Interesting. I tried several times to use a shoulder rest, but I always encountered shoulder and back stiffness. I also tried several chin rests. I finally found a Fiddlerman chin rest that fit my ergonomics, and I have played ever since without a problem -- and also without a shoulder rest.

Violin ergonomics are difficult, as attested by the large variety of devices that are available to help violinists hold and play this crazy instrument. There are also a variety of positions that have been used over the years -- holding the fiddle in the armpit, on the chest, and even on the knees like a cello. 

I understand that injuries are common among string players. Janet Horvath’s book Playing (Less) Hurt is an exhaustive description of ergonomic injuries for musicians, along with ways to minimize problems. (Ask me why I bought her book, haha!) However, she does not deal with the myriad devices that have been invented to protect us from repetitive motion injuries.

In a positive vein, I find that playing without a shoulder rest gives me freedom to play standing or sitting and  move around as the spirit (and the music) moves me. A small leather patch makes the violin less slidey on my shoulder.

If my memory is correct, Pierre H. has a good video about the benefits of playing without a shoulder rest. That video must be somewhere on the Fiddlerman site.