A longitudinal study to evaluate the development of independent walking in infants using inertial sensors: Preliminary results

Introduction: Many studies have been observing infants at the onset of walking in order to evaluate the development of different strategies and coordination [1–3]. These studies regard most of the times small groups (<10) and only few studies observed longitudinally the evolution of independent walking (on 2 or 5 subjects) [4,5]. To the author knowledge, these observations were always made using optoelectronic or video-based data. The use of wireless inertial sensors is more practical when aiming at the measurements of large populations. Moreover, inertial sensors can be worn under the clothes facilitating the experiments with infants who are not distracted by markers and can freely walk in any environment. The aim of the present study is to observe longitudinally a large group of infants using inertial sensors over a 6-month period after onset of independent walking (period in which the most dramatic changes of maturation of many gait parameters occurs [6]). This database will allow evaluating the changes in gait temporal parameters, postural stability and coordination at the beginning of independent walking. Methods: Twenty healthy infants (77 ± 2 cm, 9.3 ± 0.8 kg, 13 ± 2 months) were included in the study. All of the infants had no known developmental delays. The tests were scheduled once a month after the onset of independent walking for three months, and one after six months. When possible, a test was performed during the very first week of independent walking. Three tri-axial wireless inertial sensors (OPALS, Apdm, USA) were mounted on the lower back and on the right and left legs, respectively. The participants were asked to walk straight in the room. Heel-strike and toe-off instants were estimated from the angular velocity of the lower limbs [7]. Median stride (strT), swing (swT), stance (stanceT) and double support (dsT) times were calculated. Step-, stride-regularity (stepR and strR) and step symmetry (stepS) were evaluated using trunk vertical acceleration [8]. Up to now only five infants completed all the scheduled tests, thus the presented results are preliminary. Results: Up to now no significant trends were shown in the evaluated parameters even if, generally, the swT showed and increase with months of experience. In Table 1, median (and 25th-, 75th percentile) strT, swT, stanceT, dsT, stepR, strR, stepS, calculated on the five infants are shown for each tested period of gait maturation. Table 1. Median, 25th and 75th percentiles of evaluated gait parameters for each tested period of gait maturation. 1st week 1st month 2nd month 3rd month 6th month Median 25th perc 75th perc Median 25th perc 75th perc Median 25th perc 75th perc Median 25th perc 75th perc Median 25th perc 75th perc strT 0.81 0.75 1.06 0.71 0.65 0.72 0.68 0.66 0.71 0.71 0.71 0.75 0.75 0.67 0.79 swT 0.31 0.30 0.34 0.33 0.31 0.33 0.35 0.34 0.35 0.36 0.34 0.37 0.36 0.34 0.37 stanceT 0.42 0.41 0.70 0.38 0.33 0.39 0.34 0.32 0.37 0.38 0.34 0.38 0.39 0.32 0.42 dsT 0.35 0.35 0.35 0.33 0.33 0.34 0.34 0.33 0.35 0.35 0.34 0.37 0.38 0.37 0.38 stepR 0.48 0.31 0.50 0.34 0.33 0.38 0.26 0.21 0.33 0.39 0.28 0.41 0.36 0.33 0.39 strP 0.29 0.20 0.29 0.33 0.25 0.38 0.37 0.32 0.40 0.31 0.24 0.35 0.29 0.26 0.32 stepS 1.66 1.44 1.72 1.43 0.90 1.48 0.95 0.55 1.57 0.96 0.93 1.52 1.19 1.09 1.40 Discussion: The increased swT with months of experience evidenced the fear of falling of the infants during the beginning of independent walking. Gait regularity was low in all the infants, as expected. StepS is higher than 1, showing high symmetry but it is calculated as stepR/strideR, which values are close to 0, therefore it is not a reliable value.