Effect of Ankle-Foot Orthosis Stiffness on Muscle Force During Gait Through Mechanical Testing and Gait Simulation

Abstract

Mechanical testing and gait measurement for ankle-foot orthosis (AFO) are crucial for determining the AFO stiffness magnitude in an individual. However, information on the effect of the stiffness magnitude on the muscle force during gait is limited. This study aimed to investigate the relationship between the AFO stiffness and ankle muscle force during gait. The AFO stiffness was mechanically tested using a sixaxis robot arm. The stiffness magnitude was adjusted using different spring constants. Five stiffness conditions were set for each plantarflexion resistive (PFR) and dorsiflexion resistive (DFR) function. The effect of the PFR and DFR on the ankle muscle force during gait were determined using musculoskeletal and AFO models. Tibialis anterior (TA) and triceps surae (TS) muscle forces were calculated through gait simulation. The angle-moment relationships display hysteresis loops for each condition. One of the PFR and DFR conditions differed significantly from the others (for all, p < 0.05). In order of lower stiffness, the each PFR contribution ratio to the peak TA muscle force normalized in the no-stiffness condition was 8.4%, 10.8%, 11.3%, 13.5%, and 15.3%; while the each DFR contribution ratio to the peak TS muscle force was 16.2%, 20.9%, 25.3%, 29.8%, and 30.5%, respectively. Through mechanical testing as well as gait simulation, it was demonstrated that the magnitude of the AFO stiffness decreased the required ankle muscle force during gait. This study can contribute to more effective gait rehabilitation using AFO as well as AFO fabrication with customized stiffness for individual gait function.

Modelling the interaction between wearable assistive devices and digital human models—A systematic review

“…The interaction of the WAD and the DHM is realized by a rigid connection ( Imamura et al, 2011 ; Ferrati et al, 2013 ; Lancini et al, 2016 ) resulting in no possible shift or rotation between the two partners. This connection is done by fixing one point of the device to one point of the model’s corresponding bone (e.g., in the MHM simulation software OpenSim ( Delp et al, 2007 ; Seth et al, 2011 ; Seth et al, 2018 ) this is done by a weldJoint ( Yamamoto et al, 2021 ) or via a constraint ( Ferrati et al, 2013 )) and thereby matching the device to the human’s anatomy (see Figure 3.2) ( Ferrati et al, 2013 ; Michaud et al, 2019 ; Yamamoto et al, 2021 ). Kruif et al (2017) even align the WAD to the model’s bones, in other words assumes the device to be integrated into the human kinematical system.…”

“… Kruif et al (2017) even align the WAD to the model’s bones, in other words assumes the device to be integrated into the human kinematical system. In this classification the effect of the inserted WAD is either determined by the set stiffness of the device resulting in a force being applied to the fixation points of device and model ( Ferrati et al, 2013 ; Tröster et al, 2020 ; Yamamoto et al, 2021 ) or by applying an external force or torque equally to group 1 ( Kruif et al, 2017 ; Yin et al, 2019 ; Gordon et al, 2022 ).…”

“…For example, trying to model the shown example of the orthosis ( Figure 3 - interaction type 2) in OpenSim by applying a weldJoint between both orthosis parts and the corresponding bone (shank and foot) and a rotational joint between both orthosis parts results in a non-viable kinematic chain. A solution could be the use of a constraint as replacement for one weldJoint as done by Kruif et al (2017) or by combining both parts with other modelling solutions than a joint ( Yamamoto et al, 2021 ). The suitable workaround depends essentially on the use case and WAD that should be modelled.…”

The Determination of Assistance-as-Needed Support by an Ankle–Foot Orthosis for Patients with Foot Drop

“…Studying the effects of orthoses on the human body with MHMs provides valuable insight into their functionality and can be used to optimize the design of the devices. So, the effects of orthosis properties, like stiffness, damping, etc., on the required lower leg muscle force [32][33][34], as well as the reduction in plantarflexor muscle load and metabolic energy consumption during hopping with the aid of ankle assistance [35], the effects of different ankle exoskeleton strategies for plantarflexor muscle energetics [36] or the predictions of walking cost reductions with ankle assistance [37], have already been investigated.…”