Cautious…I think that you are reacting a bit too much…but even I would do the same thing if I were in your shoes …I guess! It’s important to know that exercises without a proper guidance or instructions can harm the muscles and you need to take a note on this.

I think your concern is legitimate. It's fine for him to want a six-pack, but going about it the wrong way could produce significant repercussions. That said, there are exercises that will eventuate in effective results but won't harm his back/neck/etc. It is very important to be highly aware of form in doing these exercises, which watching videos and taking note of the form and positioning of the head, neck, and back makes conditioning your abs significant less risky.

Another option is trying non-crunch-like ab exercises, like balancing on a stability ball or using Pilates-inspired movements.

Hope this helps some. Good luck!

To get a six pack ab proper diet and regular exercise should be done. Not all type of exercise help to loose fat. There are some specific exercises.