Computational methods for the investigation of ski boots ergonomics

Three-dimensional dynamic homogenous modeling: The biomechanical influences of leg tissue stiffness on pressure performance of compression biomedical therapeutic textiles

Patient compliance and therapeutic precision of compression textiles (CTs) are frequently limited by the inaccurate pressure distributions along biological bodies in physical-based compression therapy. Therefore, the biomechanical influences of physiological tissue material characteristics of lower extremities on compression generations of CTs need to be explored systematically to improve pressure management efficacy. In this study, we developed three-dimensional (3D) homogenous finite element (FE) CT-leg systems to qualitatively compare the pressure diversities along lower limbs with different biomaterial tissue properties under each external compression level. Simultaneously, through the obtained leg circumferential displacement, a contact analysis model was applied to quantitatively explore the impact mechanisms of soft leg indentations on the pressure performance of CTs. Based on the experimental validation study, the proposed FE systems could be efficiently utilized for compression performance prediction (error ratio: 7.45%). Through the biomechanical simulation and theoretical calculations, the tissue stiffness characteristics of applied bodies showed significant correlations (p < 0.05) with the body circumferential displacements but no correlations (p > 0.05) with pressure delivery differences of CTs. This study facilitates the pressure fit design principle and leg mannequin material selection guidance for the development and experimental assessment of CTs. It also provides effective simulation methods for pressure prediction and property parametric optimization of compression materials.

Repeatability of a bending stiffness test for snowboarding wrist protectors

Snowboarding wrist protectors are typically designed to limit impact forces and prevent wrist hyperextension. The standard for snowboarding wrist protectors (ISO 20320:2020) includes a test for measuring their bending stiffness, when fitted to a wrist surrogate. This test serves as a simple means of assessing the ability of wrist protectors to prevent wrist hyperextension. Wrist protector bending stiffness measurements have been shown to be influenced by surrogate design, protector strapping condition, and surrogate surface compliance. Currently, there is a lack of knowledge on the repeatability of bending stiffness measurements, as previous studies have conducted tests during one session. This study investigated the repeatability of a bending stiffness test, by testing two snowboarding wrist protectors (short and long) on two wrist surrogates (compliant and stiff), under three protector strapping conditions (loose, moderate, tight), across three repeated test sessions. Test session had a significant effect (p < 0.05) on torque values, with a large effect size ($$\eta_{{\text{p}}}^{2}$$ η p 2  > 0.14), indicating the test had limited repeatability between test sessions. Despite this limited repeatability, torque values increased with both wrist angle and strap tightness, as reported before, indicating consistent trends in results. The outer surface compliance of the surrogate did not significantly affect the protector’s sensitivity to test session nor strapping condition.

Evaluating wrapping alpine ski boots during on-snow carving

Introduction

Alpine ski boots enable rapid and precise force transfer between skier and ski while carving. These boots are made of rigid plastic and fit tightly commonly through four buckles. Such a fit can improve speed and control but also pain and discomfort. In athletic footwear, alterations to the upper designed to wrap the foot improve performance during rapid changes of direction and during trail running. The purpose of this study was to systematically evaluate the performance and fit of two different ski boot shell closure mechanisms: a BOA closure and a Buckle closure.

Materials and methods

This was a two-part study with 22 subjects performing on-mountain skiing and 10 of those subjects completing an in-laboratory pressure evaluation. Subjects skied in both boots three times each while data from inertial measurement units (IMUs) and plantar pressures were collected along with subjective data. In lab, static dorsal and plantar pressures were collected while the subjects flexed into the boots.

Results

The BOA boots improved subjective and objective ski performance; qualitative carving scores were greater, likely through increasing the amount of normal force applied to the ski while turning. There were no differences in edge angles between the boots, as computed from IMUs. The BOA boot also reduced static peak plantar pressures in the rearfoot along with reducing overall static pressure on the dorsum as compared with the Buckle boot.

Conclusions

This is the first study to systematically evaluate differences in ski boot closures. The improvements in carving performance in the BOA boot are supported by distinct differences in pressure distribution within each boot, which we speculate contributed to improved performance by reducing discomfort or pain while still facilitating effective force transfer.