Bone stress injuries are a terrifying problem. On one hand it’s not the most likely issue to creep up on an athlete, but when it does, you’ll scream in fright as this silent terror unleashes its killing blow onto your training program.

“What is a bone stress injury?” you ask as you begin to quiver in your seat. Simply put, it’s bone tissue FAILURE due to repetitive mechanical loading. Initially, it could be recognized as swelling in the outer periosteal layer or in the marrow. Eventually, it can progress to a legitimate stress fracture.

Perhaps the scariest part about bone stress injuries isn’t the annoying fitness losses, it’s that bone stress injuries tend to be HIGHLY predictive of future bone stress injuries (600% increased risk in females, 700% in males) that ultimately result in further horrific setbacks. This is particularly the case in the 6-12 months following the first bone stress injury.

In an ideal world, prevention of bone stress injuries comes through proper dietary intake and appropriate rates of activity increase with intermittent blocks of decreased training. In reality, people tend to under-fuel and ramp their training loads up far too quickly without taking rest days, rest weeks, and rest months, which really means that all bone stress injuries are due to training errors and you’ve brought about your own terrible demise! Bwahahahahaha! Suffer now, you will!

And this, unfortunately, leads me to the first, and most critical, spooky fact:

Distance running does not build the best quality bone structure!

Nooooo! Now that you’re covered in goosebumps and absolutely frozen in fear, let’s talk about the misconception that all the repetition of running must surely lead to strong bones because at least it’s weight bearing and you’re relentlessly smacking your skeleton into the ground a bunch.

Unfortunately, endurance running is not the best activity to create the stresses that optimize bone metabolism or build the highest bone density. Some really smart researchers have determined that we benefit best from high loads that are moved quickly to create the bending stresses and strains that stimulate bone turnover. While the forces of slow running are fairly large, it doesn’t involve sufficiently rapid or intense enough forces to encourage maximal mechanosensitivity in the bone. More specifically, for the real nerds, bone responds best to greater than a 3.5x bodyweight ground reaction force delivered in under 0.1 second. Slow distance running tends to induce under 3x bodyweight ground reaction force in a more prolonged 0.15 to 0.3 seconds.

In addition, the bone essentially becomes bored with the highly repetitious, mostly single-plane nature of long distance running after a shockingly short span of time. The best period of mechanosensitivity to get the bone’s attention occurs from 1-20 reps, diminishes between 21-60 reps, and becomes quite poor past this point. Last I checked, 60 steps would be a really short run. Have you considered becoming a 100 meter specialist for the sake of your skeleton? Oh God, anything but that!

Ideally, areas of ongoing bone damage are resolved at the same rate as new bone formation. Distance running creates a conundrum because it demands thousands of mildly stressful repetitions that aren’t necessarily going to create an equal magnitude of response in bone growth, thus there’s a tendency for the tissue to fail faster than it can repair.

So how do we get around this bony boredom debacle and save your scrawny skeleton? One option is by performing plyometrics and weight training at a separate time of day, preferably 4 to 8 hours ahead of or after a run. But it might be more reasonable to emphasize this plyo and strength work on days when you distance run less or skip running entirely, which would be optimal for muscle strength gains too. It really doesn’t take much of a dose if you encourage heavy lifts. Ideally, the spine, torso, arms, and legs are loaded with exercises like back squats, front squats, and deadlifts, 2-3 times each week for 2-4 sets of a very challenging 3-5 reps. Remember that 1-20 total reps range?

Another option relates to the fact that athletes with the strongest skeletal structures tend to come from sports that require rapid directional changes, jumping, and sprinting, which all induce more desirable multi-planar bony stresses. Consider entertaining those bored bones with regular soccer, basketball, lacrosse, tennis, aerobics, or volleyball, especially if you have less desire to strength train or simply like to mix up the week’s activities.

Early sports specialization, especially in endurance sport, is the devil’s work

Wow, that’s the most dramatically terrifying title yet, but for good reason. There’s a limited time frame during puberty to lay down the main structural components of a bone in large quantities. Based on what I just mentioned about endurance activities not doing a great job of stimulating bone production, you should realize that youngster’s skeletons very much benefit from the explosive sprinting, cutting, and jumping that are mainly performed in activities outside of endurance running. With appropriately varied long-term demands, youthful bones can even increase in size, but this is not known to happen in adulthood.

I’ll use this opportunity to also mention that many of the highest level elite athletes have exposure to other sports through childhood and puberty before they ever specialize. (Tiger Woods specialized early and you can see how unhappy that guy is now). This emphasis on variety is particularly important for movement skill development. These factors are one of many reasons the American Academy of Pediatrics recommends delaying sport specialization until ages 15-16.

To be clear, you aren’t doing your kid’s performance, skills, bones, muscles, and tendons any favors by trying to specialize them, especially before age 9, or force them into year-round single sport training. They absolutely need variety. They need to play and have fun because that’s when they learn to move their body best. And they need periods of rest every month and every year to let the growth of their body take priority. Professional athletes rely on 2-3 month off-seasons so why wouldn’t an immature human need the same thing, if not even more?

Location of a bone stress injury may indicate darker truths

Can you feel that deep, searing pain in your spine, almost like you are being stabbed with a dull, rusty butter knife? According to University of Montana PT professor and well-known running injury researcher Rich Willy, bone stress injuries that are closer to or at the body’s core (pelvis, sacrum, spine, upper femur) have a greater tendency to indicate Relative Energy Deficiency in Sport (RED-S), which is essentially the metabolic result of an insufficient intake of calories over a prolonged period of time.

Even with the world’s worst running form, excessively stressful loads should have had a chance to be filtered out and dampened by the lower leg and thigh muscles before they ever reach areas like the spine and pelvis. These central sites tend to have more metabolically active, vascularized, but less mineralized, trabecular (spongy) bone content, which heals and adapts slower than the hard cortical bone that we think of when somebody says the word “bone.”

To the contrary, the further you move away from the core (eg. tibia, calcaneus, metatarsals), the more likely a person’s biomechanics are to play a role in the onset of a bone stress injury. These folks can respond well to gait retraining, especially one of the more common interventions – a cadence increase.

This isn’t to say that gait retraining isn’t worth a look for higher fracture sites, but it’s probably not the first hurdle this athlete needs to clear. It also isn’t to say that I’m not going to drill people with questions about nutrition if they have a suspected stress fracture in the lower leg or foot. In the end, your endocrine system needs to stay healthy, which means there’s consistently enough fuel for the body to recover and heal AND perform the sport activity.

If you think carbohydrates are scary, just wait until that stress fracture shows up

The trend of “going low carb” has found popularity among some distance runners and functional fitness fanatics. High-protein people love to ramble on about how early human ancestors relied on few carbs and constantly smelled of blood. Perhaps that’s true. But another likely truth is that people didn’t “train” day in and day out because it would be wasteful to burn energy without actually accomplishing something that contributed to survival. WOOOOOO WEEEEEE WOOOOOO WEEEEEE!

Don’t worry, that’s just the sound of my bullshit alarm. Survival through frequent low intensity daily movement to scavenge and hunt food is not the same as modern intentional fitness training. Ancient people didn’t log 40 to 100+ mile running weeks as a hobby, jamming their daily distance into an hour or two of near-constant high intensity zone 3+ heart rates. They weren’t in a never-ending pursuit of 5K PRs or maxing out their back squat. They were just trying to stay alive by eating enough (which interestingly included far more carbohydrate from plant sources than Mr. Keto wants to admit). And they certainly didn’t plunk down in front of a computer to do nothing for another ten hours of the day while nibbling on their kid’s leftover Halloween candy. Comparing your metabolism and lifestyle to that of a caveman as an argument to eat less sugary crap that you shouldn’t eat anyway seems… questionable.

Much like the brain, bones like carbohydrates. Shifting your dietary habits to avoid carbohydrates before, during, and after prolonged exercise while increasing fat and protein content will alter bone metabolism, most likely in unfavorable ways that haven’t pinged on your radar.

Another time fasting becomes a factor is in the morning exerciser who skips breakfast. One day, no big deal. But weeks of running in a fasted state can have consequences for your bone health. This is especially concerning in those folks that tend to have a suppressed appetite after exercise, so even more hours pass before the body has sufficient nutrients to repair itself.

Interestingly, eating carbohydrates during prolonged running appears to negate some of the acute markers of bony breakdown after exercise. You’ll note I’m not suggesting you eat super sugary junk food all the time as high glycemic carbohydrates may actually be detrimental to bone health. Think whole grains, more fiber and emphasize eating enough calories overall, including fat and protein.

In the end, any dietary restriction creates a risk factor for energy and micronutrient deficiencies, both of which dictate performance and recovery and can lead back to the RED-S mentioned earlier. When your body needs to recover and heal, it doesn’t matter if your nutrition changes were well-intentioned. Heck, they might even be necessary for your basic health (eg. a food allergy) but you may need professional guidance to maneuver around those issues. What matters is whether your body actually has a consistently sufficient supply of macronutrient and micronutrient building blocks to take care of itself, day after day. Your body’s primary goal is sustaining itself as a living organism, not enhanced performance for leisuretime athletic endeavors. If you don’t get down goal #1, #2 definitely isn’t going to go well.

Spookiest of Sources:

Personal notes from University of Virginia Running Medicine Conference 2023

Personal notes from University of Virginia Running Medicine Conference 2020

Biomechanics and Mechanobiology of Trabecular Bone: A Review

https://www.ncbi.nlm.nih.gov/pmc/articles/PMC5101038/

Preventing bone stress injuries in runners with optimal workload https://www.ncbi.nlm.nih.gov/pmc/articles/PMC8316280/

Rich Willy’s Bone Stress Injury Masterclass

https://www.youtube.com/watch?v=7bIFh_h7P0c

Doctors of Running Podcast with Rich Willy

https://www.youtube.com/watch?v=dQfTkmef_s4&t=16s

Effect of carbohydrate feeding on the bone metabolic response to running

https://pubmed.ncbi.nlm.nih.gov/26251510/