A common misunderstanding is that when a muscle contract and a force is generated it shortens. However, as muscles produce force when they are activated, the muscle will respond differently depending on how the force developed by the muscle and the load placed on it interact with each other. This can result in muscle shortening, staying at a constant length or lengthening (Faulkner, 2003).
Resistance training to improve muscular strength is widely used by a variety of populations for many purposes including, performance enhancement, preventing or recovering from injury, and maintaining a healthy lifestyle (Roig et al., 2008). A muscle can be trained either statically or dynamically and there are 3 different types of contractions that exist. When a muscle is trained statically meaning with no movement, the active muscle is held at a fixed length, an isometric contraction (Roig et al., 2008). On the other hand, when a muscle is trained dynamically meaning with movement, we can have either a shortening of the muscle fibers which is known as a concentric contraction or lengthening of the muscle fibres known as an eccentric contraction. (Roig et al., 2008). Each of these forms of contractions have a place during rehabilitation depending on the type of injury and the stage of recovery the individual is in.
In some circumstances, it may be more beneficial to use one of these different types of contractions over the other depending on the overall goal. We will now discuss when each type of contraction is utilized and why different movements may be better in certain situations.
Many activities are not just isometric, concentric, or eccentric but rather a combination of all three muscle contractions (Taylor, 1985). Each type of contraction has a place in rehabilitation, and even though they should all be addressed it is important to determine when and why one may be beneficial.
This can be dependent on stages of healing, the type of tissue that is injured, and ultimately the type of activity that a person is returning to (Chepeha, 2020). Often during rehabilitation depending on the clinical presentation, there will be a focus on one type of contraction over another to isolate specific muscle activity.
Isometric Exercises
As mentioned, isometric exercises are when the muscle produces a force without a major change in muscle length and joint movement (Roig et al., 2008). A couple of reasons to consider isometric exercises in your rehabilitation are to prevent losing muscle mass, when the area is painful, and to protect healing tissue (Chepeha, 2020).
- Helps with developing isolated joint stability and postural control (Chepeha, 2020).
- They can be performed at a lower intensity with little to no resistance with the goal of trying to get the target muscle to contract.
- Isometric exercises can be used after recent surgery in order to protect the healing area.
- Lastly, if there are specific positions that are used often in an activity you can train the muscle using isometric exercises at a specific point in the range of motion (Chepeha, 2020)..
Eccentric Exercises
Eccentric exercises have been found to be beneficial for individuals with tendinopathies, muscle strains, and ACL rehabilitation (Lorenz et al., 2011).
Eccentric exercises are not beneficial in someone who has had a recent surgery or repair because in this instance we would not want to lengthen or stretch the muscle (Chepeha, 2020).
During eccentric exercises muscles are able to generate more force without working as hard (Roig, 2008). Compared to concentric exercises it was found that strength gains were bigger with eccentric exercises (Roig, 2008). This allows individuals to train with higher loads than they would be able to concentrically or isometrically. (Ryschon, 1997).
Concentric Exercises
“The most popular form of resistance training is raising and lowering an external weight”
(McCardle et al., 2015)
The concentric portion is when the weight is being raised and the muscle is shortening while it develops force (McArdle et al., 2015) Concentric contractions are the most basic and common form of contraction that is used to increase muscle strength and mass. Concentric contractions have been found to produce less force than eccentric ones, in other words, the body can lower more than it can lift (Roig et al., 2008).
Concentric contractions are often used in combination with eccentric contractions because exercises usually consist of both (Schoenfeld et al., 2017). This allows an individual to gain the benefits of both types of contractions when resistance training if they choose.
The following are examples of common exercises for the upper body and lower body that have a combination of eccentric, isometric, and concentric contractions. An explanation of which type of contraction occurs during each part of the movement will be described.
- Bicep curl: The concentric portion of the exercise is when the elbow is bending up. While the elbow is bending up the muscle is becoming shorter. The eccentric portion is when the arm is straightening. While the elbow is straightening the muscle is lengthening again. The isometric portion happens when you hold the arm at a 90-degree angle and hold it in that position. At this time the muscle is held at a constant length and is working but not changing.
https: //fitblissfitness.com/2020/08/07/concentric-eccentric-isometric-tempo-what-does-it-all-mean/
- Squat: During a squat, the eccentric portion of the exercise is when a person squats down and bends the knee. This is when the glute muscles that help extend the hip are lengthening. The isometric portion of the exercise is at the bottom of the squat and maintaining that position. The concentric portion of the exercise is when the knees and hips are straightening and extending the hips.
