Re:HELP PLEASE - Fullbody BEGGINER Mass Workout
In theory you could do an isolation or two at the end of the session if you wanted. You could do whatever you want, full body routines are very versatile. The point though is that the vast majority of your gains will come from progressing on the main compound lifts in the routine, any benefit from isolations will be minor or negligible.
Moreover if you are using sufficient load and intensity then the 3 main lifts will be more than enough and will make the routine quite demanding, in other words if you are lifting heavy enough on the 3 main lifts the last thing you will want to do is more, lol.
But yeah, there is no harm in chucking in an isolation or two if you want.