Agonist & Antagonist Muscles: Definition, Tips, and Exercises

Pairs of muscles in our bodies are made up of an agonist and an antagonist muscle, which control their range of motion, as well as how effectively they function. But what are each of these muscles, and how do they work together to create movement?

OriGym’s comprehensive report explores agonist and antagonist muscle pairs, how they form stretches and pulls, and how you can target these with your workouts in order to maximise your progress.

We’ll also look at expert tips and tricks on how to ensure these muscles are used to their fullest potential, and actions to take to mitigate against any potential injuries your agonist and antagonist muscles may suffer from.

Contents:

• What Is An Agonist Muscle?
• What Is An Antagonist Muscle?
• How Do Agonist and Antagonist Muscles Work Together?
• Examples Of Agonist and Antagonist Muscle Pairs
• Exercises That Use Antagonist And Agonist Muscle Pairs
• Frequently Asked Questions
• Our Conclusions

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What Is An Agonist Muscle?

First, let’s examine the agonist muscle definition. This is the tensed or “strained” muscle during an action, and acts as the primary mover during any action. It’s an absolutely crucial component of any kind of action, and works alongside the antagonist muscle to create contractions and extensions.

In any pair, the agonist muscle contracts, while the antagonist muscle relaxes, allowing for the free movement of our joints and muscles. Let’s use an everyday example of agonist and antagonist muscle pairs to fully realise the definition of the antagonist muscle and its counterpart - the biceps and triceps.

When we flex our arm (with a bicep curl, for instance), the bicep is contracted, making it the agonist muscle, and the tricep is relaxed, and therefore the antagonist muscle in this scenario.

Then, when we bring our arm back to a natural position, our bicep is relaxed (the antagonist muscle), and the tricep is contracted, and is referred to as the agonist muscle.

This logic applies to many of the movements we perform, and is an absolutely integral part of performing any exercise, as well as everyday tasks such as walking up the stairs, or reaching for something from the cupboard.

We can strengthen these agonist and antagonist muscles with simple tricep stretches, as well as by ensuring that we follow the correct form when performing exercises that use these muscles to their fullest potential. But what about the antagonist muscle definition?

What Is An Antagonist Muscle?

Alongside agonist muscles, antagonist muscles function as part of a pair that work in tandem to allow the joints and limbs to perform more complex movements. These muscles move in the opposite direction to the agonist muscles, and offset the force these muscles exert so that we don’t damage our fragile joints.

One crucial piece of information to note is that a muscle can only move in one direction. The antagonist muscle in the pair stretches or gets longer, whilst the agonist muscle contracts, which in turn creates the movement we’re looking for.

This is perhaps the main antagonist muscle definition, and what differentiates them from agonist muscles. A more concrete example of this would be the two muscles we find in our upper arms, which we used in our previous agonist muscle example - the biceps and triceps.

When we relax our arm, the bicep is the antagonist muscle, in that it’s relaxed, where the tricep is contracted, and is therefore the agonist muscle. This is reversed when we tense our arms - the bicep becomes the agonist muscle, with the tricep relaxing and becoming the antagonist muscle.

How Do Agonist and Antagonist Muscles Work Together?

Now that we fully understand the agonist and antagonist muscles definitions, and what function each of them perform, it’s important to examine how they work together to create the movements we expect, and how you can make the most of these when exercising.

Essentially, with each pair of agonist and antagonist muscles, one muscle will contract (the agonist muscle) and another will relax (the antagonist muscle) during each movement. 

Having these muscles function simultaneously is absolutely essential, in that it prevents damage to the joints and bones, as well as allowing the muscles to successfully return to their original positions. If one muscle outperforms the other, we risk overexerting ourselves, or being unable to effectively perform the actions we’re aiming for.

Overexertion (or overtraining) is often associated with more intensive activities.

Put simply, the antagonist muscle will provide the necessary resistance for the movement that the agonist muscle undertakes, allowing just the right amount of force to be used. This includes simple tasks we may not even consider, such as being able to stand up straight, or hold our arms in a natural position.

It’s also important to note that there are two primary types of these movements - isometric (an action where no movement takes place, such as pushing against an immovable surface or object) and isotonic (an action where movement does take place, such as pushing or pulling an object) contractions.

So, for instance, if you’re wondering “what is the agonist muscle in a push up”, you’ll first need to consider that it’s an isometric contraction, meaning no movement occurs. This means less pressure is placed on the agonist muscle, which here is the bicep, and there’s therefore more pressure on the antagonist muscle (in this case, the tricep).

While our bodies don’t need to be specifically conditioned towards any one of these different contraction types, it’s crucial to be aware of them in order to fully maximise the muscle gain you experience.

Examples Of Agonist and Antagonist Muscle Pairs

Let’s focus now on more practical examples of agonist and antagonist muscle pairs, as well as some of the primary functions these muscle pairs perform, and where you can expect to encounter them in your routines.

Biceps & Triceps

Perhaps one of the most immediately recognisable antagonist and agonist muscle examples, the biceps and triceps are the two largest muscles in the upper arm. We use these muscles every single day, and largely without realising that we do, as they’re used in many everyday tasks.

As we’ve touched upon in our previous sections on both agonist muscles and antagonist muscles, the biceps and triceps function as both agonist and antagonist muscles.

To recap, as we flex (or curl) our arm, the bicep functions as the agonist muscle during its contraction, whereas the tricep is the antagonist muscle, as it relaxes. As we uncurl or relax our arm, these roles are reversed, with the bicep becoming the antagonist, and the tricep the agonist muscle.

In your routines, this antagonist and agonist muscle movement is most recognisable as part of a dumbbell or barbell curl, but it also has its place in other common exercises, such as deadlifts, and the shoulder press.

Hamstrings and Quads (Quadriceps)

Two of the primary muscles in your upper legs, this is one of the prime examples of agonist and antagonist muscle pairs. Similarly to the bicep and tricep pairing we’ve just examined, these are often overlooked when it comes to their contributions to everyday tasks.

The quads and hamstrings control the extension and contraction of the knees, which are an integral part of some of the most basic things we can do, such as walking or sitting down.

When our legs are relaxed (such as when we’re in a more natural standing position), the quads function as the agonist muscle, in that they contract and tense, while the hamstring is the antagonist muscle, meaning it’s relaxed.

However, when the leg is bent (when you’re crouched or squatting, for instance), these roles are switched - the hamstring is now the agonist muscle, whereas the quads are antagonist muscles in this scenario.

While we’ve touched upon some of the more basic actions that require these agonist and antagonist muscle pairs, they’re also a fundamental part of some of the most basic exercises, and are equally important for proper form and posture.

For instance, you’ll be using this particular group of agonist and antagonist muscles for squats and specific lifts, especially those where you’ll need to keep a slight bend at the knees before hinging at the hips.

Glutes (Gluteus Maximus) and Hips

While we often use our glutes and hips without fully realising, they are crucial for maintaining the right form during exercise, as well as helping us with balance and stability in our everyday lives.

These specific agonist and antagonist muscles help with the movement of the hips, and function similarly to other agonist and antagonist muscle pairs that we’ve looked at so far.

Essentially, when you thrust the hips forwards, you’ll be tensing the glutes (making them the agonist muscles) and relaxing your hips (making these the antagonist muscles). When you return to a more neutral position, you’ll relax your glutes, which are then the antagonist muscles, and start to contract your glutes, the agonist muscles.

This is often the principle behind walking, and how more intense exercise (such as walking or running uphill) can significantly improve your cardiovascular health, as well as help to tone key areas around your glutes and hips.

You’ll also utilise this contraction and relaxation of these agonist and antagonist muscles during deadlifts and snatch movements, especially if you’re focused on lifting heavier weights. 

Other Examples Of Agonist & Antagonist Muscle Pairs

While we’ve gone into specific detail about a few of the more common antagonist and agonist muscle movements, there are a few more that don’t play as integral a role, but that are no less important, especially if you’re looking to maximise gains, and train to the highest possible level.

If you’re looking to fully train your agonist and antagonist muscle pairs, you’ll also need to look at:

• The deltoids (shoulder) and the latissimus dorsi (upper back)
• Pectoralis major (chest) and the trapezius (upper back)
• Tibialis anterior and gastrocnemius (both anterior and posterior calf muscles)
• Abdominals (stomach) and erector spinae (lower back)

There’s also smaller, more minor antagonist and agonist muscle examples in your wrist, neck, and ankles, which help with flexibility, and can play a key role in grip, movement, and stability, especially during exercises. 

Exercises That Use Antagonist And Agonist Muscle Pairs

Now that we’ve fully explored what agonist and antagonist muscle pairs, as well as both antagonist and agonist muscle examples, it’s equally important to look at how they can play pivotal roles in your exercise routine. 

Understanding the different muscles, and how each of these can have a huge impact, is crucial to creating a sustainable, effective routine. Let’s explore some key examples.

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Bicep Curl

One of the key examples that utilises the agonist and antagonist muscles, the bicep curl is a staple of many routines, and for good reason. Its easy adaptability, coupled with the wide array of potential equipment for this exercise, means it’s an ideal option for those looking to diversify their workouts.

As we’ve previously mentioned, the bicep curl goes through two main motions - the lift, and the subsequent relaxation. During the lift, the bicep becomes the agonist muscle, tensing and contracting, and the tricep is the antagonist muscle, relaxing as you lift.

This is then reversed when you lower your arm, with the bicep becoming the agonist muscle, contracting as you lower the weight, and the tricep becomes the antagonist, which relaxes as you lower the weight.

By adding weight to the mix, you’re not only placing more strain on the muscle that’s tensed (the agonist), but you’re also increasing the amount your antagonist muscle needs to stretch to offset the strain on the agonist.

With this, we would strongly recommend working your way up slowly with regards to weight, especially as this can have a huge impact, and potentially cause issues or injury if you increase it too quickly. 

Deadlifts

Another key staple of exercise routines for those who are looking to build muscle and train hard, the deadlift makes use of several different agonist and antagonist muscle pairs in order to create more complex movements.

With a deadlift, you’ll need your arms to be in a straightened position, which means your bicep is in a relaxed, antagonist muscle position, with the tricep functioning as the agonist muscle.

A deadlift starts with slightly bent knees (to avoid “locking” the knees), which requires the use of your quads and hamstrings. For the starting position, your hamstrings will be the agonist muscle, being contracted and strained, and your quads will take the place of the antagonist muscle, meaning they’re more relaxed.

As you move up to a standing position, these muscles will swap roles, with the quads becoming the contracted, agonist muscle, and the hamstrings in a more relaxed, antagonist muscle position.

Deadlifts also make use of other agonist and antagonist muscle pairs, and these are of the utmost importance when considering the right form to adopt when deadlifting, as well as ensuring you perform these exercises safely.

You’ll also need to use your hip flexors, thrusting them outwards to achieve extra lift on the bar. This involves pushing out your hips (meaning they’re in an agonist muscle position) and relaxing your glutes (they’ll be the antagonist muscle here), before returning back to a more natural position.

Finally, your wrists, while they are more minor agonist and antagonist muscles, are absolutely vital for maintaining a firm grip on the bar. Be sure to explore the various different grip options to find an option that works for you, especially as this can have a drastic effect on how impactful your lifts are.

Cardiovascular Exercise

Physical activity is integral to leading a healthy lifestyle, and one of the easiest ways to do this is to reap the benefits of cardio and aerobic exercise. It’s also one of the best ways to activate key agonist and antagonist muscle pairs at the same time, allowing you to work those muscle groups without having to specifically target them.

As you might expect, when we walk (or run), the main muscles we’ll use are our leg muscles, and predominantly our quads, hamstrings, calves and glutes. However, we’ll also be moving our arms and shoulders, which do require some antagonist and agonist muscle movements.

Let’s first focus on the legs. As we bend our knee to stride forward, we’ll primarily be utilising our hamstrings (the contracted, or agonist muscle) and our quadriceps (the relaxed, or antagonist muscle). 

These then switch roles as we place our foot back down, with the quads now contracting (agonist muscle) and the hamstrings relaxing (antagonist muscle). This represents our basic stride, and happens without us even considering it, especially on a treadmill.

Our shoulder muscles are also a driving force when we’re completing cardio exercise, and help to push the body forward. As we stride forward, we’ll also move our shoulders forward, meaning our pectoralis major (chest muscle) takes on the role of the agonist muscle, and the antagonist muscle is our trapezius (the upper back).

As we’ve seen with previous agonist and antagonist muscle pairs, these roles are reversed as we return to a natural position, with the trapezius now the agonist muscle, and the pectoralis major the antagonist muscle.

There’s also minor activity in our ankles when it comes to antagonist and agonist muscle movement. This is predominantly to ensure good balance, maintain posture, and ensure that we can continue to travel at the same pace consistently.

Frequently Asked Questions

While we’ve already touched upon all the key aspects of agonist and antagonist muscle pairs, as well as both agonist and antagonist muscle definitions, it’s still important to dispel any misconceptions, and answer some of the questions that might arise.

Why Do Muscles Work In Pairs?

With this article, we’ve predominantly focused on key agonist and antagonist muscle examples, but it’s equally important to explore the root cause of why muscles need to work in pairs, and what can happen if one muscle weakens, or doesn’t function properly.

As we touched upon earlier, each pair of muscles is made up of an agonist muscle and antagonist muscle, which alternate as we complete movements and actions. Muscles are usually found in pairs for one very specific, very important reason.

As one muscle contracts (this is the agonist muscle) and applies the necessary force to complete the action you’re aiming to complete, the opposite muscle (the antagonist muscle) provides force in the opposite direction in order to balance out the effort you’re exerting.

Without this opposing force, you seriously risk damaging your muscles, joints, and overall skeletal health, especially with movements like bicep curls or deadlifts, which can often be coupled with significant weight in addition to the muscular exertion.

While there are numerous benefits to deadlifts, it’s vitally important to understand the fundamentals, and how the necessary antagonist and agonist muscle movements form the basis of all the exercises you complete.

This principle applies to all agonist and antagonist muscle pairs across our body, including the smaller, less noticeable pairs that we find in key joints (such as our wrists and ankles).

Why Do We Need Antagonist Muscles?

This is a completely understandable question, especially as the agonist muscle movement is the one that’s predominantly responsible for applying the force we need to undertake an action or exercise.

While this is true of all agonist muscle examples, they simply would not function correctly and effectively without their counterpart, the antagonist muscle. Let’s look at an example of this.

When we bend our knee to take a stride forward, regardless of the pace at which we’re moving, we’ll use two main muscles - the hamstring and the quadriceps. 

In this scenario, our hamstring is the agonist muscle (in that it's contracted, and applying the necessary force to move the knee) and the quadriceps are the antagonist muscle (these are relaxed, and offer a counterbalance for the force that the agonist muscle is applying). 

When we re-extend our leg, these roles switch, with the agonist muscle now being the quadriceps, and the antagonist muscle the hamstring. Each muscle movement requires an opposing force, in order to ensure that we don’t overexert, and that we can return to a more natural position once we’ve finished our agonist muscle movement.

Antagonist muscles are also absolutely essential for that reason alone - they allow us to return our body to a more comfortable, natural state. However, they also help to protect bones from being damaged, and our fragile tendons, joints and ligaments from tearing or suffering painful injuries.

Is It Good To Train Antagonist Muscles?

When we’re looking to reach the pinnacle of our personal fitness, it’s natural that we’d want to pursue opportunities to activate and strengthen the muscle groups we may never have even considered. The same is true of our antagonist muscle definition and tone.

However, it can be difficult to work out exactly how we target those areas, especially as they’re predominantly used to relax our agonist muscles, or those that take the bulk of the strain.

The most simple answer to this question is that you’re likely already training your antagonist muscles without realising, especially as these often form part of every exercise, and particularly those we’ve mentioned previously.

For instance, while the agonist muscle in squat position is the hamstring, you’ll still be activating and putting strain on your quadriceps, allowing you to strengthen your antagonist muscle without consciously targeting that area. 

One crucial piece of information to note, though, is that proper warm ups and stretches are vital to ensuring a safe workout, especially when you’re aiming to work muscles that you perhaps haven’t focused on before, or that are weaker than other areas of your body.

Stretching your legs (especially using hamstring stretches) and arms prior to cardiovascular exercise, or performing key bicep and tricep stretches before lifting heavy weights can not only help you maximise your gains, but it’ll also mitigate against some of the more common injuries you could experience.

Before You Go!

This article aimed to provide you with the complete definition of the antagonist muscle, as well as how agonist and antagonist muscles work in pairs to create the movement that we expect.

Whether you were seeking inspiration for your workouts, or were looking for agonist and antagonist muscle examples to enhance your routine, our guide provides everything you need to know, and how you can utilise these unique muscle pairs.

But if you’re already familiar with how to use your agonist and antagonist muscle pairs, and are looking for a way to impart that expertise, then perhaps a career in fitness could be your calling.

OriGym’s CIMSPA-accredited personal training diploma offers the ultimate package, with expert guidance available 7 days a week, a custom-built online learning platform, unlimited career guidance, and a guaranteed interview when you graduate. 

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