The Design and Simulation of a 16-Sensors Plantar Pressure Insole Layout for Different Applications: From Sports to Clinics, a Pilot Study

Could Proprioceptive Stimuli Change Saddle Pressure on Male Cyclists during Different Hand Positions? An Exploratory Study of the Effect of the Equistasi® Device

When pedaling, the excessive pressure on the seat has the potential to produce injuries and this can strongly affect sport performance. Recently, a large effort has been dedicated to the reduction of the pressure occurring at the saddle region. Our work aims to verify the possibility of modifying cyclists’ pedaling posture, and consequently the pressure on the saddle, by applying a proprioceptive stimulus. Equistasi® (Equistasi srl, Milano, Italy) is a wearable device that emits focal mechanical vibrations able to transform the body temperature into mechanical vibratory energy via the embedded nanotechnology. The data acquired through a pressure mapping system (GebioMized®) on 70 cyclists, with and without Equistasi®, were analyzed. Pedaling in three positions was recorded on a spin trainer: with hands on the top, hands on the drop handlebar, and hands on the lever. Average force, contact surface, and average and maximum pressure each in different regions of the saddle were analyzed, as well as integral pressure time and center of pressure. In the comparisons between hands positions, overall pressure and force variables were significantly lower in the drop-handlebar position at the rear saddle (p < 0.03) and higher in hand-on-lever and drop-handlebar positions at the front saddle (p < 0.01). When applying the Equistasi device, the contact surface was significantly larger in all hand positions (p < 0.05), suggesting that focal stimulation of the lumbar proprioceptive system can change cyclists’ posture.

Sensor number in simplified insole layouts and the validity of ground reaction forces during locomotion

Research attempted to validate simplified insoles with a reduced number of sensors to facilitate clinical application. However, the ideal sensor number is yet to be determined. The purpose was to investigate the validity of vertical ground reaction forces in various simplified pressure sensor insoles and to identify an optimal compromise between sensor number and measurement performance. A Kistler force plate (1000 Hz) and 99-sensor Pedar-X insole (100 Hz) obtained force data of 15 participants during walking and jogging. Eight simplified insole layouts (3-17 sensors) were simulated. Layout performances were expressed as Pearson's correlation coefficients (r) with force plate as reference and coefficient of variation. Differences were assessed via repeated-measures ANOVA as partial eta square (η p 2 ) at p < .05. All layouts correlated with the force plate (r = .70-.99, p < .01). All layout performances were higher in jogging than in walking by r = +.07 ± .04 (η p 2 =.28-.66, p < .05). The three- and five-sensor layouts yielded the lowest correlation (r = .70-.88) and the highest coefficient of variation (11-22%). Layout performances improved constantly from 7 to 11 sensors. The optimal compromise between simplification and measurement performance, quantified via change in correlation per sensor number, was found in the 11-sensor layout, recommendable for practical settings to improve monitoring and adjusting protocols.

A method for gait events detection based on low spatial resolution pressure insoles data

The accurate identification of initial and final foot contacts is a crucial prerequisite for obtaining a reliable estimation of spatio-temporal parameters of gait. Well-accepted gold standard techniques in this field are force platforms and instrumented walkways, which provide a direct measure of the foot-ground reaction forces. Nonetheless, these tools are expensive, non-portable and restrict the analysis to laboratory settings. Instrumented insoles with a reduced number of pressure sensing elements might overcome these limitations, but a suitable method for gait events identification has not been adopted yet. The aim of this paper was to present and validate a method aiming at filling such void, as applied to a system including two insoles with 16 pressure sensing elements (element area = 310 mm²), sampling at 100 Hz. Gait events were identified exploiting the sensor redundancy and a cluster-based strategy. The method was tested in the laboratory against force platforms on nine healthy subjects for a total of 801 initial and final contacts. Initial and final contacts were detected with low average errors of (about 20 ms and 10 ms, respectively). Similarly, the errors in estimating stance duration and step duration averaged 20 ms and <10 ms, respectively. By selecting appropriate thresholds, the method may be easily applied to other pressure insoles featuring similar requirements.