Is it possible to injure other parts of your body by singing loudly and vigorously if you are middle aged and out of shape? I was just singing and felt some small joints and ligaments pop slightly in my head, jaws and neck. That felt ok and natural. What concerns me is what felt like a small blood vessel popping in my thigh. I will probably consult a doctor but I was wondering if this is ever a serious concern.
Any use of the voice should always be in relation to physical fitness in terms of being able to support the pacing of the breath with posture, expanded lower ribs and flexible abdominals. There should be no gripping or pushing, and no collapsing. The voice can be used to great benefit in any state of health or development, as long as one has knowledge about how to adjust functional demands accordingly.
Vocal frequencies can and do stimulate all parts of the body, brain and energetic field. That being said, what happened in your thigh is likely due to misaligned or unbalanced posture and some muscular compensation for that. Vocal frequencies work very differently, much more subtly.