Elsevier

Gait & Posture

Volume 65, September 2018, Pages 1-7
Gait & Posture

Full length article
Walking combined with reach-to-grasp while crossing obstacles at different distances

https://doi.org/10.1016/j.gaitpost.2018.06.167Get rights and content

Highlights

  • The presence of the prehension task did not affect leading limb obstacle avoidance.

  • Prehension decreased the toe clearance for the obstacle located after dowel contact.

  • Reaching was unaffected by the increased level of difficulty of the walking task.

Abstract

Background

Obstacle avoidance and object prehension occur regularly in real-world environments (walking up/down steps and opening a door). However, it is not known how walking and prehension change when there is an increase in the level of difficulty of the walking task.

Research question

We investigated the changes in walking and reach-tograsp when performing these two motor skills concomitantly in the presence of an obstacle on the ground positioned in different locations in relation to the object-to-be-grasped.

Methods

Fifteen young adults walked and grasped a dowel placed on a support with the obstacle positioned at the step before (N-1), during (N) and after (N + 1) the prehension task.

Results

The prehension task did not affect leading limb obstacle negotiation. Toe clearance and maximum toe elevation were lesser at obstacle position N + 1 than at obstacle position N-1 when combining grasping and obstacle-crossing task for the trailing limb. Step width increased in the presence of the obstacle-crossing task independent of obstacle location. The correlation between foot position before the obstacle and toe clearance revealed that the addition of the prehension task disrupted the relationship between these variables for the trailing limb. Foot placement and limb elevation were unaffected by the prehension task. The reaching component was unaffected by the increased level of difficulty of the walking task. The grasping component was affected by the increased level of difficulty of the walking task, as the time to peak grip aperture occurred earlier in the presence of the obstacle at position N, and may indicate a cautious strategy to grasp the dowel successfully.

Significance

Our results showed that prospective control is affected after the prehension since the attention to grasping may have impaired the acquisition of visual information for planning the trailing limb elevation.

Introduction

Although prior studies have investigated walking and reach-to-grasp separately [1,2], these two skills are often performed concomitantly. We previously investigated these combined tasks and showed that changes in walking are dependent on manual task difficulty [3,4]. For the most difficult manual tasks, participants reduced step velocity and increased margins of stability [3,4] but did not change coordination necessary to implement the grasping while walking [5]. Moreover, reaching duration and peak grip aperture velocity decreased in the presence of walking [3,4].

It is currently not clear how this combined task is modulated when there is an increase in the level of difficulty of the walking task, such as during obstacle negotiation. Obstacle avoidance and object prehension occur regularly in real-world environments, such as walking up/down steps and opening a door. Locomotion requires an intermittent visual scanning of the environment to control foot placement before the obstacle and limb elevation to deal with an obstacle [[6], [7], [8], [9]]. As the control of obstacle crossing while walking and reach-to-grasp share similar neural areas that contribute to the planning and execution of these movements [10,11], the simultaneous control of both tasks may be affected and the behavioral changes in either walking or reach-to-grasp may capture this influence.

The obstacle avoidance depends on vision to pick up information about obstacle location and size [8,12]. The initial part of obstacle clearance for the leading limb (from toe-off to foot over the obstacle) is controlled in a feedforward manner, whereas the latter part (from maximum clearance to the ground) is controlled in an online feedback-based manner [8,13]. Different studies have shown that leading and trailing limbs are independently controlled [6,8,14]. The control of the trailing limb throughout the step over the obstacle is based on feedforward visual information acquired during the approach phase [8,14]. Then, what may happen with the control of obstacle crossing when visual attention is shared with the reach-to-grasp task? To investigate this issue, we positioned obstacles at the step before, during and after the reach-to-grasp task. When obstacle negotiation and reach-to-grasp are simultaneous, the need to share visual attention between these tasks may influence how these two movements are controlled. For obstacles located at both the step before and after the reach-to-grasp task there would be enough time to pick up visual information to appropriately control both walking and reach-to-grasp tasks without interference.

An accurate foot placement before the obstacle is important to allow enough time to flex the limb and clear the obstacle [7]. The existence of a correlation between toe-obstacle horizontal distance and toe clearance represents an association between the visual and other kinesthetic inputs for the control of limb elevation, particularly for the trailing limb for which control depends on visual information acquired during the approach phase and kinesthetic inputs from the leading limb during obstacle avoidance [8]. The presence of the reach-to-grasp task may disrupt this association and compromise obstacle avoidance.

We aimed to investigate the changes in walking and reach-to-grasp when these two motor skills were combined in the presence of an obstacle positioned in different locations in relation to the object-to-be-grasped. We hypothesized: (1) For the obstacle located at the step of the reach-to-grasp task, the leading limb obstacle-crossing variables would be affected by the grasping task, especially the online control component. For the obstacle located before and after the reach-to-grasp task, the obstacle-crossing variables would be unaffected because the grasping task should not influence the feedforward and online control mechanisms. (2) The trailing limb obstacle-crossing variables would be unaffected by the presence of the reach-to-grasp task for all obstacle locations. Although participants may rely more on an online control mechanism to control arm-hand configuration to grasp the object at the same time they are stepping over the obstacle, the control of the trailing limb is still predicted to occur on the basis of feedforward visual information acquired during the approach phase. (3) Both reaching and grasping components would be affected by the obstacle at the location of the reach-to-grasp task compared to the obstacle before and after because of the division of visual attention.

Section snippets

Participants

Fifteen healthy young adults participated in this study (26.7 ± 4.9 years; 1.73 ± 0.05 m; 74.2 ± 18.0 kg). Thirteen participants were right-handed and two were left-handed. The ethics committee of the University of Massachusetts Amherst approved all study procedures.

Procedures

We placed passive reflective markers on anatomical landmarks to define a 15-segment biomechanical model (Fig. 1), three markers for reaching and grasping analyses (thumbnail, right wrist and the index fingernail, Fig. 1), one marker

Leading limb

For the foot-obstacle horizontal distances, the MANOVA revealed only a main effect of obstacle position (Wilks’ λ = 0.22, F4,54 = 15.25, p ≤ 0.001). The univariate tests indicated this effect for the toe-obstacle (F2,28 = 40.45, p ≤ 0.001) and the obstacle-heel (F2,28 = 7.81, p ≤ 0.001) horizontal distances. Toe-obstacle horizontal distance was greater in obstacle positions N-1 and N than in obstacle position N + 1 (Table 1). Obstacle-heel horizontal distance was greater in obstacle position

Discussion

We investigated the changes in the combined task of walking and reach-to-grasp with an obstacle positioned at different locations in relation to the object-to-be-grasped. Our first hypothesis was partially confirmed since the leading limb obstacle-crossing gait variables were unaffected by the grasping task with the obstacle positioned in all three locations, and we expected to observe modifications only at step N. The second hypothesis was partially confirmed because while expecting no

Conclusion

The presence of the reach-to-grasp task did not affect leading limb obstacle avoidance. However, it affected trailing limb obstacle negotiation when walking with the obstacle located one step ahead of the reach-to-grasp task. Reach-to-grasp decreased the toe clearance for the trailing limb for the obstacle located after dowel prehension due to possibly a prioritization of the planning of the lead limb. The online and feedforward control mechanisms involved with walking adaptations to avoid

Conflict of interest

The authors have no conflict of interest to report.

Acknowledgments

The first author acknowledges the scholarship provided by the Federal Agency for Support and Evaluation of Graduate Education (CAPES/Brazil).

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