Vibram, one of the manufacturers of the barefoot/five finger shoes, say that the shoes were made with the intention for use with Pilates and Yoga.
Personally, I think that there is a higher risk of damage to the foot as more of the foot is exposed as opposed to a pair of sneakers.
Too, although the client likely signed an waiver of informed consent, the fitness center can still be held liable if one injures him or herself as a consequence of training in those shoes.
I would limit use of the shoes to the class formats for which they were intended.
I have my own studio and do not see a problem with them in that setting. Our clients are always with a trainer, and dumbbells are handed over and taken back to the rack.
I personally own a pair and use them for any exercise I want to do, even though I prefer to be barefoot it I possble can.
In a regular gym setting, though, I can see why they make the wearer very vulnerable to the negligence of others. A regular pair of sneakers protects the feet much better from injury.
The whole “proper shoes” policy is really intended to deal with three main issues in my mind (prevent slips, reduce the risk of injury if dropping something on the feet, and hygiene). I don’t profess to be an expert on these shoes and have never used them myself, but they seem to satisfy reasons #1 and #3, but not necessarily #2. Looking at this strictly from the perspective of the gym or studio owner, I think that the risks outweigh any possible benefits. While some of the wearers of these shoes may be very comfortable and proficient in their use (such as Karin above), I think that Karin’s point is well-taken in that others may not be so careful around the wearers and so it could increase the gym’s risk of an injury.
We also have the same policy at our corporate wellness center.
But I must say, they are great for lower body training (squats, pistols squats, deadlifts, kettlebell swings, glute-ham raises) because they do not have an elevated heel like a regular sneaker does, so it’s easier to “sit back” and get your weight on to your heels. When your feet are planted, you can feel the floor and grip using your toes.
As a martial artist, I do most of my own training barefoot 🙂