Kinematics in Newly Walking Toddlers Does Not Depend Upon Postural Stability

Abstract

When a toddler starts to walk without support, gait kinematics and electromyographic (EMG) activity differ from those of older children and the body displays considerable oscillations due to poor equilibrium. Postural instability clearly affects motor patterns in adults, but does instability explain why toddlers walk with a different gait? Here we addressed this question by comparing kinematics and EMGs in toddlers performing their first independent steps with or without hand or trunk support. Hand support significantly improved postural stability and some general gait parameters, reducing percent of falls, step width, lateral hip deviations and trunk oscillations. However, the kinematic and EMG patterns were unaffected by increased postural stability. In particular, the co-variance of the angular motion of the lower limb segments, the pattern of bilateral coordination of the vertical movement of the two hip joints, high variability of the foot path, the elliptic or single peak trajectory of the foot in the swing phase, and characteristic EMG bursts at foot contact remained idiosyncratic of toddler locomotion. Instead the toddler pattern shared fundamental features with adult stepping in place, suggesting that toddlers implement a mixed locomotor strategy, combining forward progression with elements of stepping in place. Furthermore, gait kinematics remained basically unchanged until the occurrence of the first unsupported steps and rapidly matured thereafter. We conclude that idiosyncratic features in newly walking toddlers do not simply result from undeveloped balance control but may represent an innate kinematic template of stepping.

Development of human locomotion

“…Unsupported walking is jerky and variable, with poor balance over the single support leg (while swinging the contralateral leg), the arms raised above the waist (as balance poles), legs splayed wide apart, and short variable steps [5 , 25,[54][55][56][57][58][59]. Double support is relatively prolonged, while swing is brief.…”

“…It is often assumed that infants cannot walk independently until they achieve balance control, but it has been shown that step variability and several other gait parameters of toddlers remain unchanged even when balance is augmented with the help of a parent or experimenter hand [56]. Moreover, walking experience rather than chronological age explains improvement in performance [5 ].…”

Planar covariation of limb elevation angles during bipedal locomotion in common quails (Coturnix coturnix)

“…changes in the orientation of these segments with respect to the vertical axis, covary to form a regular loop within a single plane in three-dimensional space (Borghese et al, 1996;Bianchi et al, 1998;Grasso et al, 1998;Ivanenko et al, 2002;Ivanenko et al, 2005;Ivanenko et al, 2007;Ivanenko et al, 2008;Hicheur et al, 2006;Barliya et al, 2009;Dominici et al, 2010;Ogihara et al, 2012;Sylos-Labini et al, 2013). In humans, the plane can account for more than 99% of the total variance in the elevation angles (Borghese et al, 1996).…”

Planar covariation of limb elevation angles during bipedal walking in the Japanese macaque

“…It is well established that elevation angles of the thigh, shank and foot segments, or the orientation of these segments with respect to the vertical axis, are consistent across subjects in human bipedal walking, and the temporal changes of these segmental angles covary to form a regular loop within a single plane in three-dimensional space [1][2][3][4][5][6][7][8][9][10][11]. Such tight planar coupling of limb segment motions was also reported to be observed in postural control in cats [12] and quadrupedal walking in macaques [13].…”

“…However, what is unique about the planar law in human walking is that the constraint of planar covariation of the elevation angles is very strong and the plane could account for greater than 99 per cent of the total variance [1]. Since this planar law was first proposed by Borghese et al [1], many experimental and theoretical studies have attempted to clarify the origin and functional significance of this kinematic law in human locomotion [2][3][4][5][6][7][8][9][10][11].…”