From endorphins to PBs to carbo loading, there’s a lot to love about running. One aspect of the sport that doesn’t make the cut? Injuries, especially when they put you out for weeks, as bone stress injuries, in particular, commonly do.

Unfortunately, this type of ailment occurs often. Between one-third and two-thirds of competitive long-distance runners have a history of bone stress injuries, according to research.

In runners, these types of injuries most often occur in the tibia (shinbone), but they can also happen throughout the lower body – including in the foot, thigh, and hip bones, Dr Todd McGrath, a primary sports medicine physician with Hospital for Special Surgery in New York City, tells Runner’s World.

Here, we explain all you need to know about bone stress injuries, including the difference between stress reactions versus stress fractures, what causes stress reactions, signs you might have one, when to see a doctor, and most importantly, what you can do to prevent it from worsening.

What’s the difference between a stress reaction versus stress fracture?
Bone stress injuries are when a bone cannot withstand a load or force placed on it, and as a result, experiences a structural failure, physical therapist Nicole Haas, founder of Boulder Physiolab, tells Runner’s World.

In the case of a stress reaction, a bone can weaken and swell, but it doesn’t actually crack, McGrath explains. If left untreated, a stress reaction can eventually crack, which is when it then becomes a stress fracture. Basically, a stress reaction is a precursor to a stress fracture.

What causes stress reactions?
Typically the most common cause of stress reactions is a large ramp-up in training without enough rest, Haas says, as this can overload your bones.

How much is too much? Well, depending on your overall fitness and weekly running volume, increasing your mileage by more than 10 to 20 percent per week can elevate your risk, McGrath says.

If your mileage is on the lower end (say, 16 kilometres a week) then a 20 percent jump week to week may be fine. If you’re logging lots of kilometres  (for example, 160 a week), it’s probably wise to limit jumps to no more than 10 percent weekly, McGrath advises, though what your body can tolerate will depend on your fitness level, plus other factors.

Keep in mind running isn’t the only way to overload your bones. It’s possible to place more stress on them in other ways. For example, by taking lots of long power walks every day, or joining an intramural sports team, in addition to ramping up your running routine, Haas says.

Faulty biomechanics can also increase your risk, Haas adds. Overstriding, in particular, can increase ground reaction forces (basically, how much force is translated into the ground and then back into your body with every footstrike), which can then place your bones under elevated stress.

Another possible culprit: Nutritional issues. “If you’re not getting the energy you need, your body finds a way to get energy and sometimes that’s stealing it from the bone turnover, which can further weaken the bone,” McGrath explains. This could include folks impacted by Relative Energy Deficiency in Sport (RED-S), formerly known as the female athlete triad — basically, a condition of low-energy availability caused by chronic underfueling.

What are the signs of a stress reaction?
Understanding the signs of a stress reaction can help you determine when it’s time to seek help.

One big symptom: pain that crops up or worsens with running and improves with rest. “Sometimes it progresses to just pain with walking,” McGrath says, and as a reaction gets more severe, it can morph into chronic discomfort in a particular area, he explains.

By comparison, overuse soft tissue injuries. like tendonitis, usually cause lingering pain after activity and feel sore and stiff in the mornings, whereas sprains and strains are typically caused by a sudden, severe injury and can be distinguished based on hearing the history of what lead to the pain, McGrath explains.

Another sign of stress reactions is that the pain is usually point tenderness, meaning you can take one finger to demonstrate a specific location where it hurts, versus sweeping your hand across a broad area, Haas explains. If pushing on a bone causes or increases pain, that’s another likely sign of a stress reaction, McGrath adds.

There aren’t many visual clues, but in some cases – especially if it’s a stress reaction in your foot bones – you may notice swelling around the tender area, McGrath says.

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