Your strength and muscle size are closely correlated to one another, but you improve each through slightly different means. Strength is more about how many motor units, and thus muscle fibers, you’re contracting during a unit of time. Muscle size is caused more by how much of the chemical energy you use in the muscle fibers themselves. This causes you to “fill the muscle up” a little more when you recover.
Building strength is about how many muscle fibers you use.
Building muscle size is about how many muscle fibers you use up.
Naturally, you’re use both of these methods regardless of your training method, but it is possible to focus your training towards either strength or hypertrophy. Often times, you’ll find people training for one or the other because training for strength is somewhat in opposition to training for size. Training for strength usually involves using heavy resistance for low reps with longer rest period. This helps recruit more motor units per set so you can train your nervous system for maximum strength output.
Training for size usually involves using more moderate loads for higher reps with shorter rest periods. This helps bring the muscles to a higher state of fatigue without frying out the nervous system.
This is why a lot of people use more of a periodization plan with their training. They spend a few weeks or so focusing on strength and then change gears over to focus on hypertrophy. It’s a good plan, but what if you could focus on both strength and size in one workout?
Well you can and it’s not complicated at all. You start off with your normal strength style training for a given exercise. So start off with heavy loads, low reps and longer rest periods. After a few sets, switch over to hypertrophy style training. Use less resistance, double digit rep ranges and cut your rest periods in half. Do this for 1-2 sets.
After that you should have the best of both worlds, heavy lifting to stimulate the nervous system and a lot of muscle fatigue to stimulate some hypertrophy.