Is CoM kinematics a descriptive parameter of gait motor development? Verification on children and adults

Research question: Is CoM kinematics a descriptive parameter of gait motor development? Could it be a leading factor during gait maturation? Introduction: Independent gait starts generally around age 1, when toddlers show a wide range of walking strategies [1]. As children grow, their gait pattern begins to approximate that of an adult: by age 3, most of the adult kinematic patterns are present, but gait maturation continues until age 6 [2]. Literature shows that variability of gait kinematic is higher in children than in adults [3]: thus, segmental kinematics has not been proved to be representative of gait development. The hypothesis of the present work is that the trajectory of the centre of mass (CoM) is a leading factor during gait maturation, allowing 4- and 6-year old children (4YC and 6YC) to reach steady state points in gait development, despite the shown variability: if this is true, the variability of CoM kinematic should be lower than that of other kinematic variables. Materials and methods: 7 4YC [4 ± 0 years, 101 ± 3 cm, 17 ± 2 kg], 7 6YC [6 ± 0 years, 121 ± 2 cm, 22 ± 1 kg] and 7 young adults [23 ± 1years, 157 ± 8 cm, 61 ± 7 kg] participated in the study. Coordination exercises were used for ensuring children's level of development. Each participant performed 3 times a 5-walk-test. 3D kinematic (SmartD, Bts, Italy) was collected using Plug-in-Gait protocol. One triaxial inertial sensor (Opal, Apdm, US) was positioned at CoM level. For each walking test, joint angles, CoM trajectory and CoM acceleration were obtained. Intra-test and inter-test coefficient of variation (std%) was calculated for each variable (respectively among the 5 walks of each test and among the repetitions of the 5-walk- test). Results: Joint angles results showed higher variability in children than in adults for both the intra-test and the inter-test conditions: e.g. children hip intra/extra rotation and ankle flexion/extension std% were 4 times greater than adults’ for 4YC and twice for 6YC. CoM trajectory in the inter-test condition showed similar std% for the 3 groups, while, in the intra-test, mediolateral (ML) std% was higher in both 4YC and 6YC (5 times for the ML axis and twice for vertical (V) and anteroposterior (AP) axes). In both intra-test and inter-test conditions, children CoM acceleration showed std% similar to adults’ for the AP and the V axis, while higher on the ML one. Discussion: Obtained results support the hypothesis that CoM trajectory is a leading factor during gait maturation and could be used as descriptive parameter: both 4YC and 6YC showed %std of CoM kinematics along the sagittal plane close to the adults’ one, while %std of joint angles was always higher. Moreover, present results suggest that control of gait is focused on the progression of the CoM and not on its lateral stabilization: children variability on the ML axis was always higher than adults’ one.