When you think of a muscle contraction, you typically think of the muscle shortening. For example, when you do a biceps curl you shorten the biceps to generate enough force to curl the weight upwards. Shortening the muscle isn’t the only way your muscles can generate force. In fact, there are three ways muscles can generate force. Let’s take a look at each one.
Concentric Contractions
Concentric contractions involve muscle shortening. As the muscle shortens, it generates tension and this increased tension allows you to move the weight or resistance. As you move the weight through its range of motion, the muscle shortens and joint angle changes. Your muscles contract concentrically during the contraction phase of a bicep curl. When doing shoulder presses, the concentric phase is when you lift the weights above your head. Another example of a concentric contraction is when you use your arms to push your body up during a push-up.
Eccentric Contractions
Eccentric contraction is force generation as a muscle lengthens. With an eccentric contraction, the muscle generates tension to keep the muscle from lengthening too quickly. The force generated acts as a “brake.” Using the biceps curl example, the eccentric portion of the movement is when you lower the weight. As you lower it, the biceps muscle lengthens while generating tension to control the downward movement. Your muscles have to maintain tension that’s slightly greater than the amount of weight you’re holding to keep the weight from dropping too quickly. Eccentric contractions are sometimes referred to as “negatives.”
Another example of eccentric muscle contractions at work is when you walk downhill. As you walk, your quadriceps muscles exert a braking action by controlling the rate at which you flex your knees. With each step you take, your quadriceps and calf muscles contract eccentrically and are forced to absorb the impact of your feet as they strike the ground. No wonder downhill walking and running lead to more soreness!
Eccentric muscle contractions have benefits. When you contract a muscle eccentrically, up to 1.3 times greater tension is generated in the muscle relative to a concentric contraction. Therefore, eccentric contractions are quite effective for building muscle strength. The downside is eccentric contractions produce more muscle damage than other types of muscle contraction. Therefore, your muscles need a longer period to recover after an eccentric-focused workout. The risk of injury is also higher, especially if you haven’t mastered proper form.
Another type of training that emphasizes eccentric contractions is plyometrics. Plyometric exercises that generate explosive moves like squat jumps and tuck jumps have an eccentric phase followed by a concentric shortening of the muscle. During the eccentric phase you “preload” the muscle by storing energy in the elastic components of the muscle. This is followed by a brief pause for stabilization and then a concentric phase where you use the energy stored in the elastic tissue of the muscle to propel yourself into the air. The shorter the pause between the eccentric loading phase and the concentric phase, the more power generated. Plyometric training is designed to increase the rate at which muscles develop force, leading to greater power.
Isometric Contractions
Concentric and eccentric contractions are referred to as isotonic movements, meaning the muscle changes in length. With isometric contractions, muscles generate tension without changing length and no movement of the muscle actually takes place. An example is holding a pair of dumbbells stationary at a fixed height. Your muscles have to generate enough tension to keep the dumbbells in place as gravity tries to pull them down.
Planks are an example of an isometric bodyweight exercise. With planks, you’re using muscle tension to hold your body stationary against gravity. With an isometric contraction, the muscle never generates a force that’s greater than the load it’s supporting. The amount of tension you can generate during an isometric contraction depends on the length of the muscle you’re contracting. Muscles have an optimal length at which they can maximally generate force.
Isometric exercises are referred to as “static training.” Isometric exercises build strength but they only strengthen the muscle to a significant degree at the joint angle you’re working. To strengthen the muscle through its entire range of motion, you have to do isometric exercises that work each joint angle. Not very time expedient.
All Three Forms of Muscle Force Generation Have Benefits
Focus most of your attention on isotonic movements, an exercise that involves shortening and lengthening of the muscles. These exercises work your muscles through their full range of motion, unlike isometric angles that only work them at one joint angle. You’ll build greater strength by slowing down the eccentric movement of an exercise since eccentric movements generate more tension, but don’t do “negatives” every time you work out. Give your muscles time to recover after eccentric training – and expect to be sore afterward.
Summing it Up
Here are some points to remember about muscle contractions:
Isotonic contractions are ones that involve a change in the length of a muscle. Concentric and eccentric contractions are isotonic because the muscle changes in length.
Concentric contractions involve generating tension through shortening.
Eccentric contractions involve holding tension while a muscle is lengthening. It serves as a brake and a way to control a movement.
Isometric contractions involve no change in muscle length or joint angle. They only work the muscle at a particular angle, not over its full range of motion.
Eccentric, concentric and isometric exercises all have benefits and can be part of a balanced resistance training workout.
References:
Poloquin – Healthy. Lean. Strong. “The Power of Eccentric Training”
The Journal of Physiology, 537, 333-345. December 2001.
Short Summary:
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Benefits of Resistance Bands vs. Free Weights
Isometric vs. Isotonic Exercises: What’s the Difference?
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STS Strength 90 Day Workout Program
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