A Pilot Study to Evaluate the Relationships between Supine Proprioception Assessments and Upright Functional Mobility

Abstract

Long-duration bedrest impairs upright postural and locomotor control, prompting the need for assessment tools to predict the effects of deconditioning on post-bedrest outcome measures. We developed a tilt board mounted vertically with a horizontal air-bearing sled as a potential supine assessment tool for a future bedrest study. The purpose of this pilot study was to examine the association between supine proprioceptive assessments on the tilt board and upright functional mobility. Seventeen healthy participants completed variations of a supine tilt board task and an upright functional mobility task (FMT), which is an established obstacle avoidance course. During the supine tasks, participants lay on the air-bearing sled with axial loading toward the tilt board. Participants tilted the board to capture virtual targets on an overhead monitor during 30 s trials. The tasks included two dynamic tasks (i.e., double-leg stance matching mediolateral tilt targets over ±3° or ±9° ranges) and two static tasks (i.e., single-leg stance maintaining a central target position). The performances during the dynamic tasks were significantly correlated with the FMT time to completion. The dominant-leg static task performance showed a moderate trend with the FMT time to completion. The results indicate that supine proprioceptive assessments may be associated with upright ambulation performance, and thus, support the proposed application in bedrest studies.

Keywords: assessment; balance; bedrest; postural control; proprioception.

Figure 1

Functional mobility task (FMT). The participant (a) starts seated in a chair, and when prompted to start, (b) steps over 31 cm tall obstacles and under a horizontal bar hanging from the ceiling at shoulder height. (c) They weave through 4 vertical pylons and (d) press a button mounted on the wall. (e) They step over a 46 cm tall obstacle onto a surface of 10 cm thick medium-density foam and (f) press another button mounted on the wall. (g) They pass through a gate formed by two vertical pylons and (h) step over another set of 31 cm tall obstacles and under a hanging horizontal bar. (i) After stepping off of the foam floor, they turn right and pass between two hurdles to finish the task. The diagram is not to scale. Figure modified from [22].

Figure 2

The Gravity Bed. The Gravity Bed is used to allow for a proprioceptive challenge in a supine body orientation [14,15,16] and can be used in combination with the tilt board. The participant lays on a two-piece sled on air bearings, which allows for mediolateral movements (indicated with an arrow) with minimal friction. An axial body load toward the feet is provided by an adjustable weight and pulley system, which is attached to lateral carabiners on a harness worn by the participant.

Figure 3

The tilt board. The tilt board is proposed as a supine proprioceptive assessment tool. It includes (a) a balance board surface with positioning reference markings and (b) a passive balance board gimbal mechanism that allows for up to 20 degrees of tilt in the anterior–posterior (i.e., pitch) and mediolateral (i.e., roll) directions simultaneously, with instrumentation to record tilt angles to use in the visual feedback display. (c) Axes of rotation are displayed with the tilt board at a 0° position. (d) As an example of tilt board movement, the white arrow indicates a roll movement toward the right foot.

Figure 4

An overview of the assessment activities and experiment design. (a) The data collection session started and ended with an FMT trial, and the tilt board activities were presented in a sequence that became progressively more challenging. * The DY trials were alternated between the DY3° and DY9° until two trials were completed for each. ** The ST trials were alternated between the left and right foot until two trials were completed for each. (b–d) show photos of each assessment activity, including (b) the FMT, (c) double-leg stance for the two DY activities, and (d) single-leg stance for the ST. (e–g) show examples of tilt board performance feedback for each activity, as displayed on a computer monitor. A cursor was controlled by the tilt position of the board. The objective was to move the cursor toward a green target highlighted on the screen. The target locations varied across the 3 tilt board activity types used in this study, namely, the (e) DY3°, (f) DY9°, and (g) ST. Green markings indicate the possible locations of targets in each activity, including a range of possible target locations for the DY3° and DY9°, and one center target for the ST.

Figure 5

Spearman’s rank-order correlations comparing the relationship between the upright (i.e., the FMT) and supine assessments, namely, (left to right) the DY3°, DY9°, ST (dominant), and ST (non-dominant). The data show the average performance (across two trials) for each participant. Each plot shows a least squares reference line. The Spearman correlation coefficient is in the upper right corner of each plot, indicating the strength of the correlation. The DY9° was not performed by two participants. * = p < 0.05.

Figure 6

Spearman’s rank-order correlations comparing the relationship between the static and dynamic supine tilt board assessments. The data show the average performance (across two trials) for each participant. Each plot shows a least squares reference line. The Spearman correlation coefficient is in the lower right corner of each plot, indicating the strength of the correlation. The DY9° was not performed by two participants. * = p < 0.05.