How joint hypermobility (low muscle tone) affects yourbaby's development

Author  Pam Versfeld  MSc (Physio) UCT,  Physical Therapist  Read more 

Low muscle tone or joint hypermobility? 

Infants who appear to be floppy and have hypermobile joints are often given a diagnosis of low muscle tone.  The term muscle tone refers to the muscles' readiness for action. This readiness for action depends on the sensitivity of the stretch receptors in the muscles. If the sensitivity to stretch is very low the muscles are slow to respond and they appear to be weak and floppy. 

In infants with joint hypermobility the connective tissue that holds the muscles together and connects the muscles to the bones via the tendons is very pliable. This affects the sensitivity of the stretch receptors and the muscle's readiness for action. 

In most instances the low muscle tone is linked to joint hypermobility. However, if an infant is floppy and appears to be weak a full assessment by a pediatrician is important to rule out other causes. 

Read more Low muscle tone​

What is joint hypermobility?

Infants with joint hypermobility have joints that are able to bend further than usual and a trunk and limbs that appear to be floppy and weak. 

The increased range of  movement at the joints (sometimes called joint laxity or being double jointed) is due to differences in the connective tissue that forms the joint capsule and ligaments.

The joint capsule and ligaments hold together the bones that form the joint.  The joint capsule and ligaments are formed by a strong but pliable material called connective tissue. Connective tissue can be stretched a little way, just enough to allow the joint to move through the typical full range of movement. 
In joint hypermobility the connective tissue has more give and can be stretched further than usual. This means that the joints are less firmly held together and can be moved further than usual. 

The increased pliability in the connective tissue also affects the muscles which may appear to be floppy and are often weak. This in turn affects how the infant moves and develops and may mean that the infant is late achieving the major developmental milestones. 

R  10m pushing up on arms.jpgRoan locks her hypermobile elbow joints and bends her back more than usual.  Her hips are also abducted more than usual. 

Together these ways of moving make it difficult for her to push up onto all fours. 

sitting posture.jpgToesies sits with his back very rounded and his legs flat on the floor. 

The widely abducted position of the hips makes it difficult for him to sit erect and may also lead to tightness in the hip muscles. 

Highly sensitive/fearful infants, attention training and emotion regulation

Hypermobile (ow tone) infants, as well as preterm infants often have a highly sensitive/cautious temperament. They become upset very easily, especially when confronted with new situations or motor tasks that require effort and persistence.  

Early intervention that pays attention to training attention, helps highly sensitive/cautious/reactive infants to manage their negative emotions, and encourages them to take on challenges and learn new motor skills.  This is particularly important for hypermobile infants who have to work harder to achieve their motor milestones. Read more

Different developmental pathways for hypermobile and "low tone" infants 

Posture at birth

At birth typically developing full term infants lie with their arms and legs flexed. In fact the the muscles of the hips and knees are tight and the hips and knees cannot be completely stretched out (extended).     

The slight tightness (stiffness) in the muscles of the hips and knees helps the newborn infant to lift the arms and legs up when kicking and reaching. 

Will 6 days supine 11.jpg


Newborn hypermobile (and pre-term) infants lie with their legs and arms more extended and flat on the cot mattress. The usual tightness of the hip and knee muscles is absent and the the hips and knees can be fully extended. 

The laxity in the joints and muscles means that it requires more effort to lift up the arms to reach for toys and kick the legs.

       18 Jan supine_0.jpg  

Activity levels

Typically developing infants are very active

Within weeks active infants have  learned to keep their trunks steady when they kick, lift their legs up  and reach for toys. They also start  to push down on their feet and lift up their buttocks. All this action strengthens the muscles and gets them ready for sitting.  

supine 3m 1.jpg       5 months hands to feet.jpg

Hypermobile, low tone and premature infants may be less active and fail to develop good muscle strength. 

If the infant is hypermobile and also cautious she may not kick and reach vigorously and not develop the muscle strength needed to support the hypermobile joints and get them ready for rolling and sitting up.  

The first 6 months are important for laying the groundwork for the postural control and strength needed for sitting. 

Being active in lying allows infants  to develop a sense of how they can use their bodies to explore the world around  them and promotes visually exploring the world, using the hands to grasp and feel things and interacting with people. 

R 7m rolling 1.jpg

Read more:  Early development: kicking, reaching, looking

Tummy time 

Hypermobile, low tone and very cautious infants often hate tummy time They protest vigorously and quickly learn to flip back onto their backs when placed flat on a firm surface. 

At 10 months this little fellow has not yet learned to push up on his arms and after a while puts his head down and starts to complain.  

T 11m prone_1.jpg    T 11m prone 1.jpg       

Spending time on the tummy is important for developing muscle strength and flexibility in the back and hip muscles in readiness for crawling and walking. 

It is very important to find ways to encourage your infant to spend time lying on the tummy, propping up on the arms and eventually pushing up onto the hands and knees.  

Read more: Tracking your infant's development in prone and ways to get your infant to enjoy being on the tummy and to start pushing up into the crawling position.  

W 4m on carers chest.jpg      prone on block_1.jpg

​Hypermobile and low tone infants sometimes have difficulty learning to roll 

Learning to roll from the back onto the tummy takes lots of effort and requires many attempts to work out how to get it right. 

Rolling  requires strong neck and tummy muscle and also involves using momentum. Infants who lack the strength to lift up the head often get stuck trying to roll by extending the head and legs. 

 R 7m rolling 1_1.jpg      T 9m rolling 5_1 (1).jpg

Sitting may be delayed

Hypermobile and low tone infants often learn to sit later than normal, sometime between 8-10 months.  Delayed sitting has a knock on effect: it means delays in the development of fine motor skills, social communication skills  as well as the onset of babbling and appearance of the infants first words. 

Some infants sit with a very rounded back with the knees bent and the thighs close to the floor.

sitting posture.jpg     T 13 m unpacking box 2.jpg      

Other infants may sit with the knees straight and the legs far apart.  They can bend far forwards, often putting their heads flat on the floor.

R  active in sitting 4.jpg       R sitting reaching forwards.jpg

At a later stage, once the infant starts to move into sitting on her own she may sit between her legs in W-sitting. 

 infant w-sitting.jpg

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Hypermobile infants often develop stiffness in the hip muscles 

Because hypermobile infants lie and sit with their hips wide apart, they often develop tightness in the muscles that cross over the side of the hips. This makes it difficult for the infant to get the thighs more or less parallel when they lie on their tummies, try to get up into the crawling position and kneel upright. 

T 9m prone.jpg   R 11m up into kneeling.jpg   

To check for hip tightness
Let your infant sit on a low step with the hips and knees flexed to more or less a right angle.  Now gently move the thighs together. Is this action easy or do the legs feel a little tight?  When the infant bends forwards you may also feel how the legs want to move sideways.

T 10m sitting hip stretch_1.jpg    T 10m sit bend forwards.jpg   

If the hips muscles are tight the infant will also tend the bend the lumbar spine as you move the thighs together. In this picture of Toesies you can see the tight band of the fascia lata on the outside of the thigh just above the tips of my fingers. 

T 10m sit reach up_1.jpg   

Hip stiffness affects the infant's ability to get up onto the knees 

The  stiffness in the hip muscles affects the infants ability to get up into kneeling or onto all fours. The legs are held wide apart when they are on their tummies and this makes it difficult to get up onto the hands and knees. 

     prone on block.jpg

Hypermobile infants lock their elbows 

Hypermobile infants lock their elbows into hyperextension when they push up on their arms. As a result they do not develop the arm strength needed for getting up onto all fours and crawling. 

  R  10m pushing up on arms.jpg   supported prone kneeling.jpg

Infants may not get onto hands and knees and crawl

Hypermobile and low tone  infants sometimes do not crawl. Instead they may scoot on their bottoms to get around. 

This little fellow manages to hop along on his bottom with great speed.  

Read more: Why do some babies scoot on their bottoms

   T 15 m bottom shufflling 3_1.jpg      T 15 m bottom shufflling 4.jpg

Standing, cruising and walking may be delayed

Hypermobile infants stand with their knees locked back in hyperextension. They may also  start standing with their feet wide apart and turned out. This makes it difficult to shift the weight onto one foot to take a step. 

  R 11m stand and step 11.jpg

They often fall back with their knees straight  when they want to sit down again.

R 11m stand and fall 3_1.jpg   R 11m stand and fall 4_1.jpg          

Walking is often delayed 

Hypermobile and low tone infants tend to walk a few months later than usual, sometimes as late as 18-20 months.

However, unless the infant  has another disorder as well,  hypermobile babies eventually walk independently. As a rule of thumb, if an infant is not walking by 20 months there is some cause for concern and physiotherapy intervention is possibly needed. 
Once up on their feet, hypermobile babies may trip and fall easily even after several months of walking experience. This is often due to weakness in the leg muscles rather than a balance and coordination problem.   They may be very nervous about stepping up onto a small step, stepping over obstacles and walking on soft and uneven surfaces. 
Read more:

Hypermobility, developmental delay and brain development  

Most infants and toddlers are curious and adventurous. They spend a lot of time exploring different ways of doing things and will persist and work hard at achieving their goals. They also enjoy being social and seek out opportunities for social engagement.  By the end of the first year they are also becoming more able to manage their negative emotions as they become more goal focused. 

Hypermobile infants with a cautious nature tend to avoid new or challenging activities. They are less curious and adventurous and spend less time exploring different ways to to things.  They have slow to learn to manage negative emotions and use avoidance as their only strategy for moderating negative emotions. 

The cautious/fearful infant's avoidant  behavioral style has long term consequences:  the mind-body foundations needed for later developing motor, communication, language, emotion and cognitive tasks are not well established.  

Tracking Progress Charts

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hand function (fine motor) and communication.

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