Bone stress injuries (BSIs) occur when microdamage from sudden onset or repetitive loading accumulates without adequate recovery. Bones undergo targeted remodeling, a process where a specific type of cell removes damaged bone before a different type of cell lays down new bone. This creates a period of weakness at the damaged site, which concentrates stresses there and can lead to further damage and eventually a stress reaction or fracture. 

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Bone stress injuries are a heartbreaking injury for runners - taking time off to heal can be a huge challenge emotionally, socially and physically, so preventing them is the primary goal.

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A 2021 narrative review discussed biomechanical contributors to stress fracture in military recruits and athletes with the hopes of predicting and/or preventing BSIs with an emphasis on the lower limb.

 

With prevention in mind, can we modify how someone runs or change their gait pattern to reduce risk for bone stress injury and avoid all the negative consequences that accompany this kind of running injury?

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The short answer: We don’t know. At this point, it appears that gait characteristics may influence risk for BSI, but “there is no evidence that interventions to modify biomechanics can reduce the incidence of stress fracture.”

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The long answer: Ok, well what do we know?

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Bones undergo both internal (muscle contraction & resulting pull on bone) and external (ground reaction forces) loads. Forces from muscle contraction are the primary contributor to total bone strain during movement. Loading bone through movement and exercise leads to microdamage and then stimulates adaptive bone formation - when this damage removal (called resorption and done by osteoclasts) is balanced out with bone building & remodeling (done by osteoblasts), bone strength and toughness increase and no fracture occurs.

 

 

 

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Muscle fatigue has been associated with increased tibial stresses which may increase risk for BSI. Muscles help regulate bone strain but also increase forces on bone - making the interaction between muscles/tendons and bone pretty complex. More studies are needed in this area to help us better understand this relationship in relation to BSI risk.

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As far as running form goes, “the biomechanical gait characteristics associated with lower limb stress fracture risk are unclear”. 

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Some studies have found higher ground reaction forces in those with a history of lower limb BSIs while others have found no difference. Some research has pointed to higher vertical loading rates as a risk factor, but since these studies were done on athletes who had already had a BSI, it’s unclear if increased loading rates were a result rather than a cause of bone stress.

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Studies looking at the relationship between footstrike and lower limb BSIs have also been inconclusive, with findings pointing more to the idea that “different mechanisms likely contribute to stress fractures at different lower limb sites and in different populations”.

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Gait retraining tactics like increasing cadence, decreasing stride length and increasing step width may reduce load at various body regions, but we don’t have the research yet to say these interventions decrease stress fracture incidence. 

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With that said, “Absence of evidence does not mean evidence of absence” (thanks Dr. Carl Sagan). Further research in this area may give us more & better gait-specific interventions to help reduce risk of BSI in runners.

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Until then, to help prevent or reduce risk of stress fractures, focus on:

1. Energy availability & appropriate fueling: It’s well documented that low energy availability (LEA) is associated with increased risk for BSI. LEA can cause disturbances in sex hormones, leading to changes in bone microarchitecture and decreases in bone strength. Ensuring you and/or your runners are getting enough calories is the foundation for reducing BSI risk.

2. Sleep: Sleep restriction reduces markers of bone formation which may increase injury risk. 

3. Progressive loading & logical training: Big spikes or changes in training lead to damage formation, and without adequate rest periods and recovery to allow remodeling, bone is more susceptible to injury. 

4. Strength training & plyometrics: Strength training increases muscle strength, which may reduce fatigue and potentially mitigate bone strain. Strength and plyometrics also may contribute to improvements in bone mineral density. 

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Recovering from a bone stress injury & looking for individualized rehab? Reach out below!