"You may tire of me as our December sun is setting
'cause I'm not who I used to be."
-Death Cab for Cutie

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In the last Runners Zone Podcast, Chris mentioned the idea of looking back at your old content to discuss what you got wrong.

With that in mind, I wanted to examine my ​most-viewed YouTube video, and what I would change if I made it today.

While I still believe this video holds value, it would have been better if it had included more context on the research on bone healing.

Today, let's cover three ideas from the video that need clarification.

• Bones heal on predictable timelines
• We have substantial research on BSI healing in athletes
• Certainty is necessary to move forward with rehab

Bone healing is a guess.

Bone heals through both micro and macro mechanisms. We can see the big stuff like a healing fracture line and small stuff like bone cell activity.

Remineralization, microarchitectural changes, and bone density recovery all play a role in bone strength, a variable we have to consider when determining whether an athlete is ready to return to sport.

Repeat imaging can be helpful in determining a patient's progress in recovery, but it can't capture the cellular aspects of healing.

The only real way to know a BSI is healed is to take the bone out of the runner's body and snap it in half.

Studies on bony healing in runners is slim

If you follow running accounts on social media or have taken a course from me, you've likely heard the following two statements.

• It takes 1-3 months for cortical bone to heal
• It takes 200 days for spongy bone to heal

Cortical healing

The 1-3 month estimate for healing actually has nothing to do with running. It's from a 1991 study by ​Agerbaek that collected iliac tissue from 10 healthy individuals.

The study wasn't examining distance runners, athletes with an eating disorder, or postpartum moms, just normal people.

Most of my patients return to running after a low-risk, cortical BSI within 12 weeks, but that isn't guaranteed.

Spongy healing

Spongy bone is more prominent around the spine, hips, and pelvis, and is believed to be affected to a greater degree by underfueling, hormonal dysfunction, and other health conditions.

When you hear "spongy injuries take longer" that idea comes from ​Eriksen​ looking at 89 post-menopausal women with osteoporosis.

Later in the article, the author highlights how health conditions can drastically alter timelines.

"The remodeling cycle can be as short as 100 days in thyrotoxicosis and exceed 1,000 days in low turnover states after bisphosphonate treatment."

In my experience, injuries to the sacrum and proximal femur take longer than those to the medial tibia. Whether that's because of the specific bone, the loads going through the injury site, or something else, who knows?

But there seems to be certain people who will heal slower than others based of their unique genetics, health, and life.

Rehab timelines come from college runners (who are kind of a mess)

At different points in college, I had a mohawk, a mustache, and was called NateCarl, not Nathan.

College is a weird time.

When you hear me (or others) speak about return-to-running timelines, you need to realize the following numbers are from college athletes (something I did a poor job of conveying in the video).

Collegiate runners contend with small scholarship rosters, crazy training loads, and fast teammates, all while being responsible for feeding themselves and finding a date for Friday night. Mix in a high rate of disordered eating and dicey team ecosystems, and you have a recipe for questionable rehab decisions.

Do these studies give us a guess at when a runner will return? Absolutely!
But it's a stretch to apply these numbers to all runners.

I don't know. You don't know. And that's ok.

If I remade that video today, here's what I'd say.

It takes as long as it takes.

Let's just make sure we are making a little more progress every week and trying are best to stay patient.