The whole point of lifting weights is to trigger a growth response. Anything else is maintenance at best and a waste of time at worst. In order to hit the sweet spot, you must first push yourself beyond your comfort zone.
To achieve this, you must lift heavier and/or do more reps than you’re used to. The former is primarily what stimulates fast-twitch muscle fibers, while the latter targets slow-twitch fibers.
Some muscles have a high ratio of slow-twitch muscle fibers and may benefit from more reps with lower weight. Biceps and triceps aren’t among them. For best results, focus primarily on fairly heavy training in the 6-8 rep range (using strict form) with just the occasional couple weeks of lighter training thrown in to keep the muscles guessing.
By Neale Cranwell