Same old workout routine

How often should you switch up your workouts ? As in routine, been doing the same routine workout for about 4 months now and feel like I could use a changeup, I was adding weight every week and now it's kinda slowed up some. I hear your muscle will stop growing as much if you don't shock your muscles and change things up a bit.

I switch mine up every 8-16 weeks.

definately time to switch..i find after 8-10 weeks my body is just used to it and needs the change..also find it helpful to take few days off every time i switch my routine..

I don't switch the routine, just switch around excerises but for the most part I've been on the same routine for like 2 or 3 years now...

still making big gainz.

Instead of switching it up I just take a 2-3 week break every 4-6 months then I come back and make huge gainz.