Abstract: To clarify differences in sequential transforms of spontaneous movements between autism spectrum disorder (ASD) and healthy infants, angular acceleration and jerk root mean square (RMS) values of spontaneous movements of ASD infants and healthy infants were compared. Methods: Data of 18 premature infants were used: 3 had been diagnosed with ASD at elementary school entrance; 15 had been diagnosed as having no central nervous system and musculoskeletal system disorder and the cardiopulmonary system disorder. During 36–56 weeks postmenstrual age (PMA), premature infants were examined every 4 weeks. A three-dimensional motion analyzer measured spontaneous movements of the upper right limb in the supine position. Upper limb position data were used to calculate the angular acceleration RMS and the angular jerk RMS. Those data were allotted into 36 and 40 week PMA (term I), at 44 and 48 week PMA (term II), and at 52 and 56 week PMA (term III). RMSs was calculated at each term. Results: For angular acceleration RMSs of healthy infants, term II were significantly lower than term I (p<.05). For angular acceleration RMS of the ASD infants, term III was significantly higher than term II (p<.05). For angular jerk RMSs of healthy infants, term II and term III were significantly lower than term I (p<.05). For angular acceleration RMS and angular jerk RMS of ASD tended to increase, although there was no significant difference. For angular acceleration and angular jerk RMSs, the ASD infant value was significantly larger than the healthy infant value at term III (p<.05). Discussion and Conclusion: Spontaneous movements of ASD showed more jerkiness than those of the healthy infant group, especially at term III. Increased angular acceleration and angular jerk RMSs are initial ASD symptoms related to prognosis.
