I've been asked this question quite often. Some say 6 weeks, some say longer, some say every week to alleviate boredom! I prefer to stay consistent so i can monitor progress... weights ain't about having a fun time every session but getting RESULTS. My short answer to this question is..... if you're making good improvements on your program - why the hell change it!?
I trained today, while doing triceps dips the guy next to me was on the lat pulldown machine. While I managed to complete three sets in about 2.5 minutes, he didn't perform a single set! I see this time and time again and people wonder why they're not making gains. In order to fatigue your muscles to a point where they are broken down and rebuilt stronger bigger, they need to be stressed sufficiently.
So having a 5 minute break on an isolation exercise or checking Facebook in between sets isn't going to get you results. If you really want to use your phone in the gym - set the timer to go off 40-50 seconds after your last set and see how much gains you make in your training!
For those who don't train legs, it's time to start! Guys - don't have chicken legs with a gorilla upper body, girls - don't complain about not having toned legs or bum - train them!! if you don't have time to do a full leg session, you can always train quads/glutes then hamstrings in separate workouts. My workout today is s follows:-
5 minute warm-up on bike.
3-4 exercise to activate my quads, hamstring and glutes to get my body ready for the session and prevent injuries
Start training legs this week!
Sam Watt - Champion personal trainer and nutrition advisor