Adaptation and evaluation of shoulder manipulator setup for assessing low extremity admittance and stiffness

Abstract

Fear of pain is a psychological consequence that can hinder an athlete’s ability to resume their previous level of performance or even return to their sport. A desire exists to examine the influence of fear of pain on both mechanical and neural factors involved in postural control, particularly focusing on the lower extremities. Previous literature shows associations between jump tests and fear of pain, but existing methods cannot differentiate between neural and mechanical factors, necessitating a different approach. Given the absence of a method to measure lower extremity reflexes and intrinsic properties similar to those observed in the shoulder, the original Proprio setup was adapted for leg perturbation to investigate its impact on lower extremity postural control. The adapted setup consists of a platform for participants to stand on, with coupling provided by a stiff ankle brace. A group of seven participants performed a slack trial and multiple stiff trials in both angled and neutral positions. Metrics such as admittance, stiffness, and coherence were calculated for each trial. The suitability of the setup was evaluated based on the selectivity of results across different trials and positions. Additionally, coherence was assessed, indicating the linearity which is necessary for future parameter identification. Notable differences in admittance and stiffness were observed between different legs and trials. This demonstrates the ability of the new setup around the Proprio to differentiate between various conditions. Comparisons with previous studies on shoulder dynamics showed similar findings, suggesting accurate measurement of leg dynamics. High coherence values indicated linearity, supporting the potential for future estimation of intrinsic parameters and reflex gains in leg dynamics. Considering these factors, the adapted Proprio setup appears suitable for analyzing lower extremity postural control. The next steps include expanding the participant group for significance and parameter identification, which will enable the investigation of the impact of fear of pain on intrinsic and reflexive properties using this setup.