althera wrote...
I have read that morning erection is a self training for penis muscles.
The penis has no muscles in it. It is at the base of the penis surrounding the corpora cavernosa you have some muscles that you can clench - to postpone orgasm and harden your erection - but even normal erection doesn't require muscle power. It is the dilation of arteries supplies more blood to the organ while also restricting blood flow out of it.