How to Actually Build Muscle When You Work Out

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Despite what many workout equipment manufacturers, TV fitness personalities, and calloused gym bros might have you believe, building muscle is actually an inherently straightforward thing to do. Packing on size has got nothing to do with four sets of 10, tempo reps—or even specific exercises, for that matter. In fact, gaining muscle is not so much about what you do, but rather how you do it.

The first thing to understand is that gaining size and gaining strength are two distinctly different things. Yes, lifting for muscle growth—or hypertrophy, to use the scientific term—will yield some strength gains along the way, and vice-versa, but the way you work out will primarily move you closer toward one goal or the other. Put another way, you could use the same exercise to either pack on muscle or get stronger, depending on your approach.

Consider the difference between bodybuilders and powerlifters—two groups that rely heavily on the bench press in their training. “A powerlifter is trying to lift as much weight as possible, whereas bodybuilders are trying to increase the size of their muscles.” says Mathew Welch, MS, CSCS, ATC, USAW-1, an exercise physiologist at HSS. “Don’t get me wrong, the bodybuilders are going to get strong, but they’re not necessarily going to have the same strength as a powerlifter, and that’s because the qualities that they’re training are very different.”

“The big take-home message here is that there’s no magical exercise for hypertrophy,” says Luke Carlson, founder and CEO of Discover Strength. Instead, what we do have is a handful of research-backed principles that you can use to optimize your existing workout for muscle growth.

Ready to lock in your strategy for massive muscle gains once and for all? Here’s everything you need to know.

Hard reps equal hard muscle

“The biggest scientific discovery in strength training of the last 15 years is that we sure don’t need very much of it if you want to add muscle,” says Carlson. “But we’ve got to do it harder than we ever thought.”

Research shows us that muscle growth is driven by mechanical tension. Unlike time under tension—the amount of time a muscle spends under load, which actually does nothing for hypertrophy—mechanical tension kicks in the moment your reps begin to naturally slow down as you approach muscle failure. Trainers call these “effective reps.”

“Effective reps are defined as the last five or so repetitions in a set that brings the muscle to failure, and these reps are believed to provide the most stimulus for hypertrophy due to the mechanical tension being experienced by the active fibers,” says Welch.

“The closer you get to failure, the more motor units and muscle fibers you recruit, and the greater chance you have to increase the size of your muscle,” says Carlson. “The most important element is whether you’re getting close to muscle failure—more important than how many sets you do or how many days a week you work out.”

This means that the weight you lift is essentially irrelevant, as long as you push yourself towards muscle failure—useful knowledge for the next time you find yourself at a hotel gym with nothing more than a pair of 20-pound dumbbells. (However, as we’ll explain below, high-rep sets with lighter weights may not be the most efficient way to pack on size.)