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CONTRACTION TYPES AND HOW A PERSONAL TRAINER CAN USE THEM

Hadyn Luke posted this on Thursday 19th of April 2012 Hadyn Luke 19/04/2012

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CONTRACTION TYPES AND HOW A PERSONAL TRAINER CAN USE THEM

Todays fitness blog will discuss the different types of muscle contraction and how they are used in a training environment. Personal trainers will often find that those they are training believe that a muscle is only working when it’s shortening. In fact a muscle can be working when it’s shortening, lengthening and even when the joint action remains static.

The three main types of contraction that a skeletal muscle is capable of are:

Concentric – when a muscle shortens

Eccentric – when a muscle lengthens

Isometric – when there’s tension in a muscle but no movement in the joint action

In a gym environment, a personal trainer would devise an exercise programme that uses all three type of contraction, as they all have their features and benefits.

With any exercise that a personal trainer asks their client to carry out involving moving, holding the position and returning through the same path, there will be a concentric, an isometric and an eccentric movement in the relevant muscle. If the client brings their arm up for a bicep curl, the muscle is shortened so this is a concentric contraction. If the trainer asks them to stop part way and hold the arm in position, there would be an isometric contraction. And when the arm is being lowered again, the bicep muscle is now lengthening in an eccentric contraction.

During the bicep curl, the muscles will work in pairs, with an agonist and an antagonist. As the arm is lifted, the bicep muscle will be shortening, but the joint action can only occur if the tricep relaxes. So at this stage of the exercise, the bicep is being used concentrically as the agonist and the tricep is working eccentrically as the antagonist.

It is possible for a muscle to change from an agonist to an antagonist in a different exercise. If the arm is raised to the ceiling and then the elbow is bent so that the hand touches the back of the neck, the triceps is acting as the agonist in an eccentric contraction as the triceps lengthens.  However, if the hand is then raised from the neck to the ceiling again, the tricep is being used concentrically as it shortens but it is still the agonist, while the bicep, which is now working eccentrically and lengthening, is the antagonist.  The process of one muscle relaxing  (shortening or lengthening)  while another works to allow joint movement is called reciprocal inhibition.

Another good example you might find in a personal trainer course of a muscle that is working as the agonist while lengthening would be during a bench press. The personal trainer would position the client lying on their back with the bar held above their chest. When the client lowers the weight, their chest is working, cushioning that downward movement and stretching out the chest muscle. So the chest muscle is the agonist but it’s working eccentrically.

Of these three types of contraction, the eccentric is the strongest, then the isometric and finally the concentric. This is why it’s easier to hold a heavy object in place than it is to lift it from the floor and it is easier still to gradually lower the same object. The power in a muscle when it’s shortening is less than the power in that same muscle when it is maintaining a joint action and this is less than the strongest contraction, which is when a muscle is lengthening.

The benefits of these contraction types are as follows:

Concentric contraction – When weight training with a client, a personal trainer will know that if they stop the exercise when the client is fatigued and can no longer do a concentric contraction, then there will be less damage or DOMS (delayed onset of muscle soreness).

Isometric contraction – This is a useful contraction both during training and, at a lower intensity, to strengthen underused muscles during rehabilitation after an accident. However, the personal trainer should be aware that straining too hard during isometric contractions can increase blood pressure and increase DOMS. If a client is trying to lift or push something excessively heavy, it could initiate a response known as the Valsalver manoeuvre, which can raise the client’s blood pressure to dangerous levels.

Eccentric contraction – With a well-trained client, who has worked both the concentric contraction and the isometric contraction until they are fatigued, a personal trainer might help them so that they can continue carrying out the eccentric part of the exercise. This provides a higher intensity training for the muscle and promotes more strength gains. These forced reps are known as eccentric training (or negative training).

 A muscle will only develop strength, power or endurance in the range of movement within which it is used or trained.  Therefore it is important that the load of an exercise is not too great to inhibit the ROM performed.

We hope you have enjoyed our latest fitness blog, we would love to hear your feedback. If you would like to find out more about different types of muscle contraction training, or about personal trainer courses, visit Level 3 Certificate in Personal Training