next week of posts.

Just the tip of the iceberg, here.

In regard to longevity in wellness and running (the obvious benefits), a few resources are below:

Leisure-Time Running Reduces All-Cause and Cardiovascular Mortality Risk

Running as a Key Lifestyle Medicine for Longevity.

Reduced disability and mortality among aging runners: a 21-year longitudinal study.