A recent news report talks about litigation against Skechers from a male who claims that his Achilles tendon was ruptured from the use of their Shape Up toning shoes. The case has not been heard yet and there is no statement from Skechers.
Is the claim valid?
Toning shoes do alter the way you walk. They do alter the loads on different tissues, and yes they do make the calf muscles work harder, so they do place a greater load on the Achilles tendon. Much more is needed to rupture it though (more on Achilles ruptures), so to claim it is the cause is, in my opinion, a bit of a stretch. There must be a number of other risk factors present first and an Achilles tendon rupture is usually accompanied with simultaneous ankle dorsiflexion and knee extension. That will possibly be increased somewhat in toning shoes that have a rocker bottom. Generally a number of risk factors need to be in place for the rupture to happen, so the toning shoes can only be one of them.
As by way of analogy, there was the controversy when the Cox-2 inhibitor, Vioxx which was used as an anti-inflammatory agent was withdrawn from the market due to the increased risk for cardiovascular events. A number of people who had heart attacks or strokes while on this drug sued. Most of the cases failed, as they already had the risk factors for the heart attack or stroke (see this Wikipedia discussion) and Vioxx was not found to be the causative factor.
It will be interesting to see which way this Skechers case goes, or if it is just settled (which would be shame, as I would like to know which way the courts would rule!). Would they rule in favor of the litigant that the shoes caused the Achilles rupture or will they rule like in the Vioxx cases that other risk factors were already present?