Abstract
BackgroundIn the last decades, several powered ankle-foot orthoses have been developed to assist the ankle joint of their users during walking. Recent studies have shown that the effects of the assistance provided by powered ankle-foot orthoses depend on the assistive profile. In compliant actuators, the stiffness level influences the actuator’s performance. However, the effects of this parameter on the users has not been yet evaluated. The goal of this study is to assess the effects of the assistance provided by a variable stiffness ankle actuator on healthy young users. More specifically, the effect of different onset times of the push-off torque and different actuator’s stiffness levels has been investigated.MethodsEight healthy subjects walked with a unilateral powered ankle-foot orthosis in several assisted walking trials. The powered orthosis was actuated in the sagittal plane by a variable stiffness actuator. During the assisted walking trials, three different onset times of the push-off assistance and three different actuator’s stiffness levels were used. The metabolic cost of walking, lower limb muscles activation, joint kinematics, and gait parameters measured during different assisted walking trials were compared to the ones measured during normal walking and walking with the powered orthosis not providing assistance.ResultsThis study found trends for more compliant settings of the ankle actuator resulting in bigger reductions of the metabolic cost of walking and soleus muscle activation in the stance phase during assisted walking as compared to the unassisted walking trial. In addition to this, the study found that, among the tested onset times, the earlier ones showed a trend for bigger reductions of the activation of the soleus muscle during stance, while the later ones led to a bigger reduction in the metabolic cost of walking in the assisted walking trials as compared to the unassisted condition.ConclusionsThis study presents a first attempt to show that, together with the assistive torque profile, also the stiffness level of a compliant ankle actuator can influence the assistive performance of a powered ankle-foot orthosis.
Highlights
In the last decades, several powered ankle-foot orthoses have been developed to assist the ankle joint of their users during walking
This study evaluates the effects of a MACCEPAactuated unilateral Powered ankle-foot orthosis (PAFO), named Maccepa ankle powered orthosis (MAPO) (Maccepa Ankle Powered Orthosis) on the walking performance of healthy young users
Metabolic cost During the first minute of walking, the average net metabolic costs of the walking trials with the MAPO were from 10.3% to 14.3% higher than the one obtained during normal walking (NW) (Table 2 and Additional file 3)
Summary
Several powered ankle-foot orthoses have been developed to assist the ankle joint of their users during walking. Several PAFOs have been developed and tested to investigate their potential in reducing the biological effort of healthy users during assisted walking as compared to unassisted or normal walking [1,2,3,4,5], and to evaluate their performance when used as assistive or rehabilitation devices with weakened users such as the elderly [6, 7] and impaired subjects [8,9,10]. Several research groups have evaluated the effects of two of these assistive parameters, which are the push-off onset time [1, 3, 21, 23] and the plantarflexion assistance magnitude [1, 22, 24, 25] These studies assessed the effect that different values of these parameters have on the biological effort of healthy users during walking. As highlighted in [13], the determination of this formula is not straightforward due to the mutual influence of different parameters and to the fact that the results can be influenced by the different actuation setups and different protocols used in different studies
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