Elsevier

Gait & Posture

Volume 63, June 2018, Pages 46-51
Gait & Posture

Full length article
Transitioning from level surface to stairs in children with and without Down syndrome: Locomotor adjustments during stair ascent

https://doi.org/10.1016/j.gaitpost.2018.04.025Get rights and content

Highlights

  • Children with DS stand longer and place the feet closer to the stairs before ascent.

  • Children with DS decrease vertical toe clearance with the increase of stair height.

  • Children with DS maintain horizontal toe velocity with the increase of stair height.

  • Children with DS show similar toe clearance when walking or climbing up the stairs.

  • External ankle load increases toe clearance more in children with DS than with TD.

Abstract

Background

Children with Down syndrome (DS) often show underdeveloped motor ability and adaptation. Stair ascent is a common task to examine locomotor function and external ankle load is often used to perturb the stability of a system and observe the emergence of new patterns.

Research question

How do stair height and external ankle load affect locomotor adjustments in 5-to-11-year-old children with typical development (TD) and with DS during stair ascent?

Methods

Fourteen children with DS and 14 age- and sex-matched children with TD participated in this study. They walked along a 5-m walkway and ascended 3-step staircases of different heights (low, moderate, and high) with or without ankle load. A 3D motion capture system was used for data collection. Dependent variables included stance time and toe-to-stair distance before stair ascent, and vertical toe clearance and horizontal toe velocity during stair ascent. Mixed ANOVAs with repeated measures were conducted for statistical analysis.

Results

The DS group presented a longer stance time and a shorter toe-to-stair distance than the TD group before stair ascent. External ankle load affected, to a greater extent, the DS group than the TD group in stance time and toe-to-stair distance. During stair ascent, while the TD group generally maintained toe clearance and decreased horizontal toe velocity with the increase of stair height, the DS group decreased toe clearance and maintained horizontal toe velocity. Particularly, the DS group displayed a greater toe clearance than the TD group in the LS condition but a smaller toe clearance in the HS condition. In addition, external ankle load increased toe clearance and decreased horizontal toe velocity in both groups.

Significance

Children with DS display underdeveloped locomotor adjustments during stair ascent. External ankle load appears to help the DS group regulate toe clearance and horizontal toe velocity for different stair heights.

Introduction

Down syndrome (DS) is the most common genetic condition [1]. Children with DS often show delayed motor development and modified gait patterns such as a slower walking speed and shorter but wider steps than their typically developing (TD) peers [2], [3]. They also demonstrate underdeveloped anticipatory locomotion adjustments (ALA) with little change in step length and a longer pause in front of an obstacle [4]. An obstacle or a staircase paradigm presents an ideal setting for understanding motor strategy and adaptation. According to the dynamic systems theory, certain patterns can be defined as “attractors” to accommodate different environments and/or motor tasks [5], [6]. Due to their underdeveloped motor ability, children with DS often select a more conservative strategy (i.e., crawling instead of walking) as their attractors [2], [7] and display a higher toe clearance when crossing obstacles [8]. In clinics settings, stairs are often used to assess the gross motor function of children with or without motor disabilities and to evaluate the effectiveness of physical therapy. Practically, stair negotiation has been associated with tripping and unintentional falls in every age group [9], [10]. However, few studies have been conducted in children with DS to understand their locomotor adjustments during stair ascent.

Different from obstacle crossing, stair ascent requires one to continuously lift himself up and constrain step length and foot placement. Further, cutaneous feedback from the feet before ascent may not be useful for the transition steps from level ground to stairs [11]. Consequently, adults often produce a higher toe clearance at the first transition step than the following steps [10], [12], [13]. Adults also display a greater horizontal toe velocity at the first transition step [14], making it difficult to regain balance if tripping occurs [10], [15]. Increasing stair height usually results in a reduction in horizontal toe velocity in adults, reducing the risk of tripping [13]. It is, however, not known if similar locomotor adjustments emerge in children with and without DS during stair ascent.

When studying motor adaptation, external load is often used to increase the moment of inertia of the lower extremities and consequently the difficulty of locomotor tasks. From the dynamic systems perspective, external load presents a mechanical perturbation to a system and allows for observation of the emergence of new motor patterns. Adding load above the ankles can result in greater leg muscular activity and higher energy cost in young adults during locomotion [16], [17]. Similarly, external ankle load can increase vertical propulsive impulse and general muscular activity in children with DS during treadmill walking [18], [19]. We have found that external ankle load can decrease step velocity and toe clearance, but increase step time and step width in children with TD and DS while approaching the stairs [20]. It is therefore logical to investigate how external ankle load affects locomotor adjustments during stair ascent in children with and without DS.

The purpose of this study was to examine the spatiotemporal parameters in children with and without DS while ascending stairs of different heights with and without external ankle load. Our first hypothesis was that compared to children with TD, children with DS would display a smaller toe-to-stair distance and a longer stance time before stair ascent. Adding ankle load would result in a decreased toe-to-stair distance and an increased stance time in children with DS. Our second hypothesis was that while walking up the stairs, children with DS would show a greater toe clearance but a slower horizontal toe velocity than their TD peers. Ankle load would increase toe clearance and decrease horizontal toe velocity in both groups. Our previous work shows that children with DS primarily choose a walking strategy to ascend the low stairs, but a crawling strategy for the high stairs [20]. Our third hypothesis was that the DS group would display a greater toe clearance and horizontal toe velocity when walking up compared to crawling up the stairs.

Section snippets

Participants

Fourteen children with DS and fourteen age- and sex-matched children with TD were recruited for the study. The inclusion criteria were that the participants were able to follow verbal instructions and walk 10 m without using assistive devices. The exclusion criteria included any previous or existing neurological disorders, musculoskeletal problems, uncorrected visual impairment, or any other medical conditions that prevented them from participating in this study. This study was approved by the

Ascent preparation

Both groups generally showed a longer stance time for the trailing foot than the leading foot (Fig. 1a and b). There was a group by load (F(1,23) = 18.21, p < 0.001), a group by foot (F(1,26) = 53.63, p < 0.001), and a load by stair (F(2,46) = 3.25, p = 0.048) interaction. Post-hoc analysis revealed that external ankle load increased stance time only in the DS group. The DS group displayed a longer stance time than the TD group across the two feet (TD: 0.96 s; DS: 2.42 s), a larger difference

Ascent preparation

Our first hypothesis was generally supported in that the DS group had a longer stance time and a shorter toe-to-stair distance than the TD group. Our results are consistent with previous studies that children with DS show delayed ALA than children with TD [20], [24]. Furthermore, our result of a constant toe-to-stair distance in the two groups regardless of stair heights is similar to previous findings such that the trailing foot is placed with a similar distance from obstacles of different

Acknowledgements

This research did not receive any specific grant from funding agencies in the public, commercial, or not-for-profit sectors. The authors are thankful to all the participants and their families for their participation in this study.

References (30)

  • S.L. Vimercati et al.

    Obstacle avoidance in Down syndrome

    J. Electromyogr. Kinesiol.

    (2013)
  • M. Petrarca et al.

    Stepping over obstacles of different heights: kinematic and kinetic strategies of leading limb in hemiplegic children

    Gait Posture

    (2006)
  • S.E. Parker et al.

    Updated national birth prevalence estimates for selected birth defects in the United States, 2004–2006

    Birth Defects Res. A Clin. Mol. Teratol.

    (2010)
  • N. Virji-Babul et al.

    Stepping over obstacles: anticipatory modifications in children with and without Down syndrome

    Exp. Brain Res.

    (2004)
  • E. Thelen et al.

    Hidden skills: a dynamic systems analysis of treadmill stepping during the first year

    Monogr. Soc. Res. Child Dev.

    (1991)
  • Cited by (0)

    View full text