Antagonist and Agonist Muscle Pairs


Having trouble wrapping my brain around this basic concept.

Where I’m getting caught up is that I understand that muscles can only pull, not push. And it has something to do with antagonist/agonist Muscle pairs. So if muscles can’t push, then how am I able to do a pushup? All explanations I can find are going right over my head.

In: 1

Look at your arm. The part between your shoulder and your wrist is like two rods with a joint in the middle. You can bend it and you can extend it back to straight. You have muscles that only can pull, so you need two of them, one to close the angle between the two “rods” (biceps) and one to open the angle (triceps).

When you do a pushup, think of every single joint that needs to move, which way it needs to move and which muscle can do that. You extend your arm, so you need your triceps. At the same time you swing your upper arms from your side to the front of your chest, around the shoulder, your pecs do that. In reality a lot more muscles are involved, among other things to stabilize all the joints that need to stay where they are.

Some other terminology that may help you understand better is that muscles either contract or they relax. Ignore pull/push. And there are various types of contraction. In a pushup (and only considering the tricep movement in this example), you are performing a *concentric* contraction as you overcome gravity or raise yourself up. As you lower yourself you are still performing a contraction in the triceps called an *eccentric* contraction (as you resist gravity). Ignoring the chest/shoulders, your tricep is the agonist because it is the Prime Mover in the exercise. As you probably know the bicep is the antagonist to the tricep and it typically relaxes to let the triceps do their work (although it may not fully relax as during certain movements an antagonist acts to slow down a movement).


In anatomy and kinesiology, when talking about a specific movement, we recognize 3 funcional muscles: An agonist, antagonist and synergist

Firstly, let’s define these terms and there we’re gonna look at some examples

An agonist is the muscle that does the movement, and you’ve correctly recognize that that movement is always performed by the muscle’s contraction.

An antagonist is the muscle that does the opposite movement of the agonist. That means that while the agonist is contracting, the antagonist relaxes. While the antagonist contracts, the agonist relaxes

A synergist is a muscle that helps an agonist do that movement.

Note that if we look at any kind of movement, if it is in one direction, we have muscle A which is an agonist, while muscle B is an antagonist, however, if we do the same movement fut in the opposite direction, the roles switch; the muscle B becomes the agonist, and the muscle A becomes the antagonist. It will make more sense when we take a look on the examples

Sit on a chair with both feet on the ground. Now, start raising your toes while keeping your heel on the ground, as if you’re trying to stand on your heels. Congratulations, you just performed a movement called “dorsal flexion in the ankle”. Now, do the same, but while doing it, place your palm on the front of your shin. While preformung the movement, your palm should feel the muscles contracting on the front of your shin. That tells us that these muscles are the ones raising your foot. These muscles are agonists and synergists and their names are:

Musculus tibialis anterior (agonist)
Musculus extensor digitorum longus (synergist)
Musculus extensor hallucis longus (synergist)

Now, stand up and bend over. Place your palms on your calves and then stand on your toes. Congratulations, you have just performed a movement called plantar flexion. Your palm should feel contractions in your calves. That means that by standing on your toes, your calf muscles are the ones contracting. That means that by doing this movement, they are the agonists and synergists their names are.

Musculus gastrocnemius (agonist)
Musculus soleus (synergist)
Musculus tibialis posterior (synergist)
Musculus flexor digitorum longus (synergist)
Musculus flexor hallucis longus (synergist)

Note that standing on your heel and standing on your toes are the same movement in your ankle, just in different directions; while standing on your heel, you pring your toes closer to your shin, and while sanding on your toes, you move them away from your shin. That means that the muscles that put you on your toes and the ones that put you on your heel have the opposite effect when they contract. Therefore, the one group of muscles is the antagonist of the other group.

Now for the whole picture

When standing on your heel, the muscles on the front of your shin contract, and the muscles in your calf relax. So the muscles involved are:

M. Tibialis anterior (agonist)
M. Ext. Dig. Long. (Synergist)
M. Ext. Hall. Long. (Synergist)
M. Gastrocnemius (antagonist)
M. Soleus (antagonist)
M. Tibialis post. (antagonist)
M. Flex. Dig. Long. (Antagonist)
M. Flex. Hall. Long (antagonists)

When standing on your toes, your calf muscles are the ones contracting, and the muscles on the front of your shin are the ones relaxing. In performing this movement, the roles are reversed:

M. Gastrocnemius (agonist)
M. Soleus (synergist)
M. Tibialis post. (Synergist)
M. Flex. Dig. Long. (Synergist)
M. Flex. Hall. Long. (synergist)
M. Tibialis anterior (antagonist)
M. Ext. Dig. Long. (Antagonist)
M. Ext. Hall. Long. (Antagonist)

Now, let’s get to your pushups. Not that i’m just gonna name the two most important muscles the biceps and triceps, but know that there are a few more muscles that help you do your pushups. If you’d like a detailed explanation like the one above with names, ask and i’ll elaborate.

When lowering your body, your elboy joint is performing a flexion and the muscle contracting is the biceps (again it’s not the only one). When raising your body, your elbow is extending and the biceps is relaxing, while the triceps is contracting. Because flexion in elbow and extension in elbow is the same movement in different directions, we know that biceps and triceps are antagonsts to one another.
Therefore lowering your body flexes the biceps and relaxes the triceps. In that stage, the biceps is the agonist, and the triceps is the antagonist, while raising your body i.e. pushing, your triceps is the agonist, and biceps is the antagonist.

To conclude, it is true that muscles can’t push, they pull. However, their position and the bones that they are connected to convert their pull in the push. Therefore the contraction of triceps extends the elbow which pushes your off the floor. I. That movement, the biceps, the one flexing the elbow/is the antagonist, relaxes.

Of course, if you have further questions, feel free to ask.