Concentric and eccentric are the two main phases of muscle contraction during exercise. In a concentric contraction, your muscle shortens as it generates force, like the lifting phase of a bicep curl. In an eccentric contraction, your muscle lengthens while still under tension, like the lowering phase of that same curl. Understanding the difference changes how you train, recover, and build strength.
How Each Contraction Works
During a concentric contraction, your muscle fibers slide together and shorten to overcome resistance. Think of standing up from a squat: your quadriceps shorten to push your body upward against gravity. The muscle tension rises to meet the resistance, then stays stable as the muscle shortens.
During an eccentric contraction, the opposite happens. The external resistance (gravity, a weight, your body) is greater than the force your muscle is producing, so the muscle lengthens while still actively contracting. Lowering yourself into a squat is eccentric for your quads. You’re not just dropping down. Your muscles are working hard to control the descent.
A third type, isometric contraction, happens when the muscle generates force without changing length, like holding a plank. But most real-world movement alternates between concentric and eccentric phases.
Everyday Examples in Common Exercises
Nearly every exercise has both phases. Identifying them is straightforward once you know the pattern: the part where you lift or push against gravity is concentric, and the part where you resist gravity on the way back is eccentric.
- Squat: Lowering down is eccentric for your quads and glutes. Standing back up is concentric.
- Push-up or bench press: Lowering your chest toward the ground or bar is eccentric for your chest and triceps. Pressing back up is concentric.
- Pull-up: Pulling yourself up to the bar is concentric for your lats and biceps. Lowering yourself back down is eccentric.
- Deadlift: Lifting the bar from the floor is concentric for your posterior chain. Lowering it back down is eccentric.
- Walking downstairs: Your quads work eccentrically to control each step. Walking upstairs is concentric.
Eccentric Contractions Produce More Force
Your muscles can handle heavier loads during the eccentric phase than the concentric phase. Research on squatting found that peak forces during eccentric movement were roughly 9.5% greater than during an isometric hold, and the fastest eccentric trials produced significantly more force than the highest-velocity concentric trials. This is why you can lower a heavier weight than you can lift, and why the lowering phase of a heavy squat feels more manageable than the push back up.
This force advantage exists partly because the structural proteins inside your muscle fibers act like springs during a stretch. When your muscle lengthens under load, internal elastic elements store energy at very small scales. Your nervous system also plays a role: during eccentric work, most motor units actually decrease their firing rate or shut off entirely, while a small number of specialized, high-threshold motor units are selectively recruited. This means your body uses a different neural strategy for lowering a weight than for lifting it.
Eccentric Work Costs Less Energy
One of the most striking differences is metabolic. Eccentric exercise uses far less oxygen and energy than concentric exercise at the same workload. In cycling studies where the power output was matched at around 190 watts, oxygen consumption during eccentric pedaling was about 65% lower than during concentric pedaling. Heart rate was 35% lower as well. This roughly mirrors the difference in ATP cost, meaning your muscles burn significantly less fuel to control a lengthening contraction than to power a shortening one.
This efficiency makes eccentric training useful for people who need to build strength but can’t tolerate high cardiovascular demand, such as older adults or those in cardiac rehabilitation. You get a potent strength stimulus without the same metabolic stress.
Why Eccentric Exercise Causes More Soreness
If you’ve ever felt crippling soreness two days after hiking downhill or trying a new workout, eccentric loading was likely the cause. Delayed-onset muscle soreness (DOMS) is closely tied to the lengthening phase of exercise, not the shortening phase.
The reason involves microscopic structural damage. Intense or unfamiliar eccentric exercise causes disruption at the smallest level of muscle architecture, particularly at the junctions where contractile units connect to each other. Studies using muscle biopsies after eccentric cycling have found widespread disorganization of these structures, along with swelling in the energy-producing components of cells and damage to the membrane systems that coordinate contraction. Older adults (ages 59 to 63) show a higher percentage of this structural disorganization compared to younger adults (ages 20 to 30) after the same eccentric bout.
This damage sounds alarming, but it’s a normal part of how muscles adapt. The repair process is what triggers the muscle to rebuild stronger and more resistant to future damage. This is why the second time you do the same eccentric workout, the soreness is dramatically less.
The Stretch-Shortening Cycle
In most athletic movements, you don’t perform concentric and eccentric contractions in isolation. They flow together in what’s called the stretch-shortening cycle: a quick eccentric phase immediately followed by a concentric phase. Jumping is the classic example. You drop into a quick squat (eccentric), then immediately explode upward (concentric). The brief eccentric stretch stores elastic energy in your muscles and tendons, which is then released during the concentric push to boost performance.
The key is the transition time between phases. If you pause too long between the stretch and the push, the stored elastic energy dissipates as heat and you lose the benefit. This is why a quick countermovement jump is higher than a jump from a dead stop, and why plyometric training emphasizes fast, reactive ground contact. The speed of the transition also depends on muscle fiber type: fast-twitch fibers recoil elastic energy more effectively at higher speeds.
Eccentric Training in Rehabilitation
Eccentric-focused exercises have become a cornerstone of tendon rehabilitation, particularly for Achilles and patellar tendinopathy. The most widely used protocol for Achilles tendon pain involves heel drops performed with a straight knee and a bent knee, done twice daily, typically 3 sets of 15 repetitions for each variation, seven days a week. Load is increased progressively, often by adding weight in a backpack, once the exercise can be performed with manageable pain (generally below a 5 out of 10 on a pain scale).
For patellar tendon pain, the standard approach uses single-leg squats on a 25-degree decline board, following a similar structure of 3 sets of 15 reps, twice daily. The decline angle shifts more load onto the patellar tendon compared to a flat squat. Some protocols allow moderate pain during the exercise, while others aim for pain-free loading, and both approaches have shown benefit.
The rationale is that controlled eccentric loading stimulates tendon remodeling without the high metabolic and cardiovascular cost of full concentric-eccentric training. The slow, heavy lengthening contraction provides a mechanical stimulus that promotes structural changes in the tendon tissue over weeks to months.
How to Use Both Phases in Training
Most strength training programs naturally include both phases, but you can shift the emphasis depending on your goals. Slowing down the eccentric portion of a lift (taking 3 to 5 seconds to lower the weight) increases time under tension and amplifies the muscle-building stimulus. This technique works with virtually any exercise and doesn’t require special equipment.
Because your muscles can handle more load eccentrically, some programs use supramaximal eccentric training: loading a weight heavier than your concentric max and only performing the lowering phase, with a partner or machine helping you return the weight to the start. This approach builds strength at the higher end of your force capacity but requires careful progression to manage the increased muscle damage.
For power and speed, focusing on a fast transition from eccentric to concentric, through plyometrics and explosive lifts, trains the stretch-shortening cycle. Box jumps, depth jumps, and medicine ball throws all exploit the elastic energy stored during the eccentric phase to produce more powerful concentric output.