The Best Workout

The Advanced Fitness Terms – Repetition Types and Muscle Roles

Do you consider yourself a fitness expert? Are you giving advises to beginners in the gym? That is fine then, you are an advanced gym lover.

You are not looking for someone who let you know the meaning of a set or what a rep is. Did you get any doubt about those two gym terms? Jump straight ahead and read The Absolute Beginner’s Fitness Guide where all the fitness foundation that you need to advance to the next level.

If you try to maximise your gains there is more advanced terms that we need to know. In this post you will discover the different types of contractions that a muscle can perform. This is important to design the best gym routine and to know if our current routine has the more efficient planning.


Muscle Concentration Type

We could classify the muscle concentration according to the movements. We will just focused in the more important, so let’s see them.

There are two types of muscle contractions: isometric (muscle length does not change during contraction) and isotonic  (the most important for us)

Also there are 2 types of isotonic contractions: concentric and eccentric.

Concentric contraction or positive rep

The origin of the terms concentric and eccentric are related to muscle contraction in basic physiology science. Those terms are know for the more advanced gym user, however a lot of people will you know what a positive repetition is.

In a concentric contraction, the muscle tension rises to meet the resistance then remains stable as the muscle.

If you still don’t know it will be easy to explain with an example.  The biceps muscle in the thigh contract concentrically during the upward phase of the Dumbbell Alternate Biceps Curl movement (in the direction of the arrow), as can be seen in the adjacent picture.

Positive will be the phase of the repetition when you will put all your energy in order to made your muscle grow.

You can chose the time ratio between the concentric and eccentric concentration.

Eccentric contraction or negative rep

Concentric contraction (or negative repetition) , refers to any contraction where the muscle lengthens under load or tension.

So in the Dumbbell Alternate Biceps Curl exercise, the biceps muscle will contract eccentrically in the upward phase of the movement, as can be seen in the adjacent picture.

Tip !!!

From we recommend as a standard the next time of concentric and eccentric phase:

  • Concentric phase: 1 second.
  • Eccentric phase: 2 second.

It provides a unique contrast for stimulating strength and hypertrophy.

Consider those time as a guide of a good exercise execution practices, however it could vary depending of other factor as type of exercise, level, fitness goal.etc

Isometric contraction

An isometric contraction refers to any contraction where muscles don’t actually need to move at all to contract or develop tension.

If during the Biceps Curl the person stopped moving at a certain point and held that position for 20 seconds, the biceps muscle would be contracting isometrically, it would still be under load/tension but no movement would occur.

There are some benefit of this kind the concentration where we could take advantage of this type of concentration.

They are closely identified with common flexibility activities like yoga and stretching, but also apply to strength training and especially abdominal development.

One of the more famous isometric exercise is The Plank and the variations Side Plank.

Muscle Role during the movement

During the movement there are different roles for the muscles in order to design the best workout routine we need to know what what kind of roles an specific muscle has.

When completing movements such as bench press or leg extensions, there are a lot of different muscles involved in order to complete the movement.  Each muscle adopt the appropriate type of contraction (concentric, eccentric or isometric) and have their own specific role that they play during the movement.

There are four different roles that a muscle can fulfil during movement, these roles are:


Agonist muscle

The agonist in a movement is the muscle(s) that provides the major force to complete the movement. Because of this agonists are known as the ‘prime movers’. In the bicep curl which produces flexion at the elbow, the biceps muscle is the agonist, as seen in the image below.

The agonist is not always the muscle that is shortening (contracting concentrically). In a bicep curl the bicep is the agonist on the way up when it contracts concentrically, and on the way down when it contracts eccentrically. This is because it is the prime mover in both cases.

Antagonist muscle

The antagonist in a movement refers to the muscles that oppose the agonist. During elbow flexion where the bicep is the agonist, the triceps muscle is the antagonist. While the agonist contracts causing the movement to occur, the antagonist typically relaxes so as not to impede the agonist, as seen in the image above.

The antagonist doesn’t always relax though, another function of antagonist muscles can be to slow down or stop a movement. We would see this if the weight involved in the biceps curl was very heavy. When the weight was being lowered from the top position the antagonist triceps muscle would produce a sufficient amount of tension to help control the movement as the weight lowers.

This helps to ensure that gravity doesn’t accelerate the movement causing damage to the elbow joint at the bottom of the movement. The triceps becomes the agonist and the bicep the antagonist when the elbow extends against gravity such as in a push up, a bench press or a triceps push-down.

Synergist muscle

The synergist in a movement is the muscle(s) that stabilises a joint around which movement is occurring, which in turn helps the agonist function effectively. 

Synergist muscles also help to create the movement. In the biceps curl the synergist muscles are the brachioradialis and brachialis which assist the biceps to create the movement and stabilise the elbow joint.

Fixator muscle

The fixator in a movement is the muscle(s) that stabilises the origin of the agonist and the joint that the origin spans (moves over) in order to help the agonist function most effectively. 

In the biceps curl this would be the rotator cuff muscles, the ‘guardians of the shoulder joint’. The majority of fixator muscles are found working around the hip and shoulder joints.


you complete this advance gym user guidance if you know all of that you have almost all the tools to achieve your best self