MUSCLE GROUPS TO TRAIN TOGETHER

Muscle movements and muscle pairing must be done in a way that allows each body part adequate rest and recovery while still allowing you to hit the gym the next day. It is important to understand that when you are in the gym training you are breaking down the muscle, and the recovery time out of the gym is when your muscles repair themselves and grow. You must set yourself up for success by adequately splitting up training every muscle group across the week while maximizing rest time for each body part. That means not training two upper-body "pull" movement muscle groups on consecutive days or two upper-body "push" movement muscle groups on consecutive days. This also means using lower-body muscle days to break up the days you are working upper-body as these movements typically do not incorporate upper-body, giving those muscles a day off. 

An example of a 4 to 5 day split that allows for adequate body part rest: 

Day 1: Back and Biceps (Pull and Pull)

Day 2: Lower-Body, Quads Focus, Calves (Lower Body)

Day 3: Rest

Day 4: Chest, Shoulders and Triceps (Push, Push, and Push) 

Day 5: Lower-Body, Hams Focus (Lower Body)