Stress Fractures 101 and a Root Cause Analysis

Week #2 of rest for my tibial stress fracture has found me with slightly more time on my hands since I’m not running, and a slightly cranky attitude from missing the glorious fall running days. I’ll talk about what I’ve been doing for cross training in the next post, but today I wanted to write about my answer to a question that was posed recently by a member of my running group: “What caused the stress fracture?” To try and answer this, I first had go into a bit of detail on what exactly constitutes a stress fracture.   Dr. Wikipedia defines a stress fracture as “a fatigue-induced fracture of the bone caused by repeated stress over time. Instead of resulting from a single severe impact, stress fractures are the result of accumulated trauma from repeated submaximal loading, such as running or jumping. Stress fractures can be described as a very small sliver or crack in the bone.”

Our bones are in a constant state of remodeling, with osteoblasts responsible for repairing the bone in response to stress. In sports where extraordinary stress is applied to the bone on a frequent basis (i.e. long distance running), these osteoblasts have to work hard to keep pace with our activity. Over time, if enough stress is placed on the bone that it exhausts the capacity for the bone to repair itself, a weakened area (or stress fracture) can appear.   We’ve overwhelmed the osteoblasts and they are unable to rebuild the bone fast enough to “keep up” with the repeated stress we are placing on our bones.

Muscle fatigue can also place a role in stress fractures. Both muscle and bone act as shock absorbers to the large forces placed on our bodies with each stride we take.   If the muscles fatigue enough (say, at the end of a long run, or during a particulary intense effort), they start to force the bones of the body to absorb more of the shock. And as the bones experience more of the stress, the risk of stress fracture increases.

So. Now that we know what stress fracture are (tiny cracks in the bone from repeated trauma), we can try to answer the real question: Why did this happen?

So let’s take a closer look at a few factors in my case:



  • Nutrition/Female Athletic Triad: This one didn’t even make the root cause analysis because honestly this is an area where I feel I’m doing okay. My nutrition isn’t perfect, but I work hard to eat well, and eat enough to support my high activity level. I have a healthy BMI, and I get my period each month. (so no Female Athletic Triad for me)
  • Size of calf muscles – I’m putting this on here because there have been studies that link the size of your calves to the likelihood of stress fractures. The bigger the calf muscles, the lower your risk. I’ve got very strong (and large) calf muscles so I don’t think this was a contributing factor.
  • Shoes – I pay close attention to the mileage on my shoes and rotate several pairs. I don’t think the choice of shoes was a factor.


  • Bone Density - I put this one on there because it’s kind of a question mark. I am fairly short (at 5’4”), fairly young(ish) at 33, and have been participating in weight bearing activities for years now (which are great for building bone density!), so I don’t think I have a problem with my bone density, but I don’t know for sure. I haven’t had it tested. My mother and grandmother are both much taller, but they do have bone density problems. So this one makes the list as something that MIGHT be a contributing factor and might warrant additional investigation if I were to suffer additional stress fractures.
  • Mileage – I have been VERY diligent about slowly increasing my mileage. I took a month off after my marathon in March and then slooowly built back up to my normal range of mileage. That being said, that “normal” range is in the 60s/70s and even though my body is used to handling it, it’s still a pretty big chunk of mileage.
  • Extra stress - The beach. I knew that taking 3 kids to Myrtle Beach wouldn’t exactly be a carefree vacation, but I didn’t anticipate how much the extra stress and activity would tax my body. I had a recovery week (mileage-wise) when I was there and only logged 37 miles – BUT I had the additional stress of the waves/sand, holding kids in the ocean, and up-and-down the steps to the condo multiple times a day while loaded with stuff. Couple that with some later nights and a few days of walking around all day pushing a stroller and it’s not a surprise that I came back more tired than I’d been (despite the lower mileage week).
  • Biomechanics - I’m hoping that this is a very limited contributing factor at best. I have been doing strength training and core work consistently for a while now in hopes to provide additional stability to all of the muscles in my body. However, I know there are two areas of weakness that may have contributed to this particular injury: very tight calf muscles and limited dorsiflexion of my ankles.     The calves have been tight forever. I do stretch them and foam roll them as well, but they are chronically tight. That could be placing more stress on my tibia as my calves aren’t able to stretch to their full extension with each stride.   The other biomechanical piece is the limited dorsiflexion of my ankles that may be placing additional stress on the tibia. I had been doing exercises a few months ago to improve ankle mobility, but have since stopped. Sounds like it may be time to reintroduce those!
  • General fatigue – The week after the beach I returned to my 70 mile week of running and was upset to find that I was still dragging. I told myself to just get through the week and I’d feel better, the legs would bounce back. But the fatigue lingered. This should have been my cue to maybe take a day or two off, but I was just flabbergasted by the fact that I SHOULD have been extra peppy – with only 37 miles the week before my legs should have felt great!   But what I didn’t count on was how much the different stress from the vacation would take its toll on me.
  • Intensity & Group Runs – For our group runs this year, I’m finding myself as one of the only gals in a group of speedier guys. This is great because it pushes me to get faster, but it’s also tough at times because in order to keep up with the group (and therefore have folks to run the long run with), I have to run faster than what my long run pace should be. (averaging 7:30s over the long run vs. a pace closer to 8:00 which is probably what my long run pace should be) Since I don’t want to run all by myself on those long runs, I’ve been keeping up with the group.   The downside of that is that Saturday long run turns into more of a workout and another day of intensity when you look at my overall schedule. So when we mix one tired Jen with a few weeks with hill repeats, some faster runs with the group, plus a half marathon, we get the start of the leg pain and most likely the emergence of the stress fracture.  Given that I was still feeling the fatigue from the beach, I should have changed something and backed off on the intensity. But I went ahead with the schedule as planned and that may have been my undoing. I don’t think that the hills (which were a new addition to my schedule this year) necessarily caused the issue, but that higher intensity workout on top of the faster group runs and the half marathon may have been too much.

The Bottom Line:

With so many factors that can contribute to stress fractures, it’s hard to really say for sure what caused mine. I feel like I was training in a very smart way this summer and built my mileage very, very slowly – and only to a level where I’d had lots of experience with before. (each of my marathon cycles for the past few seasons have had 12 weeks in the 70-85 mile per week range)

The biggest “red flag” for me came after talking to a good friend of mine (and 2012 Olympic Trials Qualifier) and she mentioned that some injuries are not necessarily the result of doing more volume, intensity, or running on a different surface, etc. – but how tired or how recovered we are when we do it.  She asked me if I could pinpoint being especially worn out and tired while trying to maintain a set training schedule – even though I’d done that cycle successfully in the past. She mentioned feeling “off” – like she was grinding or pounding more than normal when trying to hit a certain pace when she was tired.   Then that in turn would make her MORE tired, and she felt that if she went through that cycle without adequate rest, she felt prone to an injury cropping up.

This made a light bulb go off in my head. I had discounted the toll the beach had taken on me because, it was a VACATION, right?!?! I had reduced my mileage! Enjoyed the break! I should be so rested and rejuvenated…..shouldn’t I??   So when I jumped right back into my 70 mile weeks and added the hill repeats, I should have listened to my body when I felt like I was dragging that first week back. At the time, I didn’t want to take extra days because I was JUST STARTING my training cycle of 12 weeks. I was at the beginning! It wasn’t time for extra days off! I’d done weeks of higher mileage in the summer and felt fantastic! What was happening? When I convinced myself to keep going and that my legs would come around, I should have been telling myself it was okay to take a few days off to let my body get rid of some of the lingering fatigue.

So that’s the best I’ve got.   Not a clear-cut cause by any stretch, but maybe it was just enough to tip me over the line from “tired” to “injured”.   In any case, I now have more information about my body and how I might modify my training in the future if I run into a similar situation. A valuable piece of info, but just wish it didn’t come with a several-week-long forced break from running!

For more awesome information on stress fractures and great info on how to overcome them, check out Camille Herron’s blog post HERE.

Next post: Cross training and a bone stim machine?

Any advice from fellow runners out there who have dealt with stress fractures in the past? Agree with my analysis? See any other red flags? I’d love to read any and all comments!