Turning while walking is a common daily activity. Individuals with unilateral impairment frequently perform turns asymmetrically. The purpose of the study was to investigate the effect of a discomfort-inducing textured insole on symmetry of turning. Nine healthy individuals performed turns to the right while walking with no insole, immediately after the insole was inserted in the right shoe, and after walking for six minutes with the insole. The duration of turning, displacements of pelvic markers, and perceived level of discomfort were evaluated. Utilizing the insole was associated with the increased level of perceived discomfort (
Thirty-five to 45% of all steps during daily life activities are made during turning movements and up to 50% of steps accounted for turning indoors [
Previous studies examining the mechanisms underlying falls during turning in individuals with stroke demonstrated that these individuals exhibit delayed initiation of turns and longer time to turn and use more steps to perform the task [
However, no studies were conducted to evaluate the effect of a discomfort-inducing insole on symmetry of turning. Thus, the aim of the study was to investigate whether a single textured insole could alter the performance of the turning. We hypothesized that discomfort created by a textured insole will cause asymmetry of turning in healthy individuals. We also hypothesized that this asymmetry would be present after a short-term use of the textured insole.
Nine volunteers (age:
The subjects were required to wear standardized sandals with no insole and with a textured insole placed in the right sandal and perform turning while walking. Standard sandals were used based on foot size; sandals also had Velcro straps allowing adjustment. During the experiments, the subjects wore standardized socks (thickness 0.6 mm, MUJI, USA). The textured insole was made of polyurethane base 1 mm high (embedded with 3 mm height and 4.3 mm base pyramidal peaks with center to center distance of approximately 16 mm) (Figure
Textured insole inserted in the sandal.
Subjects were instructed to walk along paths delineated by lines marked on the floor of the laboratory and turn 90 degrees to the right when reaching the marked turning square (Figure
Schematic representation of the experimental set-up. The square denotes the area where the individuals took turn; turning part of the task is shown with two arrows indicating the moment of the toe-off during the second step and the toe-off during the fourth step. Step numbers are shown.
The assessments of turning were performed at three time points. Time point 1 (TP1) was when the subjects walked with no insole. Time Point 2 (TP2) was commenced immediately after the subjects were provided with the insole and given a one-minute period of familiarization, and Time Point 3 (TP3) assessment was commenced after 6 min of walking with the insole. In each experimental condition subjects started walking with their comfortable speed following an instruction “walk as comfortable as possible, as you walk in daily life.” To reach their comfortable speed subjects started walking 2 meters before and continued walking 2 meters after the turning event. Five turns were performed in each experimental condition. In each trial the experimenter provided the following commands: “ready,” “go,” and “relax.”
The perceived level of discomfort associated with using a textured insole was evaluated with a Visual Analog Scale (VAS) [
Three-dimensional kinematic data was collected using a six-camera VICON 612 system (Oxford Metrics, UK). Retroreflective markers were placed over anatomical landmarks bilaterally according to the Plug-In-Gait (PIG) model (Oxford Metrics), which includes the following: second metatarsal head, calcaneus, lateral malleolus, lateral epicondyle of the femur, a marker on the lateral border of the leg (between the lateral malleolus and femoral epicondyle markers), anterior/posterior superior iliac spines, a marker on the lateral border of the thigh (between the femoral epicondyle and anterior superior iliac spines), second metacarpal, lateral epicondyle of the humerus, acromioclavicular joint, and a marker on the lateral border of the arm (between the humeral epicondyle and the acromioclavicular joint markers). Also, subjects wore head and wrists bands with four and two markers attached on them, respectively. Finally, five additional markers were attached over the following landmarks: 7th cervical vertebra, 10th thoracic vertebra, inferior angle of the right scapula, between the two sternoclavicular joints, and xiphoid process of the sternum bone. Kinematic data was acquired at 100 Hz by means of the VICON 612 data station.
Trajectories of markers were derived from the VICON system. Initial processing of the kinematic data was done using the VICON software to detect the start and end points of each turning trial. MATLAB software (MathWorks, USA) was used for offline data processing. Kinematic analysis was focused on the analysis of the displacement of pelvic markers. It was reported in the literature that positions of the pelvic markers could represent the displacements of the center of mass (COM) of the body [
Symmetry indexes (SI) were calculated using the normalized values of the position of the LASI and RASI (frontal symmetry) and LPSI and RPSI (dorsal symmetry) and the following equation [
One-way repeated-measures ANOVAs were used to compare each outcome variable (the duration of turning, normalized displacement of markers, SI, and VAS) between the three experimental conditions (TP1, TP2, and TP3). Statistical analysis was performed in SPSS Version 22 (IBM, USA). Statistical difference was set at
Turning time. Significant difference (
Normalized displacements of the Left Anterior Superior Iliacus (LASI), Right Anterior Superior Iliacus (RASI), Left Posterior Superior Iliacus (LPSI), and Right Posterior Superior Iliacus (RPSI) pelvic markers are shown. Each column represents the difference between the vertical positions of the same marker measured at the beginning and end of the turning normalized by the duration of turn and leg length. Significant difference (
Symmetry indexes calculated for the frontal (anterior) and dorsal (posterior) parts of the body. Significant difference (
Visual Analog Scale (VAS) scores obtained from all the subjects at three time points. Significant difference (
The duration of the turning in no insole condition (TP1) was
The displacements of pelvic markers in the vertical plane are shown in Figure
Symmetry indexes (SI) for the frontal part of the pelvis were
Symmetry index (SI) for the dorsal part of pelvis was
Changes in the level of the perceived discomfort are presented in Figure
Discomfort induced on one side of the body could alter movement performance [
It was reported in the literature that individuals with stroke perform the turning task slower, spending more time to accomplish the turning, than the healthy controls [
There were some differences in the normalized displacements of pelvic markers in the vertical plane between the experimental conditions. For example, smaller displacements were observed when turning with the insole (TP2) as compared to turning with no insole (TP1); this could be due to the effect of discomfort induced by an insole, preventing a subject from shifting body weight to the right side while turning. On the other hand, the observed slight increase in the displacement of pelvic markers, especially LPSI, after walking with the insole for six minutes (TP3) could be because of the habituation to the induced discomfort. This possible explanation is in line with prior literature describing adaptation of the somatosensory receptors on the plantar surface of the foot in response to the constant tactile stimulus provided by the textured insole [
Placing a textured insole in the shoe of healthy individuals is associated with gait asymmetry [
The study participants reported increased level of discomfort while turning with the textured insole in the right shoe. The reported level of perceived discomfort was significantly higher when they were provided with the textured insole compared to the no insole condition. Thus, the results of the VAS tests suggest that the use of a textured insole was indeed associated with an increased level of perceived discomfort. At the same time, the subjects did not report any problems related to using the textured insole, which suggests that they tolerated the induced discomfort well. As such, this study outcome advocates for a possibility that individuals with unilateral impairment would be able to use the textured insole as well. Prior literature supports this assumption [
The study has several limitations. First, while the outcomes show that using a single textured insole induces asymmetry of turning in healthy individuals, the findings cannot be extrapolated to clinical populations. Second, the sample size was small and we did not compare the performance of healthy individuals with individuals with neurological disorders. Third, we studied only 90-degree turning to the right side and put the textured insole in the shoe on the dominant side. Future study should be conducted with a larger sample size and involve individuals with unilateral impairment performing turning in different directions.
The results of the study indicate that using a single textured insole induces significant changes in the symmetry of turning in healthy individuals. This outcome provides a basis for future investigations of the efficacy of the textured insole in minimizing asymmetry of turning in individuals with unilateral impairments such as stroke.
The authors declare that there are no conflicts of interest regarding the publication of this paper.
This work was supported in part by the American Heart Association Grant no. 14GRNT20150040 and UIC Proof of Concept (POC) grant. The authors would like to thank Simisola Oludare for help in the design of the experiments and data processing.