How hypermobility and low muscle tone affect your infant's development

Hypermobile infants and toddlers have joints that bend further than usual, often have some muscle weakness which leads to a diagnosis of low muscle tone in most cases have a cautious nature.

Infants and toddlers with joint hypermobility may: 

  • Be late learning to sit, sit with a very rounded back or W-sit
  • Skip crawling and bottom shuffle instead
  • Hate tummy time
  • Have tight hip muscles which affects crawling, walking and balance
  • Avoid activities that are new or require effort and may have sensory issues
  • Develop coordination and attention problems as they get older

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.jpg

Toesies sits with his back very rounded and his legs flat on the floor. 

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

Read more: Causes and diagnosis of joint hypermobility

Why motivation and attention really matter

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

Promoting attention and communication skills is very important in infants at risk for autism.

Early intervention for fearful/inhibited infants and toddlers that includes attention training helps then 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

Low muscle tone and 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  

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 cannot be completely stretched out. 

   Will 6 days supine.jpg    Will 6 days on side.jpg

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. 

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

    2 weeks lying_1.jpg    2 weeks kicking_1.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 3 rattle.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.  

W 4m hold and shakes rattle_1.jpgW 4m hands to mouth_1.jpgThe 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. 

Read more: Developmental Gym:  Early development: kicking, reaching, looking

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. 

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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

Hypermobile (low tone) infants often bottom shuffle, and skip crawling stage

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.  

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

Read more: Why some infants bottom shuffle and why crawling matters.

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

If their hip and knee muscles are weak, they have difficulty bending down to retrieve objects from the floor, and take longer to sit down with good control. 

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.jpg

Walking is usually 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. 

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.  

Read more:
How attention to infant and toddler attention and communication promotors gros and fine motor development

More information

Toddler skills and exercises 

toddler gross motor_ (1).png 

  toddler leg exercises.png

Infant development and exercises 

Information, charts for tracking progress, exercises and tips for training 

focus-0-6-months.jpg  focus crawling_1.jpg   focus-sitting.jpg   focus-infant-standing-walking.jpg

2 Comments

I agree completelypam

Comment: 

Hi Maggie

I agree with you - joint hypermobility does not necessarily mean muscle weakness. I often make the point that most ballet dancers are hypermobile and very strong.

Temperament has a role to play - hypermobility plus a cautious temperament = avoidance of activities that require effort = poor strength development.

Sounds like your children were very active from a young age.

W-sitting some of the time is not a problem. W-sitting all of the time however is not good for the knees as many hypermobile adults will attest. It also reflects tightness in the iliotibial band - adults develop iliotibal band syndrome. So while you did not develop problems, many people do.

hyper mobility. w-sitting, low muscle tone etcMaggie (not verified)

Comment: 

Goo day
I disagree with the above. Both my kids sit in the W-sitting position from being a baby. Both were able to sit independently at around 5 months with legs forward and w. They loved tummy time. Crawled around 7 months. Walked at 10months. At 11months they could walk long stretches of at least 10 meters(if not longer). My eldest almost 3 can do more physical activities climbing/running etc than boys his age.
I have hyper mobility, and still sitting in W, but it never bothered me. I did lots of sport at school, including long distances. I being a girl remember that when it came to picking up weights with my legs, I beat most boys 2-3years older than me, with no prior weight training. Hyper mobility does not always indicate low muscle tone. I just wanted to add this, that the text, is thorough. But otherwise a good article