Changes in limb stiffness under conditions of mental stress

Treating the musician rather than the symptom: The holistic tools employed by current practices to attend to the non-motor problems of musicians with task-specific focal dystonia

Musicians Focal Dystonia (MFD) is a task-specific movement disorder affecting highly skilled musicians. The pathophysiology is poorly understood, and the available treatments are unable to fully and reliably rehabilitate the affected skill. Recently, the exclusively neurological nature of the condition has been questioned, and additional psychological, behavioral, and psychosocial contributing factors were identified. However, very little is known about how these factors influence the recovery process, and how, if at all, they are addressed in ongoing practices. For this study, 14 practitioners with substantial experience in working with musicians with MFD were interviewed about the elements in their approach which are directed at the cognition, emotions, attitudes, and behaviors of their patients and clients. A wide variety of tools were reported in three areas: (1) creating a supportive learning environment and addressing anxiety and perfectionism, (2) using body-oriented methods to optimize the playing behaviors and (3) consciously channeling the focus of attention to guide the physical retraining exercises and establishing new habits. The study also revealed that in-depth knowledge of the instrumental technique is profitable to retrain the impaired motor patterns. Therefore, the importance of including music educators in developing new therapeutic approaches will also be highlighted.

Assessing mental workload with wearable devices - Reliability and applicability of heart rate and motion measurements

Wearable devices are increasingly used for assessing physiological data. Industry 4.0 aims to achieve the real-time assessment of the workers' condition to adapt processes including the current mental workload. Mental workload can be assessed via physiological data. This paper researches the potential of wearable devices for mental workload assessment by utilizing heart rate and motion data collected with a smartwatch. A laboratory study was conducted with four levels of mental workload, ranging from none to high and during sitting and stepping activities. When sitting, a difference in the heart rate and motion data from the smartwatch was only found between no mental workload and any mental workload task. For the stepping condition, differences were found for the movement data. Based on these results, wearable devices could be useful in the future for detecting whether a mental demanding task is currently performed during low levels of physical activity.

Stress Tracker-Detecting Acute Stress From a Trackpad: Controlled Study

Background

Stress is a risk factor associated with physiological and mental health problems. Unobtrusive, continuous stress sensing would enable precision health monitoring and proactive interventions, but current sensing methods are often inconvenient, expensive, or suffer from limited adherence. Prior work has shown the possibility to detect acute stress using biomechanical models derived from passive logging of computer input devices.

Objective

Our objective is to detect acute stress from passive movement measurements of everyday interactions on a laptop trackpad: (1) click, (2) steer, and (3) drag and drop.

Methods

We built upon previous work, detecting acute stress through the biomechanical analyses of canonical computer mouse interactions and extended it to study similar interactions with the trackpad. A total of 18 participants carried out 40 trials each of three different types of movement—(1) click, (2) steer, and (3) drag and drop—under both relaxed and stressed conditions.

Results

The mean and SD of the contact area under the finger were higher when clicking trials were performed under stressed versus relaxed conditions (mean area: P=.009, effect size=0.76; SD area: P=.01, effect size=0.69). Further, our results show that as little as 4 clicks on a trackpad can be used to detect binary levels of acute stress (ie, whether it is present or not).

Conclusions

We present evidence that scalable, inexpensive, and unobtrusive stress sensing can be done via repurposing passive monitoring of computer trackpad usage.

Characterizing forearm muscle activity in university-aged males during dynamic radial-ulnar deviation of the wrist using a wrist robot

Functioning as wrist stabilizers, the wrist extensor muscles exhibit higher levels of muscle activity than the flexors in most distal upper-limb tasks. However, this finding has been derived mostly from isometric or wrist flexion-extension protocols, with little consideration for wrist dynamics or radial-ulnar wrist deviations. The purpose of this study was to assess forearm muscle activity during the execution of dynamic wrist radial-ulnar deviation in various forearm orientations (pronation/supination). In 12 healthy university-aged males, surface electromyography (EMG) was recorded from eight muscles of the dominant arm: flexor carpi radialis (FCR), flexor carpi ulnaris (FCU), flexor digitorum superficialis (FDS), extensor carpi radialis (ECR), extensor carpi ulnaris (ECU), extensor digitorum (ED), biceps brachii (BB) and triceps brachii (TB). While grasping a handle, participants performed dynamic radial-ulnar deviation using a three-degrees-of-freedom wrist manipulandum. The robotic device applied torque to the handle, in either a radial or ulnar direction, and in one of three forearm postures (30° supinated/neutral/30° pronated). Results indicated that forearm posture influenced the muscles acting upon the hand (FDS/ED), whereas movement phase (concentric-eccentric) and torque direction influenced nearly every muscle. The ECR demonstrated the greatest task-dependency of all forearm muscles, which is possibly reflective of forearm muscle lines of action. Co-contraction ratios were much higher in radial trials than ulnar (Radial: 1.20 ± 0.78, Ulnar: 0.28 ± 0.18, P < 0.05), suggesting greater FCU and ECU contribution to wrist joint stability in radial-ulnar movement. These findings highlight a greater complexity of wrist extensor function than has previously been reported in isometric work.

Sustained Isometric Wrist Flexion and Extension Maximal Voluntary Contractions Similarly Impair Hand-Tracking Accuracy in Young Adults Using a Wrist Robot

Due to their stabilizing role, the wrist extensor muscles demonstrate an earlier onset of performance fatigability and may impair movement accuracy more than the wrist flexors. However, minimal fatigue research has been conducted at the wrist. Thus, the purpose of this study was to examine how sustained isometric contractions of the wrist extensors/flexors influence hand-tracking accuracy. While gripping the handle of a three-degrees-of-freedom wrist manipulandum, 12 male participants tracked a 2:3 Lissajous curve (±32° wrist flexion/extension; ±18° radial/ulnar deviation). A blue, circular target moved about the trajectory and participants tracked the target with a yellow circle (corresponding to the handle's position). Five baseline tracking trials were performed prior to the fatiguing task. Participants then exerted either maximal wrist extension or flexion force (performed on separate days) against a force transducer until they were unable to maintain 25% of their pre-fatigue maximal voluntary contraction (MVC). Participants then performed 7 tracking trials from immediately post-fatigue to 10 min after. Performance fatigability was assessed using various metrics to account for errors in position-tracking, error tendencies, and movement smoothness. While there were no differences in tracking error between flexion/extension sessions, tracking error significantly increased immediately post-fatigue (Baseline: 1.40 ± 0.54°, Post-fatigue: 2.02 ± 0.51°, P < 0.05). However, error rapidly recovered, with no differences in error from baseline after 1-min post-fatigue. These findings demonstrate that sustained isometric extension/flexion contractions similarly impair tracking accuracy of the hand. This work serves as an important step to future research into workplace health and preventing injuries of the distal upper-limb.

Cognitive stress changes the attributes of the three heads of the triceps brachii during muscle fatigue

INTRODUCTION

Cognitive stress (CS) changes the peripheral attributes of a muscle, but its effect on multi-head muscles has not been investigated. The objective of the current research was to investigate the impact of CS on the three heads of the triceps brachii (TB) muscle.

METHODS

Twenty-five young and healthy university students performed a triceps push-down exercise at 45% one repetition maximum (1RM) with and without CS until task failure, and the rate of fatigue (ROF), endurance time (ET) and number of repetitions (NR) for both exercises were analyzed. In addition, the first and last six repetitions of each exercise were considered non-fatiguing (NF) and fatiguing (Fa), respectively, and the root mean square (RMS), mean power frequency (MPF) and median frequency (MDF) for each exercise repetition were evaluated.

RESULTS

The lateral and long head showed significant differences (P<0.05) in the ROF between the two exercises, and all the heads showed significant (P<0.05) differences in the RMS between the two exercises under NF conditions. Only the long head showed a significant difference (P<0.05) in the MPF and MDF between the two exercises. CS increases the ET (24.74%) and NR (27%) of the exercise. The three heads showed significant differences (P<0.05) in the RMS, MPF and MDF under all exercise conditions.

CONCLUSION

A lower ROF was obtained with CS. In addition, the RMS was found to be better approximator of CS, whereas MPF and MDF were more resistant to the effect of CS. The results showed that the three heads worked independently under all conditions, and the non-synergist and synergist head pairs showed similar behavior under Fa conditions. The findings from this study provide additional insights regarding the functioning of each TB head.

Force and electromyography responses during isometric force release of different rates and step-down magnitudes

This study investigated motor responses of force release during isometric elbow flexion by comparing effects of different ramp durations and step-down magnitudes. Twelve right-handed participants (age: 23.1 ± 1.1) performed trajectory tracking tasks. Participants were instructed to release their force from the reference magnitude (REF; 40% of maximal voluntary contraction force) to a step-down magnitude of 67% REF or 33% REF and maintain the released magnitude. Force release was guided by ramp durations of either 1 s or 5 s. Electromyography of the biceps brachii and triceps brachii was performed during the experimental task, and the co-contraction ratio was evaluated. Force output was recorded to evaluate the parameters of motor performance, such as force variability and overshoot ratio. Although a longer ramp duration of 5 s decreased the force variability and overshoot ratio than did shorter ramp duration of 1 s, higher perceived exertion and co-contraction ratio were followed. Force variability was greater when force was released to the step-down magnitude of 33% REF than that when the magnitude was 67% REF, however, the overshoot ratio showed opposite results. This study provided evidence proving that motor control strategies adopted for force release were affected by both duration and step-down magnitude. In particular, it implies that different control strategies are required according to the level of step-down magnitude with a relatively short ramp duration.

Effects of cognitive loading on lumbar flexion relaxation phenomenon in healthy people

[Purpose] The objective of this research was to examine the impact of cognitive load on the flexion relaxation phenomenon (FRP) during trunk flexion and return from flexion task. [Subjects and Methods] Twenty-two healthy subjects (18 males, 4 females) participated in the study. Each participant was exposed to 3 experimental conditions: no cognitive task, easy cognitive task and difficult cognitive task. Surface electromyography was used to measure lumbar erector spinae muscles activity level. Flexion relaxation ratio (FRR) was compared in order to assess the differences between the three experimental conditions during flexion and extension (FLX FRR and EXT FRR). [Results] The FRR was decreased with increase in cognitive difficulty; the difficult cognitive task was associated with significant lower value of FLX FRR in both sides. However, these changes were not significant in easy cognitive task. In addition, the EXT FRR was decreased in cognitive task conditions, but these results were not statistically significant except for difficult cognitive task condition in comparison to no cognitive task condition in left side. [Conclusion] These findings suggest that cognitive loading can affect FRP in healthy subjects.

Conscious Control Is Associated With Freezing of Mechanical Degrees of Freedom During Motor Learning

This study investigated whether conscious control is associated with freezing of mechanical degrees of freedom during motor learning. Participants practiced a throwing task using either error-strewn or error-reduced practice protocols, which encourage high or low levels of conscious control, respectively. After 24 hr, participants engaged in a series of delayed retention and transfer tests. Furthermore, propensity for conscious control was assessed using participants' ratings and freezing was gauged through movement variability of the throwing arm. Performance was defined by mean radial error. In the error-strewn group, propensity for conscious control was positively associated with both freezing and performance. In the error-reduced group, propensity for conscious control was negatively associated with performance, but not with freezing. These results suggest that conscious control is associated with freezing of mechanical degrees of freedom during motor learning.

Effects of mental fatigue on the development of physical fatigue: a neuroergonomic approach

OBJECTIVE

The present study used a neuroergonomic approach to examine the interaction of mental and physical fatigue by assessing prefrontal cortex activation during submaximal fatiguing handgrip exercises.

BACKGROUND

Mental fatigue is known to influence muscle function and motor performance, but its contribution to the development of voluntary physical fatigue is not well understood.

METHOD

A total of 12 participants performed separate physical (control) and physical and mental fatigue (concurrent) conditions at 30% of their maximal handgrip strength until exhaustion. Functional near infrared spectroscopy was employed to measure prefrontal cortex activation, whereas electromyography and joint steadiness were used simultaneously to quantify muscular effort.

RESULTS

Compared to the control condition, blood oxygenation in the bilateral prefrontal cortex was significantly lower during submaximal fatiguing contractions associated with mental fatigue at exhaustion, despite comparable muscular responses.

CONCLUSION

The findings suggest that interference in the prefrontal cortex may influence motor output during tasks that require both physical and cognitive processing.

APPLICATION

A neuroergonomic approach involving simultaneous monitoring of brain and body functions can provide critical information on fatigue development that may be overlooked during traditional fatigue assessments.

Muscle Contributions to Elbow Joint Rotational Stiffness in Preparation for Sudden External Arm Perturbations

Understanding joint stiffness and stability is beneficial for assessing injury risk. The purpose of this study was to examine joint rotational stiffness for individual muscles contributing to elbow joint stability. Fifteen male participants maintained combinations of three body orientations (standing, supine, sitting) and three hand preloads (no load, solid tube, fluid filled tube) while a device imposed a sudden elbow extension. Elbow angle and activity from nine muscles were inputs to a biomechanical model to determine relative contributions to elbow joint rotational stiffness, reported as percent of total stiffness. A body orientation by preload interaction was evident for most muscles (P< .001). Brachioradialis had the largest change in contribution while standing (no load, 18.5%; solid, 23.8%; fluid, 26.3%). Across trials, the greatest contributions were brachialis (30.4 ± 1.9%) and brachioradialis (21.7 ± 2.2%). Contributions from the forearm muscles and triceps were 5.5 ± 0.6% and 9.2 ± 1.9%, respectively. Contributions increased at time points closer to the perturbation (baseline to anticipatory), indicating increased neuromuscular response to resist rotation. This study quantified muscle contributions that resist elbow perturbations, found that forearm muscles contribute marginally and showed that orientation and preload should be considered when evaluating elbow joint stiffness and safety.

Neuroergonomics: a review of applications to physical and cognitive work

Neuroergonomics is an emerging science that is defined as the study of the human brain in relation to performance at work and in everyday settings. This paper provides a critical review of the neuroergonomic approach to evaluating physical and cognitive work, particularly in mobile settings. Neuroergonomics research employing mobile and immobile brain imaging techniques are discussed in the following areas of physical and cognitive work: (1) physical work parameters; (2) physical fatigue; (3) vigilance and mental fatigue; (4) training and neuroadaptive systems; and (5) assessment of concurrent physical and cognitive work. Finally, the integration of brain and body measurements in investigating workload and fatigue, in the context of mobile brain/body imaging ("MoBI"), is discussed.

Perceived distance during golf putting

This study examined the effect of anxiety states on the relationship between golf-putting distance and performance in an environment requiring high movement accuracy. Twenty-three amateur golfers attempted 15 putts at each of three putting distances, 1.25, 1.50, and 1.75m, under conditions characterized by both control demands and pressure. All attempts were recorded, and kinematic features were analyzed. Under conditions involving an audience and a monetary reward, the mean score on the State-Trait Anxiety Inventory Y-1 and the mean heart rate increased by 14 points and 11bpm, respectively. We grouped participants on an a posteriori basis using the median split. The backswing of high-anxiety performers shortened, the downswing speed declined, and the relative time to peak club-head velocity changed when putting under pressure from 1.25m. In contrast, no change in backswing or relative time to peak velocity was observed in low-anxiety performers, although impact velocity increased under this condition. These results indicate that the degree to which both low- and high-anxiety golfers were anxious about failure affected motor control at the 1.25-m distance, suggesting that a distortion in perceived distance may result from the interaction between putting distance and anxiety related to failure during golf putting.

The effects of workplace stressors on muscle activity in the neck-shoulder and forearm muscles during computer work: a systematic review and meta-analysis

Workplace stressors have been indicated to play a role in the development of neck and upper extremity pain possibly through an increase of sustained (low-level) muscle activity. The aim of this review was to study the effects of workplace stressors on muscle activity in the neck-shoulder and forearm muscles. An additional aim was to find out whether the muscles of the neck-shoulder and the forearm are affected differently by different types of workplace stressors. A systematic literature search was conducted on studies investigating the relation between simulated or realistic workplace stressors and neck-shoulder and forearm muscle activity. For studies meeting the inclusion criteria, a risk of bias assessment was performed and data were extracted for synthesis. Results were pooled when possible and otherwise described. Twenty-eight articles met the inclusion criteria, reporting data of 25 different studies. Except for one field study, all included studies were laboratory studies. Data of 19 articles could be included in the meta-analysis and revealed a statistically significant, medium increase in neck-shoulder and forearm muscle activity as a result of workplace stressors. In subgroup analyses, we found an equal effect of different stressor types (i.e. cognitive/emotional stress, work pace, and precision) on muscle activity in both body regions. In conclusion, simulated workplace stressors result in an increase in neck-shoulder and forearm muscle activity. No indications were found that different types of stressors affect these body regions differently. These conclusions are fully based on laboratory studies, since field studies on this topic are currently lacking.

Neural Correlates of Physical and Mental Fatigue

The purpose of this study was to determine the neural and muscular correlates of physical and mental fatigue. Twelve young and healthy participants (balanced by gender) performed three fatiguing conditions: 1) isometric handgrip task (HG) at 30% maximum voluntary contraction (MVC); 2) mental arithmetic (MA); and 3) combined handgrip and mental arithmetic (HG+MA). Prefrontal cortex activation, muscle activity, and task performance measures (force fluctuations and mental performance) were obtained continuously during the fatiguing conditions. Results indicated no significant difference in muscle activity and force fluctuations between the HG and HG+MA condition. Compared to the HG condition, an initial increase in the prefrontal cortex activation was observed during the HG+MA condition, with a subsequent decrease at exhaustion. Cortical activation during the MA condition was significantly lower than the other conditions across the entire duration of the fatiguing trial. Participants performed poorly with mental arithmetic during the HG+MA condition compared to the MA condition. The results suggest that the dynamic changes in the prefrontal cortex during the combined HG+MA condition, compared to the HG or MA condition, occur due to the interaction of physical and mental fatigue, which may have important implications for physical and cognitive performance.

The influence of audience and monetary reward on the putting kinematics of expert and novice golfers

We investigated changes in movement kinematics and attentional focus when expert and novice golfers performed a golf-putting task under pressure. Six male professional golfers and five male novice golfers performed 100 acquisition trials, followed by 10 trials in the pressure condition with a performance-contingent cash reward and small audience. After the 10 trials in the pressure condition, participants answered a questionnaire concerning attentional focus during both types of trial, including such aspects as conscious control of movements and the effects of distraction. A pressure manipulation check revealed a modest increase in physiological arousal, in that heart rate increased by about 10 bpm although state anxiety did not increase. A two-dimensional analysis of movement kinematics revealed that the amplitudes of arm and club movements decreased on the backswing in the pressure condition. Arm and club movement speed decreased on the foreswing in both experts and novices. Furthermore, neither experts nor novices changed their attentional focus in the pressure condition. Whereas previous studies of "choking under pressure" focused on attentional changes, the kinematic changes found in the present study were possibly caused by the influences of strategy modification and/or emotional response. Choking phenomena can be explained by attentional changes, along with the influences of strategy modification and/or emotional response under pressure.

The impact of stress factors in simulation-based laparoscopic training

BACKGROUND

This study aimed to quantify learner reactions manifesting from a realistic contextual stressor while training with a laparoscopic simulator, and to identify learner-derived stress-modifying behaviors. Stress factors are known to affect cognitive and psychomotor performance. Simulation-based medical training typically occurs in environments that are relatively stress free compared with the applied context. Training is most effective when it occurs in a highly faithful context, so the inclusion of typical clinical stressors in simulated laparoscopic learning environments may be beneficial.

METHODS

Preclinical medical students (N = 27) completed tasks using a laparoscopic simulator under the following 2 conditions: faculty direct observation (stressor) and unobserved (no stressor). The data included simulator performance, blood pressure, real-time heart rates, videotaped behavior, and pre/post surveys of latent anxiety and stress factors associated with participating in the research (eg, STAI 9).

RESULTS

Physiologic and behavioral manifestations of stress were observed for all participants during the stressor condition and during poor performance on simulator tasks. Stress was highest during periods of poor performance under the stressor condition. Focusing on the task itself mitigated stress reactions and improved performance on the simulator.

CONCLUSION

Stress reactions can be induced in a laboratory setting where simulation-based training occurs. Stressors imposed on the learner during simulation-based training may help support the acquisition of stress management skills that are necessary in the applied clinical setting. A ramped-up sequence of acquiring technical skills and clinical decision making, followed by stress management techniques, may lead to a more efficient transfer of learning from the simulated context to the clinical area.

Anxiety-induced changes in movement behaviour during the execution of a complex whole-body task

We investigated the impact of anxiety on movement behaviour during the execution of a complex perceptual-motor task. Masters' (1992) conscious processing hypothesis suggests that under pressure an inward focus of attention occurs, resulting in more conscious control of the movement execution of well-learned skills. The conscious processes interfere with automatic task execution hereby inducing performance decrements. Recent empirical support for the hypothesis has focused on the effects of pressure on end performance. It has not been tested so far whether the changes in performance are also accompanied by changes in movement execution that would be expected following Masters' hypothesis. In the current study we tested the effects of anxiety on climbing movements on a climbing wall. Two identical traverses at different heights on a climbing wall provided different anxiety conditions. In line with the conscious processing hypothesis we found that anxiety had a significant effect on participants' movement behaviour evidenced by increases in climbing time and the number of explorative movements (Experiments 1 and 2) and by longer grasping of the holds and slower movements (Experiment 2). These results provide additional support for the conscious processing hypothesis and insight into the relation between anxiety, performance, and movement behaviour.

Differential effects of mental load on proximal and distal arm muscle activity

Work-related upper extremity disorders (WRUEDs) that result from keyboarding tasks are prevalent and costly. Although the precise mechanisms causing the disorder are not yet fully understood, several risk factors have been proposed. These include the repetitive nature of the motor task and the associated sustained static working postures, but also more psychological factors such as mental load. Epidemiological surveys have shown that WRUEDs are more prone to develop in the postural muscles of the neck/shoulder area than in the executive muscles controlling the hand. The present study investigated whether the activation patterns of these two muscle types are differentially affected by an additional mental load during the performance of a repetitive tapping task. Participants tapped various keying patterns with their dominant index finger at two prescribed tempi. Mental load was manipulated by means of an auditory short-term memory task. We recorded the EMG activity of two neck/shoulder muscles (trapezius and deltoid), two upper arm muscles (biceps and triceps), and four forearm muscles (flexor digitorum superficialis, extensor digitorum, extensor carpi radialis longus and extensor carpi ulnaris) and analyzed the kinematics and impact forces of the index finger. The results confirmed that the upper limb has two functions. Specifically, activity of the executive distal musculature was increased during tapping at the higher pace, while the activity of the postural upper limb musculature was elevated due to the memory task. We argue that continuously increased muscular activity can lead to fatigue and thus eventually cause musculoskeletal complaints. The results are discussed with respect to biomechanical adaptation strategies that deal with the consequences of increased noise in the neuromotor system due to enhanced mental processing.

Muscular co-contraction covaries with task load to control the flow of motion in fine motor tasks

This study focuses on the relationship between movement-time fluctuations in fine motor tasks and changing levels of muscular co-contraction. Based on a recent neuromotor noise theory, we expected that increased task stress would increase muscular co-contraction and prolong movement times. Ten right-handed adults performed a graphic task, which elicited local movement-time prolongations. In half the trials, a distracting sound was presented as an external stressor. Besides pen-tip kinematics, two estimates of muscular co-contraction were obtained from the surface EMG measurements of eight arm and hand muscles. The results confirm the presumed co-variation of movement time and co-contraction. We conclude that muscular co-contraction forms a strategic means to adapt the flow of motion to central information processing demands.

Effects of arousal and natural baroreceptor activation on the human muscle stretch reflex

The nociceptive flexion reflex is inhibited during systole; this inhibition may be due to increased baroreceptor stimulation. It is yet to be determined whether other spinal reflexes are similarly modulated across the cardiac cycle. There is also evidence that stretch and tendon reflexes are facilitated by increased arousal. This study investigated the effects of phase of the cardiac cycle and arousal on the muscle stretch reflex components M1, M2, and M3. Stretch reflexes were elicited in leg muscles at six intervals across the cardiac cycle during rest, number repetition, and mental arithmetic. Mental arithmetic provoked increased cardiovascular arousal and facilitated both M1 and M2 compared to rest and number repetition. The stretch reflex did not vary with the phase of the cardiac cycle. While the stretch reflex is susceptible to arousal, natural baroreceptor-mediated modulation across the cardiac cycle may be specific to nociception.

Attending to the Execution of a Complex Sensorimotor Skill: Expertise Differences, Choking, and Slumps

A simulated baseball batting task was used to compare the relative effects of attending to extraneous information (tone frequency) and attending to skill execution (direction of bat movement) on performance and swing kinematics and to evaluate how these effects differ as a function of expertise. The extraneous dual task degraded batting performance in novices but had no significant effect on experts. The skill-focused dual task increased batting errors and movement variability for experts but had no significant effect on novices. For expert batters, accuracy in the skill-focused dual task was inversely related to the current level of performance. Expert batters were significantly more accurate in the skill-focused dual task when placed under pressure. These findings indicate that the attentional focus varies substantially across and within performers with different levels of expertise.

Patients suffering from nonspecific work-related upper extremity disorders exhibit insufficient movement strategies

The purpose of this research was to investigate whether patients experiencing nonspecific complaints of the forearm caused by sustained use of the personal computer exhibit deviant movement strategies as compared to healthy participants. Patients (N=10) and controls (N=24) performed a graphical aiming task combined with an auditory memory task. Force production (pen pressure), kinematic- and performance variables were recorded. During a trial, the control group gradually increased pen pressure from the stationary phases to the dynamic phase. The patients increased their pen pressure much more abruptly and to such a degree that the final pressure during real-time movement far exceeded that of the controls. Memory load led to a greater increase of pen pressure from the stationary phase to the dynamic phase in the patient group. Patients further displayed longer reaction times. The results are discussed within the framework of our recent theory on the role of neuromotor noise in the regulation of task performance under conditions of stress.

Myotonometer intra- and interrater reliabilities

OBJECTIVES

To assess the intra- and interrater reliabilities of the Myotonometer, a hand-held, computerized, electronic device that quantifies muscle stiffness (tone/compliance).

DESIGN

Reliability study.

SETTING

Research laboratory.

PARTICIPANTS

Thirty-five healthy, nondisabled adults (age range, 22-42 y).

INTERVENTIONS

Not applicable.

MAIN OUTCOME MEASURES

Two raters used the Myotonometer to evaluate subjects' lateral gastrocnemius and biceps brachii muscles. Muscles were measured in a relaxed state and during a voluntary isometric contraction. Coefficients were calculated for each muscle and each condition (relaxed, contracted). Results were analyzed by using Design II intraclass correlation coefficients.

RESULTS

Reliability coefficients were highest when the instrument exerted moderate to strong forces against the muscle (range, 0.50-2.00 kg; intrarater reliability R range, .84 - .99; interrater reliability R range, .75 - .96).

CONCLUSIONS

Myotonometer measurements had high to very high intra- and interrater reliabilities for measurements of the lateral gastrocnemius and biceps brachii muscles.

Freezing degrees of freedom under stress: kinematic evidence of constrained movement strategies

The present study investigated the effect of psychological stress imposed on movement kinematics in a computer-simulated batting task involving a backward and forward swing of the forearm. The psychological stress was imposed by a mild electric stimulus following poor performance. Fourteen participants hit a moving ball with a horizontal lever and aimed at a distant target with as much accuracy as possible. The kinematic characteristics appearing under stress were delay of movement initiation, small amplitude of movement and low variability of spatial kinematic events between trials. These features were also found in previous studies in which the experimental task required high accuracy. The characteristic kinematics evident in the present study suggested that the movement strategies adopted by the stressed participants were similar to those that appear under high accuracy demand. Moreover, a correlation analysis between the onset times of kinematic events revealed that temporally consistent movements were reproduced under stress. Taken together, the present findings demonstrated that, under psychological stress, movement strategies tend to shift toward the production of more constrained trajectories, as is seen under conditions of high accuracy demand, even though the difficulty of the task itself does not change.