5 Keys To Prevent Bone Stress Injuries In Runners

Bone stress injuries have a shockingly high incidence rate in running sports, with estimates of 4.9-21.1% in cross country runners each year (1). Having a history of bone stress injury (BSI) is a risk factor for future BSI’s, so we want to help our clients prevent them in the first place to have a long, healthy running career. Here, we’ll review 5 keys to preventing BSI’s in runners.

Why do BSI’s happen?

When a bone is loaded sufficiently, a micro crack develops. When that micro crack develops it takes about 10 days for osteoclasts to arrive at the micro crack. Once those osteoclasts arrive they resorb (break down) that damaged bone which temporarily makes the bone more porous and less stiff. Typically, this resorption happens for about 21 days, so the bone is actually becoming increasingly vulnerable and sensitive to loading (2). Then the bone begins remodeling and bone mass is restored to pre-micro damage levels.

However, if high levels of loading continue or even ramp up in volume and/or intensity when the bone is in a more porous, less stiff state, a vicious cycle is set in motion. The now porous and less stiff region of bone accumulates more stress, leading to further micro damage, which leads to increased porosity and decreased stiffness, eventually leading to a stress reaction. If this persists, it can lead to a stress fracture and potentially a complete fracture if not addressed. In short, BSI’s happen when repetitive loads on a bone outpace its ability to remodel and recover.

To dive deeper into why BSI’s happen, see Dr. Stuart Warden’s Masterclass on bone stress injuries.

Where do BSI’s happen in runners?

In long distance runners, roughly half of BSI’s occur in the diaphysis of the tibia, while the remaining tend to occur in the femur, fibula, calcaneus, tarsals and metatarsals (1). Understanding the location of where BSI’s occur is crucial not only for diagnosis, but also for prevention, since a history of BSI is a strong risk factor for developing a future BSI. For example, if a runner previously had a tarsal BSI they may be more sensitive to running uphill and this type of training might need to be increased more conservatively in order to prevent a recurrence of injury to that area.

How do we prevent BSI’s in runners?

BSI’s are multifactorial, but here we’ll focus on 5 key training considerations to decrease BSI risk:

1. Avoid major spikes in loading

As mentioned earlier, bone can remodel and adapt if loads are progressively increased. A commonly used paradigm is the “10% rule”. This guideline suggests that the workload should be increased by a maximum of 10% each week. Note, this guideline tends to work at a population level, which means it won’t fit all runners. For some runners this progression may be too fast, while others may be able to tolerate spikes in loading in excess of this guideline.

In general, there are two common situations where we see a large spike in loading:

The sedentary individual that begins running. In a study of military recruits, those with 1 month or less of running experience had an increased risk of suffering a BSI in basic training (3).
The track athlete during preseason. Research shows that collegiate level athletes have a 43% increased risk of BSI during the preseason, since they may be ramping up training too quickly after taking time off from their sport (4).

Runners in these situations likely need a slower progression to reduce BSI risk. In addition, examining other BSI risk factors helps determine how conservative their increase in workload should be. Some risk factors to consider are: hormonal status, nutrition status, presence of a bone disease, and injury history (i.e. recent immobilization, history of BSI) (2).

2. Increase volume, then intensity

The workload placed on a bone is related to the volume (number of loading cycles) and the intensity (magnitude and/or rate of load). While we want to gradually increase both over time, bone is more sensitive to changes in intensity. Research shows that fracture risk rises at a much faster rate with increases in intensity as compared to increases in volume (2). So when considering changes in training, think volume first, then intensity. For more details on how to progress volume and intensity, check out Dr. Warden’s Masterclass here.

3. Rest periods from running

To allow adequate recovery and adaptation, we want to include regular breaks from the repetitive loads of distance running. While this will vary on an individual basis, a starting point for cross country runners (who may be running high volumes year round), could be the following rest schedule (2):

Weekly: 1 day off
Every 3 months: 1-2 weeks off
Yearly participation limited to 9-10 months

Of course, runners with a lower training volume may not need as much rest, so that rest should be adjusted based on the individual’s target training and competition schedule. Also, to clarify, rest does not mean total rest from all training. We would still employ other forms of training in those rest periods such as swimming or biking to expose the body to a different loading profile than that of running.

4. Monitor environmental changes

Different environments imply a different direction and magnitude of loading. For example, running on trails and hills represents a different load pattern for the lower extremities, compared to a treadmill. Just like intensity, any changes in the environment should be introduced gradually. A general guideline is to introduce a new environmental change 1 day per week (e.g. if running 5 days per week on asphalt, trade 1 day per week for trail running) (2). Also, as we discussed previously, if an athlete has a history of BSI, they may be more sensitive to certain surface changes (e.g. a tarsal BSI and uphill running).

5. Modify running technique

Technique can significantly impact the magnitude and direction of lower extremity loads in running. A relatively easy and effective technique modification is to increase step cadence by 5-10%. Research shows that this reduction in stride length leads to decreased braking forces upon landing, resulting in a lower magnitude of load on the lower extremities (2).

Wrapping up

In summary, here are 5 training tips to prevent bone stress injuries in runners:

Avoid major spikes in loading
Increase volume, then intensity
Employ rest periods on a weekly, monthly, and yearly basis
Monitor environmental changes and introduce new training surfaces gradually
Modify technique-consider increasing step cadence

For more on the causes, prevention, diagnosis and management of bone stress injuries, take Dr. Warden’s Masterclass.

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5 Keys to Prevent Bone Stress Injuries in Runners

Why do BSI’s happen?

Where do BSI’s happen in runners?

How do we prevent BSI’s in runners?

Wrapping up

Want to learn more about bone stress injuries?

References

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