

This is not good for the vocal folds, which I can tell because I can't sing as high and I tire more easily without these stretches.

Both these things will cause my larynx to raise while I'm singing, rather than staying relaxed. On the first point, having shoulder tension and tense neck muscles can inhibit relaxed breathing and pull the vocal folds in non-ideal ways. The reason I do this is to release the huge amounts of tension that build up in my neck and upper back from slouching over my computer/phone/whatever and to strengthen the muscles that keep my head in a good position. But I do neck and back stretches and exercises to strengthen certain muscles as part of my warm up every single time I sing. You're right to be skeptical about neck exercises directly influencing the vocal folds themselves, I don't think they can (happy to be proven wrong though). Unfortunately I can't offer anything academic but I can share my personal experience and understanding. I was just wondering whether anyone has any experience on this topic - has anyone resorted to neck exercise to improve their voice? What are the effects and what are the technical reasons? Maybe some people came across such a technique with their teachers or SLPs or even incorporate it into their daily routines? Is there perhaps a very very important and specific set of neck muscles in the neck that have a massive effect on the voice (other than the vocal cords of course!)? I would be very grateful if someone could even provide academic research or some other resource regarding the validity of this technique. To be honest, I feel completely skeptical, especially since such exercises typically don't involve any voice production? Is this idea to exploit the relaxation of the muscle or of making it much thicker?

This sounds a bit gimmicky to me, almost as if suggesting that neck exercises can thicken the vocal cords. A quick search for "deep voice neck exercise" provides a lot of material suggesting that some neck exercise routine can provide serious development for one's voice.
