Head control and head-trunk coordination as a function of anticipation in sidestepping.

Head reorientation precedes body reorientation during direction change to facilitate gaze realignment, thus enhancing perceptual awareness. Whole body kinematics are dependent on the available planning time. The purpose of this study was to assess the role of anticipation on head control and head-trunk coordination during sidestepping tasks. Fourteen male collegiate athletes performed anticipated and unanticipated sidestepping tasks. Transverse plane head, trunk and heading direction, as well as head-trunk coordination were assessed. During change of direction tasks, we observed greater head orientation towards the new travel direction, followed by heading direction and then trunk direction during both anticipated and unanticipated tasks. With reduced planning time, heading in the preparatory phase and trunk rotation in the preparatory and stance phases were significantly less oriented towards the new travel direction, with no differences in head rotation. During anticipated sidestepping, significantly greater in-phase coordination was observed during the preparatory phase compared to unanticipated sidestepping. Head reorientation facilitates gaze realignment and may be prioritized irrespective of planning time during sidestepping tasks. During anticipated trials, the head and trunk move more synchronously compared to unanticipated sidestepping, highlighting the potential benefits of aligning the degrees of freedom earlier in the change of direction stride and optimizing perceptual awareness.

Postural Complexity during Listening in Young and Middle-Aged Adults.

Postural behavior has traditionally been studied using linear assessments of stability (e.g., center of pressure ellipse area). While these assessments may provide valuable information, they neglect the nonlinear nature of the postural system and often lead to the conflation of variability with pathology. Moreover, assessing postural behavior in isolation or under otherwise unrealistic conditions may obscure the natural dynamics of the postural system. Alternatively, assessing postural complexity during ecologically valid tasks (e.g., conversing with others) may provide unique insight into the natural dynamics of the postural system across a wide array of temporal scales. Here, we assess postural complexity using Multiscale Sample Entropy in young and middle-aged adults during a listening task of varying degrees of difficulty. It was found that middle-aged adults exhibited greater postural complexity than did young adults, and that this age-related difference in postural complexity increased as a function of task difficulty. These results are inconsistent with the notion that aging is universally associated with a loss of complexity, and instead support the notion that age-related differences in complexity are task dependent.

Stable Coordination Variability in Overground Walking and Running at Preferred and Fixed Speeds.

Coordination variability (CV) is commonly analyzed to understand dynamical qualities of human locomotion. The purpose of this study was to develop guidelines for the number of trials required to inform the calculation of a stable mean lower limb CV during overground locomotion. Three-dimensional lower limb kinematics were captured for 10 recreational runners performing 20 trials each of preferred and fixed speed walking and running. Stance phase CV was calculated for 9 segment and joint couplings using a modified vector coding technique. The number of trials required to achieve a CV mean within 10% of 20 strides average was determined for each coupling and individual. The statistical outputs of mode (walking vs running) and speed (preferred vs fixed) were compared when informed by differing numbers of trials. A minimum of 11 trials were required for stable mean stance phase CV. With fewer than 11 trials, CV was underestimated and led to an oversight of significant differences between mode and speed. Future overground locomotion CV research in healthy populations using a vector coding approach should use 11 trials as a standard minimum. Researchers should be aware of the notable consequences of an insufficient number of trials for overall study findings.

Sensitivity of the Toe Height to Multijoint Angular Changes in the Lower Limbs During Unobstructed and Obstructed Gait.

Tripping while walking is a main contributor to falls across the adult lifespan. Trip risk is proportional to variability in toe clearance. To determine the sources of this variability, the authors computed for 10 young adults the sensitivity of toe clearance to 10 bilateral lower limb joint angles during unobstructed and obstructed walking when the lead and the trail limb crossed the obstacle. The authors computed a novel measure-singular value of the appropriate Jacobian-as the combined toe clearance sensitivity to 4 groups of angles: all sagittal and all frontal plane angles and all swing and all stance limb angles. Toe clearance was most sensitive to the stance hip ab/adduction for unobstructed gait. For obstructed gait, sensitivity to other joints increased and matched the sensitivity to stance hip ab/adduction. Combined sensitivities revealed critical information that was not evident in the sensitivities to individual angles. The combined sensitivity to stance limb angles was 84% higher than swing limb angles. The combined sensitivity to the sagittal plane angles was lower than the sensitivity to the frontal plane angles during unobstructed gait, and this relation was reversed during obstacle crossing. The results highlight the importance of the stance limb joints and indicate that frontal plane angles should not be ignored.

The Influence of Photophobia on Postural Control in Patients With Migraine.

BACKGROUND: People with migraine exhibit postural control impairments. These patients also have an increased light sensitivity due to the disease, and it remains during the headache-free period. It is currently unknown if increased lighting levels can alter the balance control, especially in individuals with visual hypersensitivity, such as migraineurs. This study aimed to assess the balance and photophobia of women with migraine and non-headache controls under different light conditions. METHODS: This cross-sectional study consisted of 14 women with migraine (mean ± SD 30.6 ± 8.1 years old) and 14 women without any kind of headache (mean ± SD 27.2 ± 2.8 years old) screened from a tertiary headache clinical hospital and the local community. Quiet standing balance was evaluated during bipodal and unipodal support, under 3 light conditions: ambient (AMB) - 270 lx, visual discomfort threshold (VDT) - 400 lx, and intense visual discomfort (IVD) - 2000 lx. Sway area of the center of pressure was processed and compared between groups. The association of migraine with the risk of presenting a greater imbalance in the discomfort lighting conditions was verified. RESULTS: Compared to the non-headache controls, the migraine group presented greater sway area in bipodal stance under the 3 light conditions (mean difference (95% CI)): AMB 0.81 cm2 (0.19 to 1.43), P = .011; VDT 3.17 cm2 (0.74 to 5.60), P = .001; IVD 5.56 cm2 (2.75 to 8.37), P < .0001. Within-subject analysis showed increased sway area in bipodal stance among all lighting conditions for the migraine group only (mean difference (95% CI)): VDT-AMB 2.20 cm2 (0.23 to 4.18), P = .024; IVD-AMB 4.50 cm2 (2.38 to 6.62), P < .0001, IVD-VDT 2.29 cm2 (0.57 to 4.01), P = .005. The Prevalence Ratio (PR) analysis showed that migraine was associated with the risk of presenting greater imbalance in both bipodal and unipodal standing conditions for both VDT (PR value (95% CI) - bipodal: PR = 4.00 (1.02 to 15.59), P = .045; unipodal: PR = 4.00 (1.43 to 11.15), P = .008), and the IVD (bipodal: PR = 3.33 (1.13 to 9.58), P = .025; unipodal: PR = 5.50 (1.48 to 20.42), P = .010) lighting conditions. CONCLUSION: Photophobia might be a disturbing factor that worsens the balance of patients with migraine during the quiet standing posture.

Postural Control While Listening in Younger and Middle-Aged Adults.

OBJECTIVES: The motivation for this research is to determine whether a listening-while-balancing task would be sensitive to quantifying listening effort in middle age. The premise behind this exploratory work is that a decrease in postural control would be demonstrated in challenging acoustic conditions, more so in middle-aged than in younger adults. DESIGN: A dual-task paradigm was employed with speech understanding as one task and postural control as the other. For the speech perception task, participants listened to and repeated back sentences in the presence of other sentences or steady-state noise. Targets and maskers were presented in both spatially-coincident and spatially-separated conditions. The postural control task required participants to stand on a force platform either in normal stance (with feet approximately shoulder-width apart) or in tandem stance (with one foot behind the other). Participants also rated their subjective listening effort at the end of each block of trials. RESULTS: Postural control was poorer for both groups of participants when the listening task was completed at a more adverse (vs. less adverse) signal-to-noise ratio. When participants were standing normally, postural control in dual-task conditions was negatively associated with degree of high-frequency hearing loss, with individuals who had higher pure-tone thresholds exhibiting poorer balance. Correlation analyses also indicated that reduced speech recognition ability was associated with poorer postural control in both single- and dual-task conditions. Middle-aged participants exhibited larger dual-task costs when the masker was speech, as compared to when it was noise. Individuals who reported expending greater effort on the listening task exhibited larger dual-task costs when in normal stance. CONCLUSIONS: Listening under challenging acoustic conditions can have a negative impact on postural control, more so in middle-aged than in younger adults. One explanation for this finding is that the increased effort required to successfully listen in adverse environments leaves fewer resources for maintaining balance, particularly as people age. These results provide preliminary support for using this type of ecologically-valid dual-task paradigm to quantify the costs associated with understanding speech in adverse acoustic environments.

Early aging and postural control while listening and responding.

It is not unusual for communication to take place while people are involved in another activity. This paper describes a study that measures the impact of listening while also completing an active postural control task. The focus was on whether the combination of listening and balancing was more detrimental to middle-aged adults than it was to younger adults as age-related changes in both hearing and postural control can occur within this age range. Speech understanding in the presence of noise and speech maskers was measured when participants (n = 15/group) were simply standing still, as well as when they were asked to complete a balancing-with-feedback postural control task, requiring different levels of effort. Performance on the postural control task also was measured in isolation. Results indicated that dual-task costs for postural control were larger when the masker was speech (vs noise) for the middle-aged group but not for the younger group. Dual-task costs in postural control increased with degree of high-frequency hearing loss even when age was controlled. Overall, results suggest that postural control in middle-aged adults can be compromised when individuals are communicating in challenging environments, perhaps reflecting an increased need for cognitive resources to successfully understand messages.

Whole-body control of anticipated and unanticipated sidestep manoeuvres in female and male team sport athletes.

The purpose of this study was to investigate the influence of sex and planning time on spatial and temporal aspects of the whole-body centre of mass (CoM) mechanics during sidestepping performance. Seventeen female and 17 male collegiate team sport athletes completed seven anticipated and seven unanticipated sidestep trials during which three-dimensional CoM data were recorded. Female athletes had a reduced ability to reorient their CoM towards the desired direction of travel (lower medio-lateral and anterior-posterior CoM velocity) than their male counterparts, with reduced medial (closer to stance foot) and increased posterior positioning of CoM relative to the stance foot (p < 0.05). When planning time was limited, female and male athletes performed sidestepping with CoM further from the stance foot (more medial) and more anterior than in the anticipated condition (p < 0.05) at reduced medio-lateral velocities. Sex and condition control strategy differences were evident both in the preparatory phase and the stance phase. The current research draws attention to the foreseen benefits of training athletes, with particular emphasis on females, to direct CoM towards the desired direction of travel in the preparatory and stance phases within temporally constrained situations for improved performance.

Comparisons of Segment Coordination: An Investigation of Vector Coding.

The development of a methodology to assess movement coordination has provided gait researchers a tool to assess movement organization. A challenge in analyzing movement coordination using vector coding lies within the inherent circularity of data garnered from this technique. Therefore, the purpose of this investigation was to determine if accurate group comparisons can be made with varying techniques of vector coding analyses. Thigh-shank coordination was analyzed using a modified vector coding technique on data from 2 groups of runners. Movement coordination was compared between groups using 3 techniques: (1) linear average completed with compressed data (0°-180°) and noncompressed data (0°-360°), (2) coordination phase binning analysis; and (3) a circular statistics analysis. Circular statistics (inferential) analysis provided a rigorous comparison of average movement coordination between groups. In addition, the binning analysis provided a metric for detecting even small differences in the time spent with a particular coordination pattern between groups. However, the linear analysis provided erroneous group comparisons. Furthermore, with compressed data, linear analysis led to misclassification of coordination patterns. While data compression may be attractive as a means of simplifying statistical analysis of inherently circular data, recommendations are to use circular statistics and binning methods on noncompressed data.

Additional helmet and pack loading reduce situational awareness during the establishment of marksmanship posture.

The pickup of visual information is critical for controlling movement and maintaining situational awareness in dangerous situations. Altered coordination while wearing protective equipment may impact the likelihood of injury or death. This investigation examined the consequences of load magnitude and distribution on situational awareness, segmental coordination and head gaze in several protective equipment ensembles. Twelve soldiers stepped down onto force plates and were instructed to quickly and accurately identify visual information while establishing marksmanship posture in protective equipment. Time to discriminate visual information was extended when additional pack and helmet loads were added, with the small increase in helmet load having the largest effect. Greater head-leading and in-phase trunk-head coordination were found with lighter pack loads, while trunk-leading coordination increased and head gaze dynamics were more disrupted in heavier pack loads. Additional armour load in the vest had no consequences for Time to discriminate, coordination or head dynamics. This suggests that the addition of head borne load be carefully considered when integrating new technology and that up-armouring does not necessarily have negative consequences for marksmanship performance. Practitioner Summary: Understanding the trade-space between protection and reductions in task performance continue to challenge those developing personal protective equipment. These methods provide an approach that can help optimise equipment design and loading techniques by quantifying changes in task performance and the emergent coordination dynamics that underlie that performance.

Coordination analysis of players' distribution in football using cross-correlation and vector coding techniques.

The purpose of this study was to investigate the coordination between teams spread during football matches using cross-correlation and vector coding techniques. Using a video-based tracking system, we obtained the trajectories of 257 players during 10 matches. Team spread was calculated as functions of time. For a general coordination description, we calculated the cross-correlation between the signals. Vector coding was used to identify the coordination patterns between teams during offensive sequences that ended in shots on goal or defensive tackles. Cross-correlation showed that opponent teams have a tendency to present in-phase coordination, with a short time lag. During offensive sequences, vector coding results showed that, although in-phase coordination dominated, other patterns were observed. We verified that during the early stages, offensive sequences ending in shots on goal present greater anti-phase and attacking team phase periods, compared to sequences ending in tackles. Results suggest that the attacking team may seek to present a contrary behaviour of its opponent (or may lead the adversary behaviour) in the beginning of the attacking play, regarding to the distribution strategy, to increase the chances of a shot on goal. The techniques allowed detecting the coordination patterns between teams, providing additional information about football dynamics and players' interaction.

Coordination as a function of skill level in the gymnastics longswing.

The purpose of this study was to investigate the nature of inter-joint coordination at different levels of skilled performance to: (1) distinguish learners who were successful versus unsuccessful in terms of their task performance; (2) investigate the pathways of change during the learning of a new coordination pattern and (3) examine how the learner's coordination patterns relate to those of experts in the longswing gymnastics skill. Continuous relative phase of hip and shoulder joint motions was examined for longswings performed by two groups of novices, successful (n = 4) and unsuccessful (n = 4) over five practice sessions, and two expert gymnasts. Principal component analysis showed that during longswing positions where least continuous relative phase variability occurred for expert gymnasts, high variability distinguished the successful from the unsuccessful novice group. Continuous relative phase profiles of successful novices became more out-of-phase over practice and less similar to the closely in-phase coupling of the expert gymnasts. Collectively, the findings support the proposition that at the level in inter-joint coordination a technique emerges that facilitates successful performance but is not more like an expert's movement coordination. This finding questions the appropriateness of inferring development towards a "gold champion" movement coordination.

Evaluating the coupling between foot pronation and tibial internal rotation continuously using vector coding.

Excessive pronation, because of its coupling with tibial internal rotation (TIR), has been implicated as a risk factor in the development of anterior knee pain (AKP). Traditionally, this coupling has been expressed as a ratio between the eversion range of motion and the TIR range of motion (Ev/TIR) that occurs during stance. Currently, this technique has not been used to evaluate specific injuries or the effects of sex. In addition, Ev/TIR is incapable of detecting coupling changes that occur throughout stance. Therefore, the purpose of this study was to compare the coupling between eversion and TIR in runners with (n = 19) and without AKP (n = 17) and across sex using the Ev/TIR ratio, and more continuously using vector coding. When using vector coding, significant coupling differences were noted in runners with AKP (34% to 38% stance), with runners with AKP showing relatively more TIR than eversion. Similarly significant differences were noted across sex (14%-25% and 36%-47% stance), with males transitioning from a loading to propulsive coordination pattern using a proximal to distal strategy, and female runners using a distal to proximal strategy. These differences were only detected when evaluating this coupling relationship using a continuous technique such as vector coding.

Balance decrements are associated with age-related muscle property changes.

In this study, a comprehensive evaluation of static and dynamic balance abilities was performed in young and older adults and regression analysis was used to test whether age-related variations in individual ankle muscle mechanical properties could explain differences in balance performance. The mechanical properties included estimates of the maximal isometric force capability, force-length, force-velocity, and series elastic properties of the dorsiflexors and individual plantarflexor muscles (gastrocnemius and soleus). As expected, the older adults performed more poorly on most balance tasks. Muscular maximal isometric force, optimal fiber length, tendon slack length, and velocity-dependent force capabilities accounted for up to 60% of the age-related variation in performance on the static and dynamic balance tests. In general, the plantarflexors had a stronger predictive role than the dorsiflexors. Plantarflexor stiffness was strongly related to general balance performance, particularly in quiet stance; but this effect did not depend on age. Together, these results suggest that age-related differences in balance performance are explained in part by alterations in muscular mechanical properties.

Postural control during gait termination and prehension.

BACKGROUND: Challenges to postural stability emerge in the transition from locomotion to a standing posture as during gait termination, often accompanied by another task (e.g., opening a door), which may complicate control. However, less is known about postural control during terminating gait while engaged in a secondary manual task. RESEARCH QUESTION: What are the changes in postural control when terminating gait with and without a prehension task? METHODS: In a cross-sectional design, 15 healthy young adults (M=8, F=7; 27±2 years; 69±13 kg; 171±8 cm) underwent both a single task gait termination (GTO) and dual task (gait termination plus reaching; GTR). Postural Time-to-Contact (TtC) was measured using Center of Pressure (CoP) and the sternum position in anterior-posterior (AP) and medial-lateral (ML) directions over two different phases: preparatory phase and stabilization phase. Five successful trials were recorded to obtain a mean TtC. For statistical analysis of TtC, a two-tailed paired t-test was used (p =.05) as normality was satisfied. RESULTS: For the preparatory phase, there were no differences for the CoP, but TtC of the sternum position in AP was shorter in GTR than GTO (p =.001). Meanwhile, for the stabilization phase, TtCs of both the CoP and sternum position were longer in GTR in both AP and ML directions (p's <.001). SIGNIFICANCE: We suggest that for the preparatory phase, the shorter TtC of the sternum position with intact TtC of the CoP in GTR indicates that healthy young individuals are flexible, in that they smoothly integrate CoP control with the upper body demands required to also perform the prehension task. Meanwhile, for the stabilization phase, the longer TtC in dual termination and prehension task indicates that the perturbation imposed by the prehension movement did not result in reduced stabilization when returning to an upright posture.

Influence of reduced passive ankle dorsiflexion range of motion on lower limb kinetics and stiffness during gait.

BACKGROUND: The ankle dorsiflexion range of motion (ADF-ROM) during single support phase allows elastic energy storage in the calcaneal tendon, contributing to advance the body forward. Reduced ADF-ROM may influence lower limb kinetics and stiffness. RESEARCH QUESTION: What is the influence of reduced passive ADF-ROM on lower limb internal moments and stiffness during gait? METHODS: Thirty-two participants, classified into two groups according to passive ADF-ROM (smaller than 10° and greater than 15°), were submitted to gait assessment at self-selected speed with a force platform and a three-dimensional motion analysis system. Statistical parametrical mapping (SPM) analyses were used to compare the lower limbs' internal moments between groups. Independent t-tests analyzed the differences between groups on lower limb stiffness during gait. RESULTS: The lower ADF-ROM group had greater knee flexor moment (terminal stance and push-off), greater ankle abductor (i.e., shank internal rotator) moment in terminal stance and greater knee internal rotator moment in mid to terminal stance. The lower ADF-ROM group also had higher lower limb stiffness during gait. SIGNIFICANCE: Individuals with reduced passive ADF-ROM had greater lower limb stiffness and adopted a gait pattern with increased knee and ankle moments, suggesting increased loading at these joints.

Defining soldier equipment trade space: load effects on combat marksmanship and perception-action coupling.

Soldier equipment compromises task performance as temporal constraints during critical situations and load increase inertial and interactive forces during movement. Methods are necessary to optimise equipment that relate task performance to underlying coordination and perception-action coupling. Employing ecological task analysis and methods from dynamical systems theory, equipment load and coordination was examined during two sub-tasks embedded in combat performance, threat discrimination and dynamic marksmanship. Perception-action coupling was degraded with load during threat discrimination, leading to delays in functional reaction time. Reduced speed and accuracy during dynamic marksmanship under load was related to disrupted segmental coordination and adaptability during postural transitions between targets. These results show how reduced performance under load relates to coordination changes and perception-action coupling. These changes in functional capability are directly related to soldier survivability in combat. The methods employed may aid equipment design towards more optimised performance by modifying equipment or its distribution on humans.

Movement variability and skills monitoring in sports.

The aim of this paper was to present a review on the role that movement variability (MV) plays in the analysis of sports movement and in the monitoring of the athlete's skills. MV has been traditionally considered an unwanted noise to be reduced, but recent studies have re-evaluated its role and have tried to understand whether it may contain important information about the neuro-musculo-skeletal organisation. Issues concerning both views of MV, different approaches for analysing it and future perspectives are discussed. Information regarding the nature of the MV is vital in the analysis of sports movements/motor skills, and the way in which these movements are analysed and the MV subsequently quantified is dependent on the movement in question and the issues the researcher is trying to address. In dealing with a number of issues regarding MV, this paper has also raised a number of questions which are still to be addressed.

Impaired foot vibration sensitivity is related to altered plantar pressures during walking in people with multiple sclerosis.

BACKGROUND: Balance and mobility impairment are two of the most common and debilitating symptoms among people with multiple sclerosis (MS). Somatosensory symptoms, including reduced plantar cutaneous sensation, have been identified in this cohort. Given the importance of the somatosensory system in gait, it is likely that impaired plantar sensation may play a role in the walking adaptations commonly observed in people with MS, including decreased stride length and increased stride width and dual support time, often described as a cautious gait strategy. Understanding the contributions of plantar sensation to these alterations may provide targets for interventions that seek to improve sensory feedback and normalize gait patterns. This cross-sectional study determined whether individuals with MS who demonstrate reduced sensitivity of the plantar surfaces also demonstrate altered plantar pressure distributions during walking compared to a control cohort. METHODS: Twenty individuals with MS and twenty age- and sex-matched control participants walked barefoot at preferred and three matched speeds. Participants walked across a walkway with an embedded pressure plate used to quantify pressures within ten plantar zones. In addition, vibration perception thresholds were assessed at four sites on the plantar surface. RESULTS: Individuals with MS demonstrated increased peak total plantar pressures compared to control participants, that increased with walking speed. For the MS group, plantar pressures were higher on the less sensitive foot, although pressures on both feet exceeded those of the control cohort. Positive correlations between vibration perception threshold and peak total pressure were evident, although generally stronger in the MS cohort. CONCLUSION: A relationship between plantar vibration sensitivity and pressure could indicate that individuals with MS seek to increase plantar sensory feedback during walking. However, because proprioception may also be impaired, increased plantar pressure could result from inaccurate foot placement. Interventions targeting improved somatosensation may have the potential to normalize gait patterns and should be investigated.

An Exploratory Study of Walking, Listening, and Remembering in Younger and Middle-Aged Adults.

PURPOSE: The purpose of this study was to assess how needing to listen and remember information while walking affects speech perception, memory task performance, and gait in younger and middle-aged adults. METHOD: Four gait parameters (stride duration, step variability, whole-body center of mass acceleration, and mediolateral head acceleration) were measured when younger and middle-aged participants stood or walked on a treadmill while they simultaneously completed a speech-on-speech perception task and a preload memory task, singly and in combination. RESULTS: Speech perception was significantly poorer for middle-aged than for younger participants. Performance on the speech perception measure did not differ significantly between walking and standing for either group of participants, but the additional cognitive load of the memory task reduced performance on the speech perception task. Memory task performance was significantly poorer when combined with the speech perception task than when measured in isolation for both participant groups, but no further declines were noted when participants were also walking. Mediolateral head acceleration, which has been linked to loss of balance, was significantly greater during multitask trials, as compared to when participants were only walking without being required to listen or remember. Post hoc analysis showed that dual- and multitask influences on mediolateral head acceleration were more prominent for middle-aged than for younger participants. Stride duration was longer in the multitask condition than when participants were only walking. CONCLUSIONS: Results of this exploratory study indicate that gait may be impacted when individuals (both younger and middle-aged) are listening and remembering while walking. Data also substantiate prior findings of early age-related declines in the perception of speech in the presence of understandable speech maskers.