Movement variability is defined as the tendency to vary or use different movement repertoires on multiple repetitions of the same task or during a series of repeated movements. (Dusing 2016)
Movement variability is seen in the infant's earliest repetitive spontaneous movements, such as kicking and early reaching.
These repetitions vary across time, with each repetition providing different sensory-motor linkages and error messages allowing for adaptation of the motor plan for subsequent actions.
Over time, and with practice, the infant will select a few strategies which are most efficient, and reduce the use of the non-preferred strategies (reduce variability).
A lack of movement variability is frequently identified in infants and children who have developmental delays or disabilities (Kyvelidou 2010). This impacts on infants' ability to learn from experience.
Will 5 days: variability in spontaneous UE movements
In this clip you see Will (5 days) being dressed after his bath. It nicely illustrates variability in the pattern spontaneous movement of the UEs as they are repeated over time.
I have posted two clips: one at normal speed and one slow motion.
Take time to observe the clip before you read my analysis
Observe the following:
- The impact of changes in the infants state of arousal on the speed and pattern of the spontaneous movements.
- The pattern of movement of the UEs
- Position and movements of the head
Next re-watch the clips paying attention to the different features I have highlighted below.
In the first half of the video you see Will in an alert and fussing state. His upper and lower extremity movements are fast and continuous. watch out for repeated swiping actions of the UEs.
In the latter half of the video Will's state changes to alert and active. This part of the video zooms in on Will's head and upper limb actions.
You see him moving his shoulders through a large range of movement from full range shoulder flexion to an extended adducted position, with varying amounts of mounts of elbow flexion. The elbow flexion determines the position of the hand relative to the face and trunk.
You see Will exploring different shoulder/elbow combinations as he tries to bring his hand to his face. You see his mouth opening as his hands move close to his face.
Video: Will 5 days old
Dusing SC. Postural variability and sensorimotor development in infancy. Dev Med Child Neurol. 2016 Mar;58 Suppl 4:17-21. doi: 10.1111/dmcn.13045. Review. PubMed PMID: 27027603.
Vereijken B. The complexity of childhood development: variability in perspective. Phys Ther. 2010 Dec;90(12):1850-9. doi: 10.2522/ptj.20100019. Epub 2010 Oct 21. Review. PubMed PMID: 20966207. https://academic.oup.com/ptj/article/90/12/1850/2737965
Kyvelidou, A., Harbourne, R. T., & Stergiou, N. (2010). Severity and Characteristics of Developmental Delay Can Be Assessed Using Variability Measures of Sitting Posture. Pediatric Physical Therapy : The Official Publication of the Section on Pediatrics of the American Physical Therapy Association, 22(3), 259–266.