Not Training to Failure
“Henneman’s size principle clearly states that the ‘fast twitch’ muscle fibers, the ones most responsible for hypertrophy, aren’t recruited until your level of effort reaches its highest point in a set,” says Fredrick Hahn, a NYC-based personal trainer. In other words, you’ve got to max out each set to enjoy maximum hypertrophy.
If you’re regularly tearing through three sets of 10 with no problem, it’s time to make adjustments. You can do this by performing more repetitions with lighter weight, or fewer repetitions with heavier weight. Either way, the goal is to take each set to complete muscle failure, Hahn says. Of course, the most efficient way to do this is by lifting heavier weights with fewer repetitions, but research indicates that taking your muscles to failure is more critical than the load you use to get there. So lift light or lift heavy — either way, give each set your all.