Fig 1.
Overview of the components of the shoes and vibrating insole that apply mechanical vibration.
(A) The components of the shoes that apply the mechanical vibration to the soles of the feet. The main components are the vibrating insoles that contains the actuators that deliver mechanical vibration, a foam sole placed on top of the insoles to act as a shock absorber, and main body of the shoe that contains the connection pin and charging port to recharge battery. (B) The top and bottom view of the vibrating insoles. The top view shows the position of pair of actuators used to deliver the vibration to the metatarsal head (front actuators) and heel (rear actuators). The amplitude of the vibration is controlled independently for the two pairs of actuators, which allows users to apply the vibration to different areas of the foot with different amplitudes. The bottom view shows the position of the portable battery and the connection pin for the charging port of the shoes.
Fig 2.
Illustration of the process of detecting MTC.
MTC is obtained from the trajectory of the reflective marker attached to the first metatarsal in the vertical direction (MT1Z). The average MT1Z during the three-second standing is set as the baseline position of the toe. This average value is subtracted from the entire original MT1Z profile and the resulting profile is labeled as MT1Znorm. Each gait cycle of one leg is defined as the period from a heel-strike (HS) to the subsequent HS of the other leg. (The figure shows the example of one gait cycle defined to calculate MTC of the dominant foot.) The MT1Znorm during one gait cycle exhibits two peaks (green circles). MTC is defined as the lowest MT1Znorm between these two peaks (red circle).
Fig 3.
Changes in MTC distribution due to vibrations.
(A) and (B) show the means and standard error bars of the values of MTC height and variability of 17 participants, respectively, for the three vibration levels (No: no vibration, Sub: sub-threshold vibration, and Supra: supra-threshold vibration) and both feet. The triple and single asterisk indicate statistically significant difference; ***: p<0.001, and *:p<0.05, whereas NS indicates no statistically significant difference. The reduction in the variability with statistical significance is quantified as Δ (%), which is the ratio of the difference to the larger one.
Fig 4.
Changes in the lower limb joint angles at MTC due to vibrations.
(A-C) show the means and standard errors of the ankle, knee, and hip angles at MTC of 17 participants, respectively, for the three vibration levels (No: no vibration, Sub: sub-threshold vibration, and Supra: supra-threshold vibration) and both feet.
Fig 5.
Changes in the variability of lower limb joint angles at MTC due to vibrations.
(A-C) show the means and standard errors of the values of the ankle, knee, and hip angles variability at MTC of 17 participants, respectively, for the three vibration levels (No: no vibration, Sub: sub-threshold vibration, and Supra: supra-threshold vibration) and both feet. The double and single asterisk indicate statistically significant difference; **: p<0.01, and *: p<0.05.
Table 1.
Pearson’s correlation between minimum toe clearance (MTC) variability and the variability of lower limb joint angles.