Muscle Imbalances and Endurance Sports

Muscle imbalances in endurance sports represent 98% of all injuries and as such are highly preventable. How and why do they happen and what you can do about it.

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Or How Overuse Injuries Happen

Every ‘body’ tells a story.

-Vladimir Janda

This is a continuation of Part 2: Functional Anatomy, therefore if you just landed on this page, I highly advise you to start with Part 2 in order to familiarize yourself with the terms that appear in the following paragraphs.

Friends do not let friends skip leg day or so the story goes. While the desire for an estehically balanced muscles is a somewhat arbitrary place start, muscle imbalance is not always as obvious while at the same time it is something that almost everybody has had to deal at one point or another. That nagging neck pain or the chronic low back tightness that has plagued you since what seems forever. Yet the problem never really seemed to go away no matter how much you massaged the troubled area or no matter what wonder gel or cream you put on it or how many ibuprofens you took. It kept coming back…at the same spot. In worse cases you even had surgery, rehabilitation and…no improvement.  The question is why and what can you do about it.

In Part 2 of the Functional series one of the important take away points was that the human body especially when it comes to movement, cannot and should not be viewed in isolation. The model that muscles act in isolation (SP) is incomplete and as we have evolved to walk/run from head to toes there is something happening with an optimal way of doing so. There are muscles designed for posture and (joint) stability that can function at low energy cost for long periods of time, while there are muscles that activate in an on and off fashion to create movement. It all happens in a carefully orchestrated kinetic chain(s), however, when roles gets switched, somewhere along the kinetic chain you get a signal – most notably injury, inflammation and/or pain. Tissue damage and pain can cause muscle imbalance (tightness or weakness) and vice versa. The muscle imbalance can cause wrong movement patterns/bad technique and the reverse is also true and why proper movement is paramount.

Muscle imbalances and Endurance Sports

Muscle Imbalances and YOU

 Nothing in Biology Makes Sense Except in the Light of Evolution

-Theodosius Dobzhansky


Why do humans need muscle balance? All human movement is reciprocal, muscles can only pull, therefore that requires opposing muscle groups (antagonists and agonists) to be coordinated. For example when you extend your arm the triceps muscle is the agonist and the biceps is the antagonist. The roles are reversed when you move the arm towards you. It is this fact that creates the need for relative equality of length and strength between opposing muscle groups. This balance stabilizes joints in the most optimal position and provides the base for stable and efficient movement – in short being functional. The musculoskeletal and central nervous system(CNS) as well cannot be viewed in isolation since they act together – forming the sensorimotor system (SM). Your posture is a direct reflection of the health and functionality of the SM. Your posture influences the way you walk (gait) which influences how well you move and perform athletic activities.

Muscle imbalance for endurance sports
Muscle Balance (Left) and Imbalance (Right) Around a Joint


It is the freedom of movement designed in the human body that allows for more than one way to perform a movement, and since our bodies are hardwired for survival, the CNS would always prioritize joint/spine stabilization even if it has to use inefficient motion. Therefore the change in muscle recruitment alters the movement pattern and ultimately the motor program in the brain.

Every movement, athletic or not requires coordinated muscle action – also known as a kinetic chain. For example simply extending your arm starts with the muscles around your spine stabilizing the skeleton, providing a foundation from where the arm muscles can move the arm away from you. Therefore a kinetic chain can be broken down to its links. It starts with a firm foundation provided by the local stabilizers )joint stabilizers) followed by the global stabilizers and the final movement caused by the global mobilisers

Local stabilisers (joint control)>Global Stabilisers (force production/control through motion/)>Global mobilisers (Movement)

This pattern of muscle activation is a direct result of our evolution. Let me explain…

The postural or tonic muscles are older phylogenetically (they evolved first). These muscles are mostly composed of slow twitch(fatigue resistant) fibers and are involved in receptive and rhythmic activities and keeping our posture in relation to gravity; they can function at low energy cost for looooong periods of time. The tonic muscles are dominant i.e. if given the choice the CNS would always give them priority.

Priority over what?

Over the evolutionary younger phasic system muscles that are mostly fast-twitch and perfectly suited for on/off behavior – movement. The phasic muscles are (easily) fatiguable.

Granted it is not a true black and white separation and there is some overlap in function between the two systems, what is consistent is the prioritization level. In cycling terms if you have poor position and are shifting on the saddle all the time, the phasic muscles used to put power to the pedals get lower priority – energy needed for movement gets re-routed for stabilization. Though I digressed a bit….

Therefore, going back to the evolutionary priority of the muscles –  it is predictable what happens if you are always called upon – you become (literally) high strung/tense and when you are mostly ignored you become lazy and weak.

As a result muscle imbalance patterns are largely the same between individuals. Children as young as 8 show them, though not with the same severity as (more dysfunctional) adults.

  1. Muscles predominantly static, tonic, or postural are prone to get tight and are readily activated in various movements.

  2. Muscles that are predominantly dynamic and phasic in function have the tendency to grow weak

Full list of all postural and phasic muscles.

Causes of Muscle Tigthness and Weakness

How do you determine whether a muscle is tight or weak? You test its ability to resist being lengthened or its tension/tone. Muscle tension is a result of the neurological control (from the CNS) and muscle structure.

Muscle Tightness

Muscle tightness is the primary reason behind muscle imbalance and it is something most of you have had to deal at some point. Think of that tight neck when you slept in an awkward position.

When the CNS tells a muscle to get tight, its opposing buddy (antagonist) gets inhibited/switched off; it happens subconsciously – you don’t think about it, it is a protective measure. As a result the joint gets stressed due to unbalanced forces which further causes compensation/poor movement pattern. Both combined  results in an (oversuse) injury. Tight muscles are usually shorter and have a lowered activation threshold (they are more or less ‘always half on’), therefore it is those muscles that get recruited first in any movement whether they have a role in there or not, hence further contributing to the vicious imbalance cycle. Again think of your stiff neck and how you probably had to rotate your whole body to look around you.

Muscle imbalance for endurance sports
Muscle Balance (Left) Tight muscle and an Inhibited Antagonist (Right)

Why does a muscle decide to get tight in the first place?

Primary emotions such as pleasure, depression, fear – stress can do that quite well – ie when you get scared you tense up. Trigger points (TrPs) are small parts/nodules in the muscle that are super irritable and as a result can lead to increased tension in the whole tissue. There is lack of consensus on the causes of TrPs among health professionals, though nobody is denying these taut bands of tissue exist.  The most extreme case of muscle tightness is called a spasm – often this is done in order to immobilise a joint as a final protective measure. Your spine is a joint and hence why you are in a lot of pain once you life heavy with un-braced position, if that didn’t happen you would be broken in half…literally.

Structurally if a muscle is kept under tension long enough, it gets shortened as the contractile fibers gets replaced with scar tissue and logically the overall strength decreases. Shortened muscles are not painful but tender to touch.

Here I am going to stop you thinking that you can just ‘stretch a tight muscle out.’ Below you will see why.

Muscle Weakness (and Inhibition)

As mentioned above, neurologically muscles get switched off in response to their opposing buddy (antagonist) being switched on; it’s a reflex so that you don’t end up tearing a joint apart from all directions. TrPs lead to overexcited, always on tissue that gets used all the time and eventually fatigues. Fatigue itself can cause a muscle to get inhibited and change in movement pattern – I am yet to see an exhausted runner/cyclist/swimmer with anything remotely close to perfect form.

Now I come to stretching, particularly passive stretching where you just sit there for long periods of time waiting for something to happen. In the short term you are separating the contractile fibers (green and purple in the image below) so that they cannot connect with each other for a strong contraction to happen. If a muscle is kept longer than neutral for extended periods of time,  due to additional sarcomeres being added to the fiber, the length tension curve changes – the muscle gets weaker. Dynamic stretching such as leg swings is ok since it involves the CNS – you consciously move in and out of the range of motion.

Sliding filaments and Cross-bridges. Actin (green) and myosin (purple)
Sliding filaments and Cross-bridges. Actin (green) and myosin (purple)

Lastly as you already know by know a shortened/tight muscle gets readily involved in movement since it is always half-on and as such it fatigues, gets bigger (hypertrophy).  Due to the tightness oxygen cannot get everywhere and the muscle gets weaker.

The important point is that muscle weakness is directly related to over tight muscles while both cause muscle imbalance.

The theory is all nice though a picture is worth a thousand words. How does it all look in real life.

Muscle Imbalance Patterns

Postural muscles get tight, while phasic muscles get weak. All people have the same muscles therefore we all get broken the same way, only the severity differs.

Upper Crossed Syndrome

In the upper crossed syndrome (UCS) tight upper trapezius crosses with tight chest muscles and weak neck flexors cross weak lower trapezius. This leads to joint dysfunction in the upper neck or the all common neck forward with tightness and pain. Sitting with your monitor too low as well as ‘smartphone/texting neck’ are among the main culprits and causes.

Lower Crossed Syndrome

Sitting is the new smoking.

The Lower Crossed Syndrome (LCS) results due to tightness of the trunk extensor on the back that cross with the tight iliopsoas and rectus femoris muscles at the front of your hips and weak abdominals cross with weak/inhibited gluteus maximus and minimus (more details on why this is bad in Part 2). In simple terms what I just described is sitting in a chair, at work, in a car, etc. Since age 6 we spend most of our time sitting, no wonder why most of the symptoms of LCS can be found in a good number of the population, even athletes. Just taking alook at the people you see on the street you can already recognise some of the patterns.

LCS creates a dysfunction in the lumbar spine, sacroiliac and hip joints; in simple terms you get low back pain and the hip dysfunction can manifest itself in knee pain (more details in Part 1 of the series). Inhibited Gluteus maximus can lead to irritated hamstrings, etc.

Layer Syndrome

Layer syndrome represents a combination of UCS and LCS and is a more advanced form of muscle imbalance and motor dysfunction.

Muscle Imbalances for Endurance sports_layer_syndrome
Janda’s Layer Syndrome

Proprioreception and The Foot

The muscular system is always faced whether to make decisions based on commands either from the CNS or the Peripheral Nervous System (PNS) – do as you know or do as is required by the current (environmental) conditions. Therefore muscles must be able to respond to variety of stimulus including position, posture and movement also know as proprioreception. Most of the proprioreception comes from our feet, unfortunately we have put (quite often very uncomfortable) casts around them – shoes, with various ‘support mechanisms’ ultimately inhibiting our innate ability to adapt to the terrain and it is often reflected in our posture. it is the way we stand in space against gravity that is the true insight on what is going on with the sensorimotor system and as such can tell a lot about the types of muscle imbalances present. Read more about the foot in my article here. 

Which brings me to the….


Czech physician Karel Lewit noted,

He who treats the site of pain is often lost.

Therefore it is time to look at the human body as a whole. Muscle imbalances are no exception and usually result of either faulty movement pattern, bad technique and in rare occasions due to pain and muscle/bone/joint damage. Due to the evolutionary development of two muscle systems – the postural and phasic (movement) groups of muscles, the way muscle imbalances happen is largely predictable among all individuals. The sensorimotor system comprised of the musculoskeletal and the central nervous component is essential in the way we blance in space in response to gravity and ultimately how we move. As such any change is reflected in our posture and ultimately gait and movement patterns. Therefore by understanding the true causes behind imbalances, you can start treating them and be well on your way of being more functional.
What you can do today is try to sit less unless you absolutely have to and inquire about a more active (standing) workstation.
Stay tuned for the next instalments of the Functional series where I will cover addressing muscle imbalances through mobilisation as well as strength training theory and exercises.
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Functional Series

Further Reading

This article is a crystalisation of some amazing work, be sure to check it out!

[amazon text=Assessment and Treatment of Muscle Imbalance&asin=0736074007] – Phil Page, Clare Clark, Robert Lardner

[amazon template=thumbnail&asin=0736074007]

[amazon text=Muscle Function Testing&asin=1483176118] – Vladimir Janda

[amazon template=thumbnail&asin=1483176118]

[amazon text=Stability, Sport and Performance Movement&asin=1905367422] – Joanne Elphinston

[amazon template=thumbnail&asin=1905367422]

This article is for my personal use and educational purposes only, please always consult a licensed health professional. I cannot be held responsible for any damages caused by the information contained in this article.



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