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

Some pressures are more equal than others: Effects of isolated pressure on performance

It is commonly assumed that performance is impaired by pressure and that different types of individual situational factors can produce equivalent pressure. Our aim was to explore the psychophysiological effects of pressure to test this assumption. Eighty-one novices completed a golf putting task under control and eight individual pressure conditions: time, difficulty, video, team, goal, fame, shame, and distraction. Performance was measured by the number of holed putts and ball-hole distance. Psychological, physiological and kinematic measures were collected. Performance was impaired by time and difficulty conditions but improved by team, goal and shame conditions compared to control. Perceived pressure and effort were higher than control in all conditions except distraction. Conscious processing was greater than control in all conditions except distraction and time constraint. Heart rate was faster with time, team, fame and shame. Heart rate variability and muscle activity were largely unaffected. Putter kinematics provided evidence of swing profiles slowing and/or becoming constrained in conditions where conscious processing increased, while the swing became faster in the time-pressure condition where conscious processing was decreased. Taken together, these results reveal heterogenous effects of pressure on performance, with performance impaired, unaffected, and improved by individual pressure situations. Similarly, heterogeneity characterized the effects of pressure on psychological, physiological and kinematic responses associated with task performance. In sum, the evidence challenges the standard tacit assumptions about the pressure-performance relationship in sport.

Neck Muscle Coactivation Response to Varied Levels of Mental Workload During Simulated Flight Tasks

OBJECTIVE

To evaluate neck muscle coactivation across different levels of mental workload during simulated flight tasks.

BACKGROUND

Neck pain (NP) is highly prevalent among military aviators. Given the complex nature within the flight environment, mental workload may be a risk factor for NP. This may induce higher levels of neck muscle coactivity, which over time may accelerate fatigue, increase neck discomfort, and affect flight task performance.

METHOD

Three counterbalanced mental workload conditions represented by simulated flight tasks modulated by interstimulus frequency and complexity were investigated using the Modifiable Multitasking Environment (ModME). The primary measure was a neck coactivation index to describe the neuromuscular effort of the neck muscles as a system. Additional measures included perceived workload (NASA TLX), subjective discomfort, and task performance. Participants (n = 60; 30M, 30F) performed three test conditions over 1 hr each while seated in a simulated seating environment.

RESULTS

Neck coactivation indices (CoA) and subjective neck discomfort corresponded with increasing level of mental workload. Average CoAs for low, medium, and high workloads were: .0278(SD = .0232), .0286(SD = .0231), and .0295(SD = .0228), respectively. NASA TLX mental, temporal, effort, and overall scores also increased with the level of mental workload assigned. For ModME task performance, the overall performance score, monitoring accuracy, and resource management accuracy decreased while reaction times increased with the increasing level of mental workload. Communication accuracy was lowest with the low mental workload but had higher reaction times relative to increasing workload.

CONCLUSION

Mental workload affects neck muscle coactivation during combinations of simulated flight tasks within a simulated helicopter seating environment.

APPLICATION

The results of this study provide insights into the physical response to mental workload. With increasing multisensory modalities within the work environment, these insights may assist the consideration of physical effects from cognitive factors.

[Combined influence of psychological and biomechanical factors in muscular loads in soccer : A new approach for the prevention of muscle injuries]

When mental stress and musculoskeletal loading interact, the risk for injury increases due to altered body kinematics and increased muscle tension. These changes can be detected with musculoskeletal models, and mental loading and stress must be analyzed at emotional, cognitive, and behavioral levels. To investigate these kinematic and loading changes under stress, competitive athletes were subjected to mental stress during highly dynamic movements, and musculoskeletal models were used to analyze the biomechanical loading. It was shown that under mental stress, independent of the subjective perception, a strong change in muscle forces can occur. Accordingly, competitive athletes should undergo screenings to assess individual movement patterns and promote general stress resilience.

Cognitive load causes kinematic changes in both elite and non-elite rowers

The current motor literature suggests that extraneous cognitive load may affect performance and kinematics in a primary motor task. A common response to increased cognitive demand, as observed in past studies, might be to reduce movement complexity and revert to previously learned movement patterns, in line with the progression-regression hypothesis. However, according to several accounts of automaticity, motor experts should be able to cope with dual task demands without detriment to their performance and kinematics. To test this, we conducted an experiment asking elite and non-elite rowers to use a rowing ergometer under conditions of varying task load. We employed single-task conditions with low cognitive load (i.e., rowing only) and dual-task conditions with high cognitive load (i.e., rowing and solving arithmetic problems). The results of the cognitive load manipulations were mostly in line with our hypotheses. Overall, participants reduced movement complexity, for example by reverting towards tighter coupling of kinematic events, in their dual-task performance as compared to single-task performance. The between-group kinematic differences were less clear. In contradiction to our hypotheses, we found no significant interaction between skill level and cognitive load, suggesting that the rowers' kinematics were affected by cognitive load irrespective of skill level. Overall, our findings contradict several past findings and automaticity theories, and suggest that attentional resources are required for optimal sports performance.

Repeated stage exposure reduces music performance anxiety

Background

High heart rate (HR) and restlessness are two important features of music performance anxiety (MPA). In a case report of a cellist suffering from this condition, we showed that HR and restlessness decreased after repeated live performances of the same musical excerpt, thereby positively modulating objective performance criteria and subjective components. Here, we largely replicate these results in a group of 18 string players reporting MPA.

Methods

Objective measurement devices included a miniaturized electrocardiogram monitor and three 3-axis accelerometer loggers. Subjective measures included the Multidimensional Mental Health Questionnaire (MDBF) and a customized visual analogue scale (VAS) questionnaire for MPA. Non-artistic performance errors were assessed by music experts using a composite score for technical playing errors (i.e., intonation errors, omission of notes, and bowing noise). Data were collected from each study participant during three brief public solo performances of the same musical excerpt, with each performance occurring before a new audience on the same day.

Results

From the 1st to the 3rd performance, HR, VAS, and playing error scores decreased significantly. MDBF (RU scale) showed a significant increase in calmness from the 1st to the 3rd performance on stage. HR and RU, VAS, and RU, as well as bow acceleration and overall duration of playing correlated significantly across participants and performances.

Discussion and conclusion

We conclude that repeated stage exposure significantly reduces HR as well as restlessness and playing errors linked to MPA. Public performances are still successful when HR is significantly higher than during rest periods. These results underscore the importance of stage training to become accustomed to realistic public self-exposure. Musicians - especially students - should consider this component of stage training as an integral part of their practice routine. Therefore, stage training can reduce MPA, promote better live performances and prevent stress-related mental disorders and physical injuries. These result from excessive self-exercise strategies common in musicians experiencing MPA. HR monitoring should be an integral part of evaluating the effectiveness of interventions for better MPA management and efficient performance training.

Effects of Time Constraints and Goal Setting on Basketball Shooting

In sport, numerous high-pressure situations require athletes to perform motor tasks under temporally constrained circumstances. The present study investigated the effects of time constraints on anxiety, attention, performance, and mechanics of basketball free-throw shooting. Additionally, the potential benefits of goal setting were examined in relation to performance in time-constrained situations. Forty undergraduates (n = 10 elite basketball players, n = 15 experienced, n = 15 inexperienced) attempted free throws in timed, untimed, and goal-oriented conditions. In the timed condition, participants attempted to make as many field goals as possible in 30 s. In the untimed condition, participants attempted the same number of field goals as they did in the timed trial but without a time constraint. In the goal-oriented condition, participants attempted to surpass their highest number of successful field goals while once again under a 30-s time constraint. Participants in the timed condition had the worst field goal percentage (M = 45.20%, SD = 21.96%), while the untimed (M = 55.76%, SD = 21.12%, p < 0.05, d = 0.49) and goal-oriented conditions (M = 55.79%, SD = 22.92%, p < 0.05, d = 0.47) had similar field goal percentages. In addition, joint consistency in the elbow and knee increased during the untimed condition compared to both timed and goal-oriented conditions. Results indicate that a goal-oriented focus may prevent performance declines present in time-constrained situations.

An ecological-dynamical approach to golf science: implications for swing biomechanics, club design and customisation, and coaching practice

It has previously been argued that science has only made a limited contribution to the sport of golf, particularly the human element. This lack of impact could, in part, be attributed to the absence of an appropriate theoretical framework in most empirical investigations of the golf swing. This position paper outlines an ecological-dynamical approach to golf science that is better able to capture the interactions among the many structural parts of a golfer, and the relations between a golfer, his or her equipment, and his or her surrounding environment than other theoretical approaches have hitherto. It is proposed that the conjoining of principles and concepts of ecological psychology and dynamical systems theory could make a significant contribution to the enhancement of knowledge and understanding of swing biomechanics, club design and customisation, and coaching practice. This approach could also provide a platform on which to integrate the various subdisciplines of sport and human movement science to gain a more holistic understanding of golf performance.

Mental stress reduces performance and changes musculoskeletal loading in football-related movements

Purpose: Football players have a high risk of leg muscle injuries, especially when exposed to mental stress. Hence, this study investigated the musculoskeletal response of elite youth football players during highly dynamic movements under stress. The hypothesis is that mental stress reduces performance and changes the muscular forces exerted.Materials & methods: Twelve elite youth football players were subjected to mental stress while performing sports-specific change-of-direction movements. A modified version of the d2 attention test was used as stressor. The kinetics are computed using inverse dynamics. Running times and exerted forces of injury-prone muscles were analysed.Results: The stressor runs were rated more mentally demanding by the players (p = 0.006, r_s = 0.37) with unchanged physical demand (p = 0.777, r_s = 0.45). This resulted in 10% longer running times under stress (p < 0.001, d = -1.62). The musculoskeletal analysis revealed higher peak muscle forces under mental stress for some players but not for others.Discussion: The study shows that motion capture combined with musculoskeletal computation is suitable to analyse the effects of stress on athletes in highly dynamic movements. For the first time in football medicine, our data quantifies an association between mental stress with reduced football players' performance and changes in muscle force.

Back to feedback: aberrant sensorimotor control in music performance under pressure

Precisely timed production of dexterous actions is often destabilized in anxiogenic situations. Previous studies demonstrated that cognitive functions such as attention and working memory as well as autonomic nervous functions are susceptible to psychological stress in skillful performance while playing sports or musical instruments. However, it is not known whether the degradation of sensorimotor functions underlies such a compromise of skillful performance due to psychophysiological distress. Here, we addressed this issue through a set of behavioral experiments. After artificially delaying the timing of tone production while playing the piano, the local tempo was abnormally disrupted only under pressure. The results suggest that psychological stress degraded the temporal stability of movement control due to an abnormal increase in feedback gain. A learning experiment further demonstrated that the temporal instability of auditory-motor control under pressure was alleviated after practicing piano while ignoring delayed auditory feedback but not after practicing while compensating for the delayed feedback. Together, these findings suggest an abnormal transition from feedforward to feedback control in expert piano performance with psychological stress, which can be mitigated through specialized sensorimotor training that involves piano practice while volitionally ignoring the artificially delayed provision of auditory feedback.

In order to establish if the degradation of sensorimotor functions underlies the stress-associated disruption of skilful performance, Furuya et al examined participants undergoing a piano playing task under stress. Their data suggests the occurrence of a stress-induced transition from feedforward to feedback control, which can be mitigated through sensorimotor training involving piano practice while volitionally ignoring the artificially delayed provision of auditory feedback.

Factors of choking under pressure in musicians

Under pressure, motor actions, such as those required in public speech, surgery, or musical performance, can be compromised, even when these have been well-trained. The latter is often referred to as 'choking' under pressure. Although multifaceted problems mediate such performance failure in anxiogenic situations, such as compromised motor dexterity and cognitive disruption, the fundamental set of abnormalities characterizing choking under pressure and how these abnormalities are related have not been elucidated. Here, we attempted, first, to classify behavioural, psychological, and physiological abnormalities associated with choking under pressure in musicians and, second, to identify their relationship based on datasets derived from a questionnaire with 258 pianist respondents. Explorative factor analysis demonstrated eight functional abnormalities related to the musicians' choking, such as attention to the audience, erroneous motor actions, perceptual confusion, and failure of memory recall, which however did not include exaggerated attention to the performance. This suggests distraction of attention away from skill execution, which may underlie the spoiled performance under pressure. A structural equation analysis further inferred causal relationships among them. For instance, while failure of memory recall was influenced by passive behaviours manifesting under pressure, erroneous motor actions during performance were influenced by feeling rushed and a loss of body control. In addition, some specific personal traits, such as neuroticism, public self-consciousness, and a lack of confidence, were associated with the extent to which pressure brought about these abnormalities. These findings suggest that distinct psycho-behavioural abnormalities and personal traits underlie the detrimental effects of pressure on musical performance.

Effects of acute wearable resistance loading on overground running lower body kinematics

Field-based sports require athletes to run sub-maximally over significant distances, often while contending with dynamic perturbations to preferred coordination patterns. The ability to adapt movement to maintain performance under such perturbations appears to be trainable through exposure to task variability, which encourages movement variability. The aim of the present study was to investigate the extent to which various wearable resistance loading magnitudes alter coordination and induce movement variability during running. To investigate this, 14 participants (three female and 11 male) performed 10 sub-maximal velocity shuttle runs with either no weight, 1%, 3%, or 5% of body weight attached to the lower limbs. Sagittal plane lower limb joint kinematics from one complete stride cycle in each run were assessed using functional data analysis techniques, both across the participant group and within-individuals. At the group-level, decreases in ankle plantarflexion following toe-off were evident in the 3% and 5% conditions, while increased knee flexion occurred during weight acceptance in the 5% condition compared with unloaded running. At the individual-level, between-run joint angle profiles varied, with six participants exhibiting increased joint angle variability in one or more loading conditions compared with unloaded running. Loading of 5% decreased between-run ankle joint variability among two individuals, likely in accordance with the need to manage increased system load or the novelty of the task. In terms of joint coordination, the most considerable alterations to coordination occurred in the 5% loading condition at the hip-knee joint pair, however, only a minority of participants exhibited this tendency. Coaches should prescribe wearable resistance individually to perturb preferred coordination patterns and encourage movement variability without loading to the extent that movement options become limited.

The role of reinvestment in conservative gait in older adults

Previous research suggests that reinvestment (i.e. conscious control of movements) is associated with inefficient information processing and compromised movement strategies in older adults during walking. We examined whether reinvestment propensity is associated with conservative gait behaviour in older adults. Trait Reinvestment propensity was measured using the Movement Specific Reinvestment Scale (Chinese version) (MSRS-C). Thirty-eight older adults were categorized into 'Low Reinvestor Group' (LRG) (MSRS-C < 27) and another 38 were categorized into 'High Reinvestor Group' (HRG) (MSRS-C > 38). There were no significant differences in physical and cognitive abilities between groups. Participants were asked to walk along a 6-m straight level-ground walkway at a self-selected pace under conditions of no instruction (Baseline), instruction related to self-focus on body movements (BI), and instruction related to the external environment (EI). No significant difference was found in gait behaviour between LRG and HRG at Baseline. However, significant changes, indicative of conservative gait patterns, were found in LRG when given instructions that prompted them to consciously control their body movements. No changes were observed in HRG under external-related instructions that are assumed to reduce conscious motor processing and improve motor performance. Our findings contradict previous views on the association between trait reinvestment propensity and compromised motor performance in older adults, which potentially reduces justification for reducing trait reinvestment propensity in older adults. We also suggest that MSRS is insensitive to reflect the degree of conscious control during gait tasks. Our findings also implicate the potential detrimental effect of applying inward-focus-related instructions in healthcare rehabilitation settings.

Rituals, Repetitiveness and Cognitive Load : A Competitive Test of Ritual Benefits for Stress

A central hypothesis to account for the ubiquity of rituals across cultures is their supposed anxiolytic effects: rituals being maintained because they reduce existential anxiety and uncertainty. We aimed to test the anxiolytic effects of rituals by investigating two possible underlying mechanisms for it: cognitive load and repetitive movement. In our pre-registered experiment (osf.io/rsu9x), 180 undergraduates took part in either a stress or a control condition and were subsequently assigned to either control, cognitive load, undirected movement, a combination of undirected movement and cognitive load, or a ritualistic intervention. Using both repeated self-report measures and continuous physiological indicators of anxiety, we failed to find direct support for a cognitive suppression effect of anxiety through ritualistic behavior. Nevertheless, we found that induced stress increased participants' subsequent repetitive behavior, which in turn reduced physiological arousal. This study provides novel evidence for plausible underlying effects of the proposed anxiolytic effect of rituals: repetitive behavior but not cognitive load may decrease physiological stress responses during ritual.

Anxiety Influences the Perceptual-Motor Calibration of Visually Guided Braking to Avoid Collisions

We investigated whether anxiety influences perceptual-motor calibration in a braking to avoid a collision task. Participants performed either a discrete braking task (Experiment 1) or a continuous braking task (Experiment 2), with the goal of stopping before colliding with a stop sign. Half of participants performed the braking task after an anxiety induction. We investigated whether anxiety reduced the frequency of crashing and if it influenced the calibration of perception (visual information) and action (brake pressure) dynamically between-trials in Experiment 1 and within-trials in Experiment 2. In the discrete braking task, anxious participants crashed less often and made larger corrective adjustments trial-to-trial after crashing, suggesting that the influence of anxiety on behavior did not occur uniformly, but rather dynamically with anxiety amplifying the reaction to previous crashes. However, when performing continuous braking, anxious participants crashed more often, and their within-trial adjustments of deceleration were less related to visual information compared to controls. Taken together, these findings suggest that the timescale and nature of the task mediates the influence of anxiety on the performance of goal-directed actions.

State anxiety disorganizes finger movements during musical performance

Skilled performance, in many situations, exposes an individual to psychological stress and fear, thus triggering state anxiety and compromising motor dexterity. Suboptimal skill execution in people under pressure affects the future career prospects of trained individuals, such as athletes, clinicians, and musicians. However, it has not been elucidated in what manner state anxiety affects multijoint movements and thereby degrades fine motor control. Using principal component analysis of hand kinematics recorded by a data glove during piano performances, we tested whether state anxiety affects the organization of movements of multiple joints or merely constrains the amplitude of the individual joints without affecting joint movement coordination. The result demonstrated changes in the coordination of movements across joints in piano performances by experts under psychological stress. Overall, the change was characterized by reduction of synergistic movements between the finger responsible for the keypress and its adjacent fingers. A regression analysis further identified that the attenuation of the movement covariation between the fingers was associated with an increase in temporal error during performance under pressure. In contrast, neither the maximum nor minimum angles of the individual joints of the hand were susceptible to induced anxiety. These results suggest that degradation of fine motor control under pressure is mediated by incoordination of movements between the fingers in skilled piano performances. NEW & NOTEWORTHY A key issue in neuromuscular control of coordinated movements is how the nervous system organizes multiple degrees of freedom for production of skillful motor behaviors. We found that state anxiety disorchestrates the organization of finger movements so as to decrease synergistic motions between the fingers in musical performance, which degrades fine motor control. The findings are important to shed light on mechanisms underlying loss of motor dexterity under pressure.

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.

The Influence of the 'Trier Social Stress Test' on Free Throw Performance in Basketball: An Interdisciplinary Study

The aim of the present study was to explore the relationship between stress and sport performance in a controlled setting. The experimental protocol used to induce stress in a basketball free throw was the Trier Social Stress Test (TSST) and its control condition (Placebo-TSST). Participants (n = 19), novice basketball players but trained sportspersons, were exposed to two counterbalanced conditions in a crossover design. They were equipped with sensors to measure movement execution, while salivary cortisol and psychological state were also measured. The task consisted of two sequences of 40 free throws, one before either the TSST or Placebo-TSST and one after. Physiological and psychological measures evidenced that the TSST induced significant stress responses, whereas the Placebo-TSST did not. Shooting performance remained stable after the TSST but decreased after the Placebo-TSST. We found no effect of the TSST or Placebo-TSST on movement execution. A multivariate model of free throw performance demonstrated that timing, smoothness and explosiveness of the movements are more relevant to account for beginner’s behavior than stress-related physiological and psychological states. We conclude that the TSST is a suitable protocol to induce stress responses in sport context, even though the effects on beginners’ free throw performance and execution are small and complex.

Speaking rate effects on articulatory pattern consistency in talkers with mild ALS

This study investigated speaking rate effects on articulatory pattern consistency in talkers with mild amyotrophic lateral sclerosis (ALS) to better understand speech rate declines during the early stages of speech deterioration. Eight talkers with mild ALS and 11 controls repeated a sentence at their typical rate, an accelerated rate, and a reduced rate. Lip and jaw movements were captured using a 3-D motion capture system. Results showed that talkers with ALS produced more consistent articulatory patterns during typical speech than did controls. Further, rate reduction resulted in diminished pattern consistency in both groups. Fast speech also elicited less consistent articulatory patterns in talkers with ALS. Controls, by contrast, tended to produce more consistent patterns during fast speech. Relatively inconsistent patterns during fast speech suggest that ALS may negatively affect articulatory control when the speech motor system operates near its performance limit. Relatively consistent patterns during typical speech indicate a successful adaption to disease-related articulatory deficits. Rate reduction does not appear to benefit articulatory stability during early stages of speech decline.

Body actions change the appearance of facial expressions

Perception, cognition, and emotion do not operate along segregated pathways; rather, their adaptive interaction is supported by various sources of evidence. For instance, the aesthetic appraisal of powerful mood inducers like music can bias the facial expression of emotions towards mood congruency. In four experiments we showed similar mood-congruency effects elicited by the comfort/discomfort of body actions. Using a novel Motor Action Mood Induction Procedure, we let participants perform comfortable/uncomfortable visually-guided reaches and tested them in a facial emotion identification task. Through the alleged mediation of motor action induced mood, action comfort enhanced the quality of the participant’s global experience (a neutral face appeared happy and a slightly angry face neutral), while action discomfort made a neutral face appear angry and a slightly happy face neutral. Furthermore, uncomfortable (but not comfortable) reaching improved the sensitivity for the identification of emotional faces and reduced the identification time of facial expressions, as a possible effect of hyper-arousal from an unpleasant bodily experience.

Activity progression for anterior cruciate ligament injured individuals

BACKGROUND

Functional exercises are important in the rehabilitation of anterior cruciate ligament deficient and reconstructed individuals but movement compensations and incomplete recovery persist. This study aimed to identify how tasks pose different challenges; and evaluate if different activities challenge patient groups differently compared to controls.

METHODS

Motion and force data were collected during distance hop, squatting and gait for 20 anterior cruciate ligament deficient, 21 reconstructed and 21 controls.

FINDINGS

Knee range of motion was greatest during squatting, intermediate during hopping and smallest during gait (P < 0.01). Peak internal knee extensor moments were greatest during distance hop (P < 0.01). The mean value of peak knee moments was reduced in squatting and gait (P < 0.01) compared to hop. Peak internal extensor moments were significantly larger during squatting than gait and peak external adductor moments during gait compared to squatting (P < 0.01). Fluency was highest during squatting (P < 0.01). All patients demonstrated good recovery of gait but anterior cruciate ligament deficient adopted a strategy of increased fluency (P < 0.01). During squatting knee range of motion and peak internal knee extensor moment were reduced in all patients (P < 0.01). Both anterior cruciate ligament groups hopped a shorter distance (P < 0.01) and had reduced knee range of motion (P < 0.025). Anterior cruciate ligament reconstructed had reduced fluency (P < 0.01).

INTERPRETATION

Distance hop was most challenging; squatting and gait were of similar difficulty but challenged patients in different ways. Despite squatting being an early, less challenging exercise, numerous compensation strategies were identified, indicating that this may be more challenging than gait.

Environmental context affects outcome and kinematic changes at different rates during skill learning

Based on Gentile's learning model, this study used a dart-throwing task to investigate the influence of environmental context. Novice participants (N = 32) were trained in one of four conditions, while measuring outcomes and kinematics. The interaction of regulatory conditions (stationary/in motion) and intertrial variability (present/absent) created four target conditions: (1) stationary with one location, (2) stationary with five locations, (3) moving with one movement pattern, (4) moving with five starting locations. Performance outcome (radial error) and movement coordination (displacement of shoulder, elbow, and wrist) changes were investigated during three days of practice (480 trials). Radial error scores were analyzed using a 3 x 8 x 4 (Day x Trial Block x Condition) analysis of variance, repeated measures design. The transformed cross-correlation values of the kinematic trials were analyzed using a 3 x 3 x 4 (Joint x Day x Condition) analysis of variance, repeated measures design. Reducing the environmental context complexity of the skill (closed regulatory conditions and no inter-trial variability), decreased outcome errors and changed kinematics at different times in the learning. The environmental context influence was observed by a day x condition interaction on joint coordination. Inter-trial variability had its greatest influence on coordination. The environmental context should be taken into consideration when evaluating and assessing skill performance during learning.

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.

Thinking about muscles: the neuromuscular effects of attentional focus on accuracy and fatigue

Although the effects of attention on movement execution are well documented behaviorally, much less research has been done on the neurophysiological changes that underlie attentional focus effects. This study presents two experiments exploring effects of attention during an isometric plantar-flexion task using surface electromyography (sEMG). Participants' attention was directed either externally (towards the force plate they were pushing against) or internally (towards their own leg, specifically the agonist muscle). Experiment 1 tested the effects of attention on accuracy and efficiency of force produced at three target forces (30, 60, and 100% of the maximum voluntary contraction; MVC). An internal focus of attention reduced the accuracy of force being produced and increased cocontraction of the antagonist muscle. Error on a given trial was positively correlated with the magnitude of cocontraction on that trial. Experiment 2 tested the effects of attention on muscular fatigue at 30, 60 and 100%MVC. An internal focus of attention led to less efficient intermuscular coordination, especially early in the contraction. These results suggest that an internal focus of attention disrupts efficient motor control in force production resulting in increased cocontraction, which potentially explains other neuromechanical findings (e.g. reduced functional variability with an internal focus).

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.

Open-loop, closed-loop and compensatory control: performance improvement under pressure in a rhythmic task

According to explicit monitoring theories, the phenomenon of choking under pressure is due to actors focusing their attention on the execution of the skill. This step-by-step perceptually guided control may then interfere with automatic execution. In order to examine the changes in control at the sensorimotor level, we examined the rhythmic task of ball bouncing which affords detailed quantification of indicators of control based on previous research. The hypothesis was that under psychological pressure perceptually guided control should lead to decreased performance due to over-emphasis on closed-loop control and decreased compensatory control. In two experiments of different difficulty psychological stress was induced via setting up a fake competition. Results showed that, contrary to the hypothesis, performance accuracy and consistency improved together with an increase in compensatory control. Indicators for open- and closed-loop processes did not change. Only under more challenging conditions in Experiment 2, enhanced performance under pressure was accompanied by more active, closed-loop and less passive control. The results are discussed in light of task demands and the continuous rhythmic nature of the task: in more challenging tasks, control appears to be more prone to disturbance due to psychological stress. The different control demands in continuous rhythmic tasks may be less prone to interference due to psychological stress than in discrete tasks.

Analogy versus explicit learning of a modified basketball shooting task: performance and kinematic outcomes

The effects of differential instructional sets on motor skill acquisition were investigated using performance outcome and kinematic measures. Participants were provided with a single analogical instruction (analogy learning), a set of eight explicit (technical) instructions (explicit learning), or were not instructed (control). During a learning phase, participants (n=9 for each condition) performed a modified basketball shooting task over 3 days (160 trials per day). On the fourth day, participants performed a test phase consisting of two 40-trial retention tests, separated by a 40-trial secondary task transfer test, and completed a verbal protocol describing in detail the techniques that they had used to perform the task. No performance differences were found during the two retention tests, indicating similar amounts of learning for all groups. During the transfer test, performance deteriorated for both the explicit and control conditions, but not for the analogy condition. Participants in the analogy condition reported significantly fewer technical rules. Although no group differences were reported for kinematic variables, identification of movement components supported the claim that explicit learners exert conscious control over their movements, whereas analogy learners use a more implicit (unconscious or automatic) mode of movement control.

Hierarchical organization of the coordinative structure of the skill of clay kneading

An experiment was conducted to study the skill of clay kneading in pottery. This task usually requires a few years to master and is therefore well suited to study the long-term development of a complex motor skill. Participants' kneading movements were measured in 3D using a motion capture device and phase relations among coordinates and joint angles were analyzed in terms of the mutual phase relative to a reference point using the Hilbert transform. While a certain degree of periodicity was observed in all 10 participants, the behavior of the experts was characterized by a significant delay for the right elbow (i.e., the pushing arm) and the fore-aft position of the upper torso and only brief delays for the other parts, which all tended to synchronize with the reference. These findings are consistent with our notion of "differentiation within coordination", according to which skill learning proceeds in a hierarchical manner in that coordination among limb movements is established first, followed by modulations of specific limb movements within the established coordination. Although this feature of expert behavior was also apparent in our previous studies of clay kneading and samba shaking and dancing, the numbers of participants in those studies were not sufficient to draw firm conclusions. Since the present study involved more participants and a superior method of analysis, the present evidence for the principle of differentiation within coordination is more conclusive.

Variations in the relationship between radius of curvature and velocity as a function of joint motion

A power law describes the relationship between the geometric properties of a trajectory (radius of curvature) and movement kinematics (tangential velocity) in curved drawing movements. Although the power law is a general law of motion, there are conditions under which it degrades. In particular, the power law may be less explanatory of movements around certain joints. The present study considered how varying motion around different joints influenced the fit of the power law. Motions associated with finger and wrist, or elicited by an isometric force production task, were compared. The power law was most explanatory of finger motion and isometric production and least explanatory of wrist motion. The fit of the power law for finger and wrist motion suggested separate laws for each joint system. Since the fit of the power law was better for finger than for wrist motion, there is some suggestion that the power law better explains motion around fewer or simpler joint systems.

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.

Effects of attentional strategies and anxiety constraints on perceptual-motor organisation of rhythmical arm movements

Effects of anxiety on perceptual-motor organisation of rhythmical forearm movements were examined using an interrupted time series design with staggered baselines. Participants were exposed to repeated baseline sessions interrupted with two anxiety-inducing sessions. Results showed that under moderate levels of anxiety, determined from CSAI-2 and heart rate data, phase relations between oscillating forearms became more stable in in-phase (0 degrees ) and anti-phase (180 degrees ) modes, although these patterns were not maintained in baseline sessions following the anxiety manipulation. Data were consistent with participants employing a strategy of allocating greater attentional effort in stabilizing preferred co-ordination patterns under anxiety-inducing conditions. Results suggest that anxiety can temporarily act as a source of behavioural information, leading to the re-parameterisation of participants' intrinsic dynamics.

Influence of a stressing constraint on stiffness and damping functions of a ski simulator's platform motion

The aim of this study was to assess the effect of stress on a previously acquired motor coordination. Following a longitudinal learning experiment, four participants performed oscillations on a ski simulator, either in normal or stressful conditions. The results showed that the amplitude of the oscillations decreased under stress, but no significant effect was seen regarding coordination, suggesting the strong resistance to stress of overlearned behaviour. Nevertheless, for one participant, a transient regression towards a former stage of learning was observed. This result was consistent with the regression hypothesis formulated by Fuchs (1962).