Effects of physical guidance on short-term learning of walking on a narrow beam

Abstract

Physical guidance is often used in rehabilitation when teaching patients to re-learn movements. However, the effects of guidance on motor learning of complex skills, such as walking balance, are not clear. We tested four groups of healthy subjects that practiced walking on a narrow (1.27 cm) or wide (2.5 cm) treadmill-mounted balance beam, with or without physical guidance. Assistance was given by springs attached to a hip belt that applied restoring forces towards beam center. Subjects were evaluated while walking unassisted before and after training by calculating the number of times subjects stepped off of the beam per minute of successful walking on the beam (Failures per Minute). Subjects in Unassisted groups had greater performance improvements in walking balance from pre to post compared to subjects in Assisted groups. During training, Unassisted groups had more Failures per Minute than Assisted groups. Performance improvements were smaller in Narrow Beam groups than in Wide Beam groups. The Unassisted-Wide and Assisted-Narrow groups had similar Failures per Minute during training, but the Unassisted-Wide group had much greater performance gains after training. These results suggest that physical assistance can hinder motor learning of walking balance, assistance appears less detrimental for more difficult tasks, and task-specific dynamics are important to learning independent of error experience.

Introduction

Physical guidance, or force intended to reduce movement error, is often used during the rehabilitation of walking. Physical guidance may be given to a patient for a variety of reasons: to increase safety, to reduce fear, or to help complete a task that a patient may not otherwise be able to perform on their own. However, little is known about how using assistance affects motor learning of complex tasks such as walking balance. In the elderly, balance is commonly compromised, and most falls occur during walking, not standing [1], [2]. For this reason, it is important to understand how assistance affects learning of walking balance. With this understanding, more effective treatments can be designed for gait rehabilitation.

Studies on the effects of physical guidance on motor learning have varied results. Physical guidance is not helpful for learning simple movements in the upper extremity [3]. Guidance improved performance during practice trials but performance improvements were not present when the guidance was removed. One possible explanation is that physical guidance did not allow for error detection and correction. Error is a critical stimulus for driving motor learning [4], [5]. Another recent study examined a more complex movement and found slightly different results [6]. Subjects learned to trace a complex three-dimensional trajectory with the upper extremity using either robotic assistance or visual demonstration. The group that practiced with robotic assistance improved in performance but not any better than the group that used visual guidance alone [6]. In a task where subjects learned to bear weight on their legs asymmetrically, manual guidance provided little help [7].

In a more complex whole-body task (learning to use a ski simulator), subjects performed movements better when they practiced with ski poles for stabilizing guidance than without them [8]. The ski poles allowed the subjects to select the magnitude and timing of the assistive forces while maintaining focus on the task dynamics. Body-weight supported treadmill training, where patients are given manual assistance to move the lower extremities through the motions of walking, has been effective in helping subjects with neurological injury to re-learn how to walk [9], [10], [11], [12]. However, none of these studies had control groups where subjects practiced without assistance. These studies suggest that assistance is detrimental to learning easier tasks but may be helpful for more difficult tasks. Subjects performing very difficult tasks may benefit from using assistance because too many errors would not give the subject an appropriate example of the actual task [13].

The purpose of this study was to provide insight on the effects of physical guidance on short-term learning of walking balance and to explore if task difficulty alters those effects. We chose to study healthy subjects learning to walk on a narrow balance beam. Beam walking is similar to over ground walking, but is more challenging to dynamic balance because it exploits the lateral instability of walking [14]. We tested two groups of subjects that practiced walking on a 2.5 cm wide treadmill-mounted balance beam (Wide Beam) for 30 min, with or without lateral physical assistance at the hips. All subjects were evaluated on unassisted beam walking pre- and post-training. We hypothesized that subjects that received no assistance during training would have greater performance gains than subjects that received assistance. We based this hypothesis on the rationale that error drives motor learning [4], [5] and assistance tends to reduce errors. To explore the confounding effects of task difficulty on the relationship between physical assistance and learning balance, we tested two more groups of subjects (with and without assistance) on a narrower balance beam (1.27 cm-wide) (Narrow Beam). We hypothesized that the difference between performance gains in the unassisted and assisted groups would be smaller for the more difficult task (Narrow Beam) than the easier task (Wide Beam). This was based on the idea that if a task is too difficult, assistance would be helpful in producing examples of the desired task.