A perturbation-based balance training program for older adults: study protocol for a randomised controlled trial

Abstract

Background: Previous research investigating exercise as a means of falls prevention in older adults has shown mixed results. Lack of specificity of the intervention may be an important factor contributing to negative results. Change-in-support (CIS) balance reactions, which involve very rapid stepping or grasping movements of the limbs, play a critical role in preventing falls; hence, a training program that improves ability to execute effective CIS reactions could potentially have a profound effect in reducing risk of falling. This paper describes: 1) the development of a perturbation-based balance training program that targets specific previously-reported age-related impairments in CIS reactions, and 2) a study protocol to evaluate the efficacy of this new training program.

Methods/design: The training program involves use of unpredictable, multi-directional moving-platform perturbations to evoke stepping and grasping reactions. Perturbation magnitude is gradually increased over the course of the 6-week program, and concurrent cognitive and movement tasks are included during later sessions. The program was developed in accordance with well-established principles of motor learning, such as individualisation, specificity, overload, adaptation-progression and variability. Specific goals are to reduce the frequency of multiple-step responses, reduce the frequency of collisions between the stepping foot and stance leg, and increase the speed of grasping reactions. A randomised control trial will be performed to evaluate the efficacy of the training program. A total of 30 community-dwelling older adults (age 64-80) with a recent history of instability or falling will be assigned to either the perturbation-based training or a control group (flexibility/relaxation training), using a stratified randomisation that controls for gender, age and baseline stepping/grasping performance. CIS reactions will be tested immediately before and after the six weeks of training, using platform perturbations as well as a distinctly different method of perturbation (waist pulls) in order to evaluate the generalisability of the training effects.

Discussion: This study will determine whether perturbation-based balance training can help to reverse specific age-related impairments in balance-recovery reactions. These results will help to guide the development of more effective falls prevention programs, which may ultimately lead to reduced health-care costs and enhanced mobility, independence and quality of life.

Figures

Figure 1

Control of lateral stability during forward and backward steps. Volitional steps are preceded by an anticipatory postural adjustment (APA) that acts to preserve lateral stability during the step by propelling the centre of mass toward the stance leg prior to lifting of the swing foot, thereby countering the tendency of the body to fall toward the unsupported side during the execution of the step (panel A). Conversely, APAs are typically absent or severely truncated during compensatory steps; as a result, the centre of mass falls toward the unsupported side of the body during the swing phase [the body weight (mg) creates a destabilising moment of force M = mg * d (panel B)]. In older adults, inability to arrest the lateral motion of the centre of mass during the landing phase of the initial forward or backward step often leads to one or more 'extra' steps in the lateral direction, whereas young adults typically respond with a single step (panel C).

Figure 2

Perturbation platform used during balance training. Photographs of the training platform, configured for training of: A. stepping reactions, and B. grasping reactions. The surface of the platform is controlled to move 30 cm either forward, backward, left or right by means of pneumatic cylinders; the perturbation magnitude (platform velocity and acceleration) is altered by changing the pressure of the air delivered to the cylinders. A dual-axis accelerometer measures the magnitude and timing of the platform acceleration. During grasping training, handrails (equipped with force-sensing resistors to provide information about the timing of the reactions) are mounted on the platform, on one or both sides of the subject. These handrails are positioned at varying heights (87–101 cm) and distances from the subject (37–42 cm from midline) to simulate variability in handrail placement in daily life. Foam blocks are used to prevent foot movement and promote reliance on grasping reactions. A safety harness is worn at all times during training. (Image used with the consent of the model.)

Figure 3

Method to deter crossover steps during training. Large foam blocks (indicated by the shaded areas) are placed in front of and behind the feet during the lateral-perturbation trials in the first two training sessions. Subjects cannot execute a crossover step because the foam prevents the swing foot from travelling or landing in front of or behind the stance foot (panel A). The training is intended to promote instead the use of a side-step sequence (panel B). Note that both of these step patterns involve an initial step with the foot that is unloaded as a result of the perturbation-induced body motion. The foam blocks also permit a lateral step with the loaded leg (panel C); however, this pattern of stepping tends to occur infrequently [22]. Note that panels A-C depict stepping responses evoked by rightward platform translation, which causes the subject to fall to the left; this motion of the body leads to an initial increase in the loading of the left foot and an unloading of the right foot (panel D). The natural tendency is to step with the unloaded leg.

Figure 4

Experimental set-up for testing of stepping and grasping reactions. Schematic drawing showing the experimental set-up for the balance testing (performed at baseline and after the six weeks of training). The platform is semi-enclosed, with walls to the front and sides of the subject; for illustration purposes, the left wall has been rendered semi-transparent. The motion platform is controlled by a motor (located underneath the surface) to move unpredictably in one of the four directions shown. The cable-pull system also delivers unpredictable perturbations in these four directions. Four cables are attached to the belt at the waist, and are routed via a system of pulleys to a weight-drop apparatus that is located behind the front wall of the platform (out of the view of the subject). Prior to each trial, the experimenter manually connects one of the four cables to the weight. An electromagnet is then used to initiate the weight drop. When the weight is dropped, the subject is pulled unpredictably in one of the four directions, depending on which cable is attached to the weight. Prior to perturbation onset, an equivalent amount of slack (~2–4 cm) in each cable is maintained via a locking mechanism; hence, subjects are free to sway to an equal extent in any direction and cannot detect which cable is attached to the weight. During the testing of grasping reactions, a handrail (not shown) is mounted to the right of the subject (25% of body height from midline; height of rail = 55% of body height) and foam blocks (40cm high) are placed around the feet to deter stepping (similar to Figure 2B).