This is the last post in the series on infant development in prone  The series started with a question: Why do so many infants fail to learn to crawl. 

In this post you see two video clips the first shows Will's early crawling and the second clips show Will crawling at speed using a beautifully coordinated reciprocal gait pattern. 

But first: a quick review of the story so far: birth to 6 months 

Two things stand out for me

Firstly the ability to transfer weight onto one UE  with effective postural responses in the trunk and pelvis to provide a stable platform for reaching with the contralateral hand takes time to develop. In Will's case is only really present at 7 months. 

Secondly, the ability to support the head and upper torso on the UE, either on the forearms or on the hands with extended elbows, requires effective trunk extensor muscle action. 

Will at 7 months 

Will regularly transitions form extended UE support to prone pivot, with the hips fully extended and the thighs raised up off the support surface. 

Will has also started to push up into prone kneeling. 

Pushing up into prone kneeling 

Will displays a consistent sequence of movements when pushing up into prone kneeling:  he pushes down on his hands and lifts the head and shoulder girdle up off the supporting surface. He then extends the elbows, while at the same time lift the pelvis up off the supporting surface. 

This action requires recruitment of the trunk flexors (abdominal muscles) along with protraction and stabilization of the scapulae to support the increased weight being carried by the UEs as the elbows are extended. 

Once the elbows are extended, he flexes the hips and knees to move the knees under the hips, followed by a backwards shift of weight over the LEs  leading to a more even distribution of weight in and A-P direction. 

A consistent cross-over pattern of limb lifting

On repeated occasions, once Will has pushed up into prone kneeling, he lifted one hand up supporting surface, at the same time extending and abducting the contralateral hip. This cross-over pattern of limb lifting is associated with weight redistribution to provide a BOS that is as large as possible in an A-P and lateral direction. 

This cross-over pattern of limb lifting activates the trunk stabilizers proactively to maintain trunk alignment in the face of the perturbing forces generated by the limb movements.

 The hip abductors are also active in a closed chain pattern to stabilize the pelvis on the weight bearing LE.  

Final Installment:  Learning to Crawl

Commando crawling, the transition to prone kneeling and early crawling 

In the first  video clip you see Will's  exploration of his ability to move about on the floor in prone and prone kneeling over a period of 2 months (from 6 - 8 months). 

You see his early attempts to balance in prone kneeling, how he experiments with commando symmetrical commando crawling to move forwards, and his early exploration of using a reciprocal crawling pattern. 

Mature crawling 

After several months of crawling experience Will has developed an elegant and beautifully coordinated pattern of reciprocal crawling which allows him to get around at speed. 

Crawling at speed requires lateral pelvic tilt

What next?
Thoughts about crawling
The series of blogs entitled Thoughts About Crawling in response to Mindy Silva's question: Why do infants bunny hop? explores the development of reciprocal crawling 

Open access for November  Guide to the assessment of atypical prone development  

TOMT Subscribers 
Development in prone 

Training crawling How to encourage infants to get up onto their knees and crawl