Spontaneous kicking and arm waving are prevalent in the first few months of life, and have been recognized as important for appropriate motor development. Two longitudinal studies investigating the link between spontaneous movements and motor coordination will be discussed. The first study examined spontaneous leg kicking in order to investigate the development of intralimb and interlimb coordination in young infants. Using motion analysis, changes in joint coupling and degree of synchrony between joint pairs during spontaneous kicking were determined by measuring cross-correlations and phase lags between the hip, knee and ankle joints. Both fullterm and preterm infants were examined from ages 4 to 24 weeks (corrected for prematurity).

Group data revealed that different patterns of development were present for intralimb and interlimb coordination, and also for fullterm and preterm infants. For example, a gradual transition from low interlimb coupling to stronger coupling occurred over age. However, it has been argued that group data may mask dramatic developmental transitions in individual infants. As a result, further analyses were carried out to investigate the individual transition patterns.

The second study extended this research by investigating the development of coordination between all four limbs using 3-D motion analysis. The changes in joint synchrony over this period were again determined by measuring pair-wise cross-correlations and phase lags for the angular displacement of the shoulder, elbow, wrist, hip, knee and ankle joints for both the right and left sides of the body. Infants were examined at two weekly intervals from 2 weeks to 6 months of age.

In addition to intralimb coordination, the relationships between the joints of ipsilateral and contralateral limbs were examined. For both the arms and legs, strong intralimb joint couplings were present throughout the first few months of life. Preliminary results indicate, as in the earlier study, the presence of different developmental patterns for preterm and fullterm infants, and also different patterns of development for the right and left side of the body. Results are discussed in terms of their implications for understanding the processes involved in early motor development.