Resistance training—whether it be with dumbbells, barbells, or just your body weight—seems clearcut. You lift things up. You put them down. Repeat.

But take a look at your body under a microscope, and you’ll see that your working muscles are actually contracting in completely different ways depending on the phase of the exercise you’re in—and if you’re even moving at all.

The key players: concentric, eccentric, and isometric muscle contractions. Most exercises and everyday actions (think: walking, picking up and holding your groceries) involve a mixture of contraction types¹. But some movements favor one type of contraction over the others. You can even tweak an exercise to emphasize one flavor—and that comes with a unique slew of fitness benefits.

So what’s the difference between the three types of muscle contraction types, anyway, and is it really worth factoring into your training plan? Read on for your guide to concentric vs. eccentric vs. isometric muscle contractions and how to blend all three in your workouts for next-level strength, muscle gains, and functional fitness.

What is a concentric muscle contraction?

To get technical, a concentric muscle contraction is one of the two types of isotonic contractions. During this contraction, your muscle fibers are shortening and overcoming force, says Laura Su, CSCS, a strength and conditioning specialist in Seattle.

It’s easiest to imagine this contraction during a classic biceps curl. The concentric phase of the movement is when your biceps brachii are fighting (and beating) gravity to pull the dumbbell up toward your shoulder, Su explains. Or, consider a hike up a hill. When you’re trudging up an incline, your knee and hip joints aren’t fully extending, and your quadriceps and other lower-body muscles are shortening to propel yourself uphill, Su says.

When you prioritize the concentric phase of an exercise, you’ll generally try to move as explosively as possible (while still using a heavy enough load that you’re not banging out your reps at lightning speed), which can help improve power, Su says.

Concentric contractions are typically less taxing on the body, too. “You can prioritize concentric-only moves if you want less muscle damage and neuromuscular fatigue during a workout,” Su says. “For example, maybe you want some extra blood flow and volume on your legs but don’t want to get too sore. Rather than doing more split squats, you can do a heavy-loaded backward sled drag.”

What is an eccentric muscle contraction?

The second isotonic contraction, an eccentric muscle contraction is when the muscle fibers are “lengthening,” or returning to their resting length after shortening during the concentric phase. Importantly, these fibers are still producing force as they lengthen.

Think about the biceps curl: While you’re lowering the dumbbell back toward the floor and straightening your elbow, your biceps are fighting the tug of gravity. It’s almost like you’re creating force to pump the brakes on the weight so it doesn’t quickly drop back to the starting position. “The biceps are lengthening and still producing force and contracting because they’re working to decelerate your hand toward the floor,” Su says.

You can picture eccentric contractions in that hiking example, too. As you’re walking or jogging down a hill, your quads are contracting in that lengthened state, creating force to slow your body. “Otherwise, your knee would just continue to keep bending and you’d fall,” Su says.

Emphasizing the eccentric contraction of a given exercise—either by overloading or slowing down that phase of the movement—can come with a huge payoff. Eccentric contractions are known to create a significant amount of muscle damage⁸⁵³² that can potentially lead to hypertrophy (read: increased muscle size)—if you recover well, Su says. Strength gains are possible⁴, too. Eccentric exercise training is linked with greater increases in isometric strength (more on that later) than concentric exercise, and it may support greater gains in concentric strength, as well, according to a 2023 review published in the Journal of Sports Science and Medicine. 

Plus, your body can generally handle more load¹⁰⁷⁶ during eccentric contractions than concentric ones. It makes sense: In practice, you can typically slow a weight down more easily than you can accelerate it, Su says. “If I had you walk out [from a rack for] a really heavy squat, you might not be able to stand back up with it, but you can go down with it,” she says. “That would be an example of overloading the eccentric portion of it.”

This combination of potential muscle and strength gains and the ability to produce more force means eccentric work can be a useful tool to bust through plateaus, said Jill Goodtree, CPT, a NASM-certified personal trainer and Rumble Boxing instructor. Struggling to do a full pull-up? You might prioritize negative pull-ups, using a ladder or a step stool to position yourself at the top of the pull-up bar then slowly lower yourself until your arms are fully extended, says Goodtree. “If you try to do just the concentric phase, a lot of people would just dangle on the bar and not be able to do it at all,” she says.

You could use the same tactic to improve your push-ups: Begin in a high plank position, slowly lower yourself to the floor, release your hands, then drop your knees to press yourself back up to the starting position. Focusing on the eccentric phase “increases the amount of muscle fibers and strength, which, over time, would be able to help you do the full movement of a push-up from your toes,” Goodtree says.

Performing eccentric work in the gym comes with benefits out in the real world, too. While dropping your checked luggage off at the airport, you wouldn’t toss your heavy bags onto the scale; you’d slowly lower them onto the platform. “Working with muscle control—working on the eccentric phase—is really important to make sure we’re protecting our joints, protecting our spine, all those things,” Goodtree says.

With an eccentric focus, recovery time is key. Unfamiliar eccentric work tends to cause a lot of muscle damage and is linked with delayed-onset muscle soreness. So if you’re overloading your eccentric contractions or focusing on them in your workouts, give your muscles extra time for TLC before you train them again, Su says.

What is an isometric muscle contraction?

In an isometric muscle contraction, the working muscles are creating force, but there’s no visible lengthening or shortening, Su says. That’s because the force they’re producing is equal to the force they’re experiencing. As a result, there’s no joint action—nothing is moving, Su explains.

Consider a plank: Your entire core is contracting and battling the resistance of your body weight, but it’s keeping you stable and still enough to balance a cup of water on your backside. An isometric contraction could also be a 15-second or so pause at the bottom of your squat, top of your shoulder raise, or middle of your pull-up.

Isometric contractions are less taxing on the body⁹ and are quicker to recover from, so you’re able to perform them more frequently than other contraction types. Plus, introducing these pauses increases the time your muscles spend under tension, helping to build muscle endurance (how long your muscles are able to produce force), Goodtree says.

Outside the gym, improved muscular endurance means you’ll be able to, say, hold your grocery bags or sit up tall with good posture for long periods without feeling so exhausted.

How to use each muscle contraction in your workouts

So, do you actually need to account for muscle contractions when planning your workouts for the week? “I wouldn’t say you should live and die by it,” Goodtree says. “But it’s important information to know if you’re interested in getting stronger.”

To support overall health and fitness, it’s beneficial to train all types of muscle contractions. In fact, research suggests resistance training that involves both forceful concentric and eccentric contractions leads to greater improvements in strength than concentric contractions alone.

Don’t overthink it, says Su. Try exercises that incorporate all three muscle contractions by adding a “pause” to your squats, for instance. Slowly lower yourself into that invisible chair, fighting the downward pull of gravity (eccentric for the quadriceps), pause at your end range of motion (isometric), then explode up to standing, straighten your legs (concentric for the quadriceps), Su suggests.

Make sure you’re moving with control through each phase of the movement in order to nab the benefits of the associated muscle contractions. A good rule of thumb? Your concentric contraction should be just as long as your eccentric contraction, Su says. Think: one count on the way down into your squat, one count on the way out of your squat.

If you’re able to move in ultra-slow motion during the eccentric phase, that’s a sign you’re probably able to take on a heavier weight. “Yes, be controlled through all the ranges of motion, but don’t let going too slow through the ranges of motion keep you from being able to load heavier,” Su says.

Still, there’s a time and a place to prioritize certain types of contractions over others.

When to prioritize concentric muscle contractions

If you’re training for an event like a lifting competition, Su recommends steering away from cardio work that’s eccentric-heavy. Instead, focus your aerobic program on concentric muscle contractions, which don’t create as much muscle damage and neural fatigue that are tough to recover from, she explains.

Leading up to a powerlifting competition, Su herself opts for the bike or an uphill treadmill walk to get her fill of cardio rather than, say, a trail run. “[In that case], I’d be getting more eccentric load in my quads than I need to when I’m trying to save my legs for my next heavy squat day,” she says. “…[With an incline walk], I’m getting the same cardio benefit adaptation without having to tax my muscles as hard.”

When focusing on concentric work, use a load that forces you to be explosive throughout that phase of the movement but is still heavy enough that it doesn’t “look fast” during the movement, Su suggests. “This allows us to recruit more muscle fibers through the motion.”

When to prioritize eccentric muscle contractions

On the flip side, you might amp up your eccentric contractions when you’re looking to build muscle mass or bust through a fitness plateau, according to the experts. You can focus on the eccentric portion of pull-ups or push-ups when building up to the full movement, Goodtree says.

Or, say you want to beef up your quads. Using a seated leg extension machine, choose a weight you can lift with two legs but not one, Su says. Then, raise the weight (extending your legs), release one leg from the machine, and lower the weight back to the starting position with just the remaining leg. Rinse and repeat.

You can apply the same overloading technique to biceps curls and other single-side exercises to induce muscle damage and, so long as you recover well, gains, Su says. A word of caution: “Before you’re adjusting variables, make sure you can do the movement safely and effectively with good form,” she adds.

When to prioritize isometric muscle contractions

To build up muscular endurance, turn to isometric muscle contractions. You can practice isometric moves like planks, Pallof presses, V-sits, and hollow-body holds to enhance endurance throughout your core. Or, you can add an isometric element into dynamic moves already included in your workout program: Hold a squat for 15 or so seconds, pause at the bottom of your push-up before you pop back up to the starting position, or hold the top of your hip thrust for a few breaths.

The bottom line

In general, you’re best off training through your full range of motion and performing all kinds of muscle contractions in your exercises, Su recommends.

“If you want to make strength gains or you’re just trying to be healthy and active, [the type of muscle contraction] is not the most important thing,” Goodtree says. “But if you’re noticing, ‘Oh, you know what? I’ve been squatting with just the bar for, like, three years. How am I going to lift heavier weights than that?’ These are good things to think about.”