Concentric, Eccentric And Isometric Muscle Contractions: How To Apply Them In Pilates Programming
You have probably heard the terms concentric, eccentric and isometric hundreds of times throughout your Pilates education.
You may know that concentric means a muscle shortens, eccentric means a muscle lengthens and isometric means a muscle maintains its length.
But knowing those definitions is very different from being able to apply them when teaching.
Take a simple Reformer footwork exercise.
The client presses the carriage away from the footbar, pauses and then returns the carriage towards the stopper.
Which muscles are working concentrically? Which are working eccentrically? What changes when the carriage stops moving? And what happens if the client performs a similar-looking movement in a different body position or against a different direction of resistance?
These are the questions that turn anatomy knowledge into practical exercise prescription.
Understanding muscle contractions helps you recognise what an exercise is actually asking the body to do, rather than relying on the exercise name, the direction of movement or which muscle the client says they can feel.
It also allows you to make more informed decisions about resistance, range, tempo, rehabilitation and progression.
Because the same exercise can create very different muscular demands depending on how you programme it.
What Are The Three Types Of Muscle Contraction?
The three commonly taught categories of muscle contraction are:
Concentric contractions.
Eccentric contractions.
Isometric contractions.
These describe how a muscle's length changes while it is actively producing force.
The important part of that definition is that the muscle must be producing force.
A muscle being stretched passively is not necessarily performing an eccentric contraction, and a muscle remaining the same length is not necessarily working isometrically.
We need to consider both muscle activity and what is happening to muscle length.
In real movement, several muscles may be working simultaneously in different ways.
One muscle may be shortening while another lengthens under tension, and other muscles may be producing force with relatively little change in length.
That is why understanding contractions requires more than watching which direction a body part moves.
What Is A Concentric Muscle Contraction?
A concentric contraction occurs when an active muscle shortens while producing force.
This commonly happens when a muscle produces enough force to move a joint against an external resistance.
Think about performing a biceps curl with a dumbbell.
As you lift the weight towards your shoulder, the elbow flexors produce force while shortening.
That is a concentric action of the elbow flexors.
In Pilates, concentric contractions occur throughout Mat, Reformer and Studio
Equipment exercises.
Examples include the quadriceps shortening as the knees extend during the pressing phase of conventional Reformer footwork, or the elbow flexors shortening as a client bends their elbows against resistance during a suitably configured arm exercise.
However, we need to be careful about assuming that every visible movement is produced concentrically by the muscle we are focusing on.
The direction of external resistance matters.
Concentric contractions in a bridge
During the lifting phase of a conventional bridge, the hips move into extension.
The gluteus maximus can contribute concentrically to this movement as it produces hip-extension force.
The hamstrings and other muscles also contribute according to the setup and joint positions.
However, the entire bridge should not be described as one concentric contraction.
Different muscles around the hips, knees and trunk perform different roles, and the demands change throughout the movement.
The useful teaching question is:
Which muscle am I analysing, and what is happening to its length while it produces force?
What Is An Eccentric Muscle Contraction?
An eccentric contraction occurs when an active muscle lengthens while producing force.
Eccentric contractions are commonly involved in controlling movement against an external force.
Imagine lowering a dumbbell during a biceps curl.
Your elbow is extending, but you are not simply allowing the weight to fall.
Your elbow flexors continue producing force while lengthening to control the descent.
That is an eccentric action.
Eccentric contractions are important because our muscles do not only create movement.
They also help us control movement.
This is particularly relevant when lowering into a squat, descending stairs, landing from a jump or controlling the return of a loaded exercise.
Eccentric contractions in a squat
During the lowering phase of a conventional squat, the knees and hips flex.
The quadriceps produce force while lengthening to help control knee flexion, while the hip extensors contribute to controlling the descent at the hip.
When the client rises, the joint movements reverse and the relevant muscle actions change.
This means a squat is not simply a quadriceps or glute exercise.
It involves different muscular demands across the lowering, holding and rising phases.
Eccentric contractions in Reformer footwork
During conventional supine Reformer footwork, the client presses the carriage away from the footbar by extending the hips and knees.
As the carriage returns towards the stopper, the springs pull it inwards.
The client controls that return rather than allowing the carriage to move abruptly.
The knee extensors can work eccentrically as the knees flex during the controlled return.
The hip extensors may also contribute eccentrically as the hips flex.
However, the exact demands depend on the client's position, spring resistance, joint angles and how the exercise is performed.
The carriage moving towards the stopper does not automatically mean every working muscle is contracting eccentrically.
What Is An Isometric Muscle Contraction?
An isometric contraction occurs when an active muscle produces force without a meaningful change in its overall length.
The muscle is working, but there may be little or no visible movement at the joint it acts upon.
A familiar example is holding a dumbbell in a fixed position during a biceps curl.
The elbow flexors continue producing force to maintain the position even though the elbow is not visibly moving.
In Pilates, isometric contractions occur during exercises such as:
Plank holds.
Wall sits.
Static bridge holds.
Standing balance exercises.
Pauses during loaded movements.
But an exercise does not need to be completely static for a particular muscle to work isometrically.
For example, the trunk muscles may produce relatively isometric force to maintain trunk position while the arms or legs move.
This is an important distinction for instructors.
The whole body can be moving while an individual muscle or muscle group performs a predominantly isometric role.
Does A Muscle Have To Move To Become Stronger?
No.
A muscle can produce substantial force without visible joint movement.
Isometric exercises can provide a meaningful strength stimulus when the force, duration and overall training dose are appropriate.
For example, holding a challenging split-squat position requires the lower-body muscles to continue producing force even though the client is not moving up or down.
Similarly, a plank can create a substantial demand on the trunk and shoulder girdle without requiring repeated movement through those regions.
However, the absence of movement does not automatically make an exercise easy or safe for every client.
A long, heavily loaded isometric hold can be extremely demanding.
As with any exercise, the load needs to match the individual and the intended training outcome.
Why Muscle Contractions Are Not The Same As Joint Movements
This is where instructors often become confused.
You may have learned that the gluteus maximus is a hip extensor.
You then see the hip moving into extension and assume that the gluteus maximus must be contracting concentrically.
But a muscle's anatomical action does not tell you everything about how it is working during a particular task.
You also need to understand:
The direction of the external force.
Whether the muscle is producing or controlling movement.
Whether the muscle is shortening, lengthening or maintaining its length.
Whether another muscle is contributing to the same movement.
Whether the joint is moving at all.
Consider a client lowering into a squat.
The hips are flexing, yet the hip extensors can be actively controlling the descent.
The fact that the hip is moving into flexion does not mean the hip extensors have stopped working.
It may mean they are working eccentrically.
This is why analysing exercise biomechanics requires more than memorising muscle
actions.
A Muscle Lengthening Does Not Automatically Mean It Is Working Eccentrically
This is one of the most important distinctions in this article.
Imagine lying on your back and gently pulling one leg towards your chest.
Some muscles around the hip may lengthen as you move.
But if they are simply being stretched passively, they are not necessarily performing an eccentric contraction.
For an eccentric contraction to occur, the muscle must be actively producing force while lengthening.
The same principle applies during Pilates.
If the client is allowing gravity or spring resistance to move them without meaningful muscular control, you cannot assume that the intended muscle is receiving a useful
eccentric training stimulus simply because it is becoming longer.
An effective eccentric exercise requires an appropriate external demand and active muscular contribution.
Why The Direction Of Resistance Matters On The Reformer
The Reformer introduces an additional layer of complexity because spring resistance acts through the carriage, straps and pulleys.
Depending on the exercise, the springs may resist a movement in one direction and assist the movement in another.
This means that two exercises with a similar-looking joint movement can create different muscular demands.
For example, moving the arms forwards does not automatically mean the same muscles are working concentrically in every Reformer arm exercise.
You need to consider the direction in which the straps are pulling and which muscles are producing force against that pull.
Likewise, returning the carriage towards the stopper is not automatically the eccentric phase for every muscle involved in every Reformer exercise.
The correct analysis depends on the exercise setup and the muscle you are examining.
A practical Reformer analysis framework
When looking at a Reformer exercise, ask:
Which direction is the spring resistance pulling?
Which direction is the client moving?
Which joint actions are occurring?
Which muscles are producing force to create or control those actions?
Are those muscles shortening, lengthening or maintaining their length?
This approach is far more reliable than labelling an entire exercise as concentric or eccentric based on the direction of carriage movement alone.
Reformer Footwork: A Practical Breakdown
Let's use conventional supine Reformer footwork as an example.
The client lies on the carriage with their feet against the footbar and begins with the hips and knees flexed.
Phase 1: Pressing the carriage away
The client extends the hips and knees to move the carriage away from the footbar.
The quadriceps contribute concentrically to knee extension.
The hip extensors can contribute concentrically to hip extension, depending on the joint angles and setup.
Other muscles help manage the ankle, pelvis and trunk.
Phase 2: Holding the carriage
If the client pauses with the carriage stationary, the muscles responsible for maintaining the position continue producing force.
Their actions may be predominantly isometric at the relevant joints.
However, this does not mean every muscle in the body is performing an identical isometric contraction.
Phase 3: Returning the carriage
As the springs pull the carriage towards the stopper, the client controls the return.
The knees and hips flex.
The quadriceps and hip extensors can contribute eccentrically as they control the movement.
The exercise therefore exposes the lower body to different contraction demands across one repetition.
Bridge: Lifting, Holding And Lowering
The bridge is another useful exercise for teaching contraction types because the three phases are easy to observe.
During the lift, the hip extensors produce force to raise the pelvis.
During a static hold, they continue producing force to maintain hip position.
During the controlled lowering phase, they can work eccentrically as the hips flex.
However, the exact contribution of the glutes and hamstrings changes according to factors such as foot position, knee angle, range and resistance.
A bridge performed with the feet close to the pelvis does not create exactly the same mechanical demands as a long-lever bridge.
Likewise, a bridge performed with external resistance or on moving Pilates equipment may create a different loading profile.
Understanding the contraction type is useful, but it is only one part of the biomechanics.
Squats And Lunges: Why The Lowering Phase Matters
Pilates instructors often place most of their cueing emphasis on the lifting phase of a squat or lunge.
“Push through the floor.”
“Drive up.”
“Stand tall.”
But the lowering phase also creates a meaningful training demand.
As the client descends, the muscles around the hips and knees must help control the movement against gravity and any external resistance.
The ability to manage this lowering phase is relevant to everyday tasks such as:
Sitting down.
Walking downstairs.
Lowering onto the floor.
Stepping down from a platform.
Controlling a landing.
A client who can stand up from a chair may still struggle to lower themselves into the chair slowly and confidently.
That difference can provide useful information about their current capacity and movement control.
Isometric Holds In Pilates: What Are We Actually Training?
Isometric holds are common in Pilates programming.
Examples include holding:
A plank.
A bridge.
A split squat.
A wall sit.
A standing balance position.
A static arm position against spring resistance.
But the purpose of the hold should be clear.
Are you trying to improve the client's ability to produce force at a particular joint angle?
Build muscular endurance?
Maintain trunk position while another body part moves?
Practise balance?
Introduce load in a position the client can currently tolerate?
Those are different goals.
A 10-second hold at high effort does not create the same training stimulus as a 60-second hold at a much lower intensity.
Simply adding a hold does not automatically make an exercise better.
Are Isometric Exercises Always Easier?
No.
An isometric exercise can be relatively easy or extremely challenging.
Consider the difference between holding a bridge with both feet supported and holding a deep split squat against substantial external resistance.
Both may involve isometric contractions, but the force demands are very different.
Likewise, holding a plank for a few seconds may be manageable for one client and highly demanding for another.
The contraction type alone does not determine exercise intensity.
You still need to consider load, leverage, joint position, duration and the individual's capacity.
Are Eccentric Exercises Always Better For Strength?
Eccentric training can be an effective way to develop strength and improve the ability to control movement under load.
However, it is not automatically superior for every client, every muscle or every training goal.
Concentric, eccentric and isometric training can all contribute to strength development.
The appropriate emphasis depends on what you are trying to achieve.
For example, a client who struggles to control a step-down may benefit from progressively training the lowering phase.
A client who needs to improve their ability to rise from a chair also needs to practise producing force during the upward phase.
Someone returning to a demanding sport may need the ability to generate force, absorb force and maintain positions under load.
A comprehensive programme should reflect those demands rather than focusing exclusively on one contraction type.
Why Slower Movement Does Not Automatically Mean Better Eccentric Training
Instructors often use the term eccentric whenever they ask clients to move slowly.
For example:
“Take four counts to lower. We're doing eccentric work.”
The slower lowering phase may indeed increase the duration of an eccentric contraction in the relevant muscles.
But movement speed and contraction type are not the same thing.
A slow concentric movement is still concentric if the active muscle is shortening.
A slow isometric hold is not an eccentric contraction simply because it is difficult.
Likewise, a muscle can work eccentrically during a relatively fast movement.
The defining feature is what happens to muscle length while it produces force, not how many counts the instructor uses.
Does Moving Slowly Increase Time Under Tension?
A slower repetition can increase the amount of time the muscles spend producing force during that repetition.
However, the overall training effect also depends on resistance, total repetitions, sets, effort and recovery.
If slowing the exercise requires the client to substantially reduce the load, the resulting stimulus may be different rather than automatically better.
For example, a client may perform a very slow set of light Reformer footwork and experience considerable muscular fatigue.
That does not necessarily mean they have received a greater maximal-strength stimulus than they would from an appropriately loaded set performed at a different tempo.
Tempo should support the training goal.
It should not replace an understanding of load and intensity.
How To Programme Concentric Strength
If your goal is to improve a client's ability to produce force during a particular movement, the exercise needs to challenge that action appropriately.
For example, improving the ability to rise from a chair may involve progressively loaded sit-to-stands or squats.
Improving upper-body pushing strength may involve appropriately progressed pressing exercises.
The programme should consider:
Resistance.
Range.
Repetitions and sets.
Effort.
Movement quality.
Recovery.
Progression over time.
You do not need to isolate the concentric phase in every exercise.
In many conventional strength exercises, concentric and eccentric contractions occur naturally within the same repetition.
How To Programme Eccentric Control
If the goal is to improve control during a lowering or deceleration task, you may place greater emphasis on the relevant eccentric phase.
Examples could include:
Controlled step-downs.
Gradual lowering into a squat.
Controlled return during Reformer footwork.
Lowering from a calf raise.
Controlled lowering during an upper-body resistance exercise.
The key is to ensure that the target muscle is actually producing force while lengthening.
Simply asking the client to move slowly is not enough if the exercise setup does not create the intended muscular demand.
You also need to consider whether the client can tolerate the chosen resistance and volume.
How To Programme Isometric Strength
Isometric exercises may be useful when the goal involves producing force or maintaining control in a particular position.
Examples include:
Holding a split squat at a selected depth.
Maintaining a bridge against resistance.
Holding a calf raise.
Maintaining trunk position during a loaded arm movement.
Holding a shoulder position against spring resistance.
Progression may involve increasing the resistance, changing the joint angle, increasing the duration or reducing external support, depending on the objective.
However, a longer hold is not automatically a better hold.
If the goal is higher-force production, simply extending the duration of a low-load exercise may shift the emphasis towards endurance rather than the intended strength outcome.
Can Isometric Exercises Help With Pain?
Isometric exercises are sometimes used in rehabilitation because they allow a clinician to introduce or modify muscular loading without requiring repeated movement through a joint.
For some clients, this may be a useful starting point.
However, isometric exercise is not universally pain-relieving, and it should not be presented as the safest or most effective option for every painful condition.
A client may tolerate an isometric hold well in one position and experience significant discomfort in another.
The appropriate exercise depends on the diagnosis, symptom behaviour, load, joint angle and individual presentation.
Pilates instructors working with injured clients should follow relevant clinical guidance and refer for assessment when symptoms are undiagnosed, concerning or outside their scope of practice.
Can Eccentric Exercise Help With Tendon Rehabilitation?
Eccentric exercise has historically been used in many tendon rehabilitation programmes.
However, tendon rehabilitation is not limited to eccentric contractions.
Depending on the tendon, condition and stage of rehabilitation, programmes may include isometric, concentric, eccentric and other forms of progressive resistance training.
The important principle is providing an appropriate loading stimulus and progressing towards the demands of the client's activities.
An instructor should not assume that every client with tendon pain needs slow eccentric repetitions or that the same programme is suitable for every tendon.
Why Range Of Motion Changes The Training Stimulus
The joint angle at which a muscle produces force can influence the demands of an exercise.
Consider a split squat.
Holding near the top is not mechanically identical to holding near the bottom.
Likewise, the resistance experienced during a Reformer exercise may change throughout the carriage's range as spring extension and the client's joint positions change.
This means two isometric holds of equal duration can create different demands.
The same applies to concentric and eccentric training.
If you want to understand what an exercise is training, consider both the contraction type and the position in which that contraction occurs.
Why Spring Resistance Does Not Automatically Equal Muscle Force
A heavier spring setting generally increases the external spring force for a given extension, but it does not tell you exactly how much force a particular muscle is producing.
Muscle force also depends on factors such as:
Exercise setup.
Joint position.
Moment arms.
Direction of resistance.
Body weight.
Contribution from other muscles.
This is why adding springs does not necessarily increase the demand on every muscle in the same way.
It may also change the movement strategy or make one phase of an exercise more difficult than another.
The spring setting is a programming variable.
It is not a direct measurement of an individual muscle's force.
How To Identify Muscle Contractions When Teaching
When analysing an exercise, begin by choosing one muscle or muscle group.
Trying to label the entire body as concentric, eccentric or isometric is usually too simplistic.
Then work through the following questions.
1. What is the muscle's anatomical action?
For example, the quadriceps contribute to knee extension.
2. What is happening at the joint?
Is the knee extending, flexing or remaining relatively stationary?
3. What external force is acting on the body?
Consider gravity, springs, body weight, external weights and support surfaces.
4. Is the muscle actively producing force?
Is it creating movement, controlling movement or maintaining a position?
5. What is happening to the muscle's length?
Is it shortening, lengthening or remaining relatively constant?
Only then should you label the contraction.
This approach helps prevent common mistakes, particularly when working with
Reformer exercises in which the direction of spring resistance can make the muscular demands less obvious.
A Practical Example: Reformer Row
Imagine a client sitting on the Reformer and performing a conventional row against strap resistance.
As the client pulls the straps towards the body, the elbow flexors contribute to elbow flexion while the shoulder and scapular muscles produce force according to the chosen arm path.
During the controlled return, the relevant pulling muscles may work eccentrically as they resist the springs pulling the arms forwards.
If the client pauses with the straps held in position, those muscles continue producing force with relatively little movement.
However, changing the client's orientation, strap position or arm path can change the direction of resistance and the contribution of individual muscles.
This is why you should analyse the actual setup rather than assuming that every exercise called a row creates an identical muscular demand.
A Practical Example: Plank
A plank is commonly described as an isometric core exercise.
That description is useful, but it is incomplete.
During a static plank, the trunk muscles help resist unwanted movement while the shoulder girdle and lower body also contribute to maintaining the position.
However, if the client begins moving their arms or legs, the exercise may include dynamic contractions in those regions while the trunk continues performing a predominantly stabilising role.
If the client performs a moving plank variation, different muscles may work concentrically or eccentrically during different phases.
One exercise can involve all three contraction types simultaneously across different muscle groups.
A Practical Example: Standing Reformer Lunge
Consider a standing Reformer lunge.
Depending on the exact setup, the client may move the carriage away, control its return or hold a particular position.
The muscles around the hip, knee and ankle respond to the direction of spring resistance, body weight and the changing joint angles.
You cannot accurately identify every contraction by saying:
“Carriage out equals concentric. Carriage in equals eccentric.”
That rule may describe one muscle's action during one particular setup, but it will not apply universally.
Instead, identify the muscle, the joint movement and the external force.
This is particularly important when changing springs, stance or the orientation of the client.
How Contraction Types Influence Exercise Progression
Once you understand what a muscle is doing, you can make more purposeful programming decisions.
For example, a client may initially perform a supported squat through a comfortable range.
You might then introduce a controlled lowering phase, increase resistance or add an isometric pause at a selected depth.
Each change can alter the exercise's demands.
But progression should reflect the client's goal.
If the goal is improving maximal strength, extending every hold or slowing every repetition indefinitely may not be the most effective approach.
If the goal is improving control during a specific lowering task, changing the eccentric demand may be particularly relevant.
The contraction type is one variable within a broader programme.
Do You Need All Three Contraction Types In Every Pilates Class?
You do not need to create a separate concentric, eccentric and isometric block for every muscle group in every session.
Many conventional exercises already include multiple contraction types across a single repetition.
The more useful question is whether the overall programme exposes the client to the demands relevant to their goals.
For someone wanting general strength and movement capacity, a balanced programme will naturally involve producing force, controlling movement and maintaining positions.
For someone with a specific rehabilitation or performance goal, you may deliberately emphasise one demand more than another.
The objective is not to tick three contraction-type boxes.
It is to programme with purpose.
Common Mistakes Pilates Instructors Make
Mistake 1: Calling every lowering movement eccentric. A muscle must be actively producing force while lengthening. The visible direction of movement alone does not establish the contraction type.
Mistake 2: Assuming the entire body is performing the same contraction. Different muscles can perform different roles simultaneously.
Mistake 3: Confusing slow tempo with eccentric training. Speed and contraction type describe different aspects of movement.
Mistake 4: Assuming isometric means easy. Isometric exercises can involve substantial force and effort.
Mistake 5: Believing eccentric training is automatically better. The appropriate contraction emphasis depends on the goal and individual.
Mistake 6: Ignoring the direction of spring resistance. Reformer setup can change which muscles create or control movement.
Mistake 7: Using contraction types without considering load. Knowing that a muscle is working concentrically tells you very little about whether the exercise provides sufficient resistance to improve strength.
How This Changes Your Cueing
Understanding muscle contractions can improve cueing, but clients do not necessarily need a biomechanics lecture during class.
Instead of explaining every contraction type, use the information to choose cues that reflect the actual task.
For example:
During a squat, you might cue the client to control the descent rather than simply dropping into the bottom position.
During Reformer footwork, you might ask them to return the carriage smoothly rather than allowing the springs to pull them back.
During an isometric hold, you might cue them to maintain the intended position while continuing to breathe.
The science informs your coaching.
It does not need to make your coaching unnecessarily complicated.
Professional Reflection: Stop Memorising Exercise Names And Start Analysing Movement
Two instructors can teach the same Reformer exercise and create very different training stimuli.
One may choose a spring setting that creates a meaningful strength demand.
Another may choose a much lighter resistance and emphasise longer sets.
One may deliberately train control during the return phase.
Another may focus on force production during the pressing phase.
Neither approach is automatically correct or incorrect.
The question is whether the instructor understands what they are asking the body to do and whether that demand matches the client's goal.
That is the difference between memorising repertoire and understanding exercise prescription.
When you understand concentric, eccentric and isometric contractions, you can analyse unfamiliar exercises, adapt familiar ones and make more informed programming decisions without needing someone to give you a pre-written class plan.
Key Teaching Takeaways
Concentric contractions involve active muscle shortening while producing force.
Eccentric contractions involve active muscle lengthening while producing force.
Isometric contractions involve force production without a meaningful change in overall muscle length.
A muscle lengthening passively is not necessarily working eccentrically.
The direction of visible movement does not automatically identify the contraction type.
Different muscles can perform different contraction types simultaneously.
Concentric, eccentric and isometric work can all contribute to strength development.
Slower movement is not automatically better eccentric training.
Isometric exercises can be highly demanding depending on force, joint position and duration.
Spring resistance, joint angles and exercise setup influence muscular demand.
The same Reformer exercise can create different training stimuli when the setup changes.
Contraction type should be considered alongside resistance, range, effort, volume and progression.
Rehabilitation programmes should reflect the individual rather than relying on one supposedly superior contraction type.
Understanding biomechanics helps instructors make better exercise-selection, cueing and programming decisions.
Learn To Apply Anatomy And Biomechanics In Your Pilates Classes
Understanding the difference between concentric, eccentric and isometric contractions is useful.
But the real value comes when you can look at any Pilates exercise and confidently explain which muscles are working, how they are working and why changing the setup alters the training stimulus.
That is exactly the type of practical reasoning we develop through the Applied Anatomy & Biomechanics Certification at Body Form Education.
Rather than simply memorising origins, insertions and textbook muscle actions, the certification is designed to help Pilates instructors understand how anatomy applies to actual movement.
We explore how joint position, resistance, leverage and movement mechanics influence exercise selection, cueing and programming.
For instructors who want to build on this knowledge with a deeper understanding of load, intensity and progressive resistance, our Strength Pilates Principles Certification provides the next layer of exercise prescription.
Because effective Pilates programming is not simply about knowing what an exercise is called.
It is about understanding what the exercise is doing.
Explore the Applied Anatomy & Biomechanics Certification through Body Form
Education and develop the confidence to analyse movement, modify exercises and programme with purpose.
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