We all work our major muscle groups by isolating them. Some work just chest, just back, just abs, etc. Most people combine muscle groups like back and biceps or chest and triceps. We all vary the workouts to maximize the amount of time off in between and the ability to get the most reps per group. However, very few of us combine them by opposites like chest and back or chest and biceps. Or, as I like to call them, push and pull groups.
I am a big fan of doing this. I do not do a full on chest exercise and then a full back exercise. I like to mix them up with working in a few back exercises during my downtime on chest day.
For example, on the days that I plan to do multiple sets of bench presses, I like to alternate my warm up sets with some back exercise. I will do a couple of sets to warm up on the flat bench, and then I will do lat pull downs in between. I actually notice an increase in top out strength when I do this. It is like I am loading one of those old school dart guns. Then, I have all of this energy to release when I am ready.
Another trick I like to do is right before I do my final set of each to maximize is throw in another opposite muscle exercise. Since I like to max out each workout, I will do a set of pull ups right before maxing out my bench press. I love the feeling of changing gears during a workout; it is like having dessert with dinner. This is not something that is beneficial with smaller muscle groups like biceps and triceps unless you are doing exercises that stretch that muscle group. A good example of this is to do standing dumbbell curls with medium weights and allowing your arms to extend all the way. You just need to be careful not to fatigue your muscles when you are doing opposites, and the biceps and triceps already are close to doing this because on the down stretch of a bicep rep, you are flexing the tricep.
It does take some coordination though so that we do not overwork our muscles. For example, many people do chest and triceps one day and then back and biceps the next. When you do push and pull muscles, you have to give a little bit of a break n between. I do chest and triceps on Monday, cardio Tuesday, legs and shoulders on Wednesday, off Thursday, cardio Friday, back and bicep Saturday and off Sunday.