Abstract
As a whole, human sprinting seems to be a completely periodic and symmetrical motion. This view is changed when a person runs with a running-specific prosthesis after a unilateral amputation. The aim of our study is to investigate differences and similarities between unilateral below-knee amputee and non-amputee sprinters—especially with regard to whether asymmetry is a distracting factor for sprint performance. We established three-dimensional rigid multibody models of one unilateral transtibial amputee athlete and for reference purposes of three non-amputee athletes. They consist of 16 bodies (head, ipper, middle and lower trunk, upper and lower arms, hands, thighs, shanks and feet/running specific prosthesis) with 30 or 31 degrees of freedom (DOFs) for the amputee and the non-amputee athletes, respectively. Six DOFs are associated with the floating base, the remaining ones are rotational DOFs. The internal joints are equipped with torque actuators except for the prosthetic ankle joint. To model the spring-like properties of the prosthesis, the actuator is replaced by a linear spring-damper system. We consider a pair of steps which is modeled as a multiphase problem with each step consisting of a flight, touchdown and single-leg contact phase. Each phase is described by its own set of differential equations. By combining motion capture recordings with a least squares optimal control problem formulation including constraints, we reconstructed the dynamics of one sprinting trial for each athlete. The results show that even the non-amputee athletes showed less symmetrical sprinting than expected when examined on an individual level. Nevertheless, the asymmetry is much more pronounced in the amputee athlete. The amputee athlete applies larger torques in the arm and trunk joints to compensate the asymmetry and experiences a destabilizing influence of the trunk movement. Hence, the inter-limb asymmetry of the amputee has a significant effect on the control of the sprint movement and the maintenance of an upright body position.
Highlights
Running is a very natural movement: Even the first human beings had to use the strength of their legs to flee from dangerous animals, and already in ancient times people competed in races
We reconstructed the dynamics of three non-amputee and one amputee recorded sprinting trial using subjectspecific three-dimensional rigid multi-body system models with a least squares optimal control problem formulation from purely kinematic data without additional forceplate information
We reconstructed the three-dimensional dynamics of one unilateral transtibial amputee athlete and for reference purposes of three non-amputee athletes based on subjectspecific models and a least squares optimal control problem formulation
Summary
Running is a very natural movement: Even the first human beings had to use the strength of their legs to flee from dangerous animals, and already in ancient times people competed in races. It is, reasonable to assume that humans have optimized their running style over time, both for endurance running and for short sprints. There are comprehensive training recommendations for sprinters, the underlying criteria for optimal sprint performance are not precisely known It is not clear which combination of optimization criteria is minimized or maximized in (elite) sprinting. Sprint velocity is commonly defined as the product of step length and step frequency [1,2]
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