Risk factors for stress fractures in runners

The research is still a bit sparse with regards to specific risk factors that may predispose a runner to developing a stress fracture. Most research on this topic has been done on army recruits and it can’t really be applied to the running population as there are huge differences between the groups which includes things like smoking, volume and type of training.

In this article I’ll discuss what the current research shows with regards to:

• Relative Energy Deficiency in Sport (RED-S)

• Vitamin D

• Training

• Biomechanics

• Contraceptive pill

• Genetics

• Previous history of a stress fracture

Here's a video where I discuss this:

Relative Energy Deficiency in Sport (RED-S)

Relative Energy Deficiency in Sport or RED-S refers to when you don’t eat enough calories (energy) to replace what you burn when you exercise. This is not a problem if you do it on one or two occasions, but if you constantly under eat your body perceives you to be starving and it starts to prioritise certain functions in the body that it sees as crucial to your survival. As a result, other functions are shut down.

RED-S has wide spread effects on your body, but the most prominent ones include impairments of your metabolic rate, menstrual function, bone health, immunity, protein synthesis and cardiovascular health. You can read more about how this works here.

A good example of this is when a female athlete stops menstruating due to not taking in enough energy. The brain is prioritising her survival and as a result has shut down her reproductive system. It is also why elite cyclists and high level recreational cyclists are prone to developing osteoporosis.

Top Tip: If you’re doing endurance sport and a high volume of training, you have to make sure that you’re taking in enough energy to replace what you burn during your workouts. Failing to do so can lead to poor bone density and predispose you to stress fractures.

Vitamin D

Your body can’t absorb calcium, which is one of the main building blocks for strong bones, without Vitamin D. So it is no surprise that Vitamin D deficiency has been shown to cause low bone density and osteoporosis.

The main source of Vitamin D is from sunshine – you can’t really absorb enough through food. The problem is that the winter sun in countries like the UK isn’t strong enough to provide enough Vitamin D. Also, we tend to avoid the sun these days or slap on factor 50 sunscreen due to cancer risk. You can read more about how much Vitamin D you may need and how it affects your body here.

Top Tip: If you don’t get regular exposure to strong sunlight or wear sunblock/cover up when you do go out in the sun, it may be worth taking Vitamin D supplements.

Training volume

There is some evidence that runners who run more than 32km per week may be at a greater risk of developing stress fractures. This should not be interpreted as meaning that high volumes of running is bad for you. There are plenty of people clocking up massive volumes without getting injured. I think it’s just that when you do high volumes of training, it’s very easy to neglect your recovery or to under eat etc.

Top tip: Make sure that you pay careful attention to your nutrition and recovery if you do high volumes of training.

Biomechanics

I was expecting to find research showing that certain biomechanics predisposes runners to certain types of stress fractures, but there seems to be no strong evidence of this yet. The studies that are available are extremely small (5 participants) and not really well conducted.

Top Tip: Don’t worry too much about your biomechanics. Get your nutrition and Vitamin D levels right first as these definitely impact on bone health.

Contraceptive pill

There’s currently no evidence that taking the contraceptive pill is linked to stress fractures. Researchers do however caution that, because it can give the impression of having a normal menstruation cycle, it can mask the symptoms of RED-S.

Top Tip: If you’re using the contraceptive pill, you can’t use your period as an indication of whether or not you may have RED-S.

Genetics

Some research suggests that women are more prone to developing stress fractures than men, but some people also seem to have a genetic predisposition to developing poor bone density.

Top Tip: If anyone else in your close family has had stress fractures or has been diagnosed with poor bone density or osteoporosis, it may be worth getting your own bone health checked.

Previous history of a stress fracture

Runners who have previously had a stress fracture is at much greater risk of developing another one in the future. This can be for several reasons, but for me the main two are:

• It may be that you’ve not addressed the root cause of why you developed your first one e.g. are you still not fuelling properly or neglected your Vitamin D levels?

• Your genetics may predispose you to it.

Top tip: If you do ever develop a stress fracture, make sure that you understand why it happened so that you can avoid getting another one in the future.

Need more help with your injury? You’re welcome to consult one of the team at SIP online via video call for an assessment of your injury and a tailored treatment plan.

About the Author

Maryke Louw is a chartered physiotherapist with more than 15 years' experience and a Masters Degree in Sports Injury Management. Follow her on LinkedIn, ResearchGate, Facebook, Twitter or Instagram.

References:

1. Bentall, D. (2020). "RED-S: not just a female phenomenon." British Journal of Sports Medicine: bjsports-2019-101868.

2. Herbert, A. J., et al. (2019). "The interactions of physical activity, exercise and genetics and their associations with bone mineral density: implications for injury risk in elite athletes." European Journal of Applied Physiology 119(1): 29-47.

3. Mountjoy, M., et al. (2018). "IOC consensus statement on relative energy deficiency in sport (RED-S): 2018 update." British Journal of Sports Medicine.

4. Wright, A. A., et al. (2015). "Risk factors associated with lower extremity stress fractures in runners: a systematic review with meta-analysis." British Journal of Sports Medicine 49(23): 1517-1523.