When it comes to deciding on whether to do a full body workout, a 2 day split or hitting body parts only once a week managing workout volume is the key to making each of those workouts a success. The following is a simple way to set each different type of workout up.
Full Body Workouts (3 times a week – 1 exercise per body part)
Generally thought of as a beginner workout routine full body workouts because of the increased frequency of gym visits (typically 3 times a week) per muscle group only one exercise per body part for about 2-4 sets is sufficient. Full body workouts are especially great for hard gainers, those with limited time, over 40 or just starting out with weights.
Split routine (2 times a week – 2 exercises per body part)
This middle of the road split where you hit body parts twice a week you can pump up the volume a little by doing 2 exercises for 2-4 sets per exercise. With the increased recovery time between body part days you can include a compound movement along with an isolation one or another compound to hit a different aspect of the muscle to help focus on weak areas and/or to add some shape. Great for intermediate to advanced bodybuilders looking to start perfecting their physique or those are decent or easy gainers.
One Body Part a week split routine (1 time a week – 3 exercises per body part)
Finally the ever popular once a week per body part routine. With the extended recovery time you actually slightly overtrain the muscle hitting it from every angle for multiple sets (3 plus). Expect some soreness that might take a few days to pass especially when just starting it. For most though especially hard gainers the full body or perhaps the 2 day split is the way to go. Training body parts only once a week is more for mesomorphs (easy gainers) or as a shock to the body once in a while to get past a plateau.
So in a nut shell the key is the more frequently you workout the less volume you should do per workout so you can still recover and progress. All three of these types of routines can work provided of course you put the effort in but as a general rule the more frequently you workout and recover and can still progress the better.