Difference in the running biomechanics between preschoolers and adults.

BACKGROUND: High vertical loading rate is associated with a variety of running-related musculoskeletal injuries. There is evidence supporting that non-rearfoot footstrike pattern, greater cadence, and shorter stride length may reduce the vertical loading rate. These features appear to be common among preschoolers, who seem to experience lower running injury incidence, leading to a debate whether adults should accordingly modify their running form. OBJECTIVE: This study sought to compare the running biomechanics between preschoolers and adults. METHODS: Ten preschoolers (4.2±1.6 years) and ten adults (35.1±9.5 years) were recruited and ran overground with their usual shoes at a self-selected speed. Vertical average (VALR) and vertical instantaneous loading rate (VILR) were calculated based on the kinetic data. Footstrike pattern and spatiotemporal parameters were collected using a motion capture system. RESULTS: There was no difference in normalized VALR (p=0.48), VILR (p=0.48), running speed (p=0.85), and footstrike pattern (p=0.29) between the two groups. Preschoolers demonstrated greater cadence (p<0.001) and shorter normalized stride length (p=0.01). CONCLUSION: By comparing the kinetic and kinematic parameters between children and adults, our findings do not support the notion that adults should modify their running biomechanics according to the running characteristics in preschoolers for a lower injury risk.

Preliminary evidence of an association between spontaneous kicking and learning in infants between 3-4 months of age.

BACKGROUND: The timing and coordination of infant kicking may allow for activities that facilitate learning and cognitive development. OBJECTIVE: This study examined spontaneous kicking and associations with changes in kicking during a learning paradigm in typically developing infants. METHODS: Ten healthy full-term infants participated in two experiments at 3 months of age: spontaneous kicking and the mobile paradigm. The inter-limb, intra-limb, and spatiotemporal parameters during spontaneous kicking were collected by 3D motion capture. Learning was measured in the mobile paradigm where an infant's leg was tethered to an overhead mobile. The mobile offered visual and auditory reinforcement when the infant kicked. Changes in kicking rate indicate learning. Friedman tests were used to determine the dominant inter-/intra-limb kicking patterns. Spearman's rank correlation coefficients were used to assess the correlations between spontaneous kicking and performance in the mobile paradigm. RESULTS: A significant negative correlation (r = -0.72, p = 0.03) was observed between the percentages of unilateral kicking and normalized kicking rate during the extinction phase of the paradigm. There was a trend of positive correlation (r = 0.58, p < 0.10) between dissociated hip-ankle joint coupling and the last three-minute of the acquisition phase of the paradigm. CONCLUSION: Exploratory kicking behaviors elicited by visual and auditory feedback may be related to lower extremity movement control. Enhancing movement experience through appropriate external feedback may be critical in treatment programs to support infant development. Future studies to assess how exploratory motor behaviors contribute to development in motor and other domains are warranted.

EMG breakthrough during cortical silent period in congenital hemiparesis: a descriptive case series.

BACKGROUND: The cortical silent period is a transient suppression of electromyographic activity after a transcranial magnetic stimulation pulse, attributed to spinal and supraspinal inhibitory mechanisms. Electromyographic breakthrough activity has been observed in healthy adults as a result of a spinal reflex response within the cortical silent period. OBJECTIVES: The objective of this case series is to report the ipsilesional and contralesional cortical silent period and the electromyographic breakthrough activity of 7 children with congenital hemiparesis. METHODS: TMS was delivered over the ipsilesional and contralesional primary motor cortices with resting motor threshold and cortical silent period measures recorded from first dorsal interosseous muscle. RESULTS: Seven children (13±2 years) were included. Ipsilesional and contralesional resting motor thresholds ranged from 49 to 80% and from 38 to 63% of maximum stimulator output, respectively. Ipsilesional (n=4) and contralesional (n=7) cortical silent period duration ranged from 49 to 206ms and 81 to 150ms, respectively. Electromyographic breakthrough activity was observed ipsilesionally in 3/4 (75%) and contralesionally in 3/7 (42.8%) participants. In the 3 children with ipsilesional breakthrough activity during the cortical silent period, all testing trials showed breakthrough. Contralesional breakthrough activity was observed in only one of the analyzable trials in each of those 3 participants. The mean peak amplitude of breakthrough activity ranged from 45 to 214µV (ipsilesional) and from 23 to 93µV (contralesional). CONCLUSION: Further research is warranted to understand the mechanisms and significance of electromyographic breakthrough activity within the cortical silent period in congenital hemiparesis. Understanding these mechanisms may lead to the design of tailored neuromodulation interventions for physical rehabilitation. TRIAL REGISTRATION: NCT02250092 (https://clinicaltrials.gov/ct2/show/NCT02250092).