Building off of what we saw yesterday, this study shows that adding isolation exercises to a compound movement-based program did not increase gains significantly when compared to subjects performing just compound movements. This means that if you’re on a time crunch in your training you should focus on compound movements more than isolation exercises. Beginners will also make the majority of their gains from compound movements so take your time learning the big movements and focus on those when you start training.
Reference: de França, H. S., Branco, P. A. N., Guedes Junior, D. P., Gentil, P., Steele, J., & Teixeira, C. V. L. S. (2015). The effects of adding single-joint exercises to a multi-joint exercise resistance training program on upper body muscle strength and size in trained men. Applied Physiology, Nutrition, and Metabolism, 40(8), 822-826.