Picture this scenario… an athlete begins struggling with stress fractures. They rest, rehab, modify their training, and slowly return to sport. Then… they get another one. At that point, we have to start looking deeper.
Instead of only focusing on what caused too much stress on the bone, we have to ask, why wasn’t this athlete’s bone able to keep up with the stress?
We have to consider training load, biomechanics, and recovery time, but those factors are only part of the picture.
When an athlete experiences recurrent bone stress injuries (BSIs), especially alongside other signs of underfueling or Relative Energy Deficiency in Sport (REDs), we need to look beyond the injured bone and consider what may be happening throughout the entire body.
What Is a Bone Stress Injury?
The term bone stress injury describes a spectrum of bone injuries caused by repetitive mechanical loading.
Stress fractures are actually on the more severe end of that spectrum.
Bone stress injuries can progress from irritation and inflammation to bone marrow edema and, eventually, a partial or complete stress fracture.
Here’s the important thing to remember… bones aren’t static structures.
They’re constantly changing in response to the demands placed on them.
Bone tissue is continuously being broken down and rebuilt through a process called bone remodeling.
Think of it as your body’s maintenance system.
Old or damaged bone is removed through a process called bone resorption, while new bone is formed through osteogenesis.
Under normal circumstances, those processes work together to maintain strong bones that can adapt to training.
The problem occurs when the damage being created exceeds the body’s ability to repair it.
Training Creates Stress Your Body Has to Adapt To
Running, jumping, lifting and other forms of exercise create mechanical stress on bone.
That’s not necessarily a bad thing. In fact, appropriate mechanical loading can make bones stronger.
Athletes participating in high-impact and weight-bearing sports often develop greater bone mineral density as an adaptation to their sport.
But adaptation requires resources.
Imagine bone as a PVC pipe filled with a sponge.
The hard outside of the pipe represents cortical bone, which provides rigidity and strength. The sponge-like interior represents trabecular bone, a more metabolically active structure.
With appropriate training AND adequate recovery, that structure can adapt to repeated loading and become more resilient.
But when repetitive microtrauma continues without adequate repair, it’s a little like an ember slowly smoldering inside that structure.
Eventually, the damage can exceed the bone’s ability to rebuild.
That’s when we may start seeing a bone stress injury, and this is where we have to be careful about blaming training load alone.
Training Load Is Only Half of the Equation
When an athlete develops a stress fracture, it’s logical to examine training.
- Did mileage increase too quickly?
- Was there a sudden change in intensity?
- Did they change surfaces?
- Is there a biomechanical issue?
- Did they have enough recovery between sessions?
Those are important questions, but it’s only half of the equation.
Did the athlete have the physiological resources necessary to adapt to that training?
Bone formation requires energy.
It also relies on adequate protein, calcium, vitamin D, magnesium, phosphorus and other nutrients.
When an athlete isn’t consuming enough energy to support both training AND the body’s other physiological needs, the body has to start making trade-offs.
This is low energy availability (LEA), and when it begins affecting multiple physiological systems and health or performance, it may contribute to Relative Energy Deficiency in Sport (REDs).
Bone is one of the systems that can pay the price.
What Does Underfueling Have to Do With Stress Fractures?
We tend to think about food as fuel for exercise, but athletes aren’t only fueling workouts.
They’re fueling:
- Hormone production
- Immune function
- Cardiovascular function
- Digestion
- Brain function
- Growth and development
- Tissue repair
- Recovery
- Bone remodeling
When energy availability declines, the body doesn’t have an unlimited supply of resources to continue doing all of those things optimally. It has to prioritize.
Maintaining basic physiological functions takes priority over building stronger bones.
That’s one reason simply telling an underfueled athlete struggling with stress fractures to “take calcium and vitamin D” may miss the larger problem.
Those nutrients matter, but if the athlete remains in a state of low energy availability, supplements alone can’t provide the energy required for optimal bone formation and remodeling.
You can’t supplement your way out of chronic underfueling.
How Hormones and Bone Health Are Connected
The relationship between REDs and bone isn’t only about calories or calcium.
Hormonal changes associated with low energy availability can further affect the balance between bone formation and resorption.
Estrogen
Estrogen helps protect bone by reducing bone resorption and supporting bone mineral density. It also plays an important role in calcium absorption and retention.
That’s one reason menstrual dysfunction in an athlete with a history of stress fractures should raise a red flag.
A missing period isn’t simply a reproductive symptom.
It’s information about what may be happening elsewhere in the body, including bone.
Testosterone
Testosterone also contributes to skeletal health by supporting bone size and cortical thickness as well as muscle development. Greater muscle mass can create mechanical loading that helps stimulate bone formation.
This is also why REDs and compromised bone health aren’t only concerns for female athletes.
Male athletes can experience low energy availability, hormonal disruption and compromised bone health, too.
IGF-1 and Other Hormonal Changes
Low energy availability can also disrupt other hormonal signals involved in bone formation, including insulin-like growth factor 1 (IGF-1).
When those signals shift, bone resorption may begin to outpace bone formation.
Now add repetitive training on top of that. The athlete continues creating microdamage, but their ability to repair that damage isn’t keeping pace.
Some Bone Stress Injuries Should Make Us Especially Curious
Not every bone responds to low energy availability in exactly the same way.
Trabecular bone is highly metabolically active and sensitive to changes in nutritional and hormonal status.
Trabecular-rich areas include locations such as the:
- Pelvis
- Spine
- Femoral neck
Bone stress injuries in these areas can be particularly concerning when we are evaluating an athlete for REDs or low energy availability.
Location shouldn’t be interpreted in isolation, but it is another piece of the clinical puzzle.
And that’s really the point: Don’t look at one piece. Look for the pattern.
Red Flags That Should Prompt a Deeper REDs Assessment
A bone stress injury doesn’t automatically mean an athlete has REDs, and REDs isn’t the only possible contributor to poor bone health.
But when bone stress injuries and stress fractures are recurrent, or they’re showing up alongside other changes in health and performance, we should get curious.
Some questions worth asking include:
- Has this athlete had previous bone stress injuries?
- Has menstrual function changed or disappeared?
- Has the athlete experienced changes in libido or other reproductive function?
- Is bone mineral density lower than we’d expect?
- Is the athlete eating enough to support their current training load?
- Has training increased without a corresponding increase in intake?
- Are they restricting foods, food groups or carbohydrates?
- Has body weight recently changed?
- Are they intentionally pursuing weight loss or a lower body-fat percentage?
- Are they recovering appropriately between sessions?
- Have sleep, mood, energy or performance changed?
- Are there other REDs signs or symptoms present?
Sometimes, stress fractures are the symptom that finally gets everyone’s attention.
But if we look back, the body may have been sending warning signs long before the bone injury occurred.
What Happens When We Only Treat the Injury?
One of the athletes I discuss in my upcoming academic book experienced her first bone stress injury after entering collegiate athletics. She eventually experienced five BSIs.
During competitive seasons, she would lose her menstrual cycle. When an injury forced her to rest, her cycle would return.
Before one injury, her appetite had been suppressed for more than a month. She was emotionally distressed about missing another conference meet and was eager to return to sport.
Although she had been advised to take 12–16 weeks away from training, she returned after eight.
She knew she hadn’t been fueling adequately, but she wanted to get back.
Four weeks later, imaging showed that the original injury hadn’t completely healed and there was now a second injury.
That story illustrates something I want providers to think about:
What if the problem isn’t simply that an athlete returned too quickly?
What if we’re returning an athlete to the same physiological environment in which the first injury developed?
Rest can remove the training stress temporarily, but rest alone doesn’t necessarily correct low energy availability.
It doesn’t automatically restore hormonal function, address restrictive eating, or resolve fear or weight gain. It also doesn’t teach an athlete how to increase fueling when training increases again.
If those factors aren’t addressed, we may heal the current injury without addressing why the athlete was vulnerable to it in the first place.
Returning to Sport Isn’t the Same as Recovering From Stress Fractures
Athletes are understandably eager to return.
They’re worried about losing fitness, losing their spot, and watching teammates continue training while they’re sidelined.
Sometimes they’re watching the calendar, counting the weeks until the next meet, game or competition.
That’s why a return-to-sport timeline can feel incredibly frustrating.
But bone healing has a timeline whether the athlete likes it or not, and trying to rush that process can ultimately cost an athlete more time away from sport.
This is where interdisciplinary care becomes so important.
The physician may understand the grade and location of the BSI.
The physical therapist or athletic trainer may manage loading and progression.
The dietitian may recognize that intake isn’t matching physiological demands.
A mental health provider may identify anxiety, body-image concerns or fear surrounding fueling and rest.
The coach may provide important context about training and performance pressures.
Each provider sees a different piece of the athlete’s story.
We need those pieces together if we want to understand why the injury happened and reduce the likelihood of another one.
Don’t Stop at the Stress Fractures
When an athlete develops a bone stress injury, treating the injured bone is necessary, but especially when injuries keep happening, it shouldn’t be where our investigation ends.
Ask why.
- Why isn’t this bone adapting to training?
- Why isn’t it repairing adequately?
- Has fueling kept pace with training?
- Are hormones giving us additional clues?
- What else has changed in the athlete’s health?
- What patterns have we normalized because they’re common in sport?
A recurrent stress fracture isn’t always just a training-load problem.
Sometimes the injured bone is telling us to look at the whole athlete.
Want to Become More Confident Recognizing and Treating REDs?
REDs rarely presents as one obvious symptom with one obvious solution. Our job would be too easy then!
Athletes may come to you with recurrent injuries, GI symptoms, abnormal labs, hormonal changes, poor recovery or performance concerns, and it’s up to us as providers to recognize when those seemingly separate issues may be connected.
That’s exactly what we work on inside my REDs Informed Provider Certification Program®.
You’ll learn how to screen, assess and support athletes with REDs using a practical framework you can apply to the complicated, nuanced cases you see in real life.