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Running - it's more than miles

If you’ve ever listened to Dr. Kate and Dr. Kacy’s podcast, you’re familiar with the phrase “More than Miles”. But have you ever thought about what that means with your own training?

Weekly mileage is something that runners often talk about and use as a measure of their fitness, or progress towards a running goal. However, just looking at weekly mileage likely underestimates the actual training load that a runner is experiencing. A 2020 article by Paquette et. al notes that training stress – the physical stress experienced by our bodies while training, or in this case running – is affected by both external and internal load factors. External load factors include physical and mechanical stresses experienced by a runner, which includes distance, but also pace, ground reaction force, cadence, ground contact time and more. Internal load includes psychological stress from training and non-training related daily experiences, as well as physiologic load including tissue load (stress, strain etc experienced by the musculoskeletal system), heart rate, heart rate variability, and perceived exertion rate.

That was a lot of information, but what it boils down to is this: measuring the number of miles run only captures a fraction of what is experienced by the body when running. There are numerous factors, which may vary from one day to the next, that affect the training load. You also may have noticed that many of these variables, like ground reaction force, stress, strain, blood lactate, etc.- are difficult to quantify outside of a laboratory setting. The easiest calculated measure of training load proposed by these authors is duration of the run x rate of perceived exertion (sRPE).

So, if it may be one of the best ways to calculate training load, what is the rate of perceived exertion? Rate of perceived exertion, or sRPE is a person’s subjective quantification of how hard they are working. This can be affected by weather, the amount of sleep they have been getting, mental stress from work, school, and social pressures, how hydrated or fueled they are or aren’t, and more. sRPE can be measured on the Borg scale which ranks difficulty from 6 – 20, and is meant to correlate with heart rate. The Modified Borg Scale is a 0-10 scale and can also be used.

Using the volume of running multiplied by sRPE gives a more holistic view of the load that an athlete is experiencing during a run. If you have been a patient at Precision before, you probably have heard one of us say “stress is stress” (you can read Dr. Kate’s article about how social stress can lead to injury here.) Our bodies don’t know the difference between the mechanical stress on the body from a run or workout, the mental stress from work, and the physiological stress from not getting enough sleep the night before. All of that stress goes into one bucket and when the bucket overflows, we have injuries.

This is why using a duration x sRPE can be helpful for tracking changes in exertion, and reduce injury risk. Keeping a journal or spreadsheet to document minutes and sRPE of your runs can give you great insight. For instance, if you run 45 minutes at an “easy” pace on Tuesday and Thursday, but one run felt like a 4/10 and the other felt like a 7/10, it can be a good time to reflect on what was different, and what you could do to keep your easy days feeling truly easy. You can also compare week to week by totaling the sum of your training load for each week. If the total duration of running is staying the same, the training load should be about the same week to week. If you see an uptick in training load despite no change in volume, it can be a red flag that you may be at increased injury risk, and a cue for you to decrease your running volume for a week and let your body recover a bit.

Alternatively, tracking training load as minutes x sRPE can show that you are adapting to training loads well. A 60-minute run may have been a 6/10 last month, but now it’s consistently feeling like a 4/10. That shows that your fitness is improving! Or maybe you started working on your sleep hygiene and notice that sRPE on all runs is lower, a positive reinforcement that your new habit is supporting your training.

Athletes and coaches, I encourage you to look beyond weekly mileage. There is so much more to training, and only looking at miles run is missing the majority of the big picture, and increasing injury risk. Try tracking training load using duration and sRPE and see what you learn about your body and your training!

Thanks for reading, and happy running!

Dr. Elizabeth Karr PT, DPT

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