Only able to ejaculate whrn tensing muscles

I am 44 and over the last 6 months I have only been able to ejaculate by tensing my leg and back muscles. I am having no issues with erection and enjoying sex but I am only able to finish the act by straightening my self out fully. Why will this have started and how can I go back to being able to cum without having to do this?

 

…

 

I use to all ways tighten my calf muscles and they would cramp up. I would cum fast like that. Have not tried that in years.

 

This method was told to me by my GF who sometimes does it in the office. Several times I ejaculated by squeezing my legs and straining their muscles as much as possible

 

Try relaxing completely as soon as you start to come