Unlike a shirt or pants, sneakers are detrimental to movement because of the everyday pounding and abuse that our feet take. Given that we are upright beings, the feet are the only part of the body that touch the ground. This means that anything between the feet and ground will impede alignment from the ground all the way up the chain of the body. As the years pass, this continuous abuse piles up and we are left with feet and a body that is a shell of its former self.
A simple (albeit creepy) way to see this firsthand is to take a look at an elderly persons feet. I'm willing to bet that their feet have drastically changed from their teenage years.
Sneakers hinder performance because of three main factors - Fit, feel, and freedom.
Sneakers do not conform to the natural shape and size of a human foot. Why is it that sneakers are only sold in half sizes or certain widths? This means that if your foot size is actually a 10 3/4" you are forced to go with either a 10 1/2" or 11 (not to mention the width factor). In other words, sneaker companies cast us into size groups when in fact everyone's feet and toes are different. This is the very reason why we do not offer a toe sock version of Pedestals. Let's say that both you and I just happen to have the same sized foot, this does not mean that our toes are the exact same shape. Thus, making a sock that has "standard" toes is counter intuitive to optimal movement.
With thousands of nerves in our feet, the cushion and sole of a sneaker blocks the feedback from the ground. This is why sneakers are often referred to as "sensory deprivation chambers".
Think about how nice it feels to take your shoes off and walk on the beach and how awful it feels to put your shoes back on after a weekend spent in the sand.
Proprioception (our bodies awareness of where it is in space) is crucial to movement and all athletic endeavors. Our ability to balance is greatly enhanced when we can connect and create force directly into the ground. A great way to test this is doing any sort of single leg exercise with your shoes on and then with your shoes off. Try it and let us know how it went. This closer connection/glue to the ground makes you feel more stable and secure.
Shoes inhibit freedom of movement of the foot. Most people think that the sneaker moves with the foot, but that couldn't be any further from the truth. What actually happens is the foot moves within the sneaker causing the pressure to contort and alter the structure of the whole sneaker.
Below is a picture of a squat with sneakers on. You can see that both feet are pronating, but the sneakers completely exaggerate the movement. You see the lateral (outside) side of the heel coming off the ground and the medial (inside) side of the sneaker bending and shifting. This is clearly not ideal if we want optimal movement and a strong base of support.
Below you see the same squat, but with Pedestals on. While there is still some pronation, it is not nearly as dramatic. Both heels are contacting the floor and there is a strong base of support with no contortion.
It must also be noted that both of these squats were done with just body weight and no additional load. You can imagine that when we add some external load (barbell, KB, DB) this movement inefficiency will be enhanced dramatically in sneakers.
Additionally, in the first photo there is an energy leak as the shoe is absorbing a lot of force. In the second photo, force is directed right into the ground. This makes you more powerful, efficient, and safe.
While there are reasons to wear sneakers for outdoor activities to protect your feet from the elements, there are many more important reasons to not wear those same sneakers while training.
Your feet are constantly taking abuse day in and day out, so why not give them a little breathe of fresh air every time you train. Your feet will thank you for it and so will your body.