Eccentric vs. Concentric: Which One Actually Builds Muscle Faster?
Banging out reps is pretty straightforward, generally speaking. Lift the weight, lower the weight, repeat. But if you break down the anatomy of a repetition, there’s more going on than meets the eye. Rather than a single motion, a rep is actually a sequence of two (or sometimes three) phases—and one is considerably more valuable than the rest. (Spoiler alert: It's the eccentric phase.) In fact, tweaking your workouts to take advantage of this simple fact could save you both time and energy while bagging you bigger gains.
And yet, walk into any weight room in America, and you’ll find the majority of men hammering away at the dumbbell rack with no real rhyme or reason as if this weren’t publicly available information.
“There's no area that I know of where there's more research to say this is what works, and fewer people actually do it,” says Luke Carlson, founder and CEO of Discover Strength.
Ready to take advantage? Here’s everything you need to know about eccentric, concentric, and isometric training—and why you might want to consider an eccentric workout every now and then.
What’s the Difference Between Eccentric and Concentric?
Defining Concentric (The "Lifting" Phase)
A rep is typically made up of two phases—the concentric phase and the eccentric phase. In the simplest terms, the concentric phase is the “lifting” part of the rep. Take a dumbbell curl, for example. The concentric phase of the rep would be when you curl the weight up.
"During the concentric phase, your biceps muscle is getting shorter to create the lifting motion,” says Carlson. During this phase, the muscle is actually shortening in more ways than one. “It's also happening on a microscopic level—in the small protein filaments in our muscle,” Carlson explains.
During the lifting phase, microscopic proteins called actin and myosin lock together to pull the muscle inward. This "cross-bridge" action causes the entire muscle to physically shorten, generating the power needed to move the weight.
Defining Eccentric (The "Lowering" Phase)
The eccentric phase is the “lowering” portion of a rep. Sticking with the biceps curl example, the eccentric phase would be when you lower the dumbbell back down to your side.
“Here, your biceps are lengthening to create the lowering,” says Carlson. “When you're in an extended position, you have the dumbbell down at your side, you've completed the eccentric, your muscle is the longest. We call that the ‘long length’ of the muscle or ‘lengthened position.’ It’s the exact opposite of the concentric phase. Everything is getting longer in the eccentric phase.”
Where Does Isometric Fit In?
Depending on the tempo of your reps, there may be a third phase—an isometric hold. This just means the muscle is under strain, but not moving in either direction.
"Isometric is when there's no change in the muscle length,” says Carlson. “Your muscle's not shortening, and it's not lengthening. It's staying the same length.”
In the case of a dumbbell curl, an example of an isometric phase would be holding the weight with your elbow bent at a 90-degree angle, your forearm parallel with the floor.
While most people tend to focus on concentric and eccentric, rarely pausing mid-rep for an isometric, research shows that isometrics can offer serious gains. In fact, a study published in the journal Applied Physiology, Nutrition, and Metabolism found that isometric holds can be just as effective at building muscle as dynamic reps.
"I would say, in a given rep, you want to focus on all three phases—so, concentric, eccentric, and isometric,” says Carlson.
The Science of "Negative" Training: Why Eccentrics Matter
In the context of weightlifting, “negative” is just another word for the eccentric phase. Whenever you hear about negative training, all that means is a focus on the lowering phase of the rep. In fact, a negative training session might eliminate the concentric (and isometric) phase of the rep altogether, in order to isolate the eccentric completely.
The reason you’ve probably heard the term “negative” training a bunch of times—and likely never heard of “positive” training (which isn't actually a thing)—is that the eccentric phase of the rep is essentially where all of the value lies. "For almost every conceivable benefit that someone gets from exercise, it's enhanced when you focus on the eccentric phase,” says Carlson.
A 2023 study published in the journal Sports Medicine found that eccentric muscle contractions produce 40 percent more force than the concentric phase. In fact, an earlier study, published in The Journal of Strength and Conditioning Research, saw eccentric reps produce as much as 120 percent more force than concentric ones.
Ultimately, greater force means more mechanical loading (basically, the scientific term for adding weight), "and mechanical loading is one of the key stimuli for increasing muscle hypertrophy and muscle strength,” Carlson says.
Not only does negative training allow you to move more weight, but it also puts less metabolic stress on the body than if you were to do regular reps with equal eccentric and concentric portions.
“You can work your muscles much harder, but you're not as exhausted, and that's one of the big advantages of eccentric muscle contractions,” Carlson says. “If you look at the research, it's fascinating, because you'll see eccentric studies on athletes and bodybuilders, but then you'll see just as many studies on people with cardiovascular disease and elderly people, because you can work the muscle incredibly effectively without having the increased cardiovascular response.”
How to Apply This to Your Workouts
There are a couple of different ways that you can incorporate negative training into your workouts. Here are four strategies that Carlson recommends:
Tempo Focus
"The simplest way is to lift the weight for two seconds and lower it more slowly,” Carlson says. “That could be four seconds, six seconds, eight seconds, or even 10 seconds. That's the most practical way to do it.”
Machine Assisted
If you have access to machines, another simple way to practice negatives is to lift the weight with both limbs and then lower it with just one. "Picture you're on a leg extension,” Carlson says. “You’d press with both legs, take one leg off, and then lower slowly with the other. Then press it again with both legs and lower it with the other—alternating back and forth. You could do the same thing with a biceps curl machine.”
Forced Reps
Got a training partner? Try this one. “When you’re at the end of a set, and you've done as many reps as you can do, have your spotter lift the last rep for you, and then lower it incredibly slowly by yourself—30 seconds is a great goal,” Carlson says. “You can do that on literally every exercise: chin-ups, leg extension, lateral raises—anything.”
Isolated Eccentrics
“The fourth is an eccentric-only approach,” Carlson says. That means you’re not even doing the concentric part of the rep. “It’s easy to do with exercises like chin-ups, dips, and push-ups,” Carlson says. “Just start on the top and come down slowly for 10 seconds. Then reset back to the top.”
Related: How to Use RPE to Maximize Strength and Muscle Gains
FAQ
Should I focus on concentric or eccentric?
If you had to pick either eccentrics or concentrics to focus on, there’s no question about it: Go with the eccentrics. "This is one of the few areas in exercise science research that nobody debates,” Carlson says. “No one debates that eccentric training is the most important way to actually add muscle size and add muscle strength.” That said, for the sake of practicality and covering all of your bases, Carlson recommends incorporating both phases, and ideally, isometrics as well.
What exercises involve both concentric and eccentric?
Any exercise that involves lifting and lowering a weight—which is just about every exercise, with the exception of those that are inherently isometric, like a plank or wall sit—can be used to focus on eccentrics, concentrics, or both.