First off, what’s the difference between them?
Simple enough, isolation targets just one muscle group whereas compound target multiple muscle groups.
A compound exercise, such as a barbell squat, will put many muscles and joints through a significantly larger range of motion than, for example, leg extensions. Squats primarily hit the quads but you’ll also be engaging your hamstrings, glutes, calves and your lower back. Taking the example of leg extensions, you’ll only be hitting your quads.
A compound movement will always allow you to overload your muscles way more than an isolation movement thereby stimulating faster muscle growth but, does that make compound movements better?
Even though compound movements target a higher number of muscle groups than isolation, there will always be a particular muscle (primary) that reaps more benefit than the other muscles (secondary).
Let’s take a barbell squat again as an example. The primary muscle utilised would be your quads with hamstrings and glutes being the secondary muscles. So, if you were to do many heavy squats on leg day and not much else you could end up with an imbalanced physique and strength.
A way to counteract that could be by implementing sets of isolation movements specifically to target glutes and hamstrings such as lunges and hamstring curls.
Essentially, isolation movements mean you can increase volume on the secondary muscles without overtraining the primary muscles used allowing them to rest.
If your goal is to increase muscle and size quickly then implementing heavy compound exercises into your training will work wonders. The emphasis should be on movements where you push, pull, deadlift and squat.
By adding in sets of isolation movements you’ll be placing emphasis on the secondary muscles and those harder to train (calves, biceps, triceps etc.). The focus here should be on movements where you raise, extend and curl.
So, to sum up.
By effectively using both compound and isolation exercises you’ll achieve increased strength, muscle size and a balanced physique.