Characterization and intervention for upper extremity exploration & reaching behaviors in infancy.

This article aims to: 1) highlight general exploration, reaching, and object exploration behaviors as key activities of daily living in infancy, 2) describe how knowledge of early warning signs for these behaviors may improve early assessment, and 3) discuss interventions that may advance performance of these behaviors. Early intervention should focus on improving performance of these behaviors because: a) these early, interrelated upper extremity behaviors serve an integral role in global learning and development in infancy, b) among at-risk populations, differences have been observed in the quantity and quality of performance of these behaviors and, in many cases, these differences are associated with related perceptual-motor and cognitive delays. This article highlights how early assessment and intervention can target these key early behaviors in populations at risk for upper extremity disabilities, such as those born preterm, with Down syndrome, brachial plexus palsy, or arthrogryposis multiplex congentia.

Shoulder and elbow joint power differ as a general feature of vertical arm movements.

Consistent patterns of joint power underlie coordinated lower extremity behaviors such as running and walking. Recent work found that shoulder and elbow power consistently differed during reaching movements in the horizontal plane. Moreover, joint power during horizontal reaching appears correlated with motor cortical activity. It is not known if the feature of differential joint power extends to vertical plane reaches or to reaches of different movement conditions. The purpose of this study was to test for differential shoulder and elbow power during the acceleratory and deceleratory phases of fast and normal speed vertical reaches in sitting and supine positions. Our results suggest that shoulder and elbow power typically differed both within and across conditions. First, shoulder power values were positive or negative dependent largely on movement direction and movement phase. That is, for each direction and phase, the shoulder either generated or absorbed energy independent of speed or body position. Second, and unexpectedly, reaches of certain condition combinations had similar shoulder power magnitudes across directions. In contrast, elbow power values for each direction varied between positive and negative values depending on phase, speed and position, and no two condition combinations overlapped across directions. Third, as target direction, movement phase and body position varied, shoulder power at fast and normal speeds were linearly correlated, as was shoulder power in sitting and in supine. In contrast, elbow power was linearly correlated only between speeds. These results join other studies to suggest that the neuromotor control of the shoulder may be less complex as compared to the elbow as a general feature of reaching movements. This differential control has important implications for the study of reaching impairments in neurorehabilitation populations, and provides a potentially important variable in the study of cortical firing patterns.