In vivo estimation of the short-range stiffness of cross-bridges from joint rotation

Short-range stiffness (SRS) is a mechanical property of muscles that is characterized by a disproportionally high stiffness within a short length range during both lengthening and shortening movements. SRS is attributed to the cross-bridges and is beneficial for stabilizing a joint during, e.g., postural conditions. Thus far, SRS has been estimated mainly on isolated mammalian muscles. In this study we presented a method to estimate SRS in vivo in the human wrist joint. SRS was estimated at joint level in the angular domain (N m/rad) for both flexion and extension rotations of the human wrist in nine healthy subjects. Wrist rotations of 0.15 tad at 3 rad/s were imposed at eight levels of voluntary contraction ranging from 0 to 2.1 N m by means of a single axis manipulator. Flexion and extension SRS of the wrist joint was estimated consistently and accurately using a dynamic nonlinear model that was fitted onto the recorded wrist torque. SRS increased monotonically with torque in a way consistent with previous studies on isolated muscles. It is concluded that in vivo measurement of joint SRS represents the population of coupled cross-bridges in wrist flexor and extensor muscles. In its current form, the presented technique can be used for clinical applications in many neurological and muscular diseases where altered joint torque and (dissociated) joint stiffness are important clinical parameters. (C) 2010 Elsevier Ltd. All rights reserved.Rehabilitation MedicinePathofysiological analysis of movement disorders in relation to functio

Preliminary flight data from the Materials Exposure and Degredation Experiment (MEDET)

The Materials Exposure and Degradation Experiment (MEDET) was recently launched to the ISS on Space Shuttle Flight IE, as part of the EuTEF payload on the external payload facility of ESA's Columbus module. The experiment will operate in-orbit for at least 1.5 years, and has the overall objectives of evaluating the effects of the complex low Earth orbit space environment on material properties, investigating material degradation due to contamination, characterising the local ISS environment and measuring the local micro-particle flux. This paper gives a brief overview of the experiment function and the material samples which are being exposed, before presenting some of the early flight data. In this phase of the mission, all of the instruments are operating successfully, and continuously acquiring data. The preliminary results mainly concern the environmental sensors, which are operating at relatively high acquisition rates (e.g. one reading every few seconds). It has been shown that the docking of the Space Shuttle to the ISS has a significant effect on the local pressure environment. The more complex degradation experiments are acquiring at much slower rates (e.g. one reading per day) and several more months of space exposure will be required before sufficient data is generated to reach conclusions about the behaviour of the materials. However, preliminary data is presented. ©2009 American Institute of Physic

The validity and reliability of modelled neural and tissue properties of the ankle muscles in children with cerebral palsy

Spastic cerebral palsy (CP) is characterized by increased joint resistance, caused by a mix of increased tissue stiffness, as well as involuntary reflex and background muscle activity. These properties can be quantified using a neuromechanical model of the musculoskeletal complex and instrumented assessment. The construct validity of the neuromechanical parameters was examined (i.e. the internal model validity, effect of knee angle, speed and age, sensitivity to patients versus controls, spasticity severity and treatment), together with the repeatability. We included 38 children with CP and 35 controls. A motor driven footplate applied two slow (15°/s) and two fast (100°/s) rotations around the ankle joint, at two different knee angles. Ankle angle, torque and EMG of the gastrocnemius (GA), soleus (SO) and tibialis anterior (TA) muscle were used to optimize a nonlinear neuromuscular model. Outcome measures were tissue stiffness, reflex and background activity for GA, SO and TA. The internal model validity showed medium to high parameter confidence and good model fits. All parameter could discriminate between patients with CP and controls according to CP pathology. Other measures of external model validity (effect of test position, speed and age) showed behaviour along the lines of current knowledge of physiology. GA/SO background activity was sensitive to spasticity severity, but reflex activity was not. Preliminary data indicated that reflex activity was reduced after spasticity treatment. The between-trial and -day repeatability was moderate to good. The large variance between patients in the ratio of stiffness and neural resistance indicates that the method could potentially contribute to patient-specific treatment selection