Angular acceleration and angular jerk of elbow extension-flexion movement as parameters for discriminating a sequential transform of spontaneous movements in early infants.

Objective: We assessed the root mean square (RMS) of angular acceleration and the RMS of an angular jerk as expressions of the transformation of spontaneous movements in early infancy. Methods: During 36-56 weeks post-menstrual age (PMA), 15 premature infants (6 male, 9 female; 36 weeks PMA>) were measured every 4 weeks. A three-dimensional motion analyzer (Fastrak system; Polhemus Inc.) was used to measure spontaneous movements of the upper right limb in the supine infants. Upper limb position data were used to calculate the RMS of angular acceleration and the RMS of angular jerk at the elbow. The calculated data were classified into three terms: 36th and 40th week PMA (termⅠ), the 44th and 48th week PMA (termⅡ), and the 52nd and 56th week PMA (termⅢ). The typical value was the mean value for each term. Results: The RMS of angular acceleration in termⅡ was significantly less than that of termⅠ (p<0.05). The RMS values of angular jerk in termⅡ and termⅢ were significantly less than that of termⅠ (p<0.05). Conclusion: The RMS of angular acceleration and the RMS of the angular jerk are useful for expressing changes in the strength of spontaneous movements of elbow extension-flexion movements.