Probably psychology, and sometimes also due to physical...very hard to determine.

But i noticed once u get ur body to be fitter, u can maintain the erection better.

And by experienced, when actively do weight/ strength training, u can maintain the erection better on the next day, maybe it helped to boost ur body's testosterone.

Speaking of condom, previously i've used the okamota 003 and realised it's too tight and will affect erection and thus changed back to durex for more comfy experience.

So overall i think weight training is a better exercise to boost libido and to maintained it.