What are Tonic and Phasic Muscles?

What are Tonic and Phasic Muscles?

As a Personal Trainer, you need to know the difference between Tonic and Phasic Muscles. This is not only crucial for your Level 3 Anatomy and Physiology Exam but also when you are creating client plans. 

In your exam, you will be tested on your knowledge of 50 muscles, and that includes the relationship of those muscles to postural compensations (which is basically talking about Tonic and Phasic Muscles).

You need to know the difference between Tonic and Phasic Muscles and which muscles are most likely to be tonic or phasic, but also HOW they affect our client’s posture.

This blog will tell you all you need to know about Tonic and Phasic Muscles, as a Personal trainer.

Let’s start with the foundations of understanding muscles…

Muscles Work in Pairs

They work together in a cycle of contracting and relaxing to bring about movement at a joint.

This partnership is ideally like a harmonious marriage, with both parties playing give-and-take. The problem is one muscle has the propensity to be shorter and tighter, with the other having a propensity to be longer and less activated. This is like having one person in the relationship that loves to talk (all the time), and the other just has no chance to get a word in edge-ways.

Now replace the idea of talking, with the idea of contractions in a muscle – it is much the same. They can’t talk and listen at the same time – so when the muscle is contracted the other Must listen, which really means it relaxes and lengthens.

The muscle that loves to talk, is definitely the dominant one – it finds it easy to contract and “fire” to the point it always pull pulling on the joint, causing a visible shift in the skeletal alignment. In opposition, its antagonist muscle is always listening – spending most of the day relaxed, inactive and lengthened.

What are Tonic and Phasic Muscles?
what are tonic and phasic muscles

The Dominant muscle – the talkative one – is what we will phrase as TONIC.

The antagonist to this is relaxed and “listening” – we’ll call this PHASIC

Look at this diagram – can you see how the Tonic muscle is physically pulling the bone out of alignment. This change in alignment – is exactly why you (Personal Trainers) need to know about Tonic and Phasic Muscles.

A well-maintained programme with plenty of flexibility and strength work, alongside minimal trauma to the tissue, is a good place to start to maintain great alignment in the body.

Many clients are exposed to faulty loading which just encourages the Tonic and Phasic muscles to react in their instinctive ways.

Faulty Loading Patterns

Now, before we go on, let me clarify the term “faulty loading.” Faulty loading means any over-use, under-use, abuse (such as trauma) or disuse (such as not getting adequate exercise!).

Tonic muscles tend to shorten in response to over-use, under-use or trauma, whereas phasic muscles tend to lengthen and weaken in response to these types of stimuli. These effects can lead to musculo-skeletal imbalance and joint instability when postural and phasic muscles are located on opposing sides of the agonist-antagonist relationship.

You learn about how tonic and phasic muscles affect posture in your Level 3 Anatomy and Physiology exam, and again in more detail in the Level 4 Low Back Pain Qualification.

To help you prepare for your level 3 Anatomy and Physiology exam and understand about tight and weak muscles in the body, we have donated an entire video tutorial about posture within our Level 3 Anatomy and Physiology Revision Mastery Bootcamp. Click the link below to find out more and learn everything you need to for your exam:

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Which Muscles are Tonic and Phasic?

When asked which muscles are tonic and which are Phasic – research generally varies massively. This table shows a summary of the main Tonic muscles in the body and the main Phasic muscles in the body.

what are tonic and phasic muscles table

These relationships are the key to understanding common patterns of postural imbalance such as the upper-crossed and lower-crossed syndromes in your client.  What this really means is reducing and hopefully irradicating joint and back pain once and for all.

You learn about how tonic and phasic muscles affect posture in your Level 3 Anatomy and Physiology exam, and again in more detail in the Level 4 Low Back Pain Qualification.

Let’s take an example: Sitting At A Desk All Day

The problem is that the nature of our inactive clients’ environments is most likely to favour the recruiting of tonic muscles.

The body is a dynamic system (that just means it can change how it works), and it adapts to the things it is asked to do. If you’re constantly asking it to sit at a desk all day and only squat when you need to go to the toilet, it’s going to begin to default towards using tonic muscles.

Additional point – the body doesn’t understand that we got a desk job.

Evolution is playing catch up right now – if we’re inactive the body interprets that as a sign something is amiss (as in we are living in a cave and there is no food around). So it also lowers mood, cognitive functions and sex drive to name a few.

Basically it slows everything down and gets good at being miserable and storing fat to conserve energy and help us “survive.”  Sound like something your clients might want to reverse?

Unfortunately, this also means that the brain will essentially disconnect from the phasic muscles.

This is bad because when we start to exercise again, we won’t be able to use these muscles. So as mentioned earlier joint stability will be poor, and furthermore, we’ll instead ask tonic muscles to do things that phasic muscles should do.

An example of this is clients trying to do Press-Ups with their elbows up way too high, because their pecs are being recruited and their lats and triceps are not. Or even worse, the hams and glutes are phasic muscles (mostly) and the erector spinae (lower back muscles) are tonic.

This is why people claim deadlifts and squats are bad for their back. They can’t activate their glutes and hamstrings after years of sitting in a chair, so when the small back muscles contract over a bent over spine they get quite sore.

There are several more examples, and basically, in any functional movement, the body should attempt to recruit phasic muscles as the prime movers.

That just makes sense right!

Fixing Imbalances

So you and your client now understand what is happening. Now we have to address how we fix it.

As we mentioned, phasic and tonic muscles have some different properties.

Tonic muscles contract slowly and have great endurance. They’re also prone to overactivity and finally, tend to tighten when they’re overactive.

Phasic muscles contract quickly (yes this is due to fibre distribution) and have poor endurance. They’re prone to lengthening when they’re weak, and this coupled with the tightening of an overactive antagonistic tonic muscle about a joint can cause a misalignment in the joint. Fixing this can have a massive impact on alleviating joint pain (especially in the back). Failing to fix it will result in you losing a client to injury.

So, next time you programme your client’s training session – think about Phasic muscles – think “What muscles do I need to innovate in order to improve my client’s posture?”

Until next time,

Neale “The Tonic and Phasic” Bergman

Dedicated to more

Hayley ‘structured revision’ Bergman

PS – AND whenever you’re ready… here are 3 ways I can help you  

1. Check out my FREE online training  

Level 3 Anatomy and Physiology: Three Secrets To Pass Your Exam ~ WEB CLASS REPLAY : https://parallelcoaching.co.uk/anatomy-and-physiology-level-3-secrets-webclass

2. Contact us with “REVISION” as the subject line and I’ll give you details so you can pass your exam with TOP MARKS and confidently.  

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3. Check out what learners are saying:




1 thought on “What are Tonic and Phasic Muscles?”

  1. Eileen Newsome

    Thank you for a well thought out and descriptive review. As a massage therapist I always strive to help my clients understand their body mechanics.

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