Tangentially related to the concept of stronger vs weaker muscles is the idea of overactive vs underactive muscles.
What are overactive muscles? What are underactive muscles? What are the most common overactive and underactive muscles, and how do you determine if you have an overactive vs underactive muscle?
In this article, we will discuss what causes overactive and underactive muscles, how to determine the difference between the two, and what you can do to correct these muscle imbalances.
We will cover the following:
- What Causes Overactive and Underactive Muscles?
- What Are Overactive Muscles, and What Are Underactive Muscles?
- How to Fix Overactive and Underactive Muscles
Let’s jump in!
What Causes Overactive and Underactive Muscles?
Let’s look at what causes overactive and underactive muscles to develop before we look at the signs and symptoms.
In other words, what causes muscle imbalances to develop?
The primary causes of muscle imbalances that result in overactive and underactive muscles are repetitive movements or chronic static postures, poor posture in general, injury, or stress.
In the face of any of these problems, the body compensates by allowing movement to occur but along the path of least resistance rather than necessarily the ideal biomechanical path. This compensation is known as relative flexibility.
Unfortunately, muscle imbalances tend to be a feedforward cycle in which the initial muscle imbalance continues to contribute to the development of a more significant disparity between the overactive vs underactive muscles.
This is exemplified in the case of someone with lower crossed syndrome, which is one of the most common clinical manifestations of overactive and underactive muscles developing from prolonged sitting.
Essentially, as the pattern of dysfunction persists, it becomes more and more prominent because one side of the joint continues to get tight and “short“ from overactive muscles while the other side of the joint becomes overstretched, underactive, and lengthened.
Then, as compensatory movement patterns develop to mitigate the difficulties of short and long muscles and the muscle imbalance is around a joint, the overactive muscles continue to take on the brunt of the workload because the underactive muscles have become weak and ineffective at supporting the body for the activity.
A common case of this occurs with the glutes and hamstrings.
Many people develop “dead butt“ syndrome, which is characterized by underactive glute muscles.
Because the glutes and hamstrings both function to extend the hip, if the glutes are not being properly activated and recruited for hip extension, and you are relying too much on your hamstrings, the hamstrings will keep getting stronger and stronger because these muscles will be taking on the majority of the workload extending your hip.
Essentially, the glutes are getting too much of a “free ride “ and are not getting the opportunity to be strengthened because you are not engaging them in hip extension activities or exercises.
A vicious cycle ensues because the hamstrings will continue to get stronger and stronger, evidenced by being overactive and shortened, and the glutes will get weaker and weaker while lengthened and underactive.
Unless you take deliberate steps to not only learn how to properly activate the glutes and develop the necessary strength, the muscle imbalance or disparity between the overactive vs underactive muscles will just continue to snowball.
Eventually, this can increase the risk of injuries, such as high hamstring tendinopathy due to overworked hamstrings, pelvic and hip alignment issues, low back pain, etc.
What Are Overactive Muscles, and What Are Underactive Muscles?
Although it is common that overactive muscles are also short, tight, and strong, while underactive muscles are long and weak, this is not always the case, and believing it to be an absolute truth can impede fixing muscle imbalances.
There are two reasons why these absolute groupings can be a fallacy.
- Just because a muscle feels tight does not necessarily mean that the muscle is actually short.
- Just because a muscle is short doesn’t guarantee that it is overactive and strong. Similarly, just because a muscle is long does not guarantee that the muscle is also underactive and weak.
Let’s look at each of these potential discrepancies in overactive and underactive muscles relative to short and strong vs overstretched and weak muscles.
In terms of the first factor, a muscle may feel tight for reasons other than it being physiologically shortened or contracted.
Our muscles contain sensory organs known as muscle spindles, and the tendons that connect muscles to bone contain sensory organs known as the Golgi tendon organs (GTOs).
The muscle spindles are specialized receptors embedded within the belly of fascicles of muscle fibers (bundles of muscle fibers in a muscle).
These specialized sensory receptors detect changes in the stretch or length of a muscle as well as the rate of change in length.
For example, if you are performing a static hamstring stretch by standing upright and reaching down towards your toes, the muscle spindles embedded within the hamstrings will detect the lengthening or stretching of the hamstrings as well as the gradual and gentle progression of the stretch as you carefully perform the movement.
When the muscle spindles detect that the muscle fibers are getting stretched too much that they may tear or damage may occur, a negative feedback loop occurs where the muscle spindles send sensory signals to the brain via afferent neurons.
Then, in the central nervous system, the overstretching is detected, and a reactive signal is sent back through the efferent motor neuron that causes you to stop stretching the muscle or ease up on the stretching to prevent muscle damage.
Similarly, if you are sprinting and you overstride and rapidly overstretch your hamstring, the muscle spindles initiate a protective mechanism to try and prevent injury by causing you to rapidly and reflexively retract your leg and shorten your stride.
The Golgi tendon organs function in a similar manner, except they detect changes in muscle tension and the rate of this tension change.
These specialized GTO receptors are located near the origin and insertion point of a muscle (where the muscle first attaches to the bone up top and where the muscle attaches to the bone at the opposite end of the muscle).
When a muscle is stretched, the Golgi tendon organs are deformed or compressed, which sends a signal to the CNS to contract the muscle, termed autogenic inhibition.
However, this contraction can occur when the muscle is in the length and position. Then, that muscle can still feel tight even though it is actually overstretched.
A good example is with an anterior pelvic tilt in which the hamstrings are actually overstretched and lengthened but may feel tight because of the firing of the Golgi tendon organs and the subsequent contraction of the hamstrings in their lengthened state.
This may make you feel like you need to stretch your hamstrings even though the hamstrings are not actually shortened.
Over time, you can develop chronic hamstring tightness despite the muscles being in a lengthened position.
The second common way in which we can conflate overactive vs underactive muscles with short and strong vs long and weak muscles has to do with the length-tension relationship of muscles.
Muscles contract through a mechanism called the sliding filament theory of muscle contraction. Without getting into the weeds of anatomy and physiology, essentially, there is an overlap of contractile proteins within a muscle known as actin and myosin filaments.
There is an ideal amount of overlap between these muscle filaments when the muscle is in its resting state, which will help maximize the force-generation capacity of a contraction.
If a muscle is too short, there is too much overlap between the filaments, and thus there is not enough distance that these filaments can’t “slide” together, which is what causes a muscle to shorten when it is contracted.
Basically, the muscle would already be mostly contracted, so there wouldn’t be enough range of motion in the contractile units to generate an optimal amount of force.
On the other end of the spectrum, when a muscle is lengthened, there is not enough overlap between the contractile units, so they can’t effectively “grip onto one another.“
This, too, will decrease the potential force and tension generation of the muscle.
The reason why this matters is that in either scenario, either a short or long muscle will feel functionally weak. So just because a muscle is effectively short does not necessarily mean that it is strong.
How Do I Know If I Have Overactive and Underactive Muscles?
There are various signs and symptoms of muscle imbalances or overactive and underactive muscles surrounding a joint.
Depending on where you have overactive vs underactive muscles in your body, you may have postural deviations when you are in a static position and/or movement dysfunctions or range of motion issues.
There are five main kinetic chain checkpoints: the head, shoulders, hips, knees, and feet. If any of these joints are out of alignment, it is usually a sign that you have overactive and underactive muscles surrounding the joint.
Then, there are various functional movement screens that can help identify overactive vs underactive muscles, such as the FMS battery of movement tests or a basic overhead squat assessment.
Manual muscle testing and range of motion assessment conducted by a skilled practitioner are also usually essential for identifying muscle imbalances.
Getting an assessment from an experienced physical therapist is usually the best way to identify overactive and underactive muscles and to develop an effective treatment plan to fix muscle imbalances.
Other clinical signs and symptoms of overactive and underactive muscles include:
- Joint pain
- Postural deviations
- Decreased range of motion
- Feeling like one leg is longer than the other leg
- Uneven shoulders or hips when you stand
- Back pain
- Injuries with running or walking, such as runner’s knee or IT band syndrome
- A sway back or a flat back
- A noticeable anterior or posterior pelvic tilt
How to Fix Overactive and Underactive Muscles
Usually, a combination of self-myofascial release, such as foam rolling, along with stretching, is necessary for tight and overactive muscles, and targeted muscle activation exercises and strengthening exercises are used for weak and underactive muscles.
Identifying and correcting the root cause of overactive vs underactive muscles is also necessary to prevent further escalation or relapse of the muscle imbalance.
Again, a physical therapist will best be able to develop a treatment plan to correct overactive and underactive muscles.
For foam rolling exercises to target specific muscles, check out our guide here.
