Well, it won't happen from the lack of exercise directly, but it certainly can happen from Coronary Artery Disease, or clogging of your arteries due to many different possible causes, some of which can be prevented by exercising. Plaque buildup can reduce blood flow to your penis, making it hard to get an erection.

Coronary Artery Disease, is usually caused by clogging, or hardening of the arteries, also known as Atherosclerosis. Atherosclerosis is the buildup of cholesterol and plague on the inner walls of the arteries. It can be caused by smoking, high blood pressure, high cholesterol, steroid abuse or misuse, uncontrolled estrogen levels, and more. So, your rowing machine may only help you in certain situations. But hey, I guess it can't hurt right? No seriously, I'm a big believer in the benefits of exercise and strength training.

It's funny that you wrote about this, because on the Adult Swim channel on t.v., they recently added a commercial about a guy who has a limp dick because he smoked cigarettes and plague built up in his arteries! They even made a little song about his limp dick and why it happened.

This should answer your question
https://www.youtube.com/watch?v=BCstmBw-2oU

Back again eh?

"A doctor said that if I didn't do enough excersise my penis.Could stop working.., Due to lack of circulation."..,best pick up line at a gay bar.

I suggest you and your 2 friends do a circle jerk daily for exercise and that will get circulation to everyone's penis.
nice that you named your penis "ruder"
this is "full homo"
time to let your gay pride rainbow flag fly on the front lawn.., bob.