Stress fractures: How to avoid stress fractures

Stress fractures are an extremely debilitating occupational hazard for any athlete involved in endurance running, and in my work with the Australian triathlon team, one of my key aims is to prevent such injury. Among triathletes, bone stress fractures are most commonly seen in the tibia, femur, navicular and metatarsals⁽¹⁾.

Stress fractures usually have an insidious onset – although occasionally a bone will fracture suddenly. Wolff’s law states that a bone naturally grows in proportion to the stress applied to it. So for a bone-related stress injury to develop, the stress applied to the bone from running must exceed the body’s ability to adapt: osteoblastic bone growth cannot keep up with the training stresses being imposed, and bone degeneration occurs.

The severity of stress-related bone injury develops on a continuum as shown below.

Stress fractures generally arise from a combination of predisposing factors. But among injured triathletes there are two consistent signs:

• inadequate shock absorbtion
• malalignment of the lower limb.

Numerous studies have described lower-limb malalignment as the cause of stress fractures but intrinsic shock absorbtion of the leg is often ignored⁽¹⁾. Poor shock absorbtion has two common causes:

• reduced ankle dorsiflexion
• poor calf endurance.

Reduced ankle dorsiflexion

To attenuate shock to the lower limb effectively during running, the ankle needs sufficient range of motion to absorb the stresses. Poor dorsiflexion is often a result of tight calf musculature and hypomobile ankle joints. Ankle sprains, over the long term, can lead to both problems. Poor and/or infrequent stretching habits can also lead to reduced ankle dorsiflexion.

Ankles and calves should be stretched daily, before and after activity, to prevent the development of stress-related symptoms.

The most effective calf stretch is performed with the foot supported on a small foot-long board leaning against a wall at a 45 degree angle. The knee should be straight, with the body as upright as possible. Try and resist the temptation to bend at the hips with the backside sticking out as this reduces the effectiveness of the stretch.

Keep the foot in alignment, with the lower leg in neutral rotation. As with all stretches, the move into the stretch should be performed gently and slowly to the point of tension but never pain, and the position should be held for approximately 30 seconds without bouncing.

Calf stretch

Muscle endurance

Adequate shock-absorbtion via the control of the muscles of the lower limbs during running is extremely important. For triathletes, the endurance nature of training and racing requires high levels of calf, quadriceps and gluteal muscle endurance to limit the impact on the bones of the lower limbs.

Because 60% of forces when running are absorbed by the ankle/calf complex (the other 40% being transmitted proximally)⁽²⁾, once calf endurance – and the shock absorbed by the eccentric contractions – fails, the bones of the leg become vulnerable to excessive impact. This process may be amplified as the athlete tires.

Calf muscle endurance can be easily measured by the number of single leg calf raises off the floor that an athlete can perform. There have been no studies to gather normative data on the expected number of calf raises but, anecdotally, adequate calf endurance would be indicated when the athlete can do 30 to 40 repetitions on each leg.

To date there is no research that can confirm whether poor calf endurance is the cause or effect of stress fracture, but whichever way around, if the athlete demonstrates asymmetry, then intervention is indicated. If 30 to 40 reps cannot be performed, the athlete should do three sets of single-leg calf raises daily, each set performed to failure (ie, the calf muscle is fatigued to the point where another rep is not possible). Calf raises should never be performed before running, as this is likely to pre-fatigue the muscles.

Other causes

It is also important to rule out extrinsic factors in bone stress injury such as training errors or poor footwear. If, for instance, the athlete increases their running training by too much, too soon, and/or potentially runs in shoes that are too old and have lost their supportive structure, they are increasing their risk of developing lower limb bone stress injuries.

References

1. Brukner P and Khan K (1993): Clinical Sports Medicine. Sydney: McGraw-Hill Book Company.
2. Cook J et al (2000): Patellar Tendinopathy – new approaches to a chronic problem. Phys. SportsMed. 28(6): 31-46.