If your training split calls for “chest and forearms,” for God’s sake, do chest first. A study published in the Journal of Sports Science and Medicine showed that the muscle group that gets hit first in a workout makes greater size and strength gains than the muscles that follow.
The study followed two groups of recruits from the Brazilian Navy Sergeants School in Rio de Janeiro. One group trained smaller body parts first (biceps and triceps), and a second group prioritized the lats and pecs. After 12 weeks, no matter the size of the muscle, the body parts that were trained first enjoyed the most significant improvement in hypertrophy and strength development.
Building your body is all about at-tacking your weak points. With that in mind, be sure that the first muscle group you work each day is the body part you need to bring up the most.