Context
Sitting erect on a bench or chair while performing a task with the hands s a common activity children encounter in their everyday and school lives.
- Sitting at a table for school work: drawing, cutting, handwriting, constructing, building puzzles.
- Sitting at a table for meals is another common activity.
- Sitting is also used aa a stable position when getting dressed and undressed, including: putting on trousers, socks and shoes.
Fundamental requirements for sitting erect on a bench or stool
Range of Motion
- Pelvis in neutral position with slight flexion in the lumbar spine.
- 900 flexion at the hip with neutral hip abduction / adduction and rotation.
- Knee flexion to 900
- Dorsiflexion to 900
- Extension of the thoracic spine – especially at the thoracolumbar junction
- Lower cervical spine in neutral flexion/extension
- Slight extension of the upper cervical spine to bring the face vertical
COM , LOG and hip muscle action
The COM of the head, arms and trunk (HAT) lies just anterior to T8
The relationship of the LOG relative to the flexion/extension (F/E) axis of the hips depends on the alignment of the trunk.
►Typically the LOG falls just posterior to the F/E axis of the hips – this creates an extension moment at the hips and the iliopsoas muscles are activated to maintain the upright position.
►However if the trunk is tilted forwards slightly, the LOG will fall anterior to the F/E axis of the hips creating a flexor moment at the hips. The hamstring muscles are activated to maintain the position of the pelvis.
Muscle action for quiet sitting erect
When sitting erect quietly, the head is balanced on the trunk, and the trunk is balanced on the vertical pelvis. The muscle activity needed to maintain the position depends on the exact alignment of the segments relative to each other which in turn influences the position of the LOG relative to the COM of each segment.
► Low levels of activity in the lower cervical extensor muscles to keep the head erect, with intermittent activity in the deep neck flexors to steady the head on the spine when the head is moved.
► Low levels of activity in the trunk extensors to maintain the erect posture
► Low levels of activity in the abdominal muscles – depending on the alignment of the trunk
► Hip flexion or extension action depending on trunk alignment
Iliopsoas activity when the LOG falls posterior to the F/E axis of the hip joints
Hamstring activity when the LOG falls anterior to the F/E axis of the hip joints
Maintaining a stable head and trunk for hand tasks
Any movement of the upper or lower extremities affects the relative position of the COM for each segments and increases the muscle work needed to maintain a steady head and trunk.
Activities that require using the hands for grasping, lifting and manipulating objects and tools require a stable head and trunk when moving the arms.
When moving the UE for hand tasks the head serves as the frame of reference for alignment and balance. The head is kept erect and steady and adjustments of the trunk and pelvis are made to maintain the COM over the BOS.
►Anticipatory postural responses in the neck muscles usually precede any actions that require lifting and moving one or both hands.
►Adjustments in the alignment of the trunk and pelvis occur in anticipation of, and during, lifting one or both arms up and forwards, sideways or across the body.
Difficulties some children experience with sitting erect
Children with movement and postural difficulties (DCD, generalized joint hypermobility, Down syndrome, "low muscle tone") will display one or several differences in alignment and postural adjustments.
Child adopts a slumped posture
The child may sit with:
- the trunk flexed and the neck extended to keep the face vertical;
- the pelvis in posterior tilt wit associated hip extension;
- the hips abducted, and sometimes in medial rotation;
- the ankles plantar flexed.
This posture is usually seen in children who have limited mobility/extensibility in the dorsolateral fascial system of the lower quadrant. This includes the lumbodorsal fascia and its connections to the gluteal fascia, the iliotibial band and the fascia lata.
Typically hip adduction in 900 of flexion is limited, SLR, especially SLR with dorsiflexion is limited to 450 or less, and there is resistance to passive extension of the spine in sitting. See:Assessment of LE flexibility
Additionally upper cervical flexion may also be restricted. If a child habitually sits with the trunk flexed, the upper cervical region will be extended to bring the face vertical. This leads to tightness in the cervical extensor muscles. See Assessing upper cervical flexion.
Child finds sitting erect tiring and uncomfortable
Children who habitually sit with a slumped posture find sitting erect tiring and uncomfortable.
► Neck discomfort is associated with restricted ROM of the upper cervical flexion (O-C1) as well as weakness in the cervical flexor muscles.
► Back discomfort, often in the thoracic region which is associated with restricted thoracic trunk extension and thoracic muscle weakness (muscles tire quickly).
► Discomfort in the LEs associated with limited extensibility muscle and fascial structures that cross from the lumbar region over the posterior and lateral aspects of the hips. This is usually associated with limited straight leg raise, reduced popliteal angle and restricted adduction of the hip when the hip is flexed to 900.
Child not able to keep the head erect and steady
Children with weakness or poor flexibility in the neck muscles find it difficult to hold the head erect and steady for long periods of time. They will often prop the head up on one arm.
The child may also have slow or absent anticipatory postural responses when the UEs are moved.
Responses to UE movement in children with poor trunk and head stability
Trunk tips sideways when arm is lifted.
Trunk tips backwards when the arms are lifted forwards.
Child uses a less mature shoulder pattern for hand activities
Effective use of the hands for tasks such as drawing handwriting, cutting with scissors and using a knife and fork all require the ability to reach forwards with the shoulder(s) in flexion lateral rotation which brings the hands in front of the chest and allows for forearm rotation to position the hands relative to objects. (See Shoulder control for drawing and handwriting)
Many children with movement difficulties have limited external rotation of the shoulder and tend to lift the hand forwards with the shoulder in abduction and medial rotation. A slumped posture when drawing and writing is sometimes adopted to adapt to the tendency to abduct the shoulder.
Tutorial: Sitting erect for table top work, drawing and handwriting
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Difficulties children have with shoulder control for handwriting
Assessment of lumbar and LE flexibility - with normative values
Intervention
Intervention and training program - with PDF handout for parents and teachers
