Trail Tips

The Body Doesn’t Know Miles, It Knows Stress

Let’s start with a thought exercise. Remember: the brain burns a lot of calories, so make sure you have some chocolate ice cream handy to replenish your glycogen stores afterward.

Imagine a run where you go out and frolic in the forest for an hour, letting your body flow on downhills and push a bit on uphills. You get back, and you are glistening with the post-workout glow composed of sweat, joy and a little bit of stray mucus. That’s a great run, right?

Now imagine some other scenarios, like we’re conducting an imaginary scientific study. In the control group, the runner goes watchless, showing off a scandalously naked wrist. In another group, the runner wears a GPS watch, uploads the file afterward and is dismayed to be 42 seconds behind their best climb time on the hill, with a slower overall pace than expected.

Take bridge engineering for example. When calculating maximum load, it’s a physics equation. It doesn’t actually matter how the bridge feels that day.

Those athletes had the same run, but one is relaxed and the other discouraged. We’ll get back to why that matters in a second. Before that, imagine yet another group, this one with an athlete that has a watch that gives mile splits. At the first mile, it beeps and vibrates. They look down and see . . . crap, 10 seconds slower than it felt. That runner turns around and goes home.

All three runners came in with the same physiology that day; however the third runner will develop less after the shorter run.

Here’s the really cool part: a developing area of training theory indicates that the relaxed runner may adapt more positively than the discouraged runner even though they underwent the same stimulus. On top of that, the stress they took into the workout can change how they perform and adapt.

Stress is the canvas on which athletes paint their training. If the canvas is waterlogged (or on fire), it’s tough to paint the Mona Lisa.

The Brain and Nervous System Can Be as Important as the Heart and Lungs

To summarize some of the work by researcher and coach John Kiely, the neurobiological context of training matters, often in non-linear and difficult-to-predict ways. Stress can cause long-term changes in adaptation processes from the cellular to the systemic levels. That way of thinking goes against how we traditionally envision cause-and-effect.

Take bridge engineering for example. When calculating maximum load, it’s a physics equation. It doesn’t actually matter how the bridge feels that day.

What if, instead of that, the bridge’s load-carrying capacity changed based on how the bridge felt about itself and what it was doing and what all the other bridges were saying about it? That would make it really hard to be a bridge engineer. The self-loathing bridge might break down at the first gust of wind, while the self-believing bridge might laugh in the face of earthquakes, even though all the other input variables are identical.

As much as it’s comforting to think we can control all of the variables, there is often little explanation beyond the amorphous concept of “stress.”

The same conundrum is faced by many runners, with input and output connected by an unpredictable maze of internal variables that are difficult to measure. Collectively, these internal variables can be characterized as stress: anything from higher training load causing fatigue or a busy life causing elevated levels of the hormone cortisol or menstrual cycle variability (or a judgmental GPS watch).

Anecdotally, I see stress-related phenomena all the time in coaching. My favorite examples involve “GPS dead zones” where watches consistently show faster paces (like some tracks) or slower ones (often forested areas or trails with lots of switchbacks). In my experience, runners in the fast zones improve more rapidly than those in the slow zones, likely because they deal with less negative stress about their running.

If I were a contestant on Shark Tank, I would pitch a GPS watch that tells runners they are going 30 seconds per mile faster than they are.

“But they aren’t actually going faster,” Mark Cuban might say. “You’re lying.”

“They aren’t actually going faster yet,” I’d respond. “Just wait six months.”


I also see it with injuries and health. An athlete might be going through a stressful time at work, or a divorce or a pet’s death, and suddenly an injury appears. In some instances, it’s a diagnosable physical ailment, likely caused by increased stress that made the body less able to absorb a training stimulus. But here’s the really interesting thing: sometimes, the athlete will get an MRI that is entirely clean of ailments despite severe pain. On a few occasions, the pain lifted when the clean MRI results came back. On others, the severe pain vanished after the stress passed.

Psychosomatic pain could be playing a factor, when there are physical manifestations of mental struggles. But giving it a label could stigmatize it—just know we all go through it to a certain extent, even if it’s just fresher legs after a promotion or sorer legs after a crappy presentation.

I have seen miraculous workouts after runners got engaged, terrible ones when an athlete is distressed about work, long-term fitness growth in a time of spiritual contentedness and everything in between. As much as it’s comforting to think we can control all of the variables, there is often little explanation beyond the amorphous concept of “stress.”

There Are No Universal Answers to the Stress Problem

The stress equation is complicated. Stress influences how you feel going into a workout, how your body performs during the workout and how it adapts after the workout.

Some underlying psychological mechanisms are likely similar to those discussed last week, related to positive self-talk. Maybe an uplifting or relaxed internal narrative makes for better daily runs by reducing perceived exertion (which, in itself is a catch-all, susceptible to several different variables), which makes for a better running over time.

In addition, as theorized by Kiely and shown in narrower circumstances across many studies, the neurobiological context of training changes how physiology works. If there is a surplus of negative stress, then it could lead to negative outcomes independent of what an athlete actually does in training.

This all sounds a bit up in the clouds, I get it. However, the takeaway message is simple: Think about stress (but not so much that it stresses you out). Every mile is not created equally for a single athlete over time, let alone when comparing across athletes. With that in mind, here are five quick-hitter things to remember or try:

  • Don’t try to do the training of someone living a different life

A pro runner might lounge around napping all day while you sleep 4 hours a night. The runner down the street might work a chill office job while you do manual labor. Heck, your competitor might just naturally handle the same stresses differently than you do, with their neurological wiring set to Matthew McConaughey while yours is set to Gilbert Gottfried. So cut yourself some slack and don’t compare. As McConaughey would say, you’ll be alright, alright, alright.

  • Monitor stress over time, rather than viewing training in a silo

Tracking mood and emotions can help you determine how ready your body is for increased training, or you might find that you do best in a heightened state where you are dealing with good stressors that keep you engaged.

Usually, stress is subjective, but some people swear by heart-rate variability, a semi-controversial tool that measures changes in duration between heart beats. You could use resting heart rate in the AM as well. Just remember that even with those metrics, how they apply to you could be different than how they apply to others.

  • Find relaxation techniques that work for you

Some people love meditation, some like reading, others like Netflix and chilling. For everyone, the more sleep the better. Just make sure you don’t elevate constant stress as a virtue to be cultivated, like you’ll see in many big law firms or universities.

  • If you use GPS, consider removing mileage from the watch face

Your runs should be independent of what your watch is telling you about your runs. GPS can add purpose to training, provide some fun data to peruse and even help you make more memories through a digital snapshot. However, I ask athletes not to be aware of mile splits, and do almost all intervals by time instead of distance. And if you can’t separate what the watch says from your perception of the run and yourself, ditch it altogether.

  • Think in terms of months and years, not days and weeks

The body is complicated, which makes sense because life and the universe are complicated. If the body handled stress in a straightforward, predictable way, it would be entirely out of character for what we know of existence. The unpredictability is especially evident if you zoom in and view training on the small-scale. Great workouts can come out of nowhere, as can injuries and three-hour crying episodes and the worst runs of your entire life. There’s a lot of noise mixed in with a little signal.

Instead, zoom out. Try to view your running training through a prism of long-term stress. Pay attention to how you actually feel (and not just physically). And remember to laugh as much as possible. There are no studies about how laughter affects performance, but we know smiling improves running economy. Thus, through a little extrapolation about what we know of stress and smiling, laughter might be the most productive workout you can do.

—David Roche partners with runners of all abilities through his coaching service, Some Work, All PlayHis book, Happy Runner, is co-written with his wife Megan and available for pre-order now at Amazon.