Wouldn't any shoe, and especially any running show of the last 40 years, return some level of energy? I mean, the entire concept of a shoe is a mechanical enhancement over running barefoot. Any equipment at all is a defacto enhancement above and beyond a "pure" non-mechanically aided base line. So if you accept and level of equipment, then it all becomes about where to draw the line, which type of enhancements are sanctioned, which not, etc.