IF YOU'RE LIKE most guys in the gym, when you’re doing a big lift—whether it’s a max bench, a PR squat, or the last rep of a strip set of curls—you’re focused on one thing: Getting that weight up.
But that’s only part of the rep. Each lift you do actually has three distinct phases: the concentric phase, the eccentric phase, and the isometric phase. Understanding the difference between the three can unlock new strength and size, help to safeguard from injury, and improve your performance on those big lifts—and in the rest of your life.
Concentric, Eccentric, Isometric: Here’s What They Mean
The Concentric Phase
The part of the lift you’re usually focused on (again, the getting the weight up)? That’s the concentric portion of the lift.
“What we’re looking at with the concentric portion is a shortening of the muscle,” says Jarrod Nobbe, C.S.C.S., the head weightlifting coach for the Athletic Lab Weightlifting team and Garage Gym Reviews. Take the biceps curl, for instance. As you bend your elbow and you raise the weight towards your shoulder, your biceps brachii gets shorter as it contracts.
The concentric portion is usually the part of the exercise that you think of as “the lift”—it’s the pressing portion of a bench press, standing up out of a squat, pulling the bar from the ground on a deadlift, or pushing down in a triceps pushdown.
The Eccentric Phase
Then there's the other part of the exercise, the eccentric phase. That's when you’re lowering the weight back to the floor in a set of deadlifts, the descent of a squat, or lowering the weight towards your chest on the bench.
“The muscle is lengthening. In an eccentric movement, the force of the contraction is less than the force giving upon it, so the muscle can lengthen at an appropriate time,” says Guillermo Escalante, DSc, C.S.C.S., a professor at California State University in Santa Barbara and NASM’s subject matter expert for the Bodybuilding and Physique Coaching certification. So instead of just letting the weight drop to your chest in a bench press, the your muscles are resisting gravity, providing some force against the weight so its speed is controlled.
Even though you tend to put more focus on the concentric portion of the lift, you’re typically stronger during the eccentric portion, says Mike Nelson, Ph.D., C.S.C.S., an associate professor at the Carrick Institute.
“The way your muscles are wired, they’re stronger in an eccentric than a concentric for most people,” says Nelson. That’s easy to understand: You’re probably able to control more weight bringing the bar down to your chest on a bench press—the eccentric portion—than you could press back up in the concentric portion.
The Isometric Phase
But there's actually one more phase that you shouldn't ignore. The isometric portion of the exercise happens between these other two phases. If you’ve heard of isometric exercises before, it’s probably for stuff like planks or squat holds—moves where you hold a contraction in one spot and engage your muscles against an outside force, like gravity or a fixed bar. This can be an ideal opportunity to ratchet up time under tension, which in turn can spur strength and size gains.
But moving lifts (called isotonic exercises) also have an isometric portion, when the weight isn’t moving between reps, even if it’s just for a split second.
Why You Should Care About the Eccentric Phase
So why does understanding the phases of your lifts matter? You're still going to pick the weight up and put it down, right?
If you're trying to train smart, you'll put your knowledge to good use. For starters, putting some focus on both the concentric and eccentric portions of a lift can help you get bigger and stronger.
“The eccentric component is actually where there’s a lot more demanded of the muscles,” says Escalanate. Controlling the eccentric portion of a lift instead of just letting it drop quickly “is a nice way to overload the muscle and create mechanical tension. And that mechanical tension can ultimately lead to muscle growth.”
In addition to building muscle size, some of the strength you’ll gain with a more controlled eccentric, Nobbe says, will be in your joints and tendons. This increased stability may make you stronger in the concentric portion of your lift—so by controlling the weight down on a bench press, for example, you may ultimately be able to press more weight back up.
Paying attention to the eccentric portion of your lifts will also transfer to the rest of your life, Nobbe says, because whether you think about it or not, you’re in situations all the time where you need to control an eccentric movement.
“Whether it’s an activity of daily life or sport, any time you change direction, if you plant and cut, if you stop and start … every time you go from moving to stopping, go side to side, accelerate or decelerate, you’re experiencing a varying amount of eccentric muscle action,” he says. Running downhill or walking down stairs, for instance, requires slowing down your movement. “That’s why it’s important to train with this in mind. We’ve prepared the body for these kinds of movements, and we’re prepared to do them more efficiently and effectively.”
One thing to note: More time in the eccentric phase of a lift can increase how sore you get post workout. This type of training is a new stress on the muscles, Nobbe says, and creates micro trauma that you’ll need to recover from.
How to Use These Phases to Reach Your Goals
For most gym-goers, Nelson says, the best bet is to focus on bringing control to the eccentric portion of a movement, then a forceful, fast concentric to finish a rep. Lowering the weight under control can reduce the amount of joint pain you might experience.
“Think about the case where you’re not controlling the weight in a dumbbell bench press—now at the bottom, where all that tissue is stretched, you’re taking more of an impulse load” at the bottom, right into the joint, he says. Basically, you’re slamming on the brakes instead of easing the brakes into a stop. “And part of your brakes are the joint structure, the soft tissue, and the implement hitting you in the shoulder—all stuff you don’t want. What I do want is the muscle and tendon to take most of that load in the ‘braking’ motion.”
If you get stronger at that “braking” motion, Nelson says, it may reduce your risk of injury not just in the gym, but out in the world—if you’re about to fall and land on your shoulder, for example, you’ll be better able to absorb forces as you “brake” your body to break your fall.
Performing the concentric portion of the movement forcefully will help you train and build power, a measure of how fast you can create force, according to Nobbe. And it may also create more muscle size because more of your muscle fibers are recruited.
“Imagine if you have a load and you’re going to move it slow. Your brain turns on some amount of muscle fibers to make this thing go,” Nelson says. But if you want to move the load quickly in a concentric contraction, “in order to get the thing accelerated, you have to recruit more fibers and more actual tissue, because something has to provide the force,” including more fast-twitch muscle fibers.
The weight doesn’t actually have to move fast to get this effect. You just have to be trying to move it fast. If you’re struggling against a really heavy load in a squat, for example, you might not be standing up that fast—but you’re pushing with all your might, you’re still getting this benefit of a “fast” concentric.
“We’re going to try to find some acceleration and velocity coming out of the bottom of the squat or bench press to get some power development out of it,” Nobbe says. That remains true even if the weight doesn’t move fast.
Emphasize the Eccentric Phase to Bust Through Plateaus
You can handle 20 to 30 percent more weight in the eccentric portion of a lift than the concentric, Escalante says. Taking advantage of this by lowering a weight extra slow “requires more motor units at that time—over time, your body will adapt, and it will enhance your strength.”
You can incorporate this type of tempo training by going from a controlled eccentric to one that’s four or five seconds long.
You can also try lowering a heavier weight than you can lift back up, Nelson says: This is the idea behind a negative pullup, for example. If you can find someone you trust to spot you, you can do a short set—or even one rep—like this at the end of a squat or bench press workout, too, he says, lowering a weight that’s heavier than you can lift, then having your spotter help you back up.
No matter which of these plateau-busting strategies you choose, don’t overdo it.
“Program this smartly: It’s not something you want to do on a day to day basis, or even a week to week basis,” Escalante says. These techniques can be demanding on the body, and can require extra time for recovery. Implement this type of overload training for a set or two, and focus on doing so when you’ve hit a plateau to help you break through.
Speed Up the Eccentric for Explosive Movement
For advanced athletes, slowing down the eccentric portion too much can actually limit the amount they can push in the concentric portion of a lift, Nelson says.
The theory is that “your brain is saying, ‘if you can’t control this load fast, we’re not going to let you move it fast,’” he continues. If you can control the load a little faster, doing so may let you fire up your concentric lift for slightly more power.
This requires you to be strong enough in the eccentric phase to actually control the load at speed, he says. So don’t start with a faster, controlled eccentric—work up to it.
Use a Periodized Plan to Get the Best of Both Worlds
Even if your exercises and workout don’t change, mixing up the speeds of your eccentric and concentric portions of lifts can help you increase strength and keep your training fresh, Escalante says. This is referred to as tempo training. You can use periodization, which typically means you have training plan that blocks out different focuses for specific portions of time, to organize our your workouts.
“About 50 to 60 percent of the time, live in that range of controlling both the eccentric and concentric at a relatively easy tempo,” he says. “Maybe 10 to 20 percent of the time, implement some [slower] eccentric work. And then 10 to 20 percent of the time, implement some more explosive concentric work.”
That might look like a four-week block of a normal tempo, one week of eccentric focus, one week of concentric focus, and then a de-load week before starting over.
“And now you have kind of a periodized approach to your training that’s programmatic and methodical,” he says. Ultimately, this can help you get stronger, keep track of what’s working, and recover effectively.
