As its name suggests, a concentric exercise focuses on the concentric phase of a movement, which is when your muscle shortens. You can modify exercises so that you're only performing the concentric movement, but it's not as beneficial as using a full range of motion.
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Concentric exercise is the shortening phase of a movement. You need assistance through the eccentric portion to isolate the concentric portion.
Sliding Filament Theory
Your muscles contract and lengthen to allow you to move. This concept is based on the "sliding filament theory of muscle contraction." According to a June 2016 study published in Global Cardiology Science & Practice, this theory explains how all types of muscles contract.
The interaction between actin and myosin, two of the major proteins in a muscle cell, is key to making a muscle contract. According to a November 2019 research paper published in the International Journal of Molecular Sciences, myosin uses small heads to stick to actin, which acts as an anchor. Myosin then pulls on the actin to cause muscle contraction.
As Oregon State University notes, the muscle shortens when myosin pulls on actin. A nerve signals the muscle to contract over and over until it reaches its shortest point. When that muscle needs to relax, a shield forms over actin, which prevents myosin from latching on and pulling.
This is essentially how a muscle contracts. There are two basic types of contractions, according to the Wentworth Institute of Technology: eccentric and concentric. They are called contractions because the muscles are working in both cases — but in a different way.
Types of Contractions
In an eccentric contraction, the muscle is lengthening. However, there is still tension in the muscle to control the movement. In a weight-lifting movement, the eccentric portion of the movement is the easier part, where you're lowering the weight. In a bicep curl, it would be the part of the movement where you're extending your elbow.
An eccentric movement is considered a contraction because your muscles are slowly letting go. If they simply relaxed and gave way, the weight would drop in an instant, and you might be injured.
The concentric contraction, on the other hand, is the tougher part of the movement. That's when you're actually lifting the weight and struggling. Some people may want to isolate each type of contraction and focus on them separately, which is possible if you have some help from a friend.
For example, when doing bicep curls, you can have someone help you lift the dumbbell. This would take the stress away during the concentric phase of the movement. You can also have them help you lower the weight so that you can focus on the concentric phase.
Some advanced cable machines may give you more resistance in one part of the movement and less in another. Interestingly, each phase of the movement seems to cause different adaptations in muscle tissues.
Eccentric and Concentric Exercise
Lifting weights stimulates your muscles to grow and become stronger. A September 2017 review featured in the Journal of Strength and Conditioning Research indicates that both concentric and eccentric contractions can stimulate muscle growth. Scientists recommend including both types of movements in a weight-training program.
Another review, which was published in Frontiers in Physiology in July 2017, reports similar findings. After analyzing several studies, researchers concluded that muscle growth was similar between eccentric and concentric lifting, but each type of movement affected the muscle differently. This means that you can't substitute one type of movement for the other.
In terms of strength gains, there doesn't seem to be much of a difference. A small study published in the February 2020 issue of the_ Journal of Strength and Conditioning Research_ shows that concentric and eccentric movements lead to similar improvements in leg strength. The subjects were asked to do slow and fast contractions to see if the speed made any difference, but it didn't.
- Journal of Strength and Conditioning Research: "Comparison of the Effects of Eccentric, Concentric, and Eccentric-Concentric Isotonic Resistance Training at Two Velocities on Strength and Muscle Hypertrophy"
- Frontiers in Physiology: "Skeletal Muscle Remodeling in Response to Eccentric vs. Concentric Loading: Morphological, Molecular, and Metabolic Adaptations"
- Journal of Strength and Conditioning Research: "Hypertrophic Effects of Concentric vs. Eccentric Muscle Actions"
- Wentworth Institute of Technology: "Eccentric and Concentric Movements"
- International Journal of Molecular Sciences: "Special Issue: The Actin-Myosin Interaction in Muscle: Background and Overview"
- Global Cardiology Science & Practice: "Muscle Contraction: Sliding Filament History, Sarcomere Dynamics and the Two Huxleys"
- Oregon State University: "Muscle Fiber Excitation, Contraction, and Relaxation"