Differences Between Agonist and Antagonist Muscles

You may have heard the phrase “opposites attract” when it comes to relationships, but did you know that opposites actually do work really well together. This is especially true where muscles are concerned.

Antagonistic muscle pairs, made up of an agonist and an antagonist, are muscles that are opposite to each other and work together to produce efficient movement patterns.

Once you’ve gained an understanding of what they are and how they work, you can actually use them to maximize the effectiveness of your workouts, see results faster, and ultimately spend less time in the gym.

What are agonist muscles?

When you move your muscles there are two jobs that your muscles are doing while working together to make that movement happen.

These jobs belong to the agonist and antagonist muscles involved in the movement.

Have you ever thought of what happens when you flex your biceps?

If you bend your arm at the elbow to flex your biceps, then that muscle on the front of your upper arm will contract and thicken a bit. During this action, your biceps muscle is the agonist.

Your agonist muscles are the prime movers of a movement.

This means that they are the main muscles responsible for the movement that you’re executing through a contraction. A contraction is when your muscles tense or shorten in length.

A contraction is when your muscles tense or shorten in length.

In the example above, the biceps muscles were the prime movers that made the biceps flex happen.

The other main muscle involved in the movement is the antagonist.

During a biceps contraction, the antagonist would be your triceps, which is located on the back of your upper arm. Instead of tightening during a biceps flex, this muscle relaxes and elongates.

Main takeaway: agonist muscles are the prime movers or the muscles that are contracting during an exercise.

What are antagonist muscles?

Antagonist muscles are the ones that oppose your agonist muscles. So if your agonist muscles are working, then your antagonist muscles will usually be resting or stretching.

They’re often located opposite each other because of the way that they work together to facilitate movement throughout your body.

In the example above using the biceps curl, the triceps shouldn’t really be tightening during that movement.

Instead, your triceps will be stretching and elongating as you curl the weight up and flex your biceps.

Main takeaway: antagonist muscles work opposite of the agonist muscles so they elongate and stretch during the concentric or primary contraction phase of an exercise.

Agonist vs antagonist muscles

Agonist vs antagonist muscles

The relationship between agonist and antagonist muscles is kind of like a lazy game of tug-o-war, where one muscle is pulling and the other is just kind of letting the action happen.

This is a super simplified way to look at it though because while your antagonist muscle is not working super hard, it’s still working a bit.

The antagonist is not ever fully resting, but because it isn’t the prime mover most of the tension will be on the agonist.

Agonist and antagonist muscles are responsible for different movements, which is why they work so well together. They’re opposites.

So, let’s continue with the biceps and triceps example in order to further break down the relationship between the two.

During a biceps curl, your upper arm is flexing at your elbow, which means that the angle of your elbow joint is getting smaller or decreasing as your forearm comes in toward your upper arm.

This type of movement that happens as the joint angle decreases is called flexion.

Your biceps are pulling muscles that facilitate flexion, and your triceps are pushing muscles that facilitate extension.

While your biceps are busy trying to pull weight by contracting or flexing and thickening, your triceps aren’t working to push anything.

They’re pushing muscles, so they’re able to relax and essentially take a break because they’re not involved nearly as much during biceps flexion or a biceps curl.

However, as you begin to lower your upper arm and increase the joint angle your arm will start to straighten out again.

This is extension, during which your triceps muscle will jump in a little more because its job is to extend the elbow.

How do antagonistic muscles work together?

Antagonistic muscles work together in a few different ways in order to foster movement around your joints:

  • Coactivation
  • Reciprocal activation
  • Reciprocal inhibition

Coactivation

Coactivation

When your muscles work together in an antagonistic pair, as your biceps and triceps do, they must both contract to some extent in order to stabilize your elbow joint.

This is referred to as coactivation because both muscles are working together at the same time to control movement around your joints.

So even though you’re doing a biceps curl and extending your elbow on the way down, which would cause the triceps to contract in order to control the movement, your biceps are still the prime mover or the muscle that’s responsible for the action of a biceps curl.

The distinction between the motions that each muscle group is responsible for is part of what makes them such great teams that work well together.

This is also why you can use antagonist and agonist muscle pairings to maximize your workouts and recovery.

Reciprocal activation

Reciprocal activation

Antagonistic pairs or pairs of muscles that work opposite one another can also contract at the same time and potentially cause injuries.

Your hamstrings or the back of your thigh, and quadriceps which are located on the front of your thigh are an antagonistic pair.

They both work together to help you walk, sit, stand-up and many other actions.

However, if both of those muscles contract at the same time instead of taking turns appropriately, then they can end up competing with each other.

Reciprocal activation is slightly different from coactivation in that during coactivation the muscles are working together at different intensities, but during reciprocal activation, they’re basically fighting each other for control.

Generally, one muscle group will win the competition and this is what can lead to injury.

So, in the example of the hamstrings and quadriceps, if you aren’t used to sprinting and you decide to take off as fast as you can your legs will tense up as you try to exert as much force as you can.

Both your quadriceps (front of your thigh) and your hamstrings (back of your thigh) work together with your calves and other supporting leg muscles to allow you to run at full speed and sprint.

However, since your quadriceps are the biggest muscle group in your legs, they tend to take over.

This is why you may get injured if you sprint all out without warming up or training properly.

When two muscle groups are simultaneously activated and try to tense at the same time, the bigger and often stronger of the two will take over.

Let’s say you try to sprint without training properly, and both your hamstrings and quadriceps tense and try to contract at the same time because they aren’t used to this type of training.

Since your quadriceps are usually the bigger and stronger muscle, they’ll take over and this will force your hamstrings to back down in the form of a pulled muscle because they can’t keep up.

This is part of the reason that it’s important to work your way up when adding advanced techniques, such as sprinting, to your fitness routine.

Reciprocal inhibition

Reciprocal inhibition

Usually, when you have an antagonistic pair of muscles such as the hamstrings and quadriceps, or the biceps and triceps, as one tightens the other will relax and elongate.

Your brain and central nervous system will usually recognize when the agonist is contracting or shortening, and signal the antagonist to relax and stretch.

While this happens during an exercise, the principle of reciprocal inhibition also happens when you’re stretching.

It can be used to maximize your stretching if you know which muscle to focus on tightening so that the other can fully relax.

For example, if you want to stretch your hamstrings you can use a mind-muscle connection to actively flex your quadriceps and it will cause your hamstrings to elongate and stretch a little more.

Reciprocal inhibition also helps you to be able to walk around without falling over.

As you take a step, your quadriceps and hamstrings work together to tighten and relax in a pattern that keeps you upright and able to balance.

Of course, there are other muscles that help too, but the main antagonistic pairs are the ones responsible for the bulk of the movement.

Common antagonistic pairs

Below are some examples of the most commonly used antagonistic pairings and their respective main movement patterns.

  • Biceps: pulling/flexion
  • Triceps: pushing/extension
  • Back: pulling
  • Chest: pushing
  • Hamstrings: pulling
  • Quadriceps: pushing

Flexion vs extension

Flexion vs extension

Antagonistic pairs are also responsible for flexion and extension actions.

Flexion happens when you lessen a joint angle, such as during a biceps curl where you’re minimizing the space between your forearm and biceps.

Extension is when you increase a joint angle. An example of this would be a triceps pushdown.

During this movement, you’d start with your elbows bent and your palms down while grasping a bar attached to a cable in front of you.

As you exert force to push the bar down and straighten your arms, you’re engaging your triceps as the prime mover and decreasing the joint angle at your elbow.

This is extension because you’re decreasing the joint angle by straightening your arm.

In this example of a pushing movement, your triceps become the agonist and your biceps would be the antagonist because you aren’t pulling so they’re able to rest.

Your muscles are able to switch roles as you perform different movements. Whichever muscle is the prime mover and responsible for most of the action will be the agonist.

So, just because your biceps act as the agonist in a biceps curl, doesn’t mean it’s always the agonist in every movement.

For example, during a triceps pushdown it switches roles and acts as the antagonist.

How to use antagonistic pairs in your workouts

Supersets

Antagonistic pairs are often used during supersets because they allow one muscle to be worked while the other is resting.

This can help you to decrease the overall time of your workout because you don’t have to spend as much time resting, and it can also increase muscle growth and calorie burn.

A superset is when you do two exercises back to back.

This can be done by targeting the same muscle or you can target opposite muscles in order to maximize your muscle growth response and add a different stimulus to your workout to prevent a plateau.

Supersets are a slightly more advanced technique that can be used once you’ve established a good fitness foundation, as they can be pretty taxing on your system and may require a bit more recovery.

Prevent premature fatigue

You can also use antagonistic pairs during a full-body workout in order to stave off fatigue. This may look like doing a back exercise for a few sets, and then doing a few sets of a chest exercise next.

Using this method would allow you to still feel strong while working your chest because it’s responsible for pushing while giving your back a rest from all of the pulling.

Plus, while your chest is busy contracting, it gives your back some time to elongate, relax and stretch because it would be the antagonist during a chest exercise.

Conclusion

There are many ways to use antagonistic pairs of muscle to maximize your workouts by adding variety and taking advantage of the way that our bodies move.

Understanding the difference between agonist and antagonist muscles may behoove you in achieving better results.

Whether you’re a beginner or an advanced lifter, these principles can be applied in order to make your workouts more effective, break through plateaus if you’ve stopped seeing results, as well as aid in recovery.

Leave a Comment