Full length articleTransitioning from level surface to stairs in children with and without Down syndrome: Locomotor adjustments during stair ascent
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)
- et al.
Gait development during lifespan in subjects with Down syndrome
Res. Dev. Disabil.
(2011) - et al.
Modeling dynamic resource utilization in populations with unique constraints: preadolescents with and without Down syndrome
Hum. Mov. Sci.
(2004) - et al.
Obstacle crossing in 7–9-year-old children with Down syndrome
Res. Dev. Disabil.
(2016) - et al.
Location of minimum foot clearance on the shoe and with respect to the obstacle changes with locomotor task
J. Biomech.
(2013) - et al.
Stair walking transitions are an anticipation of the next stride
J. Electromyogr. Kinesiol.
(2011) - et al.
Biomechanical analyses of stair-climbing while dual-tasking
J. Biomech.
(2015) - et al.
Toe spatiotemporal differences between transition steps when ascending shorter flight stairways of different heights
Appl. Ergon.
(2017) - et al.
Kinetic patterns of treadmill walking in preadolescents with and without Down syndrome
Gait Posture
(2014) - et al.
Comparison and evaluation of two common methods to measure center of mass displacement in three dimensions during gait
Hum. Mov. Sci.
(2006) - et al.
Stair negotiation time in community-dwelling older adults: normative values and association with functional decline
Arch. Phys. Med. Rehabil.
(2011)