coupling between the brain and behavior. Developmental theory and neuroscience support this principle, but only recently has technology advanced sufficiently to allow us to begin testing these proposals. Thus, our goals for this paper are to 1. review briefly some classic motor patterns that emerge during
Ryota Nishiyori and Beverly D. Ulrich
Simon Wang and Stuart M. McGill
Spine stability is ensured through isometric coactivation of the torso muscles; however, these same muscles are used cyclically to assist ventilation. Our objective was to investigate this apparent paradoxical role (isometric contraction for stability or rhythmic contraction for ventilation) of some selected torso muscles that are involved in both ventilation and support of the spine. Eight, asymptomatic, male subjects provided data on low back moments, motion, muscle activation, and hand force. These data were input to an anatomically detailed, biologically driven model from which spine load and a lumbar spine stability index was obtained. Results revealed that subjects entrained their torso stabilization muscles to breathe during demanding ventilation tasks. Increases in lung volume and back extensor muscle activation coincided with increases in spine stability, whereas declines in spine stability were observed during periods of low lung inflation volume and simultaneously low levels of torso muscle activation. As a case study, aberrant ventilation motor patterns (poor muscle entrainment), seen in one subject, compromised spine stability. Those interested in rehabilitation of patients with lung compromise and concomitant back troubles would be assisted with knowledge of the mechanical links between ventilation during tasks that impose spine loading.
C. Buz Swanik, Scott M. Lephart, Frank P. Giannantonio and Freddie H. Fu
Anterior cruciate ligament (ACL) injury disrupts static and dynamic knee restraints, compromising functional stability. Deafferentation of ACL mechan-oreceptors alters the spinal reflex pathways to motor nerves and muscle spindles in addition to the cortical pathways for conscious and unconscious appreciation of proprioception and kinesthesia. These pathways are required by the feed-forward and feedback neuromuscular control systems to dynamically stabilize joints. Feed-forward motor control is responsible for preparatory muscle activity, while feedback motor control regulates reactive muscle activity. The level of muscle activation, preparatory or reactive, influences muscular stiffness, thereby providing dynamic restraint for the ACL-deficient athlete. Rehabilitation protocols should incorporate activities that enhance muscle stiffness while encouraging adaptations to peripheral afferents, spinal reflexes, and cortical motor patterns. Four elements crucial for reestablishing neuromuscular control and functional stability are proprioceptive and kinesthetic awareness, dynamic stability, preparatory and reactive muscle characteristics, and conscious and unconscious functional motor patterns.
Mark L. Latash, John P. Scholz and Gregor Schöner
Driven by recent empirical studies, we offer a new understanding of the degrees of freedom problem, and propose a refined concept of synergy as a neural organization that ensures a one-to-many mapping of variables providing for both stability of important performance variables and flexibility of motor patterns to deal with possible perturbations and/or secondary tasks. Empirical evidence is reviewed, including a discussion of the operationalization of stability/flexibility through the method of the uncontrolled manifold. We show how this concept establishes links between the various accounts for how movement is organized in redundant effector systems.
Theo Mulder, Rob den Otter and Baziel van Engelen
The flexibility of the human motor system is remarkable. Even when parts of the system are damaged, the output often remains optimal or near-optimal. The neuromotor system is designed to keep the output optimal by shifting between input sources. This capability is termed the principle of continuous adaptation. This article describes an experiment in which patients suffering from a hereditary motor and sensory neuropathy, type la (Charcot Marie Tooth disease, type la), had to perform fine motor movements. We examined whether they were able to regulate these movements in spite of the fact that the somatosensory input and motor output was substantially impaired as a result of the chronic, slowly progressing neuropathy. It was predicted that these patients were able to perform fine movements as long as the movements were well known and over-learned. Furthermore, it was predicted that these patients would compensate for the loss of somatosensory information by becoming more dependent on vision. A second prediction was that the quality of the motor performance would break down when these patients had to perform a novel motor pattern. The performance of the patients (n = 10) was contrasted with the performance of 20 healthy subjects. The results indicated that the patients, indeed, were able to perform the over-learned movements and that their performance deteriorated significantly when they had to perform a novel motor pattern. No indication, however, could be found for visual compensation.
Sydney Y. Schaefer, Stacey L. DeJong, Kendra M. Cherry and Catherine E. Lang
This study investigated whether grip type and/or task goal influenced reaching and grasping performance in poststroke hemiparesis. Sixteen adults with poststroke hemiparesis and twelve healthy adults reached to and grasped a cylindrical object using one of two grip types (3-finger or palmar) to achieve one of two task goals (hold or lift). Performance of the stroke group was characteristic of hemiparetic limb movement during reach-to-grasp, with more curved handpaths and slower velocities compared with the control group. These effects were present regardless of grip type or task goal. Other measures of reaching (reach time and reach velocity at object contact) and grasping (peak thumb-index finger aperture during the reach and peak grip force during the grasp) were differentially affected by grip type, task goal, or both, despite the presence of hemiparesis, providing new evidence that changes in motor patterns after stroke may occur to compensate for stroke-related motor impairment.
Brian Morin and Greg Reid
Previous descriptions of the motor performance of autistic persons have often confounded autism and mental retardation. Therefore, this study compared high functioning autistic individuals to functionally retarded subjects matched closely on chronological age and measured intelligence. Quantitative and qualitative scores for balance, throwing, catching, jumping, and running test items were obtained in a formal testing situation. Also, for autistic subjects, the relationship between qualitative performance on the formal test items and the quality of motor patterns elicited during guided play was determined. It was concluded that the selected test items generally represented reliable indices of the motor performance of autistic persons and that performance during formal testing essentially mirrored that of guided play. While there was some trend toward inferior qualitative scores by autistic individuals compared to their matched counterparts, there were no meaningful quantitative differences between the groups. It is possible that the poor motor performance associated with autism is largely a factor of mental retardation.
Alexander S. Aruin and Gil L. Almeida
The hypothesis that persons with Down syndrome are likely to trade mechanical efficacy of motor patterns for safety was tested in a study of postural adjustments associated with fast voluntary movements. Control subjects and subjects with Down syndrome performed bilateral shoulder flexion and extension movements “as fast as possible” while standing on a force platform. Anticipatory changes in the background activity of postural muscles were seen in both groups of subjects. Subjects with Down syndrome demonstrated simultaneous EMG bursts in postural “agonist-antagonist” pairs. Subjects with Down syndrome also demonstrated patterns of deviations in the major postural joints, suggesting that they were using a different strategy which may be a correlate of “clumsiness.” It was concluded that practice in conditions of changing components of a motor task is the most promising way to encourage the central nervous system of persons with Down syndrome to search for alternative strategies and improve these individuals' ability to solve everyday motor problems.
Sandy K. Beveridge and Sandy K. Gangstead
This study investigated the effects of teaching experience and instruction on visual retention and knowledge of selected sports skills. Prior to and after 30 hours of instruction, 31 experienced teachers and 29 undergraduates were administered the Utah Skills Analysis Test (USKAT) to assess both visual retention of performance and knowledge of correct motor patterns. Before instruction, teachers performed slightly better than undergraduates on the perceptual portion of USKAT, whereas there were no significant differences on the knowledge portion. A repeated measures analysis indicated significant treatment effects across groups on both perceptual and knowledge measures, with undergraduates exhibiting greater pretest to posttest gains than teachers on both dependent variables. A one-way ANOVA conducted on gain score data of subjects blocked into high, medium, and low functional performance levels based upon pretreatment scores revealed significant differences in perceptual performance between the blocks. It was concluded that (a) both teachers and undergraduates demonstrated the ability to improve performance in qualitative skills analysis, (b) undergraduates appear more responsive to specific instructional protocol than experienced teachers, and (c) entry level performance may influence the impact of the protocol on sport skill analysis performance.