Isolating specific muscle groups is key to maximizing the growth potential in the muscles you’re targeting.
Full body workouts are good for beginners and ensure you build a solid base, but once you’ve built significant mass all over your body it’s time to step your training up a notch and incorporate isolation exercises to continue spurring on new growth.
If you’ve been training for say 6 months using only compound exercises such as the barbell curl and the bench press as your primary arm exercises then your muscles are missing out and there will still be muscle fibres that you haven’t yet developed to their potential.
For example, your biceps are made up of 2 heads, with the rest of your arm being the triceps. If you’re not isolating both heads of your bicep then you’re missing out on potential new growth.
The same thing goes for other muscles groups in your body, especially your back. Your back muscles are: The posterior deltoid (rear shoulder), terres major, trap muscles, the latissimus dorsi (lats – upper, middle and lower) and lastly the erector spinae muscle.
You must ensure your training program works all of your muscle groups to their fullest which is why I recommend isolating muscle groups once you’ve built a good foundation using mainly compound exercises.
Take the time to dig around my site to find different exercises to isolate each muscle group but remember you must allow sufficient rest between exercises, especially when you’re isolating them, so that your body is able to repair and generate new muscle tissue.