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It's one of those debates that pits clinicians in the trenches against scientists in the lab: Can sticking a specially shaped insert into your running shoe really cure injuries?

"Clinically, we know that it works, we know that it relieves pain," says Reed Ferber, a University of Calgary kinesiology research and director of the university's Running Injury Clinic. "But the question is: How?"

Decades of studies on orthotic shoe inserts have left biomechanical researchers puzzled, since the effect of the inserts seems to be highly unpredictable for different people and different kinds of inserts. A new study by Dr. Ferber and mechanical engineer Brittany Benson finally offers some answers about how one type of inexpensive off-the-shelf orthotic may offer relief to plantar fasciitis sufferers – at least temporarily.

Previous orthotics studies treated the foot as a solid block that moved as a single unit. Using a sophisticated eight-camera motion-capture apparatus, Dr. Ferber analyzed the "multi-segment" motion of the foot in three dimensions, tracking the relative position of three markers along the length of the foot.

With each step you take, your arch collapses slightly. This causes a slight lengthening of the plantar fascia, a thick band of connective tissue running from the heel to the ball of the foot. Too much lengthening of this connective tissue can cause inflammation, resulting in a common source of heel pain called plantar fasciitis that is notoriously difficult to get rid of.

In the study, 20 healthy volunteers with an average age of 24.6 were filmed by the motion-capture system while walking on a treadmill with and without orthotics in their shoes, to determine whether the amount that their plantar fascia lengthened with each stride was changed by the inserts.

The orthotics used in the study were "semi-custom" Softec Response models, made by Calgary-based Sole Inc. At $50 a pair, they're much cheaper than custom-made orthotics, which typically cost $400 or more, but they're a step up from off-the-shelf non-customizable inserts. To customize them, you heat them in the oven for three minutes at 90 C, then insert them in your shoe and stand on them for two minutes.

(Sole Inc. made a charitable donation that helped support the research, but had no input in the design or analysis of the study, Dr. Ferber notes.)

The results were clear. With the heat-treated orthotics, 17 of the 20 volunteers saw a reduction in plantar-fascia strain by an average of 34 per cent. Using the orthotics without heat-treating them reduced strain in only seven of the volunteers, which suggests that moulding the orthotics to the individual feet really did make a difference.

To Dr. Ferber, the study makes a strong case for humble off-the-shelf heat-mouldable inserts as a first response when people notice signs of plantar fasciitis.

"I would definitely recommend them," he says, "because we now have fairly definitive data that there will be a reduction in plantar-fascia strain."

That doesn't mean that they provide a final answer to plantar-fascia problems, though. The orthotics may provide enough temporary relief that you can focus on addressing the underlying causes, which often relate to weak muscles in the lower leg. Dr. Ferber points in particular to weakness in the tibialis posterior, a muscle in the calf, as a frequent culprit in plantar fasciitis, as well as other common injuries such as shin splints, Achilles tendinopathy and stress fractures.

It's no coincidence that the causes of these lower-leg injuries are intertwined – and that means orthotics may be able to play a role in all of them. To find out whether that's true, Dr. Ferber is currently recruiting runners for a large randomized trial to study whether wearing semi-custom orthotics reduces the incidence of all types of lower-leg injury. (For information on how to enroll, visit

For now, though, Dr. Ferber's advice is simple: Strengthen your calves. "There are seven muscles in the calf and they provide 80 per cent of the power to propel you forward," Dr. Ferber says. "Calf-raises strengthen them all."

Alex Hutchinson blogs about research on exercise at His new book - Which Comes First, Cardio or Weights? - is now available.