Dynamics of human movement

The part of (bio)mechanics that studies the interaction of forces on the human skeletal system and its effect on the resulting movement is called rigid body dynamics. Some basic concepts are presented: A mathematical formulation to describe human movement and how this relates on the mechanical loads acting on the skeletal system. These equations of motion depend on the mechanical properties of the skeletal system, such as dimensions and mass distribution. It is applied to describe and analyze human gait

Ambulatory Assessment of Ankle and Foot Dynamics

Ground reaction force (GRF) measurement is important in the analysis of human body movements. The main drawback of the existing measurement systems is the restriction to a laboratory environment. This paper proposes an ambulatory system for assessing the dynamics of ankle and foot, which integrates the measurement of the GRF with the measurement of human body movement. The GRF and the center of pressure (CoP) are measured using two six-degrees-of-freedom force sensors mounted beneath the shoe. The movement of foot and lower leg is measured using three miniature inertial sensors, two rigidly attached to the shoe and one on the lower leg. The proposed system is validated using a force plate and an optical position measurement system as a reference. The results show good correspondence between both measurement systems, except for the ankle power estimation. The root mean square (RMS) difference of the magnitude of the GRF over 10 evaluated trials was (0.012 plusmn 0.001) N/N (mean plusmn standard deviation), being (1.1 plusmn 0.1)% of the maximal GRF magnitude. It should be noted that the forces, moments, and powers are normalized with respect to body weight. The CoP estimation using both methods shows good correspondence, as indicated by the RMS difference of (5.1 plusmn 0.7) mm, corresponding to (1.7 plusmn 0.3)% of the length of the shoe. The RMS difference between the magnitudes of the heel position estimates was calculated as (18 plusmn 6) mm, being (1.4 plusmn 0.5)% of the maximal magnitude. The ankle moment RMS difference was (0.004 plusmn 0.001) Nm/N, being (2.3 plusmn 0.5)% of the maximal magnitude. Finally, the RMS difference of the estimated power at the ankle was (0.02 plusmn 0.005) W/N, being (14 plusmn 5)% of the maximal power. This power difference is caused by an inaccurate estimation of the angular velocities using the optical reference measurement system, which is due to considering the foot as a single segment. The ambulatory system considers separat- - e heel and forefoot segments, thus allowing an additional foot moment and power to be estimated. Based on the results of this research, it is concluded that the combination of the instrumented shoe and inertial sensing is a promising tool for the assessment of the dynamics of foot and ankle in an ambulatory setting

Principle design of an energy efficient transfemoral prosthesis

In the pursuit of realizing an energy efficient transfemoral prosthetic, in this paper we present a preliminary study on a principle design. In particular, the design is based on the idea that the efficiency of the system can be realized by energetically coupling the knee and the ankle joints. In order to allow the energy transfer during the normal walking, we propose to introduce continuous controllable springs, which basically act as passive actuators

Is High-frequency stiffness a measure for the number of attached cross-bridges?

Muscle stiffness is an important property for movement control. Stiffness is a measure for the resistance against mechanical disturbances in muscular-skeletal systems. In general muscle stiffness is assumed to depend on the number of attached cross-bridges. It is not possible to measure this number in vivo or vitro. In experiments, high frequency perturbations are used to obtain a measurement of stiffness. In this paper a simulation study is presented concerning the correlation between the number of attached cross-bridges and high-frequency stiffness. A model based on the sliding-filament theory was used for the simulation of dynamic contractions. It is concluded that these two methods of muscle stiffness determination do not yield compatible results during lengthenin