The purpose of this dissertation is to gain a better understanding of the contribution of torque changes to the early changes in leg joint coordination of typically-developing full-term infants, clarify the differences between leg joint coordinations and torques of preterm and full-term infants, and determine whether preterm infants have the potential for a greater amount of out-of-phase leg joint coordination when interacting with an infant-activated mobile that reinforces out-of-phase leg joint coordination.;The first study investigated the contribution of torque changes to the early changes in leg joint coordination of typically-developing full-term infants. We analyzed kicking actions within 10 full-term infants and between 6 and 15-weeks of age using a three-dimensional kinematics and kinetics approach. We found that although 73% of joint angle pairs demonstrated a change from an in-phase intralimb coordination pattern at 6-weeks to an increased variety of intralimb joint coordination patterns at 15-weeks, there was not an obvious developmental change in net joint torques or intersegmental dynamics. Further analysis supported that a greater variety of hip-knee joint coordinations from 6 to 15-weeks of age was associated with a decreased influence of knee muscle torques which allowed passive knee gravitational and motion dependent torques to have a greater influence on the coordination of the kick, contributing to a greater variety of hip-knee joint coordinations.;The second study investigated the contribution of torque changes to the early changes in leg joint coordination of preterm infants. From 6 to 15-weeks, preterm infants demonstrated less in-phase coordination in 30% of joint angle pairs, versus 73% of joint angle pairs in full-term infants. At 6-weeks preterm infants as compared to full-term infants demonstrated less in-phase coordination in 4 of 15 joint angle pairs, but this difference resolved at 15-weeks. Similar to full-term infants, there was not an obvious developmental change in net joint torques or intersegmental dynamics from 6 to 15-weeks. Although PT infants exhibited a greater variety of hip-knee coordinations from 6 to 15-weeks of age, unlike full-term infants, no differences were noted in the intersegmental torques. However, the PT infants demonstrated a smaller change in hip-knee coordination from 6 to 15-weeks which may have been insufficient to document the relation between intersegmental dynamics and joint coordination.;The final study investigated whether preterm infants could generate a greater amount of out-of-phase joint coordination when participating in an innovative learning task which utilized an infant-activated mobile. Fourteen full-term infants and 6 preterm infants participated at 3–4 months corrected age. Each infant participated in 2 sessions of mobile reinforcement on consecutive days. During each session, the infant was positioned supine under an overhead infant mobile. Day 1 consisted of a 2-minute non-reinforcement condition (spontaneous kicking) followed by a 6-minute reinforcement condition (the infant mobile rotated and played music when the infant moved either foot vertically across a virtual threshold). Day 2 consisted of a 2-minute non-reinforcement condition, 6-minute reinforcement condition, and 2-minute non-reinforcement condition. The full-term group, but not the preterm group, increased the percentage of mobile activation to meet performance criteria the 2nd day. Neither group met learning criteria. However, both the full-term and preterm groups included infants that learned the contingency between their leg action and mobile activation. Infants were separated into infants that learned the contingency and infants that did not learn the contingency. Infants who learned the contingency demonstrated a greater amount of out-of-phase hip-knee joint coordination during the reinforcement condition on the second day as compared to spontaneous kicking during the initial non-reinforcement condition on the first day. This coordination change was not demonstrated by the group of infants that did not learn the contingency. These results indicate that some full-term and preterm infants can demonstrate a greater amount of out-of-phase hip-knee joint coordination when participating in a task in which their leg actions are reinforced with mobile activation. (Abstract shortened by UMI.).
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