Gait motor control: What happens after a sudden increase in height during adolescence?

Introduction: Gait motor control is a topic of well-known high relevance among the scientific community: its comprehension is indeed fundamental in order to understand what happens in pathologic and/or elderly subjects. The sudden increase in height that usually happens during adolescence can be an interesting environment for understanding how gait motor control works when, having reached a mature manifestation of gait [1], suddenly encounters peripheral constrictions (changes in segment lengths). It is indeed common to observe low gross motor coordination in this population: this could be due to sudden peripheral changes that adolescents have and that affect the output of the controller, which has been previously organized on different segment dimensions. Stability and variability indices [2] can be useful in detecting the manifestation of this lower coordination, i.e. indicating adolescents that undergo a sudden growth as less stable than their not grown peers. Moreover, these indices could give information about the direction/plane on which the motor control encounters more difficulties when sudden segment changes happen. The aim of the present study is to apply stability indices on trunk acceleration data collected during gait of a large group of adolescents. Data will be collected longitudinally in order to evaluate gait changes after height increases. Methods: 280 15-year-old adolescents were included in the study and will be followed longitudinally for one year. Present results are preliminary and regard 20 male subjects: 10 declared to have had a sudden increase in height during the previous three months (more than 3 cm) (Grown, 15 y, 72 ± 15 kg, 174 ± 6 cm) and other 10 not (NotGrown, 15 y, 70 ± 10 kg, 171 ± 6 cm). Measures of acceleration of the trunk (L5 level) were collected using one tri-axial wireless inertial sensor (OPALS, Apdm, USA) (sampling frequency, 128 Hz). The participants were asked to walk at self-selected speed back and forth four times in a 10 m long corridor in two conditions: free walking and walking performing a mental dual task (DT). For all the participants and each condition 30 strides were analyzed [3]: turns were excluded from the analysis. The following methods for quantifying gait stability were applied: stride time variability, Poincaré plots, harmonic ratio, short term Lyapunov exponents, maximum Floquet multipliers, recurrence quantification analysis and multiscale entropy [2]. An unpaired t-test (level of significance of 5%) was performed on the two groups for each method: t-test was right- or left-tailed hypothesizing higher stability in the NotGrown group. Results:t-Test results showed no differences between the two groups for stride time variability, Poincaré plots, harmonic ratio, short term Lyapunov exponents and maximum Floquet multipliers. Recurrence quantification analysis and multiscale entropy showed statistically significant results for the two groups in the DT condition when applied on the AP axis and indicated correctly the NotGrown as more stable than the Grown. Discussion: Preliminary results suggested that during normal walking no stability indices could discern between Grown and NotGrown adolescents. In DT condition, recurrence quantification analysis and multiscale entropy identified the Grown group as less stable than the NotGrown, suggesting that a focused attention to the task make the two groups not discernible, while, during DT, some manifestations of low coordination appeared. Moreover, the AP direction seemed to be the most sensitive to the differences between the two groups: further studies are needed in order to understand if this result is indicative of a focused direction of the motor control during gait. Present results are preliminary and are based on two different groups of adolescents, who declared whether they recently grew or not. More detailed and significant results will be obtained through the longitudinal study on the 280 adolescents included.