I have had alot of people ask me why we do so many total body, multi-joint compound movements and often avoid doing isolated body part movements. There are many reasons why. The big reason I use total body multi-joint training is to get the most bang for your buck, in terms of the amount of results for time invested. The squat to overhead press is a classic example of a total body, multi-joint movement. This exercise uses most of the major muscle groups to execute the movement. In addition to the prime movers, a zillion smaller, secondary stabilizer muscles are used to assist the prime movers and to stabilize the core. So with one exercise, you utilize the max number of muscles to execute the drill.
So if I wanted to work each muscle group separately, my workout would take ten times longer and I would have to do a whole bunch of different exercises for x number of sets and reps. Simply put: efficiency. Secondly, another big reason to use multi-joint total body movements is to cause the greatest metabolic response with the least volume of work. Ever heard of working smarter, not harder? You want to invoke the greatest long term calorie burn in the least amount of time. The metabolic response to an exercise like the squat to overhead press is huge compared to say, a leg extension or leg curl.
So in the strength & conditioning and fat loss arenas, total body, multi-joint, compound movements are the most effective way to go, in my experience. Do isolation exercises have their place?- of course they do. It all depends on what your goals are. I see people, who say they want to tone up and get lean, doing long, slow, steady state cardio and a bunch of isolation exercises with light weights every day. Does this work? For some people it works better than others but usually for only brief periods of time. Then you plateau and the frustration begins.
So based upon your goals, find the most effective method and plan that will get you to your goal sooner rather than later. Don't waste your time doing mediocre stuff that will drain your time, wallet and motivation. Do your research, make a plan and then hit it hard and fast with a vengeance. Your odds of success will be greatly improved.
Dempsey's Resolution Fitness