Article by Gill Cummings-Bell BA (Hon’s) M.Sc. PGCE. MBA. ACSP

Using concentric, eccentric and isometric action with spring tension

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Remember These Words from Your Courses?

Prime mover. Agonist. Antagonist. Synergist. Fixator.

You probably remember learning these words during your early anatomy training, perhaps trying to revise and understand them for an exam or an anatomy worksheet. But do you understand how these muscle roles work during a movement on the apparatus or on the mat? More importantly, do you visualise those roles while teaching the exercise can you see the anatomy in action on the body?

Do you consider:

• Which muscles initiate and provide the main force for the movement?
• Which muscles apply force to assist the movement?
• Which muscles apply force to stabilise another part of the body?
• Which muscles oppose the movement and need to relax and lengthen to allow smooth movement?

I know I am asking more questions than I am answering at this stage, so let’s roll this out a little further.

Think of Snow White and the Seven Dwarfs: one central character working alongside a group of smaller helpers. Everyone contributes to the story, but they do not all have the same role.

Let’s push back a bit to our level 2 & 3 Courses:

We can use this over-simplification to understand muscles roles as they are working together in a similar way.

When a muscle or muscles are acting as:

• The Prime Mover, or Agonist, it is the muscle providing the main force/initiating and executing the intended movement.
• The Antagonist muscle opposes the action of the agonist and is generally inhibited to allow free movement with some exceptions in movements that involve a principle referred to as Lombards Paradox which we will discuss later.
• The Synergists are muscles that assist the prime mover and may help control or prevent unwanted movement in the moving joint. These are muscles that act on the same joint as the prime mover and are found generally crossing the same joint as the agonist
• The Fixators they stabilise a non-moving part of the body so that other parts of the body remain stable and held in position whilst movement is occurring in a particular part of the body. These are muscles that act on other joints not the moving joints. Think of them as acting on joints we are trying to hold still.

Muscles can take on any of these roles during a movement, and their roles may change as the movement progresses.

Remember That Muscles Work in Pairs? Let’s look at that role a little more.

The antagonist opposes the action of the agonist. It is generally some level of inhibition to allow the agonist to contract and produce free movement. This relationship is known as Reciprocal Inhibition.

Think again about lifting a shopping bag. As the elbow bends, the biceps act as the agonist and contract concentrically. The opposing triceps will have some level of inhibition from contracting, allowing them to relax and lengthen so that the elbow can bend freely. This helps our understanding of why muscles need to have length in order to relax, lengthen out, and allow an opposing movement to occur when they are acting in opposition to a prime mover or agonist.

This is a useful principle for teachers to understand and visualise. Which muscle is producing the movement, and which opposing muscle needs to relax and lengthen to allow that movement to take place? If the opposing muscle doesn’t have enough length, we can work to improve the available length/range of the antagonist that oppose big ranges of movement so that they can stretch and release further. An example would be in Leg Circles, if  contracting the quadriceps at the knee (remembering as well that Rectus Femoris is also a synergist in hip flexion as it crosses the hip) and hip flexors at the hip, bringing the hip into hip flexion, the hamstring  relaxes to allow the hip to come into flexion. If the hamstrings can’t release their tension point into a lengthened stretch this will restrict the hip flexion.

However, there are some movements in which muscles that we might expect to oppose one another are active together. This is known as co-contraction.

When Opposing Muscles Work Together: Lombard’s Paradox

Lombard’s paradox is an example of co-contraction involving two-joint muscles. The classic example is the simultaneous activity of the rectus femoris and the hamstrings as we rise from a squat.

These muscles appear to oppose one another:

• The rectus femoris crosses both the hip and knee. It can flex the hip and extend the knee.
• The biarticular hamstrings  cross both the hip and knee. They can extend the hip and flex the knee.

If we look only at those actions, we might expect the muscles to cancel each other out. Yet, as we rise from a squat, both the hip and knee extend, and both muscle groups can be active as we have two joint actions.

How does this happen? Because their leverage differs at each joint:

• The hamstrings can have a greater effect in producing hip extension than their opposing effect of knee flexion.
• The rectus femoris has a greater effect in producing knee extension than its opposing effect of hip flexion.

Their actions therefore combine to support the overall movement: the hamstrings contribute to extending the hip as synergists, while the rectus femoris contributes to extending the knee as agonist. Both working simultaneously.

The gluteus maximus and the other quadriceps muscles also play major roles in rising from a squat. Lombard’s paradox does not suggest that the rectus femoris and hamstrings perform the movement alone. It demonstrates that muscles commonly viewed as antagonists may co-contract and contribute to the same overall movement.

Keep the Two Principles Clear

• Reciprocal inhibition: the agonist contracts while the antagonist may have an element of inhibition, allowing it to relax and lengthen so that movement can occur freely. The biceps and triceps during elbow flexion provide a clear example.
• Co-contraction: muscles with apparently opposing actions are active at the same time to contribute to or control a movement. Lombard’s paradox during the upward phase of a squat provides the example.

This distinction keeps reciprocal inhibition straightforward before introducing the more complex idea that muscle roles may change according to the joints involved and the movement being performed.

What are the Contracting Muscles Actually Doing?

Once we have identified a muscle’s role at a particular moment in a movement, we can consider the type of muscle contraction it is undergoing to fulfil that role.

The traditional term isotonic encompasses two dynamic phases:

• Concentric
• Eccentric

The second type of contraction is isometric.

Throughout contraction we also need to be able to visualise or see the muscle’s line of pull so that we can consider not only how it generates force and which type of contraction is executed but also which joint or joints it crosses and when its contraction is initiated what is the line of pull. This helps us understand the movement and describe its intended feeling to the client.

It also takes us back to the fundamentals of Pilates, particularly Centring, Control and Precision.

On the Reformer or varied Pilates apparatus that has springs, there is an additional consideration: understanding these muscle actions helps us use spring tension more effectively.

Concentric: Producing the Movement

During a concentric muscle action, an active muscle produces force while shortening.

Think of lifting a shopping bag from the floor. As you bend your elbow, the biceps shorten to help lift the bag.

Now take this principle onto the Reformer. During the Footwork Series, for example, the quadriceps act concentrically to extend the knees and move the carriage away from the stopper generating force to overcome the initial spring tension and throughout the movement as the spring extends increasing spring tension according to the spring’s rate.

The client is moving against the increasing tension of the springs, but we cannot decide which muscle action is occurring simply by watching whether the springs are opening or returning. We need to use our diagnostic eye and visually analyse the above roles and actions. See them in action on the client.

Ask yourself:

• What is the joint action or multiple joint actions that are occurring or being held in a fixed position?
• Identify the muscle’s role in the movement. Then identify the action it is using to fulfil that role
• Where is the muscle situated that is initiating the movement or assisting the movement or holding that joint in position?
• Which joint or joints does it cross?
• What is its line of pull i.e when the sliding filament theory takes effect in which line of pull will contraction occur? This is important for precision and also to ensure the correct muscles initiate and or execute the action.
• Is it shortening and generating force, lengthening and remaining under tension or maintaining its length while generating force? Recognising in those descriptions which muscles are working concentrically, eccentrically or isometrically.

This gives us a much fuller understanding than simply observing the direction of carriage travel.

Eccentric: Controlling the Movement

During an eccentric muscle action, the active muscle remains under tension force while lengthening.

Imagine carefully lowering that shopping bag back to the floor. You are not simply letting go and allowing gravity to take over. The same muscles that helped lift the bag now help control its descent under an eccentric contraction, as they lengthen. We also experience this when walking downstairs. The muscles of the legs control the lowering of the body from one step to the next. Without that eccentric control, we would drop heavily onto each step.

Do you know people are generally stronger eccentrically through a movement than they are concentrically? Let’s leave that explanation for another article.

On the Reformer, the overall spring tension generated through the stretching of the spring,  increasing spring tension as the spring lengthens, may use its stored elastic energy to ‘spring’ back to its original position and therefore assist the returning movement. The teacher’s task is to educate the client not merely to return the carriage, but to reduce the tempo of the return bringing the concentration to the muscle and remain under tension as it lengthens and control the assistance provided by the springs. The relevant muscles may work eccentrically as they lengthen, preventing the carriage from returning too quickly.

An example at this stage is useful. If we are executing a Footwork Series exercise on the reformer we would open the carriage, stretching the spring using the quadriceps concentrically. If we allow the muscle to relax and we just allow the spring to return to it’s original position the muscle will relax without any work or overload benefits. If we focus on the quadriceps remaining under tension and resist the returning action of the spring we work eccentrically with all the muscle physiology benefits that it brings.

Slowing the tempo may help the client recognise and control this phase. It gives them time to resist the spring’s assistance, manage the pathway of the carriage and maintain muscular activity instead of simply relaxing and allowing the springs to take over.

However, moving slowly does not automatically mean that eccentric work is taking place. We still need to ask:

Which muscles are active, and are they lengthening along their line of pull while controlling the movement?

More Eccentric Detail: Applying This to Footwork

Now that you understand the springs from Parts One and Two, what can you visualise during an exercise such as the Footwork Series?

As the carriage moves away from the stopper, the springs lengthen and their tension generally increases. The quadriceps act as agonist and shorten concentrically to extend the knees and overcome that increasing spring tension.

At the point of greatest carriage travel, spring tension is at its highest. As the carriage returns, the springs assist the movement towards the stopper. If the client simply relaxes the agonist, the spring tension will largely determine the speed of the return.

If, instead, the client keeps the quadriceps active as the knees bend, those muscles can work eccentrically to control the returning carriage.

This is where a change of tempo can be useful. A slower, deliberately controlled return can bring the client’s attention to the correct muscles and keep them active under eccentric loading. The aim is not simply to move slowly, but to maintain force while the working muscles lengthen.

Isometric: Providing a Stable Base

During an isometric muscle action, a muscle can produce force by shortening and contracting but staying in the shortened contracted position to hold the position. Equally it can produce force at medium length or lengthened and remain the same length in an isometric contraction.  This type of action is often used to stabilise another part of the body, holding it still whilst a different body part is moving. 

Think about ‘The Hundred’ once you have lifted into the classical/traditional lifted position. Most of the body is fixating and stabilising whilst the shoulder is moving.  As an example, and just to name a few, the hip flexor muscles (Psoas Major and Iliacus) will hold and fix the legs in flexion at the hip throughout the exercise, the Quadriceps will hold the knee in extension, abdominal muscles (Rectus Abdominus and Internal & external Obliques) will hold the spine in a flexed position whilst the shoulder muscles (Anterior deltoid, Pectoralis major (upper/clavicular fibres), Coracobrachialis,  Biceps brachii (long head, acting as a weak synergist)  are producing force to move the shoulder joint.

I love The Hundred when I am visualising anatomy at work in an exercise. We can see it all in this exercise. The way muscles change roles from agonist prime mover to get into a position, then those muscles then changing to fixation such as when we lift the legs into hip flexion as a moving joint, then holding them in fixation whilst we then move into another part of the movement such as spinal flexion using the abdominals and then the abdominals fixate working to control the centre. These are just examples and not an analysis of the whole movement.  Whilst most joints in the body are being fixated, the shoulder joint moves in flexion and extension and its muscles work both concentrically and eccentrically as prime movers.  A lot to think about in every exercise.  I think the genius of The Hundred being the warm up exercise is that it involves the whole body in different ways at different times, as well as working to embody the  principles of the method. There is so much fixation work through isometric contraction in this exercise and very little movement work. Of course we haven’t forgotten about the principles and breath control, we can save these for the next analysis. 

On the reformer Footwork has a similar role, the whole body is actively involved in muscle contraction be that isometric work through fixation such as the abdominals and other trunk muscles maintaining the centred position of the trunk and pelvis or muscles stabilising the feet, hips, shoulder girdle or head and neck, while the leg muscles are acting as agonists and synergists at the knee to open and stretch the springs and move the carriage. The principles of the method as well as the anatomy are all visible to your diagnostic eye in exercise.

This is just a small example of the genius of the principles of the method: the movement we see is anatomically and biomechanically is only part of the exercise. The work of muscles stabilising, controlling or preventing unwanted movement is equally one of the most important roles of muscle in all exercise. 

Do You Visualise These Roles While Cueing?

When teaching, it is easy to concentrate on the visible movement of the carriage:

• Is it opening far enough?
• Is it moving in a flowing event tempo way?
• Is the client keeping it under control?

But can you also visualise what is happening beneath the movement?

Ask yourself:

• Which joint actions am I seeing and are they correct, which muscles are acting as the prime movers to move those joints? Which muscles are assisting or controlling the joint action as synergists? Which muscles are stabilising parts of the body as fixators?
• Which opposing muscles need to relax and lengthen through reciprocal inhibition or are they co-contracting to stabilise in actions such as Lombards Paradox?
• Is the prime mover working concentrically or eccentrically during which phase of the movement and can I use this more effectively for the client in my cues?
• Are the muscles acting as prime movers or synergist overcoming increasing spring tension, or eccentrically controlling the spring-assisted return?
• Does a muscle’s role change when the direction changes or when in position and then holding a position whilst another movement comes in? Could a prime mover in one part of the exercise become a fixator in another?

These questions help us move beyond cueing and teaching only the shape of an exercise. They encourage us to teach and cue its intent and apply it more specifically to the needs of the client and the mechanics of the apparatus. Learning this in texts books doesn’t help. Seeing it on your client’s body does.

Do You Describe the Feeling for Your Client?

Most clients do not need a detailed anatomy lesson while they are moving. However, to cue effectively, the teacher (we) need to understand the anatomy, physiology and biomechanics of the movement: what is working, when it is working and how it is working. Most importantly of all, is it working on this client? Many movements can be executed without the right muscles involved, in the right role.

On the apparatus, there is an additional layer of understanding because we must include the mechanical effects of the springs, ropes, carriage, gravity and the client’s position.

Our understanding of muscle roles and actions can directly affect the success of the exercise’s intent for that client.

As an example:

For the concentric phase of Footwork, you might cue:

Press the carriage away, gradually overcoming the increasing tension of the springs by lengthening from the knee to the hip, holding the foot and ankle still.

For the eccentric return:

As you knees bend to and you feel the springs pulling the carriage back, slow down the movement and visualise a slow lengthening between knee and hip.  Control the pull of the springs and guide the carriage home.

For the isometric work of the fixators:

Allow the legs to move while keeping the pelvis and trunk quietly organised with the neck long at the back, the rib down and the foot and ankle still. Control with your breath.

These cues help the client experience the difference between creating movement, controlling movement and providing stability while movement occurs elsewhere.

Why Is This Important?

When a teacher chooses an exercise from the repertoire, it should be chosen with an intention appropriate to the client’s needs to enhance their embodiment of the method and improve their overall movement and wellness.

It then becomes important to use muscle action and spring tension to support that intention. Understanding the difference between concentric and eccentric action allows us to apply force differently during the outward and returning phases of an exercise, opening of the springs and closing of the springs.

Eccentric training can support increases in strength and muscle size and may produce adaptations in muscle architecture, including changes in fascicle length. However, the outcome depends on factors such as load, range, speed, exercise selection, dosage and the needs of the individual client.

The benefits keeping teaching focus on all phases of the movement are numerous.

Eccentric work may offer particular benefits for some intended outcomes for some clients.  Each type of muscle contraction and action has a purpose. Each phase of a movement should be executed with intent.

The skill lies in deciding which action should be emphasised for which part of an exercise, for which client and at which point in their programme.

Contractions and Springs: A Summary

Now that we understand the springs more from article one and two, it is useful now to apply a more indepth anatomy analysis of the reformer exercises. Understanding how and when to cue the clients focus on the muscles groups or body part working in the agonist or synergist concentric action to overcome the initial spring tension and the increasing spring tension as the spring extends. As the springs energy wants to return the spring towards their original length, assisting the movement, do we want the client to relax and be assisted or do we want the client to use eccentric action to resist and control that assistance? 

The Reformer gives us a valuable opportunity to explore this relationship because its springs provide a variable load. The amount of initial spring tension changes as spring extension increases, spring tension/force increases according to the spring’s rate,  the teacher can influence the muscular demand through spring selection, range, tempo, position and cueing.

In theory, this makes sense. In practice, the eccentric phase is often missed. The focus on the isometric stabilisation joints can also be missed. i.e how often do you cue quadricep focus when holding the legs in the full classical position in The Hundred, do your cues just focus on one element or do you break the movement down and cue through each phase the changing role and emphasis. Whilst you don’t need to bombard them with anatomy you can cue effectively using your wonderful visualisation for different body parts acting differently within different phases.

Clients may put considerable effort into the concentric phase as they move the carriage against spring tension, assuming the intent of the exercise is about loading the legs, but then they allow the springs to return the carriage with little muscular control. Footwork is a clear example of varied intent in varied parts of the exercise: unless the return is purposefully taught, clients may pay much less attention to it than to the outward phase or the centring, control and precision of the exercise. Deciding what the intent is of each phase is key.

It is therefore worth paying more attention to all mucles actions on all phases including isometric fixating muscles or body parts and eccentric phase assisted or resisted movements and cueing it with greater clarity. The aim is not simply to slow every return, but to help the client maintain appropriate muscular force while the active muscles shorten, lengthen or remain fixated and under force.

Initially, a client may find this difficult. They may never have considered that a muscle can lengthen while continuing to work. Because the springs assist many returning movements, the muscular effort may also feel less obvious. Your cueing helps them stay connected to every phase of the movement and every body part executing the exercise entirely within method.

A Check and Challenge for the Teacher

The next time you teach an exercise, watch one complete repetition and ask:

• Which muscle initiates and provides the main agonist concentric force for the movement?
• Which muscles assist it the movement and provide synergist force to assist or control the movement?
• Which muscles stabilise other parts of the body in an isometric fixation role?
• Which opposing antagonist muscles need to relax and lengthen?
• Do any of these roles change during the exercise at different phases?

Then consider the springs:

• During which phase is the client overcoming increasing overall increasing spring tension?
• During which phase is spring tension assisting the client?
• Could the client work differently during the spring-assisted phase to gain greater benefit?
• Is the chosen tempo supporting the intended muscle action?
• Which fixators are maintaining alignment, and can they do so for the full duration of the movement?

Finally, listen to your cueing.

Are you simply describing where the body should go, or are you helping the client understand how the movement should feel?

That is how we bring anatomy off the course notes and into the teaching session, where it becomes useful.