Walking the return to run path after a bone stress injury (BSI) is often like navigating a minefield. Mentally draining, tedious, and potentially hazardous. Some obstacles we can see far away while others lie hidden carefully, waiting to pop up when you least expected. One step, one awkward movement, one run, and you’re back to where you started.
This is how a typical return to training and competition looks. A runner begrudgingly crutches into their physician’s office with a stress fracture diagnosis and beautiful black boot. The million-dollar question of “When can I run again?” is proposed, and unemotional calculation occurs. The runner quickly circles the specific date on their calendar and heads to the gym to tread water and spin on a bike. Time slowly passes like a kid waiting for Christmas. As the sun rises on the morning of the circled date, the runner happily exits their front door and starts their return to run progression.
Is this the best way to handle these injuries? How should we navigate returning to training and racing?
Let’s handle the first question…first.
How should we figure out when we can run?
The standard approach to this is similar to calculating the slope of a line—a simple formula. Determine the specific injury and follow a typical timeline for returning to running. The table below from Miller et al found that tibial stress fractures returned to running at 13 weeks. Flip through your calendar, earmark that future date, and patiently twiddle your thumbs to pass the time.
While this approach is common, I think we can do much better. Let’s start by discussing how bone healing impacts our decision.
Mending broken bones
We think BSIs heal through two different methods. The first method is targeted remodeling and is slow, tedious, yet effective. Targeted remodeling uses tiny cells called osteoblasts & osteoclasts to remodel our bones. Remodeling happens without our conscious thought and adjusts its effectiveness depending on what we eat, our stress levels, and what exercise we partake in for the day.
The second option is non-targeted remodeling. It’s a more systemic response that happens quickly. Our bone has a rapid increase in bone formation and makes a callus on the fracture site. Envision the hands of a Cross-fitter after a 6-month block of training. If targeted remodeling is an appropriately sized band-aid for a cut, non-targeted remodeling is mummifying your entire hand for a hangnail. It’s not as pretty, maybe a little over the top, but allows a quicker return to activity.
It’s important to understand how these injuries heal because it affects how we assign a timeline for returning to running, training, and competition. To figure out when we can run after a BSI, we need to answer three questions.
What type of bone is involved?
We have two types of bone in our body: cortical and spongy.
Cortical bone is along the outer margin of our long bones and is very strong. It takes between 4 weeks to 3 months for cortical bone to heal from an injury. Tibial and metatarsal BSIs are more “cortical” in nature. That’s a big reason why we can return fairly quickly to running following these injuries.
Spongy bone is present at the end of our long bones and is more central in our skeleton. The bones of our spine, pelvis, and proximal hip are more spongy. This tissue takes longer to heal and is affected to a greater degree by low energy availability and altered hormone function. It can take around 200 days for the normal spongy bone to heal. BSI’s of the sacrum, pelvis and femoral neck fit this category.
The type of bone involved plays a critical role in categorizing a BSI as high or low risk. Higher-risk BSIs take longer to return to training and competition (~ 26 weeks) while lower-risk BSIs have a shorter timeline (~ 13 weeks) This table adapted from Tenforde et al describes how we categorize our different running bones.
What grade is the injury?
To be diagnosed with a BSI, you need to have pain and relevant imaging. MRI is the gold standard for BSI diagnosis, with radiographs and bone scans less likely to pick up an injury. Every BSI gets graded I-IV based on its appearance on imaging. Nattiv et al found the higher the grade of the BSIs the longer the expected recovery timeline. Specifically, they found that for every one-unit increase in MRI grade, time to a full return to sport increased by approximately 48 days. The table below highlights different ways to grade a BSI based on MRI.
Who is the individual?
Every person is unique. Every skeleton is unique. Two different people can have the same grade and type of injury but have very different recovery paths. The medications we take, the sports we play, our relationship with food, and our genetics influence the strength of our skeleton. Our job, our relationships and our individual life can enhance or inhibit a full recovery. Our specific situation can shift the timeline and potential for healing substantially.
Stronger, more robust bones do a better job of healing. Unfortunately, endurance athletes are more likely to have deficits in bone mineral density (BMD) and bone strength than other sports. The uniqueness of each skeleton makes each recovery timeline different. An athlete with their first BSI, a history of playing multidirectional sports, and an appropriate relationship with food will have a different return to running than a runner with a history of multiple BSIs, disordered eating tendencies, and an inactive childhood.
Suppose a runner meets the criteria for the Athlete Triad or RED-S. In that case, it can take days to weeks to regain their energy deficit, months to recover proper hormone function, and years to recover our bone mineral density. Those are much longer time frames than the times for bone recovery and the average time for returning to running. If we have deficits in these three areas, our anticipated return to running and competition needs to change.
How should we progress back to training and competition?
The initial run progression following a BSI generally lasts a couple of months. During this phase, there is often little advice besides printing out a standard return to run protocol and continuing some basic exercises. There is a big difference between an athlete starting a run progression, returning to training with their team or group, and returning to competition. Those three phases have different goals and priorities which we must define throughout the process. The progression through those phases should be thoughtful, slow, and frankly dull.
This is a typical initial run progression and one I often use post-BSI. We run every other day, repeat each stage twice, and slowly increase our running volume. We’re not worried about pace, and we consistently check in with how the athlete is feeling physically and mentally.
There’s often a question hidden within the question “When can I run?”. The hidden question most runners want to be answered is “When am I going to be myself again.” It’s often not about when I can run for 1 minute, but when can I lace up at the start line and redline to the end of a race. Most runners navigate the initial phase of recovery without any problems but get off the tracks during the next phase.
If I have a runner diagnosed with a low-risk BSI on January 1st, I think it’s reasonable for them not to compete till the late fall. This allows the body a long time to adjust to the physical demands of running and gives us a more extended runaway for improving our bone health and progressing our nutritional strategy. A typical progression would look like this. During the first two months of running, the goal is to progress to running four days a week for 45-60′. Next, progress one training implement per month slowly increasing the volume/intensity throughout the month.
Month 1: Add in strides
Month 2: Add in tempo running
Month 3: Add shorter intervals
Month 4: Add longer intervals
When I say “competition,” I mean both the actual race and the necessary training to show up and “leave it all on the track/road/trail”. The goal of that first race would be to complete the race without any performance expectations. That would mean that a low-risk BSI, with an uninterrupted recovery, would return to competition 7-8 months following the diagnosis. That’s a long time.
In my opinion, that is how an ideal progression back to the initial competition would unfold. That’s different than what usually occurs.
Normally, there is a point when the steady, even slope of training quickly steepens like the face of a mountain. Consciously or subconsciously, there is a moment where training flips back to their previous training. Normally this sharp increase in training happens because the runner is discharged from rehab and left to their own devices or wants to enter a race.
Why should we take such a conservative approach?
First, the re-injury rate for BSIs is high. There is a 21% recurrence rate in collegiate runners, meaning the exact same injury. Runners with a history of a BSI at any site have an 11-17% decrease in tibial bone strength. For many runners, they start their recovery from a deficit. This is probably why many runners will sustain another BSI in a different bone or the opposite leg in the year following the initial injury. That risk is probably due to those three questions we already answered. Second, the mental challenge of returning to competition is often more challenging than the physical.
A few years ago, I was sitting at the finish line of a track meet. A patient of mine had returned for their first race in over six months. I was so excited for them. There was lots of anxiety, nervousness, and anxiousness as they lined up at the start. This talented runner with high aspirations would finish 45 seconds slower than their PR, take a few steps past the finish line, and collapse in tears. Not because of physical pain, but the self-reported mental pain of seeing the “worst performance of their career”. Over the next few months, they would be diagnosed with another injury and to my knowledge never return to running.
The athlete had met the “timeline” for returning to competition, but the medical team (myself included) left the putt short. We needed to take more time. We needed to push back when they would start racing. We certainly should have done a better job preparing them mentally for the race. They didn’t need more exercises. They didn’t need more “work on their form”. They needed more time and communication. There needed to be a mutual discussion around priorities, goals, and expectations. That conversation needed to happen multiple times over those six months.
One question I now ask every runner when they return to competition is…
How will you handle seeing the slowest time you’ve ever raced?
I hope the answer is something close to, “I’ll be ok with it for now because I know it’s a step towards where I want to be.”
If a high school or college runner applied this more conservative timeline, they would likely sacrifice a full year of eligibility. That’s quite the ask and I haven’t come to this conclusion lightly. I’ve seen too many runners that stay on the hamster wheel of stress fracture, after stress fracture, after stress fracture. I’ve had too many athletes jump back to competition too soon without the appropriate mental preparation to finish farther back in the pack with a time much slower than they’re used to.
When will we know a runner is 100% ready for competition?
We won’t know if an athlete is ready for competition until the competition is over. I’m no magic fortune teller and can only make an educated guess based on my experience, the literature, and knowledge of the individual. There is an inherent risk with physical activity whether we are discussing running, basketball, or pickleball. Increasing the training load of an individual increases the risk for injury. When dealing with adults the ultimate decision is theirs if they want to take a different approach different than myself. I believe it is my job to discuss the potential risks, benefits, and outcomes with them so they can make an informed decision. The ball is in their court.
The road to recovery after a BSI is long. If we get it right (always a challenge) we put our athletes in a better position to have a long relationship with running.
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Nathan Carlson PT, DPT, USATF
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Nattiv A, Kennedy G, Barrack M et al. Correlation of MRI Grading of BSI with Clinical Risk Factors and Return to Play; 5 Year Prospective Study in Collegiate Track and Field Athletes. Am J Sports Med. 2013 August; 41(8): 1930–1941.
Miller T, Jamieson M, Everson S et al. Expected Time to Return to Athletic Participation After Stress Fracture in Division I Collegiate Athletes. Sports Health. 2018 July; 10 (4): 340-344
Risk Factors, Diagnosis and Management of Bone Stress Injuries in Adolescent Athletes: A Narrative Review
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Popp K, McDermott W, Hughes J et al. Bone Strength Estimates Relative to Vertical Ground Reaction Force Discriminates Women runners with Stress Fractures History. Curr Osteoporos Rep. 2021 Jun;19(3):308-317.