Building size through muscle mass is called hypertrophy and there are 2 types.
In simple terms Sarcoplasmic hypertrophy is growth of the muscle due to increases in fluid in the muscle with Myofibril hypertrophy being growth through thickening of the muscle fibres.
An athlete should really be looking to build size through myofibril hypertrophy as the thickening of the muscle fibres through increases in the number of myofibrils results in the ability of the muscle to contract harder producing more force which can transfer into sports performance. Training in this style is performed by athletes with goals of hitting or tackling hard, running faster, changing direction at speed and explosive jumps.
Training for myofibril hypertrophy generally looks something like this. Compound multi-joint exercises, 3-5 exercises recruiting a large number of muscle groups working most if not all of the body. 3-5 sets, 3-6 reps, 2-4mins rest.
Back squat 4×4 3 mins rest
Weighted pull-ups 4×6 3mins rest
Bench press 4×5 3mins rest
Bent over row 4×6 2mins re
Sarcoplasmic hypertrophy gains will produce fewer gains in actual force production capabilities and ultimately because of this the athlete will be bigger but unable to produce much more force so is often slower. This style of training is commonly performed by bodybuilders who’s ultimate goal is just to be as big as possible.
Training for sarcoplasmic hypertrophy generally looks something like this. Body part splits, isolation exercises, 4-6 exercises per muscle group of 3-5 sets for 10-15 reps with 60-90s rest.
Bench Press 4×12 90s rest
Incline DB Press 4×12 90s rest
DB Flys 4×10 60s rest
Press ups 3xmax reps 60s rest
Make sure you know which sort of hypertrophy you are training for and how you should be training for it.