While neuroscientists identify increasingly complex neural circuits that control animal and human gait, biomechanists find that locomotion requires little control if principles of legged mechanics are heeded that shape and exploit the dynamics of legged systems. Here, we show that muscle reflexes could be vital to link these two observations. We develop a model of human locomotion that is controlled by muscle reflexes which encode principles of legged mechanics. Equipped with this reflex control, we find this model to stabilize into a walking gait from its dynamic interplay with the ground, reproduce human walking dynamics and leg kinematics, tolerate ground disturbances, and adapt to slopes without parameter interventions. In addition, we find this model to predict some individual muscle activation patterns known from walking experiments. The results suggest not only that the interplay between mechanics and motor control is essential to human locomotion, but also that human motor output could for some muscles be dominated by neural circuits that encode principles of legged mechanics.

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A Muscle-Reflex Model That Encodes Principles of Legged Mechanics Produces Human Walking Dynamics and Muscle Activities

This paper presents a methodology for implementing natural language morphology in the functional language Haskell. The main idea behind is simple: instead of working with untyped regular expressions, which is the state of the art of morphology in computational linguistics, we use finite functions over hereditarily finite algebraic datatypes. The definitions of these datatypes and functions are the language-dependent part of the morphology. The language-independent part consists of an untyped dictionary format which is used for synthesis of word forms, and a decorated trie, which is used for analysis.Functional Morphology builds on ideas introduced by Huet in his computational linguistics toolkit Zen, which he has used to implement the morphology of Sanskrit. The goal has been to make it easy for linguists, who are not trained as functional programmers, to apply the ideas to new languages. As a proof of the productivity of the method, morphologies for Swedish, Italian, Russian, Spanish, and Latin have already been implemented using the library. The Latin morphology is used as a running example in this article.

Functional morphology

The purpose of this study was to compare surgical recommendations made by clinicians experienced in gait analysis when using information provided from the clinical examination and videotape, with recommendations made after the addition of kinematic, kinetic, and electromyographic (EMG) data. Ninety-one patients with a diagnosis of cerebral palsy were seen in the gait laboratory as part of the surgical decision-making process. Experienced clinicians reviewed video and clinical examination data for each patient and made surgical recommendations. Joint kinematics and kinetics and EMG data were then reviewed, and a second set of surgical recommendations was made. Comparisons between these recommendations showed that the addition of gait-analysis data resulted in changes in surgical recommendations in 52% of the patients, with an associated reduction in cost of surgery, not to mention the human impact of an inappropriate surgical decision, which is more likely without gait analysis. When changes in recommendations were made, an increase in surgical recommendations was observed for the gastrocnemius (59%) and rectus femoris (65%), whereas decreases were observed for the hamstrings (61%), psoas (78%), hip adductors (83%), femur (86%), and tibia (64%).

Alterations in surgical decision making in patients with cerebral palsy based on three-dimensional gait analysis

Stance phase stability and swing phase clearance, prerequisites for normal ambulation, often are lost in the gait of children with cerebral palsy. Lengthening of the hamstrings usually will improve stance-phase knee extension but will not greatly alter swing-phase knee flexion. This paper presents the outcome of transfer of the distal end of the rectus femoris in conjunction with hamstrings lengthening in 37 knees, and compares it with a control group of 24 knees in which only hamstrings lengthening was done. In the first group swing-phase knee flexion was improved by 16.0 +/- 14.4 degrees, compared to 9.5 +/- 7.5 degrees in the control group, and residual knee flexion in stance was reduced to 8.9 +/- 8.1 degrees, compared to 15.1 +/- 13.8 degrees in the controls. Poor outcome in the transfer-plus-lengthening group was associated mainly with foot rotation in excess of 8 degrees internally or externally, or postoperative knee flexion in stance. Criteria for selection of cases and methods of improving surgical outcome are discussed.

Rectus femoris transfer to improve knee function of children with cerebral palsy.

Hamstrings and psoas lengths during normal and crouch gait: Implications for muscle‐tendon surgery

Distal elongation of the hamstrings was performed for contracture due to neurogenic disorders in 66 patients. A follow-up study on 34 of the patients with cerebral palsy is reported here. The success of the operation was judged by functional evaluation including joint measurement and gait analysis. The advantages of this operation and the need for prolonged aftercare are discussed.

J U Baumann

Papers

Distal hamstring lengthening in cerebral palsy. An evaluation by gait analysis.