Yet before you down your pre-workout shake and head to the gym with the goal of doing dumbbell shoulder presses with irons that are 10 pounds heavier than the ones you used last week, take a deep breath and hear me out on something. Training as heavy as you can, workout after workout, may not actually be the best way to build muscle or even strength! Yes, you read that right. According to research that’s been accumulating over the past couple of years, as well as my own research in the real lab known as the gym, going with lighter weight and higher reps may be even better for maximizing muscle growth. Before you spit out your shake and skip on to the next article, do yourself a favor and read this if you truly want to pack on as much muscle as you can. If not, continue with what you’re doing, but don’t be surprised when those gains come to a sudden halt. You’ve been warned.
In the world of strength-training science, rep ranges are categorized into what’s known as a repetition maximum continuum (see the figure included below). This breaks down the rep ranges into three main categories: 1) muscle strength, 2) muscle hypertrophy (growth), and 3) muscle endurance. Research and years of training have previously shown that the rep range of 1–6 reps per set is best for increasing muscle strength; and the rep range of 7–12 reps per set is best for increasing muscle growth; while reps of 12 and higher are best for increasing muscle endurance. This has always sounded solid based on what we know about muscle physiology and the energy systems used during these types of workouts, as well as the results that athletes have seen over the years training these ways.
So most bodybuilders end up training in the 6–8 rep range, maybe going as high as 10 reps occasionally, as this rep range allows them to look and feel the most impressive in the gym, hoisting as much weight as they can, while doing just enough reps to stimulate muscle growth. Theoretically this sounds like the smartest plan based on the repetition maximum continuum. It’s pure science, right? But alas, as science often demonstrates, there is new research that turns this way of thinking upside down.
Another tidbit that strength scientists have learned in the laboratory is the fact that muscles are recruited (called into contract) from smallest to biggest. This is known as the size principle. To keep things simple, there are two main types of muscle fibers—slow-twitch muscle fibers and fast-twitch muscle fibers. Slow-twitch fibers are those with the most endurance and are also the smallest and weakest. The fast-twitch muscle fibers are those that have less endurance but have the most strength and power and grow the biggest.
When you pick up a weight and do a biceps curl, the slow-twitch muscle fibers in the biceps are recruited first to contract and then lift the weight. If the load is too heavy for the few slow-twitch muscle fibers that were recruited, the brain signals the rest of the slow-twitch muscle fibers available in the biceps to assist their pals. If the weight is still too heavy, the brain starts calling on some of the bigger fast-twitch muscle fibers in the biceps to assist those small, weak, and pathetic slow-twitch fibers. If the weight is still too heavy, then the brain calls in the rest of the big and strong fast-twitch muscle fibers to assist and the weight is curled up. Of course this all occurs in a matter of microseconds.