The EZ Run Belt is the curious invention of Joe Sparks, a student and teacher of Nicholas Romanov's Pose method of running. This device is designed to aid runners in learning Pose running by preventing them from overstriding. Its design is very simple. It consists of little more than a belt and ankle cuffs. A pair of bungee chords is hooked to the back of these parts so that the chords run behind the hamstrings and calves, applying tension that tends to bend the knees unless the tension is resisted.
Joe Sparks recently sent me an EZ Run Belt to try, and try it I did. Now, it must be noted that I taught myself not to overstride a few years back by switching to minimalist running shoes (which discourage the heel-first footstrike that is characteristic of overstriding) and by using the proprioceptive cues I describe in my book Brain Training for Runners. So when I first began running with the EZ Run Belt I did not notice any change in my stride, although I felt the resistance, for sure.
But then I tried reverting to my old heel-first stride, and I was delighted to find that the bungee chords' tension forced me to begin retracting my swing leg in the moment preceding footstrike, as every runner should do but as only the fastest runners actually do. Most runners just passively allow their foot to drop to the ground and then they initiate backward thrust. Better runners activate their glutes and hamstrings and begin to open up their hips just before the foot lands, effectively beginning the thrust phase of the stride prior to impact. This not only prevents overstriding but it also reduces ground contact time and boosts efficiency.
It is possible to correct overstriding without learning to begin retracting the swing leg before footstrike, and I did just that when I changed my form a few years back. I made my switch from a heel-first to a midfoot landing by angling my whole body forward from the ankles, as Romanov also teaches. I've been lazier about forcing myself to begin the backward thrust before footstrike, however. So I was intrigued that the EZ Run Belt seemed to encourage this correction.
After testing the EZ Run Belt I still feel that switching to minimalist running shoes and using proprioception (that is, body awareness) are the two best means to correct overstriding. The use of proprioception is utterly indispensible. But I believe that the EZ Run Belt could complement proprioceptive efforts to correct overstriding by teaching the runner what it feels like to begin retracting the swing leg before footstrike. For this reason I would recommend using the EZ Run Belt in a slightly different way than Joe Sparks does.
Sparks recommends wearing the belt for one to five minutes at a time. I would instead encourage the runner to run for 30 seconds with the belt and then unhook the bungee chords from the ankle cuffs and immediately run 30 seconds normally, during which time the runner should concentrate on recreating the feel of running with the belt as fullyl as possible. This process would be repeated several times to encourage a translation of the EZ Run Belt's corrective effect to free running. Because, ultimately, if you can make yourself run right without technical aids, you cannot change your stride.