Weak "core" muscles and poor trunk stability in children

Parents of children with movement difficulties (joint hypermobility, low muscle tone, autism, DCD) are often told by teachers, doctors and therapists that their child has "weak core muscles". Exercises to strengthen the "weak" core muscles may be suggested. 

In many cases children are said to have a weak core because they have poor posture when sitting and standing.   

xleg slumped_0.jpg   

However, core muscle weakness is only one part of the problem

The trouble with the core muscle strength explanation for poor posture is that it does not take into account:

  • the many factors that influence trunk and neck posture and stability; 
  • the complex coordination of  many different muscles needed to achieve the neck and trunk stability that the child lacks. 

Staying erect, and keeping the head and trunk steady when moving the arms and the legs, or changing the position of the body is regulated by a set of postural response mechanisms: including

  • Anticipatory postural responses: that activate the trunk and neck muscles in preparation for a change in the position of the body.
  • Balance responses: that change the alignment of the different segments of the body to maintain balance
  • Postural stabilization mechanisms: that maintain the erect trunk posture over long periods of time

Try the following

Stand erect holding a 2 liter bottle of water in your hands.

Now lift the bottle to shoulder height, keeping the arms straight. Lift and lower the bottle several times and pay careful attention to what is happening in your body. 

  • Does your trunk and head stay steady? You may notice that your head tilts forwards slightly.
  • Pay attention to the muscles in the front of your neck? Feel them contracting as they work to keep the head stable. 
  • Feel what is happening in your feet. As you lift the bottle you will notice a subtle backwards weight shift onto your heels. 

Next, keeping your arms at shoulder height, turn the bottle upside down and then the right way up again 10 times. .

  • You may notice how your abdominal and upper back muscles increase their activity to keep the trunk stable.

What are the core muscles?

In most instances the term "core"  muscles refers to the trunk muscles that work to hold the trunk erect and steady when the limbs are moved. The core muscles include the deep spinal extensor muscles as well as the transverse and diagonal abdominal muscles.The neck muscles also play an important role in maintaining a steady and stable head posture. 

These muscles need to work together in a coordinated manner to keep the head and trunk steady when moving the arms and the legs, with different actions requiring different patterns of  coordination.  

The many small neck muscles work together to keep the head erect and stable. 

neck muscles.jpg

The many deep back muscles that work together to extend the spine.

deep spine extensors.jpg

Three layers  of abdominal muscles work together in a coordinated manner to stabilize the lower back and pelvis

   external obliques.jpg    internal obliques.jpg

transverse abdominus.jpg

Core muscle action and flexibility

Normal flexibility is essential for effective core muscle action. For example, if the hip muscle flexibility is limited, the child will sit with the pelvis tilted back and the back flexed. In this position the back extensor muscles are overstretched and cannot work effectively to stabilize the trunk. 
Additionally, to compensate for the flexion of the spine, the neck is extended, which leads to overstretching and weakness of the neck flexor muscles. The neck extensor muscles may be tight. 

xleg slumped_0.jpg        Child-stand-hollow-back.jpg

Core muscles, posture and stability in standing

When standing erect with good alignment the pelvis is more or less vertical, there is a slight hollowing of the lumbar spine, the thoracic spine is curved very slightly in the opposite direction and the head is balanced on the torso. 

The hips are fully extended, with the knees slightly flexed and the feet facing forwards or slightly turned out.

   Hollow lumbar spine (1).jpg     

The  core muscles work to align the pelvis vertically, keep the spine erect and balance the head on the torso. 


What happens when the arms are moved?

When the arms are lifted forwards there is a very rapid recruitment of the neck and trunk muscles to keep the head and trunk steady:

  • The neck flexor muscles are activated to hold the head steady as the arms are lifted (controlled by the anticipatory postural response mechanisms).
  • The thoracic spine extensor muscles are activated the support the weight of the arms as they are lifted. 
  • The abdominal stabilizer muscles are activated to stop the trunk from tipping backwards. 

The postural response mechanisms are responsible for coordinating the actions of the core muscles: just enough contraction, at precisely the right time and in the right sequence. 


If a child's postural response mechanisms are slow or ineffective, the core stabilizer muscles are not activated to keep the head and trunk steady. The head and trunk may tip back slightly when both arms are lifted, or sideways if one arm is lifted. 

Try the following 

Instruct your child to stand with the arms lifted to shoulder height and parallel with the floor, and to stay in this position for 20 slow counts. 

Stand reach.jpg

Is she/he able to keep the trunk upright and hold the position easily for 20 slow counts?  Or does the trunk start to drift backwards, the arms drift up or down?  

Arms drift down_2.jpg

If your child has difficulties holding the position steady, the underlying problem probably related to slow and ineffective postural responses along with core muscle weakness.  

My child stands with the knees hyperextended and a hollow  back

As mentioned earlier, when standing erect with good posture, the trunk is balanced on the pelvis and the pelvis is balanced on the legs.

In order to achieve this alignment the knees needs need to be very slightly flexed, and the hips need to by fully extended so that the pelvis can assume a vertical position. 


Children with joint hypermobility will often stand with the knees hyperextended and the pelvis tilted forwards. To compensate for the pelvis being tilted forwards, the lower back is hollow. 

The anterior tilt of the pelvis is usually associated with some limitation of hip extension. 


Good trunk stability and everyday function 

Good head and trunk stability in standing is needed for many everyday activities, including ball skills, running, jumping, and walking on rough ground or up steps and stairs, which all require require good core muscle strength, as well as effective postural response mechanisms. 

   5y 3m outdoor walking_1.jpg     4y climbs trees_1.jpg   T 3y 2m kicking ball 6.jpg

Core muscle strength and stability when kicking a ball 

This sequence clearly shows how the trunk muscles need to work hard to keep the trunk erect as the child rapidly moves through different positions when kicking a ball. 

R kicking 1_2.jpg  R kicking 2_1.jpg  R kicking 3_1.jpg

Posture and stability in sitting

Sitting erect requires good flexibility in the hip, spine and neck muscles to allow the spine to be held erect with the head balanced on the spine.

The spine extensor muscles, especially in the upper back work to keep the spine erect.

Head balanced on torso.jpg+

As soon as the arms are lifted the muscles of the neck and trunk are activated the keep the trunk and head steady.  Good postural response mechanism ensure that the right muscles are activated at the right time, in the right sequence and with just the right amount of force. 


The postural response mechanisms that activate the neck and trunk muscles to hold the head and trunk steady, develop over time in young children, becoming effective at 4-5 years of age.

Younger children tend to move the trunk and arms as a single unit - when the arm is lifted sideways, the trunk tips sideways. If the child reaches forwards and across the body, the trunk twists forwards at the same time. 

2y 9m reach across.jpg   2y 9m reach forwards.jpg


What can be done to improve trunk muscle strength and stability?

1  The best way to improve core muscle strength, stability and postural control is to select exercises that strengthen the core muscles, and at the same time train more effective postural responses, as well as increase stamina and postural awareness. 

2  Your exercise program should also include stretching exercises for tight muscles, especially the neck extensor and hip muscles. 

3  Good posture is a habit: attention to posture when working at a table needs to be reinforced throughout the day until it becomes the new habit. 

4  Lastly, an exercise program to improve core strength and stability needs to include activities in standing, sitting and lying to cover all the different ways that the core muscles need to work in everyday function. 


How to asses core muscle strength and core stability



Exercises to include in your child's trunk muscle strength and stability training 

Stretching exercises to improve neck, lower back and hip muscles flexibility

Poor flexibility due to tight muscles affects a child's posture, with overstretching of some muscles which become weak, and tightness in other muscles which tend to be overactive. 

Stretching exercises need to carefully target tight muscles and not stretch already lax joint structures. 

Reach clasp twist right_1.jpg      prone extended arm support knees flexed_1.jpg    Supine pelvic tilt lift legs.jpg

Sitting exercises to improve neck and thoracic muscle strength and postural responses.

Sitting exercises which involve moving the arms slowly against resistance should be included, along with rapid repeated movements of the arms to activate and strengthen weak neck and trunk core muscles. 

A core strength and stability exercise program should also include activities and ideas to that encourage the child maintaing an erect posture working at a table over extended periods of time. 

lifting-bid-bottle-2_3.jpg  sit-arms-sideways.jpg

Exercises in lying to improve abdominal muscle strength for stabilizing the pelvis and lumbar spine 

There are many fun exercises which strengthen the abdominal muscles and improve the child's ability to hold the pelvis steady while moving the legs. These exercises are also good for stretching tight lumbar muscles. 

half plan sag.jpg   prone-knees-on-ball_1.jpg   


Standing exercises to improve the child's ability to hold the trunk steady when moving the arms and legs

stand step Throw high from above head_1.jpg  stand foot ball eyes closed_1.jpg   standing-ball-stick_1_0.jpg

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Selected bibliography

Assaiante, C., Mallau, S., Viel, S., Jover, M., & Schmitz, C. (2005). Development of postural control in healthy children: a functional approach. Neural Plasticity, 12(2-3), 109–18; discussion 263–72. doi:10.1155/NP.2005.109  

Cignetti, F., Zedka, M., Vaugoyeau, M., & Assaiante, C. (2013). Independent Walking as a Major Skill for the Development of Anticipatory Postural Control: Evidence from Adjustments to Predictable Perturbations. PLoS ONE, 8(2), e56313. http://doi.org/10.1371/journal.pone.0056313

Ludwig, O., Mazet, C., Mazet, D., Hammes, A., & Schmitt, E. (2016). Changes in Habitual and Active Sagittal Posture in Children and Adolescents with and without Visual Input – Implications for Diagnostic Analysis of Posture. Journal of Clinical and Diagnostic Research : JCDR, 10(2), SC14–SC17. http://doi.org/10.7860/JCDR/2016/16647.7283

Saavedra, S. L., van Donkelaar, P., & Woollacott, M. H. (2012). Learning about gravity: segmental assessment of upright control as infants develop independent sitting. Journal of Neurophysiology, 108(8), 2215–2229. http://doi.org/10.1152/jn.01193.2011 Article

Van Balen, L. C., Dijkstra, L. J., & Hadders-Algra, M. (2012). Development of postural adjustments during reaching in typically developing infants from 4 to 18 months. Experimental Brain Research. Experimentelle Hirnforschung. Experimentation Cerebrale, 220(2), 109–119. http://doi.org/10.1007/s00221-012-3121-9