Dynamic postural control but not mechanical stability differs among those with and without chronic ankle instability.

The purpose of this investigation was to compare dynamic postural control and mechanical ankle stability among patients with and without chronic ankle instability (CAI) and controls. Seventy-two subjects were divided equally into three groups: uninjured controls, people with previous ankle injury but without CAI, and people with CAI. Subjects completed a single-leg hop-stabilization task, and then had an anterior drawer test and lateral ankle radiograph performed bilaterally. The dynamic postural stability index was calculated from the ground reaction forces of the single-leg hop-stabilization task. Ankle joint stiffness (N/m) was measured with an instrumented arthrometer during the anterior drawer test, and fibula position was assessed from the radiographic image. Patients with previous ankle injuries but without CAI demonstrated higher frontal plane dynamic postural stability scores than both the uninjured control and CAI groups (P<0.01). Patients with and without CAI had significantly higher sagittal plane dynamic postural stability scores (P<0.01) and increased ankle joint stiffness (P=0.045) relative to the control group. The increased frontal plane dynamic postural control may represent a component of a coping mechanism that limits recurrent sprains and the development of CAI. Mechanical stability alterations are speculated to result from the initial ankle trauma.

Differences in lower extremity alignment between males and females. Potential predisposing factors for knee injury.

AIM: The goal of this study was to compare measures of lower extremity alignment between males and females, which may account for gender differences in anterior cruciate ligament injury rates. Static lower extremity alignment has been implicated as predisposing individuals to anterior cruciate ligament injury and may vary between males and females. An initial step in identifying relevant risk factors for injury is to determine those factors that vary between genders. METHODS: Thirty male and 27 female college aged individuals with no history of lower extremity injury participated. Three indices of lower extremity alignment were measured on each subject: quadriceps angle, thigh foot angle, and subtalar joint range of motion ratio. RESULTS: Q-angles in females exceeded values for males by 4.4 degrees (p<0.001). Thigh foot angle for females was 3.6 degrees greater than for males (p=0.020). Subtalar joint movement ratio did not vary between genders (p=0.573). CONCLUSION: Previous research suggests that abnormal alignment may predispose individuals to anterior cruciate ligament injury. The present findings may help to explain the difference in anterior cruciate ligament injury rates between males and females. Any tangible links between lower extremity alignment and anterior cruciate ligament injury rates must be confirmed with prospective studies.

Stroke motor recovery: active neuromuscular stimulation and repetitive practice schedules.

OBJECTIVE: To investigate progress toward motor recovery in patients with chronic hemiparesis (mean time since stroke 3.2 years), comparing different types of practice schedules. DESIGN: To increase voluntary control of the upper extremity, active neuromuscular stimulation was administered during blocked and random practice schedules as patients performed three specific movements: wrist/finger extension, elbow joint extension, and shoulder joint abduction. METHODS: 34 stroke subjects volunteered to participate and were randomly assigned to one of three treatment groups: blocked practice (the same movement was repetitively performed on successive trials) combined with active neuromuscular stimulation; random practice (different movements on successive trials) along with active stimulation; or no active stimulation assistance control group. Subjects completed two days of 90 minute training for each of two weeks with at least 24 hours of rest between sessions. A session was three sets of 30 successful active neuromuscular stimulation trials with the three movements executed 10 times/set. RESULTS: Mixed design analyses on three categories of behavioural measures indicated motor improvements for the blocked and random practice/stimulation groups in comparison with the control group during the post-test period, with a larger number of blocks moved, faster premotor and motor reaction times, and less variability in the sustained muscular contraction task. CONCLUSIONS: Upper extremity rehabilitation intervention of active stimulation and blocked practice performed as well as stimulation/random practice. Moreover, these purposeful voluntary movement findings support and extend sensorimotor integration theory to both practice schedules.

Impact forces and neck muscle activity in heading by collegiate female soccer players.

Three soccer header types (shooting, clearing and passing) and two heading approaches (standing and jumping) were manipulated to quantify impact forces and neck muscle activity in elite female soccer players. The 15 participants were Division I intercollegiate soccer players. Impact forces were measured by a 15-sensor pressure array secured on the forehead. The electromyographic (EMG) activity of the left and right sternocleidomastoid and trapezius muscles was recorded using surface electrodes. Maximum impact forces and impulses as well as the EMG data were analysed with separate repeated-measures analyses of variance. Impact forces and impulses did not differ among the header types or approaches. Higher values were found for jumping versus standing headers in the mean normalized EMG for the right sternocleidomastoid. In addition, the integrated EMG was greater for the right sternocleidomastoid and right and left trapezius (P < 0.05). The sternocleidomastoid became active earlier than the trapezius and showed greater activity before ball contact. The trapezius became active just before ball contact and showed greater activity after ball contact. The increased muscle activity observed in the neck during the jumping approach appears to stabilize the connection between the head and body, thereby increasing the stability of the head-neck complex.

An insole pressure measurement system: repeatability of postural data.

This study analyzed the ability of an in-shoe plantar pressure measurement system to provide repeatable measurements of postural sway data for both healthy and clinical patients. Each participant's in-shoe pressure data were recorded for three trials during each test session during quiet stance. Healthy individuals (n = 9) participated on three consecutive days while clinical participants (n = 5) were tested on one day. Nine response variables were measured to assess their postural stability. Intrasubject measures were evaluated using the Kerlinger reliability procedure. Values provided directly by the Parotec System for a single day of testing yielded the following average coefficients: r = 0.95 (left), r = 0.97 (right) with mean coefficient values from the three day tests of: r = 0.98 (left), r = 0.98 (right). Variables calculated from raw data on a single day produced mean coefficients of: r = 0.77 (left), r = 0.76 (right) and over three days of: r = 0.65 (left), r = 0.66 (right). The ability to record highly reproducible data of postural sway parameters should assist clinicians to treat patients more confidently for balance deficiencies.

Practice as an intervention to improve speeded motor performance and motor learning in Parkinson's disease.

Individuals with Parkinson's disease have difficulty initiating and performing complex, sequential movements. Practice generally leads to faster initiation and execution of movements in healthy adults, however, whether practice similarly improves motor performance in patients with Parkinson's disease remains controversial. To assess the effects of practice on motor performance, patients with Parkinson's disease and control subjects practiced two, rapid arm-reaching tasks with different levels of movement complexity for 120 trials each over 2 days. Response programming was studied by analyzing the overall reaction time latency of each movement and its fractionated sub-components, premotor and motor time. Practice effects were investigated by comparing pretest performance to immediate and delayed retention test performances (10-min and 48-h rest intervals, respectively). Both patients with Parkinson's disease and control subjects improved speeded performance of sequential targeting tasks by practice and retained the improvement across both retention test intervals. Finding a learning effect for persons with Parkinson's disease supports practice as an effective rehabilitation strategy to improve motor performance of specific tasks for patients with Parkinson's disease.

Modeling surgical expertise for motor skill acquisition.

BACKGROUND: This work is part of an ongoing effort to introduce an innovative medical teaching technique to assist the efficient acquisition of surgical hand skills required to perform an inguinal hernia repair with a McVay technique. The purpose was to determine the effect of expert cognitive modeling, auditory elaboration, and split-screen video analysis on the surgical hand movements required while performing inguinal hernia surgery on cadavers. PURPOSE: Six surgical residents were videotaped performing a McVay procedure inguinal hernia in a pretest-posttest control group design. The experimental group received expert cognitive modeling, auditory elaboration, and split-screen analysis after the pretest. RESULTS: A distinct advantage for surgical instrument control and manipulation was found for the experimental group on the posttest surgeries. Less time was required to perform the operation, and more purposeful movements were exhibited by the experimental group. CONCLUSION: The treatment condition favored mindfulness learning of the McVay technique for an inguinal hernia repair.

Precision hypothesis and the end-state comfort effect.

Recently, motor control research has emphasized the planning of macroscopic aspects of control. In object manipulation studies, when participants complete a movement in a comfortable posture, an end-state comfort effect is attained. One explanation for this effect is the precision hypothesis, which states that precision increases when participants are in a comfortable position. This research directly tests the precision hypothesis in two experiments. In Experiment 1, participants picked up a dowel and touched a large or small target on a wall. For the second experiment, the same procedure was followed using a pinpoint target. The probability analyses of the first experiment indicated that the end-state comfort effect was magnified in the small target condition and that the point-of-change effect (Short and Cauraugh, 1997) appeared only when end-state comfort was magnified. Error analyses in Experiment 2 showed that participants were more accurate when in a more comfortable position. The present findings indicate that the precision hypothesis plays a significant role in the end-state comfort effect.

Verbal instructional sets to normalise the temporal and spatial gait variables in Parkinson's disease.

Gait in Parkinson's disease is characterised by slowed velocity; shuffling, small steps; and absent arm swing. Drug therapy intervention is beneficial in improving mobility, though with prolonged use its effects may diminish. The purpose of this study was to examine whether Parkinsonian patients could improve their gait patterns in response to five instructional sets: natural walking; walking while deliberately swinging the arms; walking with large steps; fast walking; and walking while counting aloud. Eight subjects with idiopathic Parkinson's disease and eight age matched control subjects were tested using motion analysis. The findings indicated that parkinsonian patients followed the instructions which immediately altered a series of single walking variables. Simultaneously, automatically activated changes occurred in other gait variables producing more normal gait. The instructional set is a strategy which can aid normalisation of Parkinsonian gait although its benefits may depend on the stage of disease progression and the degree of attention to the instructions.

Planning macroscopic aspects of manual control: end-state comfort and point-of-change effects.

A recent emphasis in motor control research is the planning of macroscopic features and how variables such as efficiency and comfort influence the planning process. This paper extends the work by Rosenbaum and Jorgensen (1992) by further studying the end-state comfort effect. In the first experiment, participants picked up a dowel using an underhand or overhand grip and touched one end to a numbered target on the wall. The height of the #9 target was set at the height of participants' right shoulder. The second experiment involved awkwardness ratings. Participants touched the 14 targets with the dowel as well as with a small dumbbell and the comfort of the end position was rated on a seven-point scale. In the third experiment, participants moved a dumbbell to the targets in the same procedure as the first experiment. Overall, the probability analyses indicated that as the end-state comfort effect was magnified, the sequential effect vanished and a distinct point-of-change effect appeared. Optimization theory and the knowledge model readily explained the phenomena of the end-state comfort effect, the sequential effect, and the point-of-change effect. The present findings indicate that comfort has a powerful influence on the planning of motor performance.

Maximizing performance feedback effectiveness through videotape replay and a self-controlled learning environment.

This study was designed to examine whether participants who could control the schedule of performance feedback (KP) would learn differentially from those who received a rigid feedback schedule while learning a complex task. Participants (N = 48) were randomly assigned to self-controlled KP (SELF), summary KP (SUMMARY), yoked control (YOKE), or knowledge of results only (KR) conditions. Data collection consisted of an acquisition phase and a 4-day retention phase during which right-handed participants performed a left-handed ball throw. Overall, throwing form improved across trial blocks during acquisition, with the SUMMARY, SELF, and YOKE groups showing more improvement than the KR group. During retention, the SELF group retained a higher level of throwing form and accuracy in comparison to the other groups. Results suggest that when given the opportunity to control the feedback environment, learners require relatively less feedback to acquire skills and retain those skills at a level equivalent to or surpassing those who are given more feedback but receive it passively.

Focus of attention during motor skill performance.

The effect of strategy instruction on response time in a sequential keypressing task was compared during acquisition and retention. Specifically, this study determined the influence of: (1) an awareness strategy, (2) a non-awareness strategy, (3) a Five-Step Approach strategy and (4) a control condition. Sixty-four subjects completed 250 trials of nine sequential keypresses, and 50 trials of a dual task (keypresses and verbal report). Faster response times were found for the Five-Step Approach and non-awareness strategies during both acquisition and retention. Introducing beginners to strategies that are used by highly skilled performers facilitated response times.

Effects of traditional and reversed bandwidth knowledge of results on motor learning.

The effects of two types of bandwidth (BW) knowledge of results (KR) were investigated on the acquisition and immediate retention of a timing task. Traditional and reversed BW KR groups were compared with two yoked control groups. Forty-eight randomly assigned subjects completed 60 acquisition trials and 20 no-KR retention trials. Acquisition analysis indicated a greater timing accuracy for the traditional BW group in comparison to the reversed BW group. During retention, less absolute constant error was found for both BW groups than for their yoked controls. Absolute performance changes were analyzed to further differentiate the contributions of quantitative and qualitative KR available in both types of BW conditions. This analysis revealed a significant KR x Trial Type interaction. Reliable changes in performance were observed after quantitative trials for the traditional BW group, whereas for the reversed BW group, reliable changes were observed after qualitative trials. This reversed BW group finding, along with the retention accuracy findings, indicated that the qualitative information was used to learn the timing task.

The effect of frequency of kinetic feedback on learning an isometric force production task in nondisabled subjects.

BACKGROUND AND PURPOSE: The purpose of this study was to investigate the effects of kinetic feedback frequency and concurrent kinetic feedback on the performance and learning of an isometric force production task in young, nondisabled adults. SUBJECTS: Twenty-four nondisabled, right-hand-dominant adults (18 male, 6 female), aged 19 to 33 years (mean = 22.5, SD = 4.1), participated in this study. METHODS: Eight subjects in each of three kinetic feedback groups performed an isometric elbow extension task in an attempt to minimize error between their effort and a force template over a 5-second period. Feedback was provided (1) concurrently with and after each attempt (concurrent feedback), (2) after each attempt (100% feedback), or (3) after every other attempt (50% feedback). Immediate and delayed (48-hour) retention tests were performed without feedback. Separate analyses of variance for repeated measures were used to compare task error among the three feedback groups for acquisition, immediate retention, and delayed retention trials. RESULTS: A significant interaction was found during the acquisition trial blocks, but at each trial block, subjects in the concurrent feedback group exhibited less error than did the subjects in either the 50% or 100% feedback group during the acquisition trials. For the immediate retention test, the 50% and 100% feedback groups exhibited 58% and 39% less error, respectively, than did the concurrent group. For the delayed retention test, the 50% and 100% feedback groups exhibited 52% and 26% less error, respectively, than did the concurrent group. In the immediate and delayed retention tests, subjects in the 50% feedback group displayed less error (31% and 36%, respectively) than did the 100% feedback group. CONCLUSION AND DISCUSSION: When permanent changes in the performance of a motor task are desired, concurrent feedback about task performance may be less desirable than feedback that is provided after the task has been completed. In addition, when feedback was used after the task had been completed, a lower frequency of feedback resulted in more permanent changes in the subjects' ability to complete the task.

Speed-accuracy tradeoff during response preparation.

The speed-accuracy operating curve was investigated in a movement precuing two- or four-choice reaction time task. Four levels of response preferences were manipulated with subject instructions and postresponse information: (a) accuracy, (b) reaction time latency, (c) accuracy and reaction time latency, and (d) no preference. Eighty subjects completed 480 discrete keypressing responses with the index and middle fingers of both hands. The mixed design mean reaction time analysis indicated faster performances for the reaction time latency and the accuracy and reaction time latency groups than the no preference group. Additionally, the percent correct analysis revealed two significant interactions: (a) Trial Block x Precue x Response Preference, and (b) Delay x Precue x Hand Position. Overall, the present findings provide partial support for the speed-accuracy operating curve predictions. Caution is advised when drawing chronometric inferences based only on reaction time data or when response accuracies are extremely high.

Time needed to change the isometric force production of a response.

This study investigated the time needed to change a motor program that specified the elbow flexor muscles to gradually increase the isometric force production from 15% to 75% of one's maximum voluntary contraction (MVC). A double-stimulation paradigm was used with the restriction that subjects (N = 12) be at 15% of their MVC before the presentation of the first stimulus. Subjects reacted to the first stimulus (randomly presented) by gradually increasing their isometric force from 15% to 75% of their MVC and then reacted to the second stimulus by altering the force production in one of four ways: (a) increasing the force to the 75% level rapidly instead of gradually, (b) discontinuing the increase and maintaining the level of force attained, (c) discontinuing all force production, or (d) reversing the direction of force so that it is produced by the elbow extensors. The data revealed that more time was needed to increase the force rapidly than to perform any of the other three conditions.

Psychomotor decline can be described by discontinuities in response trajectories: comments on Vrtunski and Patterson (1985).

Five methodological and experimental design concerns are identified in Vrtunski and Patterson's (1985) article. The discussed concerns involved: (a) the use of misleading premotor segment terminology, (b) the uncertain status of the repeated measures sphericity assumptions, (c) mean calculations across unequal trials of the four levels of stimulus conditions, (d) improper selection of a main effect for post hoc analysis and discussion of these results when a significant interaction was present, and (e) conflicting text and table values. These concerns have prompted us to question their psychomotor decline conclusions. And unless Vrtunski and Patterson can convince us that these concerns are unjustified, we have no choice but to doubt seriously the validity of their conclusions.

Proprioceptive feedback as a mediator in interlimb timing.

Prior findings regarded as evidence for proprioceptive feedback as a mediator in interlimb timing can also be interpreted as evidence for motor outflow because they came from research that had subjects make voluntary movements, and such movements allow for both feedback and outflow to operate. The present study was designed to resolve this controversy by determining if these findings could be replicated with passive movements which allow for feedback, but not outflow, to operate. The interlimb timing task studied was one where subjects made the timing response with their right hand while moving their left arm during the 1.5-sec interval to be timed. Three groups of 16 male college students performed 50 trials of the right-hand response with knowledge of results, under one of three left-arm conditions: (a) passive movement, (b) voluntary movement, and (c) no movement. The results indicated that the findings were replicated with passive movements and this was interpreted as support for the involvement of proprioceptive feedback in interlimb timing.