Stress Fractures: Genetics, Endocrine Health, and Frequent Poor Recovery



“I could drop a hammer on your foot”…anyone get the reference?

My first assumption, assuming that a runner is at an appropriate weight, is the biomechanical inefficiencies of their foot strike. The inefficiency may stem from muscle weakness or a less than optimal stride regarding knee lift and the loading phase of each step, but that too, can be caused from muscular imbalance or weakness. I have read that the cause may be from weak piriformis muscle, weak knee lift, tight calves, heel striking instead of mid foot striking or forefoot striking, the loading phase of each step is too heavy, etc.

Basically: there is no one answer because it depends on the individual but it always comes down to: cumulatively, the runner’s load per step was casing too much stress on their bones in the foot or tibia or femur or pelvis because their stride was inefficient or it was efficient but due to poor bone density from genetics, poor endocrine health, or over-training was still was too much stress on the site of injury.


A study from the National Institute of Health, “Engrailed Homeobox-1 Gene,” found from that our risk for fractures and osteoporosis is tied to the variation in the homeobox-1 gene that produces a protein, EN1, that makes up part of our bone density, so some people may be more prone to lower bone density. “The team genetically altered En1 levels and confirmed that it plays an important role in bone physiology. Loss of En1 results in low bone mass, probably due to high bone turnover.” I would like to point out that this study is not specifically studying young athletes, but still worth considering when pondering why some runners seem to do everything right (good shoes, soft surfaces, etc) and still manage to struggle with  fractures or when older athletes struggle with osteoporosis.

Endocrine Health

Endocrine Health is a significant factor, especially for females, but males have to worry about it, too. Honestly, as a female I feel very lucky in having a monthly way of checking to see if my hormones levels are where they need to be. I feel bad for male runners, as they are running around (literally) clueless. I will say this is more of a factor that may be a reason for lower bone density in females because most males don’t diet or watch their figure nearly as much as females, especially at young age when females are both very self critical of their bodies trying to alter it through dieting to look a certain way and when they should be building bone mass.

If a female runner’s menstrual cycle starts to become irregular or absent, guess what?…most doesn’t care and are even thrilled about mother nature skipping out on the expected monthly visit. Most women honestly have no idea that this means it is increasing their chances of possibly getting a stress fracture, losing fertility, or developing osteopenia or osteoporosis in the future. Numerous fellow female runners and female or male medical professionals have told me and my fellow female runner counterparts that it is normal for the menstrual cycle to disappear with intense training and that it will come back when we stop exercising so much. While this may be common, it is not healthy.

In the article run by Runner’s World, “Bone health in Highly Trained Female Athletes”:

Nineteen studies have been conducted in which the bone strength (measured as bone density) of normally menstruating women was compared to the bone strength of athletes with irregular or absent periods. Fifteen of these studies showed that bone density was significantly lower in amenorrheic or oligomenorrheic athletes. Three of the four remaining studies showed a trend towards lower bone density in amenorrheic/oligomenorrheic athletes…Women in late adolescence and early adulthood should still be building bone. Studies that measure athletes at a single time point cannot tell us if osteopenic athletes simply stop building bone or if they also breakdown existing bone. However, three studies have been conducted in which amnorrheic/oligomenorrheic athletes were measured yearly. These studies found amenorrheic athletes in their late teens and early twenties not only fail to gain, but actually begin to lose bone. The magnitude of bone loss is serious. Amenorrheic/oliomenorrheic athletes have 8 to 31% lower bone density than normally menstruating athletes, and 3 to 24% lower bone density than non-exercising, normally menstruating controls. Alarmingly, many of these women have extremely low bone mass; some have bone densities comparable to women in their 70’s and 80’s.”

Missing a menstrual cycle indicates that the runner is either very stressed, has some kind of endocrine dysfunction, or usually, is creating too large of energy deficits to function have a normal menstrual cycle. I emailed Camille Herron, a  biomedical researcher at Oklahoma City University and professional runner (2015 50k and 100k female world champion) about her take on this subject as an educated elite distance runner:

Q: As an elite distance runner and biomedical researcher, what is your response when someone says, “It is normal to miss a period or have an irregular menstrual cycle?”

A: “First off, I’m not a physician, and anyone who has an irregular cycle should consult with their physician first. If you’re of childbearing age, whether an athlete or not, it’s usually not normal to have an irregular cycle, but there can be genetic factors as well. From what I learned in my grad school nutrition courses is that getting regular periods is largely linked to energy balance– energy expenditure vs. energy intake. If this is off-kilter, it starts to impact the whole hormonal milieu, including estrogen levels and getting regular periods. It can lead to the whole female athlete triad and impact bone health as well. Monitoring your monthly period is a great way to know if you’re fueling adequately to meet energy expenditure demands. When it starts to deviate from what is normal for you, that can be a red flag that something isn’t right, usually meaning you need to eat more. I believe in intuitive eating, really listening to your body, and fueling it when it needs it.”

Q: How does missing a menstrual cycle affect the endocrine system and affect a woman’s long term running career?

A: I’ve been fortunate to be educated and surrounded by some of the experts, including my grad school nutrition professor Dr. Melinda Manore. There’s a whole cascade of interlinked hormones that are impacted if you’re not in energy balance, including the metabolic hormones (~thyroid, cortisol, leptin), reproductive hormones, and ultimately impacting ~bone, immune system, cardiovascular health, and running performance. I always say it takes a healthy body to perform at your best!

Q: As females, we are fortunate in that we get signals that we are placing too much stress on the endocrine system, but males don’t have a monthly way of assessing that–1)do you think that this potential for endocrine system disruption still exists in males and 2)What can they watch for as signs and symptoms?
A: The “man equivalent” of estrogen is testosterone. I’ve heard of several elites developing low testosterone issues. It can impact the same hormonal cascade as women! I really suggest that men work with their physicians if they’re deviating from normal in terms of fatigue, injury, immune function, and performance. Ideally, you should be getting blood work done 2-4 times a yr to monitor for possible hormonal and nutritional issues. I keep all of my paperwork so I know what my personal thresholds are– it’s good to know what these values are when you both feel good and feel bad.


I should really put this as: over-training or training hard with frequent poor recovery. Obviously, if the runner goes from averaging 30 miles a week to 60 miles a week, that is too high of a sudden change in volume. The same would go if they drastically increased the intensity of their training as well. Most coaches are aware of this and don’t drastically change the workload to avoid the consequence of sudden changes in training, which include injury. So most runners (I say most because there are those crazy workaholic type of kids) follow their prescribed training or follow it closely enough so that it wouldn’t fall too outside the appropriate amount, so why then out of nowhere did the running60-70mpw-for the whole year-out of nowhere-stress fracture come from? Most likely chronic under recovery, but a drop in performance or ability to work out hard will be probably be detected prior to running on fatigued muscles for an extended period of time. Low fat diets and not getting adequate carbohydrate and protein after hard sessions to repair muscle are some dietary reasons linked to stress fractures.Running at a hard effort too often, running on hard surfaces, and never taking days off or breaks off also would contribute to poor recovery either from day to day or season to season.

Sarah Bradley
Expanding on her passion for distance running, Sarah Bradley, is a young lady who finds great enjoyment in interviewing people on their journey pertaining to the sport of track and field and writing about various topics within the sport. She wishes the insights, experiences, and self reflections shared may serve someone, somewhere. Beginning running recreationally at age 18, she has since found substantial improvement. She is mostly silly, but on occasion--when she drinks enough coffee--she is fully enticed in the pursuit of her very best.

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