Learn how to identify and address your imbalances to reduce the risk of injury.
In any given year, more than one in five runners will sustain a stress fracture. In the United States alone, this translates to nearly 2 million stress fractures annually (1). In one of the largest studies to date, Matheson and colleagues (2) evaluated 320 athletes with stress fractures and noted that 4 percent of stress fractures occurred while playing basketball, 5 percent while playing tennis, 8 percent while in aerobics class, and a surprising 69 percent of these athletes developed stress fractures while running. Although it is generally believed that runners get stress fractures because the high impact forces associated with running cause the bones to break down, this is not always the case. In Matheson’s classic study of 320 athletes with stress fractures, only 20 percent of the stress fractures could be related to an increase in running mileage and/or the transition to training on a hard surface (2).
In many cases, stress fractures are not the result of weak bones cracking when exposed to excessive stress, they are the result of various biomechanical factors in which healthy bones break down when exposed to otherwise manageable impact forces. Though rarely considered, muscle strength plays an important role in the prevention of stress fractures. In an interesting study of muscle volume and the development of stress fractures, researchers from Australia (3) determined that a 10-millimeter reduction in calf circumference was associated with a fourfold increase in the incidence of tibial stress fracture.
Certain muscles play an important role in protecting various bones from trauma. The best example of this is the piriformis muscle. While most medical experts claim the piriformis is an unimportant rotator the hip, recent research shows that the piriformis muscle plays a key role in preventing stress fractures by reinforcing the femoral neck (see first image above). Without adequate support from the piriformis muscle, the femoral neck would crack when exposed to the normal bending forces present during midstance while running. My favorite way to strengthen the piriformis muscle is with the exercises listed in the second image in the gallery at the top of this page.
RELATED: Understanding Foot Fractures
While the piriformis muscle plays a vital role in protecting the femoral neck from injury, the iliotibial band has recently been shown to contain an extensive fascial expansion that protects the femur from stress fractures, as demonstrated in the third image in the gallery above. While running, the tensor fasciae latae (TFL) and gluteus maximus muscles create a compressive force in the iliotibial band that travels through the fascial expansion and prevents the femur from bending. As a result, weakness of these hip abductor muscles may increase the likelihood of suffering a femoral shaft stress fracture. The single leg cone jump illustrated in fourth photo above is an effective way to strengthen the hip abductors. The TFL can be targeted by performing exercise B in the second image above with the leg positioned behind you.
Because they create a compressive force in the shafts of the metatarsals, the toe muscles play an important role in protecting the metatarsal shafts from stress fractures. By embedding strain gauges in cadaveric feet before and after pulling on the muscles that flex the toes (see image #5 above), researchers from the University of California determined that comparable to the piriformis and iliotibial band, the toe muscles create a compressive force that lessens bending of the metatarsal shafts (4). The authors speculate that strengthening the digital flexors “may play a role in the prevention of metatarsal stress fractures.” To decrease the potential for metatarsal injury, runners with weak toes should do the toe exercises illustrated in image 6 above. To determine if your toes are weak, inspect the insoles of your running shoes. Ideally, you will notice visible indents beneath the tips of all of the toes.
Another common cause of stress fractures is calf tightness. As demonstrated in several studies (5,6), tightness in the calf causes a premature lifting of the heel while running, which transfers a significant amount of force into the forefoot, as demonstrated in the seventh image above. In fact, one study found that individuals with tight calves were 4.6 times more likely to sustain a metatarsal stress fracture (5). As a result, maintaining adequate calf flexibility is essential in the treatment and prevention of metatarsal stress fractures.
RELATED: Are we really born to run?
In order to get back to running as soon as possible, athletes with stress fractures should avoid using over-the-counter nonsteroidal medications, since these drugs have been shown to interfere with bone remodeling (7,8). Recent research also suggests that certain nonsteroidal medications can inhibit tendon repair following a sports injury (9). Despite their proven negative effect on bone health, these drugs continue to be used a first-line intervention for the management of stress fractures.
To return to sport following a stress fracture, many sports docs recommend the “10 Percent Rule,” in which the injured runner is told to increase his or her running distance by 10 percent per week. Even though the 10 Percent Rule continues to be used by many coaches and experts, a study published in the American Journal of Sports Medicine in 2007 showed that this approach does not alter reinjury rates (10). Additionally, because runners heal at different rates, conventional formulas used to predict recovery time for specific stress fractures are extremely inaccurate. For example, some experts incorrectly claim that metatarsal stress fractures heal in 6 weeks while femoral stress fractures heal in 12 weeks. Rather than relying on inaccurate formulas, a more appropriate way to return to running following a stress fracture is to wait until the damaged bone is pain-free for two weeks with daily activity before attempting a trial run. If at any point during that two-week period the bone begins to ache, you have to start all over again. To maintain fitness, runners with stress fractures can ride a stationary bike and/or swim during the waiting period. Because swimming has a tendency to tighten the calves, it is important to stretch after each pool workout, especially if you have a metatarsal stress fracture.
Depending upon the severity of the stress fracture, I recommend the injured athlete return to running with a walk/run combination. A typical first workout is to walk a quarter mile, slowly jog a quarter mile, and repeat this cycle for two miles. It is very important to run on alternate days and monitor symptoms: if the fracture site becomes uncomfortable, you’ll have to take another two weeks off running and get back to cross-training. As long as you remain symptom-free, you can increase the distance of your alternate day runs by one mile per week. At the end of the second week, you can transition to running only, but you’ve got to run at least two minutes per mile slower than your usual pace and keep your stride length short and your cadence high. Even slight reductions in stride length can make a big difference as a recent study found that a 10-percent reduction in stride length will decrease impact forces by 20 percent (11). Regarding running form, runners with stress fractures in the tibia or femur should be encouraged to switch to a midfoot strike pattern, while runners with midfoot or forefoot stress fractures should learn to land on their outer heels. Although many running coaches discourage a heel-striking pattern for fear it will reduce efficiency and increase impact forces, these claims are unfounded. Making initial ground contact with the outer heel reduces stress on the metatarsals and for all but the fastest runners, heel striking patterns are efficient (12) and safe (13).
Because athletes recover at different rates, it is important to increase weekly mileage on a case-by-case basis with significant increases in weekly distance only after the first three weeks. If the stress fractures are recurrent and/or severe, you should consult with an experienced sports medicine specialist. Certain dietary factors, such as low levels of vitamin D3 and/or inadequate intakes of protein are occasional causes of recurrent stress fractures. However, more often than not, recurrent stress fractures are usually the result of overlooked imbalances in strength and/or flexibility. In most cases, the addition of a few simple stretches and exercises can greatly reduce the risk of reinjury.
1. The Piriformis Muscle
The piriformis muscle (white arrow) creates a compressive force that protects the femoral neck from stress fractures while running (black arrows).
2. Strengthening Exercises
3. IT Band/Femur
Because the iliotibial band has a fibrous slip that covers the back of the femur (A), glute max and the tensor fasciae latae (TFL) create a compressive force that protects the femur from stress fractures while running.
4. Strengthening Exercise
While standing on one leg on an unstable surface (such as the AirEx Balance Pad), pivot forward at the hip so you touch the top of a cone placed in front of you. Immediately jump up and repeat the cone-touch on a neighboring cone.
5. Propulsion Phase
Cadaveric experiment evaluating pressures beneath the forefoot and metatarsal bending strains present during propulsion.
6. Toe Strengthening Exercise
Place a flat piece of TheraBand on the floor beneath your foot. Stabilize it with the heel and forefoot and pull the opposite end of the TheraBand to your knee, thereby lifting your toes. While maintaining tension on the TheraBand, force the toes downward (arrow).
7. Gastroc Tightness
Isolated tightness in the gastrocnemius muscle causes the heel to leave the ground prematurely (arrow), greatly increasing the potential for metatarsal stress fractures.
8. Tibial Stress Fracture
9. Tibial Stress Fracture
About The Author:
Dr. Thomas C. Michaud has been treating elite and recreational runners in the Boston area for more than 30 years. He has written several technical textbooks on clinical biomechanics, and has recently authored the book “Injury-Free Running: How to Build Strength, Improve Form, and Treat/Prevent Injuries,” available on Amazon.
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