Hannelore, the only neck muscles are trapezius going down the side and linking to shoulders -- workout will not affect chin area, or anything other than trapezius. There are some little connectors (ligaments? not sure, but NOT muscles) by your jawline. What I've heard -- I'm a trained weight lifter and know all about that but not much about beauty stuff -- is this: open your mouth as wide as possible, then close your mouth by bringing your jaw all the way forward. You should feel the tension/stretch the whole time. I have no idea if this actually works, but it won't hurt to try.
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