If adults are carrying an object and start to experience a loss of balance, they frequently maintain hold of that object instead of dropping it. In these loss-of-balance situations, adults tend to maintain hold of the object, instead of freeing both hands to aid in balance recovery. The current study investigated the ontogeny of this behavior by examining if infants also maintain hold of objects when experiencing a fall. Sixteen newly standing infants were video-recorded while standing and holding a toy and standing while not holding a toy. Similar to adults, when infants experienced a loss of balance, they did not drop held objects. However, maintaining hold of objects only partially interfered with the use of upper-limb protective strategies while falling. These results suggest that the tendency to maintain hold of an object while falling is present early in development and with little independent standing experience.
Amanda J. Arnold and Laura J. Claxton
James R. Chagdes, Joshua J. Liddy, Amanda J. Arnold, Laura J. Claxton and Jeffrey M. Haddad
Portable force-measurement technologies are becoming increasingly popular tools to examine the maturation of postural motor milestones, such as sitting and standing, in infants. These convenient, low-cost devices provide numerous opportunities to characterize postural development outside of the laboratory. However, it is important to understand the unique challenges and technical limitations associated with collecting center of pressure (CoP) data using portable force-measurement technologies in infant populations. This study uses a mathematical model to examine issues that emerge when using portable force-measurement technologies to collect sitting and standing postural data in infants. The results of our mathematical simulations demonstrate that the CoP errors from portable force-measurement technologies depend on the posture examined (e.g., sitting vs. standing), the anthropometrics of the person (e.g., height and weight), the frequency of body sway, and the experimental setup (e.g., an additional support surface being placed on top of the device). Recommendations are provided for developmental researchers interested in adopting these technologies in infant populations.
Joshua J. Liddy, Amanda J. Arnold, HyeYoung Cho, Nathaniel L. Romine and Jeffrey M. Haddad
Holding an object has been found to reduce postural sway during quiet standing. However, people normally stand to accomplish suprapostural goals, such as fitting a key into a lock. Postural control should therefore be assessed by examining postural outcomes in the context of suprapostural task performance. This study assessed whether holding an object increased standing postural stability and improved the performance of a concurrent precision manual task. A total of 15 young adults performed a precision manual task with their dominant hand while holding or not holding an object in their nondominant hand. Postural stability was assessed using measures of postural sway and time to boundary. Suprapostural task performance was assessed as an error count. Holding did not influence postural sway or suprapostural task performance. Discrepancies among previous studies coupled with the present findings suggest that the effects of holding an object on standing posture are highly sensitive to the experimental context. The authors provide several explanations for their findings and discuss the limitations of previous suggestions that holding an object may have clinical relevance for balance-compromised populations.