Assessing the impact of dual-task reactive step practice in people with Parkinson's disease: A feasibility study

Reactive stepping is impaired in people with Parkinson's Disease (PD) but can be improved with training. However, it is unclear if reactive steps can be improved when performing a concurrent cognitive task, a common and fall-relevant circumstance. We assessed the feasibility and preliminary effectiveness of dual-task reactive step training. Specifically, we measured whether stepping and cognitive reaction time are improved after one day of dual-task reactive step practice and if improvements are retained 24 h later. Sixteen people with PD and 13 age-matched healthy controls (HC) underwent repeated from-stance support surface perturbations that elicited a reactive step while performing an auditory Stroop task. Participants returned the following day to reassess dual-task reactive stepping performance. Cognitive, neuromuscular, and stepping outcomes were calculated. Increased step lengths were observed for both groups after practice (p < 0.001). Cognitive reaction times also improved through practice; however, this was more pronounced in the HC group (group by time interaction- p < 0.001). No changes were observed for step latency, margin of stability, or EMG onset through practice. Step length and cognitive reaction time improvements were retained 24 h after practice in both groups (step length: p < 0.001; cognitive reaction time: p = 0.05). This study provides preliminary evidence for the effectiveness of dual-task reactive step training to improve step length in people with PD. The improvements in step length without compromising cognitive reaction times suggest that participants improved reactive stepping without a robust attention shift toward the postural task. Future research is necessary to determine optimal training protocols and determine if such training protocols impact falls in PD patients.     

Everyday tasks impair spatiotemporal variables of gait in older adults with Parkinson's disease

IntroductionAlthough it is known that individuals with Parkinson's disease (PD) have difficulties performing dual-task activities, most of the studies have verified the effect of dual tasks on gait using tasks that are uncommon to perform while walking. However, the realization of tasks involving gait that really represents the daily activities carried out by the participants, allow us to detect real fall risk situations of individuals with PD during their gait.ObjectiveOur aim was to verify the influence of daily-life dual-tasks on gait spatiotemporal variables of the older adults with PD.Methods20 older adults without PD and 20 older adults with PD participated in the study. Gait kinematic was analyzed under three different conditions: walking without dual task, walking carrying bags with weight, and walking talking on the cell phone.ResultsOlder adults with PD presented lower speed (p = .001), cadence (p = .039), and shorter step length (p = .028) than older adults without PD during walking without dual tasks. When walking while carrying bags with weight, older adults with PD had a lower speed (p < .001), cadence (p = .015), shorter step length (p = .008), and greater double support time (p = .021) compared with older adults without PD. During walking while talking on the cell phone, older adults with PD walked with lower speed (p < .001), cadence (p = .013), shorter step length (p = .001) and swing time (p = .013), and increased double support time (p = .008) and support time (p = .014) in relation to older adults without PD.ConclusionDaily-life dual tasks impair the spatiotemporal variables of gait in the older adults with PD, which was most evident during walking talking on the cell phone.     

The construct of balance control in primary school-aged children: Unidimensional and task-specific

The aim of this study was to determine the dimensionality and task-specificity of balance control by investigating the relationships between different tasks and the degree to which these tasks belong to the same construct in primary school-aged children. Seventy-four South African children were randomly selected from a sample of convenience. They performed 18 different balance tasks that were grouped into four balance scales: the Performance and Fitness (PERF-FIT) static balance score, the PERF-FIT dynamic balance score, the PERF-FIT moving cans balance score and the Balance Sensory score. Spearman rank correlations were calculated between the scores. Principal component analysis (PCA) was used to investigate the number of factors within the construct. Moderate to good correlations were found between: i) PERF-FIT Moving cans balance score and the Balance Sensory score (r = 0.605, p < 0.001); ii) PERF-FIT static balance score and the PERF-FIT Moving cans (r = 0.586, p < 0.001); iii) PERF-FIT static balance score and the Balance Sensory score (r = 0.541, p < 0.001). All other correlations were low to fair. The PCA revealed one component. The three PERF-FIT items (moving cans-, static- and dynamic balance score) and the Balance Sensory score explained 59.4% of the variance of total balance performance.     

Task-specificity of balance training

Despite much research on balance training, it is still unclear whether balance training leads to highly task-specific adaptations or rather non-specific adaptations. Hence, in this study we examined whether balance training increased performance only in the balance task that was trained or also in non-trained tasks. Forty healthy participants (28 m 12 f, 25 ± 4 years, 177 ± 10 cm, 73 ± 14 kg) were assigned to one of two training groups (TGs) or a control group. Both TGs completed six sessions over 2 weeks, only the training device differed. Before and after the training, performance in the trained task as well as in additional untrained tasks was recorded. ANOVAs showed that each TG outperformed the other groups only in the task they had trained (e.g., task trained by TG1: +225% in TG1, only +41% and +30% in TG2 and control, group * time interaction, p < 0.001; Untrained task 1: TG1 +48%, TG2 +48%, and control +30%, no significant interaction, p = 0.72). In summary, 2 weeks of balance training resulted in highly task-specific effects, no transfer even to very similar tasks was observed. Therefore, we recommend identifying and training exactly those tasks that need improvement, and test the efficacy of training programs using specific tests instead of general tests with limited functional relevance.     

Different neuromuscular control mechanisms regulate static and dynamic balance: A center-of-pressure analysis in young adults

The analysis of the center of pressure (CoP) trajectory, derived from force platforms, is a widely accepted measure to investigate postural balance control. The CoP trajectory could be analyzed as a physiological time-series through a general stochastic modeling framework (i.e., Stabilogram Diffusion Analysis (SDA)). Critical point divides short-term from long-term regions and diffusion coefficients reflect the level of stochastic activity of the CoP. Sample Entropy (SampEn) allows quantifying the CoP complexity in terms of regularity. Thus, this study aimed to understand whether SDA and SampEn could discriminate the neuromuscular control mechanisms underpinning static and dynamic postural tasks. Static balance control and its relationship with dynamic balance control were investigated through the CoP velocity (Mean Velocity) and the area of the 95th percentile ellipse (Area95). Balance was assessed in 15 subjects (age: 23.13 ± 0.99 years; M = 9) over a force platform under two conditions: static (ST) and dynamic, both in anterior-posterior (DAP) and medio-lateral (DML) directions. During the DAP and DML, subjects stood on an unstable board positioned over a force platform. Short-term SDA diffusion coefficients and critical points were lower in ST than in DAP and DML (p < 0.05). SampEn values resulted greater in ST than in DAP and DML (p < 0.001). As expected, lower values of Area95 (p < 0.001) and Mean Velocity (p < 0.001) were detected in the easiest condition, the ST, compared to DAP and DML. No significant correlations between static and dynamic balance performances were detected. Moreover, differences in the diffusion coefficients were detected comparing DAP and DML (p < 0.05). In the anterior-posterior direction, the critical point occurred at relatively small intervals in DML compared to DAP (p < 0.001) and ST (p < 0.001). In the medio-lateral direction, the critical point differed only between DAP and DML (p < 0.05). Overall, SDA analysis pointed out a less tightly regulated neuromuscular control system in the dynamic tasks, with closed-loop corrective feedback mechanisms called into play at different time intervals in the three conditions. SampEn results reflected more attention and, thus, less automatic control mechanisms in the dynamic conditions, particularly in the medio-lateral task. The different neuromuscular control mechanisms that emerged in the static and dynamic balance tasks encourage using both static and dynamic tests for a more comprehensive balance performance assessment.     

Task specificity and neural adaptations after balance learning in young adults

BackgroundOnly 30 min of balance skill training can significantly improve behavioral and neuromuscular outcomes. However, it is unclear if such a rapidly acquired skill is also retained and transferred to other untrained balance tasks.Research questionWhat are the effects of a single balance training session on balance skill acquisition, retention, and transferability and on measures of neural plasticity examined by transcranial magnetic brain stimulation (TMS) and inter-muscular coherence?MethodsHealthy younger adults (n = 36, age 20.9, 18 M) were randomly assigned to: Balance training (BT); Active control (cycling training, CT) or non-active control (NC) and received a 20-min intervention. Before, immediately and ~ 7 days after the interventions, we assessed performance in the trained wobble board task, untrained static standing tasks and dynamic beam walking balance tasks. Underlying neural plasticity was assessed by tibialis anterior motor evoked potential, intracortical facilitation, short-interval intracortical inhibition and long-interval intracortical inhibition using TMS and by inter-muscular coherence.ResultsBT, but not CT (18%, d = 0.32) or NC (−1%, d = −0.02), improved balance performance in the trained, wobble board task by 207% (effect size d = 2.12). BT retained the acquired skill after a 1-week no-training period (136%, d = 1.57). No changes occurred in 4 measures of balance beam walking, in 8 measures of static balance, in 8 measures of intermuscular coherence, and in 4 TMS measures of supra-spinal plasticity (all p > 0.05).SignificanceHealthy young adults can learn a specific balance skill very rapidly but one should be aware that while such improvements were retained, the magnitude of transfer (32%, d = 0.94) to other balancing skills was statistically not significant. Additional studies are needed to determine the underlying neural mechanisms of rapid balance skill acquisition, retention, and transfer.     

Keeping balance during head-free smooth pursuit: The role of aging

Standing balance is often more unstable when visually pursuing a moving target than when fixating on a stationary one. These effects are common in both young and older adults when the head is restrained during visual task performance. The present study focused on the role of head motion on standing balance during smooth pursuit as a function of age. Three predictions were tested: a) standing balance is compromised to a greater extent in older than young adults by gaze target pursuit compared to fixation, b) older adults pursue a moving target with greater and more variable head rotation than young adults, and c) greater and more variable head rotation during the smooth pursuit task is associated with greater Center of Pressure (CoP) sway. Twenty-two (22) older (age: 71.7 ± 8.1, 12 M / 10 F) and twenty-three (23) young adults (age: 23.6 ± 2.5, 12 M / 11 F) stood on a force plate while either fixating a stationary or smoothly pursuing a horizontally moving target (31.9° peak-to-peak visual angle). CoP (Bertec Balance Plate), head kinematics (Vicon Motion Analysis) and head-unconstrained gaze (Pupil Labs Invisible) were synchronously recorded. The root means square (RMS) of CoP velocity increased during smooth pursuit compared to fixation regardless of age (p < .05), while the interquartile CoP range increased only in older and not in young participants (p < .05). We also calculated the head rotation range (peak to peak cycle amplitude) of motion and variability (SD of range of motion) across the cycles of the smooth pursuit task. Older adults pursued the moving target employing more variable (p = .022) head yaw rotation than young participants although the mean range of head rotation was similar between groups (p =. 077). The amplitude and variability of head yaw rotation did not correlate with CoP sway measures. Results suggest that head-free pursuing of a moving target decreased balance to a greater extent in old than young individuals when compared to fixation. Nevertheless, postural sway during head-free smooth pursuit was not associated with the extent or variability of head rotation.     

A concurrent attention-demanding task did not interfere with balance recovery function in standing and walking among young adults – An explorative laboratory study

This study aimed to explore the ability to overcome unannounced surface perturbations of different magnitudes during standing and walking under single-task and dual-task conditions. Balance recovery abilities during perturbed walking and concurrently performing cognitive tasks has rarely been investigated although it provides more ecological information in regard to real-life situations than perturbations during single-task conditions (i.e., just walking). Thirteen young adults were asked to perform: 1) a cognitive task while sitting; 2) perturbed standing; 3) a concurrent cognitive task during perturbed standing; 4) perturbed walking; and 5) a concurrent cognitive task during perturbed walking. The cognitive task was to perform number subtractions by seven. The participants were instructed to “try to avoid a fall” during the perturbation trials. Step threshold, cognitive task performance, and 3D kinematic analysis of the first recovery step, i.e., the spatiotemporal characteristics, were compared between all conditions. Step threshold and the spatiotemporal parameters of the first recovery stepping responses were similar between all task conditions. Cognitive performance was also unaffected by the postural challenges in all task conditions. These results suggest that the first balance recovery stepping response among young adults is automatic. Furthermore, young adults seem to have sufficient motor-cognitive resources to perform concurrently both balance recovery and cognitive tasks with no interference effects.     

Exploring how arm movement moderates the effect of task difficulty on balance performance in young and older adults

Emerging evidence highlights that arm movements exert a substantial and functionally relevant contribution on quiet standing balance control in young adults. Ageing is associated with “non-functional” compensatory postural control strategies (i.e., lower limb co-contraction), which in turn, may increase the reliance on an upper body strategy to control upright stance. Thus, the primary purpose of this study was to compare the effects of free versus restricted arm movements on balance performance in young and older adults, during tasks of different difficulty. Fifteen young (mean ± SD age; 21.3 ± 4.2 years) and fifteen older (mean ± SD age; 73.3 ± 5.0 years) adults performed bipedal, semi-tandem and tandem balance tasks under two arm position conditions: restricted arm movements and free arm movements. Centre of pressure (COP) amplitude and frequency were calculated as indices of postural performance and strategy, respectively. Especially in older adults, restriction of arm movement resulted in increased sway amplitude and frequency, which was primarily observed for the mediolateral direction. Further, increasing balance task difficulty raised the arm restriction cost (ARC; a new measure to quantify free vs. restricted arm movement differences in postural control) that was more prominent in older adults. These findings indicate the ARC provides a measure of reliance on the upper body for balance control and that arm movement is important for postural control in older adults, especially during tasks of greater difficulty.     

Influence of cognitive and motor tasks using smartphone during gait: EMG and gait performance analysis – Dual-task study

Previous studies reported changes in spatiotemporal gait parameters during dual-task performance while walking using a smartphone compared to walking without a smartphone. However, studies that assess muscle activity while walking and simultaneously performing smartphone tasks are scarce. So, this study aimed to assess the effects of motor and cognitive tasks using a smartphone while simultaneously performing gait on muscle activity and gait spatiotemporal parameters in healthy young adults. Thirty young adults (22.83 ± 3.92 years) performed five tasks: walking without a smartphone (single-task, ST); typing on a smartphone keyboard in a sitting position (secondary motor single-task); performing a cognitive task on a smartphone in a sitting position (cognitive single-task); walking while typing on a smartphone keyboard (motor dual-task, mot-DT) and walking while performing a cognitive task on a smartphone (cognitive dual-task, cog-DT). Gait speed, stride length, stride width and cycle time were collected using an optical motion capture system coupled with two force plates. Muscle activity was recorded using surface electromyographic signals from bilateral biceps femoris, rectus femoris, tibialis anterior, gastrocnemius medialis, gastrocnemius lateralis, gluteus maximus and lumbar erector spinae. Results showed a decrease in stride length and gait speed from the single-task to cog-DT and mot-DT (p < 0.05). On the other hand, muscle activity increased in most muscles analyzed from single- to dual-task conditions (p < 0.05). In conclusion, performing a cognitive or motor task using a smartphone while walking promote a decline in spatiotemporal gait parameters performance and change muscle activity pattern compared to normal walking.     

The effects of initial movement dynamics on human responses to postural perturbations

Falls are a major cause of injury, and often occur while turning, reaching, or bending. Yet, we have little understanding of how an ongoing feet-in place activity at the onset of imbalance, and its associated cognitive and biomechanical demands, influence our ability to recover balance. In the current study, we used an ankle-rocking paradigm to determine how the nature of the baseline task influences the balance recovery response to a backward support surface translation. Fourteen participants were instructed to “recover balance without stepping” and were perturbed at vertical while standing quietly (“S”), while ankle rocking and moving forward (“A_f”), or while ankle rocking and moving backward (“A_b”). The results showed that changes in rocking velocity at the time of the perturbation elicited changes in the incidence of stepping, magnitude of trunk angular displacements (p < .01), and the onset latencies of distal muscles (gastrocnemius and soleus, both p < .01) used to recover balance. In addition, plots of onset latencies across all muscles showed that onset latencies appeared to occur earlier in many muscles when participants held a static position compared to when they performed a dynamic task at the onset of the perturbation. The results suggest that muscle activities used to recover balance are tailored to the nature of the perturbation and the ongoing task, and that onset latencies are later when participants are performing a dynamic as opposed to static task at the time of a perturbation. These findings support previous research suggesting that automatic postural responses are highly adaptable to environmental, situational, and task demands.     

Adaptation of lower limb movement patterns when maintaining performance in the presence of muscle fatigue

Adaptations in lower limb movement patterns were examined when performance was maintained during a fatiguing repetitive loading task. Forty recreationally active male and female participants performed single-leg hopping to volitional exhaustion at 2.2 Hz to a submaximal height. Spatio-temporal characteristics, mechanical characteristics and variability of the knee-ankle and hip-knee joint couplings were determined at 20% increments during the duration of the hopping task. Variability of the knee-ankle and hip-knee couplings in the flexion/extension axis significantly increased during the loading and propulsion phases during the hopping task (p < 0.05). Performance (vertical stiffness, hopping frequency and height) did not change significantly during the task (p > 0.05), however foot contact time increased progressively during this task (p < 0.05) and maximum hop height significantly decreased after the task (p < 0.05). The observed increase in variability between adjoining lower limb segments demonstrated the ability of the neuromotor system to adapt and maintain performance even with the onset of fatigue. This finding highlights that during the performance of a rapid and repetitive loading activity, performance can be preserved when there is variability in the neuromotor system.     

Boredom,motivation, and perceptions of pain: Mechanisms to explain the effects of self-control exertion on subsequent physical performance

ObjectivesPrior self-control exertion has been shown to have a detrimental effect on subsequent physical performance. However, some potential underpinning mechanisms of the effect have yet to be examined. The present study explored whether exerting self-control reduces subsequent physical performance; and also examines the role of boredom, motivation, perceptions of pain, and sustained attention as mechanisms to explain these performance effects.MethodsIn a within-subjects order-balanced crossover design, 63 participants completed a self-control exertion task (incongruent Stroop) and non-self-control exertion task (congruent Stroop) for 4 min. Immediately after, participants completed a wall-sit task until volitional exhaustion. Task-specific boredom was measured following the Stroop task and following the wall-sit task. Participants’ perceptions of pain and motivation were measured every 30 s during the wall sit task. Upon completion of the wall-sit, participants completed a test of sustained attention.ResultsFollowing the self-control exertion task, participant’s wall-sit performance time was reduced (136 ± 62 s), compared to when they completed the non-self-control exertion task (144 ± 57 s, p = 0.05, d = 0.14). Participant’s task related boredom was significantly higher during the non-self-control exertion task (4.30 ± 1.23), compared to the self-control exertion task (3.82 ± 1.22) (p < 0.001, d = 0.39); but boredom was not different during the wall-sit task (p = 0.79). Prior self-control exertion also led to increased overall perceptions of pain (p = 0.02) and reduced overall (p = 0.01) and initial (p = 0.02) motivation during the wall-sit task. However, no differences in initial perceptions of pain (p = 0.16) or sustained attention (response time, p = 0.99; response accuracy, p = 0.78) were observed. Additional within-subjects mediation analysis revealed that differences in wall-sit performance time could not be explained by differences in task related boredom during the Stroop task, overall perceptions of pain, or overall and initial motivation (all p > 0.05).ConclusionsThe prior exertion of self-control resulted in a decrement in subsequent physical performance. Furthermore, individuals’ perceptions of task related boredom were higher during the non-self-control exertion (congruent Stroop) task, whilst overall perceptions of pain were higher, and initial and overall motivation were lower, following the self-control exertion (incongruent Stroop) task. However, mediation analysis revealed that these mechanisms did not explain the difference in wall sit performance time between the conditions.     

The predictive relationships between advanced dynamic balance and physical activity/quality of life in Parkinson's disease

Gait and balance problems commonly occur in Parkinson's disease (PD). However, balance tasks with only one performance objective (e.g., sit-to-stand) may not be sufficient, compared to dual motor tasks (e.g., carrying a tray while walking), to be applied to the assessments and interventions which are designed to promote PD patients' balance functioning, physical activity (PA) and health-related quality of life (HQoL). The aim of this study, therefore, was to determine whether advanced dynamic balance, measured by a demanding motor-motor dual task, is a significant predictor of PA/HQoL in older adults with and without PD. Participants with (n = 22) and without (n = 23) PD were assessed using the Berg Balance Scale (BBS), the single leg hop and stick series task (SLHS), the Physical Activity Scale for the Elderly (PASE), and the Parkinson's Disease Questionnaire–39 (PDQ39). We calculated the R² change, namely the incremental validity, between the multiple regression models before and after adding the scores on the BBS/SLHS. While controlling for biological and socioeconomic covariates, competence in the SLHS task provided moderate and large levels of incremental validity to PA (ΔR² = 0.08, Cohen's f² = 0.25, p = .035) and HQoL (ΔR² = 0.13, Cohen's f² = 0.65, p < .001), respectively. In particular for participants with PD, the SLHS explained significantly more variance in HQoL in relation to psychosocial functioning (ΔR² = 0.25, Cohen's f² = 0.42, p = .028) compared to the BBS (p = .296). Assessing advanced dynamic balance by means of a highly demanding dual-task paradigm was not only strongly associated with PA but also covered a wider spectrum of HQoL components. This approach is recommended for use in evaluations and interventions carried out in clinical and research settings in order to promote healthy living.     

Effect of psychostimulant medications on static balance performance in adults with attention deficit hyperactivity disorder: Within-subjects repeated-measure study

ObjectiveThis study examined the effect of psychostimulant medications nPS) on balance and functional motor performance in adults with attention-deficit/hyperactivity disorder (ADHD).MethodsParticipants completed two sessions (off-medication and on-medication) in a within-subjects repeated-measure study design. There was a minimum of seven days between the two sessions. During both sessions, participants stood for 30 s per condition on a force platform. The conditions were: feet-apart with 1) eyes-open and 2) eyes-closed; feet-together with 3) eyes-open and 4) eyes-closed. Participants performed three trials of timed up and go (TUG) and lateral step-up test (LSUT) during both sessions. Outcome measures were sway area (SA [cm²]), average sway velocity (SV [cm/s]), TUG average time (s), and average number of LSUT repetitions. Data were analyzed using multivariate repeated measures analysis of variance and paired t-tests for examining PS effects on balance (SA and SV) and functional motor performance (TUG and LSUT), respectively.ResultsThe sample included 45 adults (35 females; mean age = 28.4 ± 6.3 years). The repeated-measures MANOVA indicated that PS was associated with better SA [F(1,44) = 9.6; p = 0.003;η_p² = 0.18] but not with SV [F(1,44) = 1.0; p = 0.319;η_p² = 0.02]. PS was associated with significantly better SA with decreasing base-of-support [F(1,44) = 9.9; p = 0.003;η_p² = 0.18]. Additionally, PS use was associated with better TUG [t(1,44) = 2.65; p = 0.014;Cohen's d = 0.39] but not LSUT performances [t(1,44) = −0.68; p = 0.499;Cohen's d = −0.10].ConclusionsPS was associated with better SA and TUG in adults with ADHD. Further studies are needed to investigate the effects of PS on balance performance using rigorous designs in this population.ImpactHealthcare providers should screen for PS status and balance when treating adults with ADHD to enhance safe motor performance.     

Effects of dynamic and isometric motor practice on position control,force control and corticomuscular coherence in preadolescent children

In this study, we investigated the effects of motor practice with an emphasis on either position or force control on motor performance, motor accuracy and variability in preadolescent children. Furthermore, we investigated corticomuscular coherence and potential changes following motor practice.We designed a setup allowing discrete wrist flexions of the non-dominant hand and tested motor accuracy and variability when the task was to generate specific movement endpoints (15–75 deg) or force levels (5–25% MVC). All participants were tested in both tasks at baseline and post motor practice without augmented feedback on performance. Following baseline assessment, participants (44 children aged 9–11 years) were randomly assigned to either position (PC) or force control (FC) motor practice or a resting control group (CON). The PC and FC groups performed four blocks of 40 trials motor practice with augmented feedback on performance.Following practice, improvements in movement accuracy were significantly greater in the PC group compared to the FC and CON groups (p < 0.001). None of the groups displayed changes in force task performance indicating no benefits of force control motor practice and low transfer between tasks (p-values:0.08–0.45). Corticomuscular coherence (C4-FCR) was demonstrated during the hold phase in both tasks with no difference between tasks. Corticomuscular coherence did not change from baseline to post practice in any group. Our findings demonstrate that preadolescent children improve position control following dynamic accuracy motor practice. Contrary to previous findings in adults, preadolescent children displayed smaller or no improvements in force control following isometric motor practice, low transfer between tasks and no changes in corticomuscular coherence.     

Response inhibition and avoidance of virtual obstacles during gait in healthy young and older adults

Adjustments of preplanned steps are essential for fall avoidance and require response inhibition. Still, inhibition is rarely tested under conditions resembling daily living. We evaluated the ability of young and older adults to modify ongoing walking movements using a novel precision step inhibition (PSI) task combined with an auditory Stroop task.Healthy young (YA, n = 12) and older (OA, n = 12) adults performed the PSI task at 4 individualized difficulty levels, as a single and dual task (DT). Subjects walked on a treadmill by stepping on virtual stepping stones, unless these changed color during approach, forcing the subjects to avoid them. OA made more failures (40%) on the PSI task than YA (16%), but DT did not affect their performance. In combination with increased rates of omitted Stroop task responses, this indicates a “posture first” strategy. Yet, adding obstacles to the PSI task significantly deteriorated Stroop performance in both groups (the average Stroop composite score decreased by 13% in YA and 27% in OA). Largest deficit of OA was observed in rates of incorrect responses to incongruent Stroop stimuli (OA 35% and YA 12%), which require response inhibition. We concluded that the performance of OA suffered specifically when response inhibition was required.     

Effects of age,speed, and step length on lower extremity net joint moments and powers during walking

During walking older adults' gait is slower, they take shorter steps, and rely less on ankle and more on knee and hip joint moments and powers compared to young adults. Previous studies have suggested that walking speed and step length are confounds that affect joint moments and powers. Our purpose was to examine the effects of walking speed and step length manipulation on net joint moments and powers in young and older adults. Sixteen young and 18 older adults completed walking trials at three speeds under three step length conditions as marker position and force platform data were captured synchronously. Net joint moments were quantified using inverse dynamics and were subsequently used to compute net joint powers. Average extensor moments at each joint during the stance phase were then computed. Older adults displayed greater knee extensor moment compared to young adults. Older adults showed trends (p < .10) of having lower ankle and higher hip moments, but these differences were not statistically significant. Average ankle, knee, and hip extensor moments increased with speed and step length. At the fast speed, older compared to young adults generated lower average ankle power (p = .003) and showed a trend (p = .056) of exerting less average moment at the ankle joint. Age-associated distal-to-proximal redistribution of net joint moments was diminished and not statistically significant when the confounding effects of walking speed and relative step length were controlled. These findings imply that age-related distal-to-proximal redistribution of joint moments may influence the different speeds and step lengths chosen by young and older adults.     

Acoustic pre-stimulation modulates startle and postural reactions during sudden release of standing support surface in aging

Falls contribute to injuries and reduced level of physical activity in older adults. During falls, the abrupt sensation of moving downward triggers a startle-like reaction that may interfere with protective response movements necessary to maintain balance. Startle reaction could be dampened by sensory pre-stimulation delivered immediately before a startling stimulus. This study investigated the neuromodulatory effects of pre-stimulation on postural/startle responses to drop perturbations of the standing support surface in relation to age.Ten younger and 10 older adults stood quietly on an elevated computer-controlled moveable platform. At an unpredictable time, participants were dropped vertically to elicit a startle-like response. Reactive drop perturbation trials without a pre-stimulus (control) were alternated with trials with acoustic pre-stimulus tone (PSI). A two-way mixed design analysis of variance comparing condition (control vs. PSI) X group (younger vs. older) was performed to analyze changes in muscle activation patterns, ground reaction force, and joint angular displacements.Compared to younger adults, older adults showed lower neck muscle electromyography amplitude reduction rate and incidence of response. Peak muscle activation in neck, upper arm, and hamstring muscles were reduced during PSI trials compared to control trials in both groups (p < 0.05). In addition, knee and hip joint flexion prior to ground contact was reduced in PSI trials compared to control (p < 0.05). During post-landing balance recovery, increased knee and hip flexion displacement and time to peak impact force were observed in PSI trials compared to control condition (p < 0.05).PSI reduced startle-induced muscle activation at proximal body segments and likely decreased joint flexion during abrupt downward vertical displacement perturbations of the body. Older adults retained the ability to modulate startle and postural responses but their neuromodulatory capacity was reduced compared with younger adults. Further research on the potential of applying PSI as a possible therapeutic tool to reduce the risk of fall-related injury is needed.     

Effects of manipulating specific individual constraints on performance outcomes,emotions, and movement phase durations in Rugby Union place kicking

Place kicks present valuable opportunities to score points in Rugby Union, contributing almost half of all points scored at international level. From an ecological dynamics perspective, place kickers adapt to interacting task, environmental, and individual constraints in performance environments. The aim of this study was to analyse effects of specific manipulations of individual constraints (fatigue; expectation for success) on place kicking performance, movement phase durations, heart rate and self-reported emotions. Under representative task and environmental constraints on an outdoor training pitch, 12 experienced, male place kickers completed four testing sessions under every combination of manipulated high/low expectation for success and manipulated levels of high/low acute fatigue. Within each session of 12 place kicks, performance outcomes from three kicking locations of varying difficulty were recorded. ANOVA revealed a two-way interaction between fatigue and expectation manipulations on mean success percentage (p < 0.05), with higher success under low fatigue + low expectation (M ± SD = 58 ± 13%) and high fatigue + high expectation (M ± SD = 56 ± 14%), compared with separate manipulations of high expectation (M ± SD = 49 ± 14%) or high fatigue (M ± SD = 51 ± 14%). There were no significant effects on any movement phase durations. Manipulating expectation significantly heightened mean heart rate (p < 0.05) and influenced emotions reported by place kickers, including higher anger scores when there was high expectation for success. Coaches are encouraged to integrate place kicking into representative game scenarios in practice environments to faithfully represent key performance constraints (e.g. fatigue; expectation for success) in preparing kickers for competitive situations.