. We constructed a physiologically realistic model of a lower-limb, mammalian muscle spindle composed of mathematical elements closely related to the anatomical components found in the biological spindle. The spindle model incorporates three nonlinear intrafusal fiber models (bag 1 , bag 2 , and chain) that contribute variously to action potential generation of primary and secondary afferents. A single set of model parameters was optimized on a number of data sets collected from feline soleus muscle, accounting accurately for afferent activity during a variety of ramp, triangular, and sinusoidal stretches. We also incorporated the different temporal properties of fusimotor activation as observed in the twitchlike chain fibers versus the toniclike bag fibers. The model captures the spindle's behavior both in the absence of fusimotor stimulation and during activation of static or dynamic fusimotor efferents. In the case of simultaneous static and dynamic fusimotor efferent stimulation, we demonstrated the importance of including the experimentally observed effect of partial occlusion. The model was validated against data that originated from the cat's medial gastrocnemius muscle and were different from the data used for the parameter determination purposes. The validation record included recently published experiments in which fusimotor efferent and spindle afferent activities were recorded simultaneously during decerebrate locomotion in the cat. This model will be useful in understanding the role of the muscle spindle and its fusimotor control during both natural and pathological motor behavior. I N T R O D U C T I O NThe muscle spindle is a sense organ found in most vertebrate skeletal muscles. In a typical mammalian lower limb muscle, several tens (or even hundreds) of muscle spindles can be found lying in parallel with extrafusal fibers and experiencing length changes representative of muscle length changes (Barker 1962;Eldred et al. 1962). The spindle has been found to play a dominant role both in kinesthesia and in reflexive adjustments to perturbations (Hulliger 1984;Matthews 1981). Its sensory transducers (primary and secondary afferents) provide the CNS with information about the length and velocity of the muscle in which the spindle is embedded. The spindle provides the main source of proprioceptive feedback for spinal sensorimotor regulation and servocontrol. At the same time that the spindle supplies the CNS with afferent information, it also receives continuous control through specialized fusimotor efferents (static and dynamic fusimotor efferents) whose task is to shift the spindle's relative sensitivities over the wide range of lengths and velocities that occur in various natural tasks (Banks 1994;Matthews 1962).The spindle consists of three types of intrafusal muscle fibers: long nuclear bag 1 and bag 2 fibers and shorter chain fibers ( Fig. 1A) (Boyd et al. 1977). Typically, one bag 1 , one bag 2 , and about four to 11 chain fibers lie in parallel within a spindle (Boyd and Smith 1984). The bag 1 ...

We developed a physiologically realistic mathematical model of the Golgi tendon organ (GTO) whose elements correspond to anatomical features of the biological receptor. The mechanical interactions of these elements enable it to capture all salient aspects of GTO afferent behavior reported in the literature. The model accurately describes the GTO's static and dynamic responses to activation of single motor units whose muscle fibers insert into the GTO, including the different static and dynamic sensitivities that exist for different types of muscle fibers (S, FR, and FF). Furthermore, it captures the phenomena of self- and cross-adaptation wherein the GTO dynamic response during motor unit activation is reduced by prior activation of the same or a different motor unit, respectively. The model demonstrates various degrees of nonlinear summation of GTO responses resulting from simultaneous activation of multiple motor units. Similarly to the biological GTO, the model suggests that the activation of every additional motor unit to already active motor units that influence the receptor will have a progressively weaker incremental effect on the GTO afferent activity. Finally, the proportional relationship between the cross-adaptation and summation recorded for various pairs of motor units was captured by the model, but only by incorporating a particular type of occlusion between multiple transduction regions that were previously suggested. This occlusion mechanism is consistent with the anatomy of the afferent innervation and its arrangement with respect to the collagen strands inserting into the GTO.

Golgi tendon organs (GTOs) located in the skeletal muscles provide the central nervous system with information about muscle tension. The ensemble firing of all GTO receptors in the muscle has been hypothesized to represent a reliable measure of the whole muscle force but the precision and accuracy of that information are largely unknown because it is impossible to record activity simultaneously from all GTOs in a muscle. In this study, we combined a new mathematical model of force sampling and transduction in individual GTOs with various models of motor unit (MU) organization and recruitment simulating various normal, pathological and neural prosthetic conditions. Our study suggests that in the intact muscle the ensemble GTO activity accurately encodes force information according to a nonlinear, monotonic relationship that has its steepest slope for low force levels and tends to saturate at the highest force levels. The relationship between the aggregate GTO activity and whole muscle tension under some pathological conditions is similar to one seen in the intact muscle during rapidly modulated, phasic excitation of the motor pool (typical for many natural movements) but quite different when the muscle is activated slowly or held at a given force level. Substantial deviations were also observed during simulated functional electrical stimulation.

Purpose: The benefits of advanced hydraulic microprocessor controlled knee (MPK) joints have been well established and repeatedly confirmed. The Genium knee was introduced in 2011 containing an enhanced control concept including additional sensors and improved algorithms enabling a range of new functions for transfemoral amputees (TFAs). A systematic review was conducted to evaluate the effect of the Genium knee on ambulation, mobility, activities of daily living (ADLs) and quality of life compared to standard MPKs. Materials and Methods: The review was conducted according to PRISMA Guidelines and Recommendations of the State-of-Science Evidence Report Guidelines of the American Academy of Orthotists & Prosthetists. Results: Twelve articles were included in the review and reported primarily on active subjects (MFCL-3/4) transitioning from C-Leg to Genium knee systems. The overall validity of the evidence was medium to high with the exception of one article having low validity. Synthesis of biomechanical analyses concludes that gait during level walking, stairs and ramps is more physiological and symmetric following accommodation and use of the Genium in community ambulating TFAs. Further, sound side loading and compensatory motions are reduced. Transitioning from C-Leg to the Genium knee additionally resulted in significant improvements in mobility, quality of life and the performance in activities of daily living (ADLs). Conclusion: A high level of evidence was identified when assessing the ability of Genium to improve gait quality and safety and performance in ADLs. While individual studies report significant improvements in terms of quality of life and mobility, additional studies are needed to increase the evidence level. ä IMPLICATIONS FOR REHABILITATION Microprocessor controlled prosthetic knees (MPKs) are well-established devices to serve patients with transfemoral amputation. Studies conducted mostly with the C-Leg MPK show that such knees significantly increase patient safety, ambulation, mobility, performance in activities of daily living and quality of life. Genium MPK includes advanced features which enable a range of new functions and functional benefits to patients. Transitioning from conventional MPKs (i.e., C-Leg) to Genium MPK resulted in more physiological gait, more equally distributed loading between the prosthetic and sound limbs, as well as reduced compensatory movements on the sounds side. These outcomes could potentially reduce the long-term risks of secondary physical complications in prosthetic users (i.e., osteoarthritis, osteoporosis). Genium significantly improved mobility, performance in activities of daily living, and quality of life in the patients using a conventional MPK (C-Leg). Different functioning principles of the MPKs presently available are responsible for different performance levels the knees offer to users. The amount of clinical evidence is also knee-dependent, with the C-Leg knee being most extensively tested in clinical studies. This systematic review concludes that ...

Meridium was appreciated by amputees with a preference for natural walking and requirement to safely and comfortably negotiate uneven terrain and slopes. Clinical relevance Amputees preferring Meridium perceive benefits with safe, comfortable, and natural walking. While the perception of benefits regarding the negotiation of uneven terrain and slopes is very high, the correlation to product preference is moderate. Individual assessment and trial fitting might be essential to identify patients who benefit greatly.