Cortical and Subthalamic Nucleus Spectral Changes During Limb Movements in Parkinson's Disease Patients with and Without Dystonia.

BACKGROUND: Dystonia is an understudied motor feature of Parkinson's disease (PD). Although considerable efforts have focused on brain oscillations related to the cardinal symptoms of PD, whether dystonia is associated with specific electrophysiological features is unclear. OBJECTIVE: The objective of this study was to investigate subcortical and cortical field potentials at rest and during contralateral hand and foot movements in patients with PD with and without dystonia. METHODS: We examined the prevalence and distribution of dystonia in patients with PD undergoing deep brain stimulation surgery.  During surgery, we recorded intracranial electrophysiology from the motor cortex and directional electrodes in the subthalamic nucleus (STN) both at rest and during self-paced repetitive contralateral hand and foot movements. Wavelet transforms and mixed models characterized changes in spectral content in patients with and without dystonia. RESULTS: Dystonia was highly prevalent at enrollment (61%) and occurred most commonly in the foot. Regardless of dystonia status, cortical recordings display beta (13-30 Hz) desynchronization during movements versus rest, while STN signals show increased power in low frequencies (6.0 ± 3.3 and 4.2 ± 2.9 Hz peak frequencies for hand and foot movements, respectively). Patients with PD with dystonia during deep brain stimulation surgery displayed greater M1 beta power at rest and STN low-frequency power during movements versus those without dystonia. CONCLUSIONS: Spectral power in motor cortex and STN field potentials differs markedly during repetitive limb movements, with cortical beta desynchronization and subcortical low-frequency synchronization, especially in patients with PD with dystonia. Greater knowledge on field potential dynamics in human motor circuits can inform dystonia pathophysiology in PD and guide novel approaches to therapy. © 2022 The Authors. Movement Disorders published by Wiley Periodicals LLC on behalf of International Parkinson and Movement Disorder Society.

Increased Attentional Focus on Walking by Older Adults Limits Maximum Speed and Is Related to Dynamic Stability.

BACKGROUND AND PURPOSE: Older adults with lower balance confidence demonstrate a reduced willingness to experience instability as the task of walking becomes more challenging (i.e., walking with a faster speed). However, the specific reason why is not known. The purpose of this study was to investigate the extent to which capacity of increasing walking speeds relates to the attentional requirements (i.e., automaticity) of walking. METHODS: Sixteen young (31 ± 5.85 years) and 15 older participants (69 ± 3.04 years) began walking on a treadmill at 0.4 m/s, and speed was increased by 0.2 m/s until the participant either chose to stop or reached a speed of 2.0 m/s. Sixty steps were collected at steady-state speed for each walking trial. Kinematic data were collected, and the margin of stability in the anterior direction (MOSAP) at heelstrike was quantified for each step. The timed up and go (TUG) and TUG dual (TUGdual) task were performed, from which an automaticity index (TUG/TUGdual × 100) was calculated. Older individuals were grouped based on whether they did or did not complete all walking speeds (i.e., completers [n = 9] or noncompleters [n = 6]). The fastest walking speed attempted (FSA), automaticity index, and MOSAP were compared, and correlations were assessed between the FSA/MOSAP and the automaticity index. RESULTS: A significant difference was identified in an average MOSAP at heelstrike between older completer and noncompleter groups (p < 0.001). Further, older adults with lower automaticity index choose to stop walking at lower speeds (p = 0.001). The FSA was positively correlated with the automaticity index (ρ = 0.81, p < 0.001). Finally, the average MOSAP at FSA and the automaticity index were also negatively correlated (r = -0.85, p < 0.001). CONCLUSION: Older adults with lower automaticity of walking choose to stop walking at speeds before they completed all walking speeds, which may relate with increased attentional demands required to maintain dynamic stability at higher walking speeds. Given that these were otherwise healthy adults, the combination of FSA and an automaticity of walking may help to identify individuals who should be considered for an assessment to identify walking problems.

Effect of Increasing Obstacle Distances Task on Postural Stability Variables During Gait Initiation in Older Nonfallers and Fallers.

OBJECTIVE: To compare the scaling of the postural stability variables between older nonfallers and fallers during gait initiation (GI) while stepping over increasing obstacle distances. DESIGN: Cross-sectional study. SETTING: University research laboratory. PARTICIPANTS: A sample of participants (N=24) divided into 2 groups: older nonfallers (n=12) and older fallers (n=12). Participants had no known neurologic, musculoskeletal, or cardiovascular conditions that could have affected their walking, and all were independent walkers. All the participants had an adequate cognitive function to participate as indicated by a score of more than 24 on the Mini-Mental State Examination. INTERVENTIONS: Not applicable. MAIN OUTCOME MEASURES: The primary dependent variables were peak anterior-posterior (AP) center of mass (CoM)-center of pressure (CoP) separation during anticipatory postural adjustments (APAs), AP CoM-CoP separation at the toe-off, and peak AP CoM-CoP separation during the swing. Secondary dependent variables were AP trunk angle during GI. Within- and between-repeated measures analysis of variance was used to compare means between groups across different task conditions for all the dependent variables. RESULTS: There was a main effect of group for peak AP CoM-CoP separation during APA (P=.018), an interaction effect between group and condition for AP CoM-CoP separation at toe-off (P=.009), and a main effect of condition for peak AP CoM-CoP separation during the swing (P<.001). We also found a main effect of group for peak AP trunk angle during the swing (P=.028). CONCLUSIONS: For GI while stepping over increasing obstacle distances, older fallers adopt a more conservative strategy of AP CoM-CoP separation than nonfallers prior to toe-off and demonstrate increased peak AP trunk lean during the swing. AP CoM-CoP separation prior to toe-off during the GI task may be a critical marker to identify fallers and warrants additional investigation.

Development of Dynamic Measures to Assess Balance Confidence and State Anxiety While Walking at Increasing Speeds in Young and Older Adults.

The purpose of this study was to determine the test-retest reliability and construct validity of tools to assess how balance confidence (BC) and state anxiety (SA) change with progressively increasing walking speeds. Sixteen young adults and 15 older adults attended two sessions. Individuals began walking on a treadmill at 0.4 m/s Participants chose to continue increasing the treadmill speed (up to 2.0 m/s) or to discontinue the protocol while rating their BC and SA after completing each speed. BC at participants' fastest speed attempted demonstrated high and moderate test-retest reliability among young (intraclass correlation coefficient [ICC] = .908) and older adults (ICC = .704). SA for young adults and older adults was good (ICC = .833) and fair (ICC = .490), respectively. Our measures also correlated with measures of dynamic stability while walking for young (r = -.67, p = .008) and older adults (r = .54, p = .046). Our dynamic measures of BC and SA are valid and reliable in young and older adults.

Effects of Thrust Magnitude and Duration on Immediate Postspinal Manipulation Trunk Muscle Spindle Responses.

OBJECTIVE: The purpose of this study was to characterize trunk muscle spindle responses immediately after high-velocity, low-amplitude spinal manipulation (HVLA-SM) delivered at various thrust magnitudes and thrust durations. METHODS: Secondary analysis from multiple studies involving anesthetized adult cats (N = 70; 2.3-6.0 kg) receiving L6 HVLA-SM. Muscle spindle afferent recordings were obtained from L6 dorsal rootlets before, during, and immediately after HVLA-SM. L6 HVLA-SM was delivered posteriorly-to-anteriorly using a feedback motor with peak thrust magnitudes of 25%, 55%, and 85% of cat body weight (BW) and thrust durations of 25, 50, 75, 100, 150, 200, and 250 ms. Time to the first action potential and muscle spindle discharge frequency at 1 and 2 seconds post-HVLA-SM were determined. RESULTS: A significant association between HVLA-SM thrust magnitude and immediate (≤2 s) muscle spindle response was found (P < .001). For non-control thrust magnitude, pairwise comparisons (25%, 55%, 85% BW), 55% BW thrust magnitude had the most consistent effect on immediate post-HVLA-SM discharge outcomes (false discovery rate < 0.05). No significant association was found between thrust duration and immediate post-HVLA-SM muscle spindle response (P > .05). CONCLUSION: The present study found that HVLA-SM thrust magnitudes delivered at 55% BW were more likely to affect immediate (≤2 s) post-HVLA-SM muscle spindle response.

Randomized, Controlled Trial of Exercise on Objective and Subjective Sleep in Parkinson's Disease.

BACKGROUND: Sleep dysfunction is common and disabling in persons with Parkinson's Disease (PD). Exercise improves motor symptoms and subjective sleep quality in PD, but there are no published studies evaluating the impact of exercise on objective sleep outcomes. The goal of this study was to to determine if high-intensity exercise rehabilitation combining resistance training and body-weight interval training, compared with a sleep hygiene control improved objective sleep outcomes in PD. METHODS: Persons with PD (Hoehn & Yahr stages 2-3; aged ≥45 years, not in a regular exercise program) were randomized to exercise (supervised 3 times a week for 16 weeks; n = 27) or a sleep hygiene, no-exercise control (in-person discussion and monthly phone calls; n = 28). Participants underwent polysomnography at baseline and post-intervention. Change in sleep efficiency was the primary outcome, measured from baseline to post-intervention. Intervention effects were evaluated with general linear models with measurement of group × time interaction. As secondary outcomes, we evaluated changes in other aspects of sleep architecture and compared the effects of acute and chronic training on objective sleep outcomes. RESULTS: The exercise group showed significant improvement in sleep efficiency compared with the sleep hygiene group (group × time interaction: F = 16.0, P < 0.001, d = 1.08). Other parameters of sleep architecture also improved in exercise compared with sleep hygiene, including total sleep time, wake after sleep onset, and slow-wave sleep. Chronic but not acute exercise improved sleep efficiency compared with baseline. CONCLUSIONS: High-intensity exercise rehabilitation improves objective sleep outcomes in PD. Exercise is an effective nonpharmacological intervention to improve this disabling nonmotor symptom in PD. © 2020 International Parkinson and Movement Disorder Society.

Older but not younger adults rely on multijoint coordination to stabilize the swinging limb when performing a novel cued walking task.

Motor flexibility, the ability to employ multiple motor strategies to meet task demands, may facilitate ambulation in complex environments that constrain movements; loss of motor flexibility may impair mobility. The purpose of this study was to determine the effects of obesity (a specific model of mobility impairment) and advanced age on motor flexibility during a task that constrained foot placement while walking. Twenty-one community-dwelling obese (OB) and 25 normal weight (NW) older adults (46 total older adults-OA) and 10 younger adults (YA) walked normally on a treadmill (baseline) then walked while stepping on lighted cues projected onto the treadmill at locations corresponding to average foot placement during normal walking (cued). The uncontrolled manifold (UCM) analysis was used to partition total variance in a set of seven lower-limb segment angles into components that did ("bad" variance) and did not ("good" variance) affect step-to-step variance in the trajectory of the swing foot. Motor flexibility was operationalized as an increase (baseline to cued) in total variance with an increase in good variance that exceeded the change in bad variance. There was no significant group × walking task interaction for total and good variance for OB vs NW, but there was a strong and significant interaction effect for OA vs YA (p < 0.01; Cohen's d > 1.0). Whereas YA reduced both good and bad variance, OA increased good variance beyond the change in bad variance. In OA, these changes were associated with several functional measures of mobility. Cued walking may place greater demands on OA requiring greater reliance on motor flexibility, although otherwise healthy older obese adults may be able to compensate for functional and cognitive declines associated with obesity by increasing motor flexibility under such tasks. The extent to which motor flexibility is employed during novel or constrained tasks may be a biomarker of healthy aging and a target for (re)habilitation.

Comparison of Resistance-Based Walking Cardiorespiratory Test to the Bruce Protocol.

Hurt, CP, Bamman, M, Naidu, A, and Brown, DA. Comparison of resistance-based walking cardiorespiratory test to the Bruce Protocol. J Strength Cond Res 34(12): 3569-3576, 2020-Cardiorespiratory fitness is assessed through graded exercise tests that determine the maximum amount of sustained mechanical work that an individual can perform while also providing health- and fitness-related information. This article describes a novel method to perform graded exercise tests that use posteriorly directed resistive forces. The purpose of this investigation was to validate a novel resistance-based test (RBT) in comparison with a traditional speed- and incline-based test (SIBT) in a cohort of nonimpaired individuals. Twenty nonimpaired individuals, 8 men and 20 women age 28.4 ± 9.6, range 20-54 years old performed 2 maximal exercise tests. The SIBT used the Bruce Protocol and increased treadmill incline and speed every 3 minutes. The RBT used a robotic device interfaced with the treadmill that provided specified horizontal resistive forces at the center of mass calculated to match each Bruce Protocol stage while individuals walked at 1.1 m·s. Subjects obtained ∼3% higher maximum V[Combining Dot Above]O2 measure using the speed- and incline-based method (dependent t-test p = 0.08). V[Combining Dot Above]O2peaks between tests were strongly correlated (r = 0.93, p < 0.001). Peak values of secondary physiologic measures (i.e., max heart rate and respiratory exchange ratio) were within 3% between tests. We found a significant linear relationship between mass-specific work rate and measured V[Combining Dot Above]O2 stage by stage for both tests, but no significant difference between each linear fit (p = 0.84). These data suggest that horizontal resistive forces, while walking on a treadmill, can be used to increase aerobic effort in a way that closely simulates work rates of the Bruce Protocol.

Lower extremity joints and muscle groups in the human locomotor system alter mechanical functions to meet task demand.

To facilitate movement through mechanically complex environments, terrestrial animals have evolved locomotor systems capable of flexibly altering internal mechanics to meet external demands. They do this by shifting imposed workloads between joints/muscle groups (central mechanical flexibility) and/or by altering the function of individual joints/muscle groups (local mechanical flexibility). In human locomotion research, central mechanical flexibility is well established and regularly reported. Local mechanical flexibility at major lower extremity joints and muscle groups, however, has received relatively less attention. We used an emerging biomechanical analysis known as functional indexing to test the hypothesis that lower extremity joints and muscle groups within the human locomotor system alter their mechanical function to meet altered locomotor demands. Thirteen healthy adults walked across a range of speeds (0.8, 1.2, 1.6, 2.0 m s-1) and slopes (0 deg, +5 deg, +10 deg) to determine whether hip, knee and ankle joints and their extensors and flexors altered their mechanical function in response to increased speed and slope. As walking speed increased, the knee and its extensors altered their function to behave more like mechanical springs while the ankle and its extensors altered their function to behave more like motors. As slope increased, all three joints and their extensors decreased spring- and damper-like behavior and increased motor-like behavior. Our results indicate that humans - similarly to many other terrestrial animals - utilize local mechanical flexibility to meet the demands of the locomotor task at hand.

Effect of progressive horizontal resistive force on the comfortable walking speed of individuals post-stroke.

BACKGROUND: Individuals post-stroke select slow comfortable walking speeds (CWS) and the major factors used to select their CWS is unknown. OBJECTIVE: To determine the extent to which slow CWS post-stroke is achieved through matching a relative force output or targeting a particular walking speed. METHODS: Ten neurologically nonimpaired individuals and fourteen chronic stroke survivors with hemiplegia were recruited. Participants were instructed to "walk at the speed that feels most comfortable" on a treadmill against 12 progressively increasing horizontal resistive force levels applied at the pelvis using a robotic system that allowed participant to self-select their walking speed. We compared slope coefficients of the simple linear regressions between the observed normalized force vs. normalized speed relationship in each group to a slope of -1.0 (i.e. ideal slope for a constant relative force output) and 0.0 (i.e. ideal slope for a constant relative speed). We also compared slope coefficients between groups. RESULTS: The slope coefficients were significantly greater than -1.0 (p < 0.001 for both) and significantly less than 0 (p < 0.001 for both). However, compared with nonimpaired individuals, people post-stroke were less able to maintain their walking speed (p = 0.003). CONCLUSIONS: The results of this study provide evidence for a complex interaction between the regulation of relative force output and intention to move at a particular speed in the selection of the CWS for individuals post-stroke. This would suggest that therapeutic interventions should not only focus on task specific lower-limb strengthening exercises (e.g. walking against resistance), but should also focus on increasing the range of speeds at which people can safely walk.

Exercise-based fall prevention: can you be a bit more specific?

Trip-specific perturbation training reduces trip-related falls after laboratory-induced trips and, prospectively, in the community. Based on an emerging body of evidence, we hypothesize that using task-specific perturbation training as a stand-alone approach or in conjunction with conventional exercise-based approaches will improve the effectiveness of fall prevention interventions significantly.

An apparent contradiction: increasing variability to achieve greater precision?

To understand the relationship between variability of foot placement in the frontal plane and stability of gait patterns, we explored how constraining mediolateral foot placement during walking affects the structure of kinematic variance in the lower-limb configuration space during the swing phase of gait. Ten young subjects walked under three conditions: (1) unconstrained (normal walking), (2) constrained (walking overground with visual guides for foot placement to achieve the measured unconstrained step width) and, (3) beam (walking on elevated beams spaced to achieve the measured unconstrained step width). The uncontrolled manifold analysis of the joint configuration variance was used to quantify two variance components, one that did not affect the mediolateral trajectory of the foot in the frontal plane ("good variance") and one that affected this trajectory ("bad variance"). Based on recent studies, we hypothesized that across conditions (1) the index of the synergy stabilizing the mediolateral trajectory of the foot (the normalized difference between the "good variance" and "bad variance") would systematically increase and (2) the changes in the synergy index would be associated with a disproportionate increase in the "good variance." Both hypotheses were confirmed. We conclude that an increase in the "good variance" component of the joint configuration variance may be an effective method of ensuring high stability of gait patterns during conditions requiring increased control of foot placement, particularly if a postural threat is present. Ultimately, designing interventions that encourage a larger amount of "good variance" may be a promising method of improving stability of gait patterns in populations such as older adults and neurological patients.

Novel lower-extremity dexterity assessment for Parkinson's disease: validation against measures of arm dexterity and general mobility.

PURPOSE: To establish criterion and construct validity of a novel, clinically feasible assessment of lower-extremity dexterity for PD patients. METHODS: Thirty-three PD patients performed a unilateral lower-extremity dexterity task "off" and "on" dopaminergic medications with each leg. The task involves iteratively tapping targets with the foot in a specified pattern, and the measured outcome is the time to complete the movement sequence, with longer times indicating worse performance. We correlated leg movement time with standard, validated measures of gait (comfortable and maximal walk speeds), general mobility (timed up and go), upper-extremity dexterity (9-Hole Pegboard), and elements of the Unified Parkinson Disease Rating Scale (MDS-UPDRS). RESULTS: We found significant relationships between lower extremity dexterity and each of these tasks "off" and "on" medications. Task performance also captures known features of PD, including dopamine-mediated improvement in performance and asymmetrical symptom presentation. CONCLUSIONS: This task provides a simple assessment of lower extremity function that correlates with validated measures of dexterity, gait, and mobility. It provides objective, continuous data, is inexpensive, requires little technical expertise/equipment, has a small physical footprint, and can be administered quickly. These features increase the feasibility of implementing this assessment tool in clinical settings.Implications for rehabilitationWe introduce a novel task that captures lower extremity dexterity in individuals with Parkinson's disease (PD).The task is validated against gold standard measures of upper extremity dexterity, gait, and general mobility.Performance on the task is sensitive to known features of PD, including dopamine-mediated improvements and asymmetrical symptom presentation.The task is easy to implement and provides higher quality data compared to other common clinical assessments (e.g., MDS-UPDRS).

Effects of backward-directed resistance on propulsive force generation during split-belt treadmill walking in non-impaired individuals.

Introduction: Backward-directed resistance is the resistance applied in the opposite direction of the individual's walking motion. Progressive application of backward-directed resistance during walking at a target speed engages adaptive motor control to maintain that speed. During split-belt walking, a motor control strategy must be applied that allows the person to keep up with the two belts to maintain their position on the treadmill. This situation becomes more challenging when progressive resistance is applied since each limb needs to adapt to the greater resistance to maintain the position. We propose that strategies aimed at changing relative propulsion forces with each limb may explain the motor control strategy used. This study aimed to identify the changes in propulsive force dynamics that allow individuals to maintain their position while walking on an instrumented split-belt treadmill with progressively increasing backward-directed resistance. Methods: We utilized an instrumented split-belt treadmill while users had to overcome a set of increasing backward-directed resistance through the center of mass. Eighteen non-impaired participants (mean age = 25.2 ± 2.51) walked against five levels of backward resistance (0, 5, 10, 15, and 20% of participant's body weight) in two different modalities: single-belt vs. split-belt treadmill. On the single-belt mode, the treadmill's pace was the participant's comfortable walking speed (CWS). In split-belt mode, the dominant limb's belt pace was half of the CWS, and the non-dominant limb's belt speed was at the CWS. Results: We assessed differences between single-belt vs. split-belt conditions in the slope of the linear relationship between change in propulsive impulse relative to change of backward resistance amount. In split-belt conditions, the slower limb showed a significantly steeper increase in propulsion generation compared to the fast limb across resistance levels. Discussion: As a possible explanation, the slow limb also exhibited a significantly increased slope of the change in trailing limb angle (TLA), which was strongly correlated to the propulsive impulse slope values. We conclude that the motor control strategy used to maintain position on a split-belt treadmill when challenged with backward-directed resistance is to increase the propulsive forces of the slow limb relative to the fast limb by progressively increasing the TLA. Clinical trial registration: ClinicalTrials.gov, identifier NCT04877249.

The Immediate Effects of Different Types of Augmented Feedback on Fast Walking Speed Performance and Intrinsic Motivation After Stroke.

Objective: To examine the immediate effects of different types of augmented feedback on walking speed and intrinsic motivation post-stroke. Design: A within-subjects repeated-measures design. Setting: A university rehabilitation center. Participants: Eighteen individuals with chronic stroke hemiparesis with a mean age of 55.67±13.63 years and median stroke onset of 36 (24, 81) months (N=18). Interventions: Not applicable. Primary outcome: Fast walking speed measured on a robotic treadmill for 13 meters without feedback and 13 meters with augmented feedback on each of the 3 experimental conditions: (1) without virtual reality (VR), (2) with a simple VR interface, and (3) with VR-exergame. Intrinsic motivation was measured using the Intrinsic Motivation Inventory (IMI). Results: Although the differences were not statistically significant, fast-walking speed was higher in the augmented feedback without VR (0.86±0.44 m/s); simple VR interface (0.87±0.41 m/s); VR-exergame (0.87±0.44 m/s) conditions than in the fast-walking speed without feedback (0.81±0.40 m/s) condition. The type of feedback had a significant effect on intrinsic motivation (P=.04). The post hoc analysis revealed borderline significance on IMI-interest and enjoyment between the VR-exergame condition and the without-VR condition (P=.091). Conclusion: Augmenting feedback affected the intrinsic motivation and enjoyment of adults with stroke asked to walk fast on a robotic treadmill. Additional studies with larger samples are warranted to examine the relations among these aspects of motivation and ambulation training outcomes.

Enhancement of Muscle Shortening Torque Preloaded with Muscle Lengthening is Joint-Specific.

Our cross-sectional study aimed to investigate joint specificity of concentric muscle torque enhancement after a maximum eccentric contraction for the knee versus ankle joints across two different movement velocities (120°/s and 180°/s). After a familiarization session, 22 healthy young adults randomly performed concentric (CONC) and maximum eccentric preloaded concentric (EccCONC) muscle strength tests of the knee extensors and ankle plantar flexors of the non-dominant leg on an isokinetic strength testing device. We calculated the ratio between EccCONC and CONC (EccCONC/CONC) for all the conditions as the marker of concentric muscle torque enhancement. Separate two-way (joints x velocity) within repeated measures ANOVAs were used to determine joint-specific torque differences at 120°/s and 180°/s. CONC and EccCONC were greater for the knee extensors versus ankle plantar flexors at 120°/s and 180°/s (32.86%-102%; p < 0.001 for both); however, EccCONC/CONC was greater for the ankle plantar flexors than knee extensors at 120°/s (52.4%; p < 0.001) and 180°/s (41.9%; p < 0.001). There was a trend of greater EccCONC/CONC for the knee extensors at 180°/s than 120°/s (6.6%; p = 0.07). Our results show that greater concentric muscle torque enhancement after a maximal eccentric contraction occurs for the ankle plantar flexors versus knee extensors. Whether the joint- specificity of concentric muscle torque enhancement after a maximal eccentric contraction differentially affects sports performance is unknown. Our data provide a reference framework to investigate joint-specific concentric muscle torque enhancement for general and clinical athletic populations.

Effect of psychostimulant medications on functional balance performance in persons with Attention-Deficit/Hyperactivity Disorder: A systematic review.

RATIONALE: Balance impairments are highly prevalent and underscreened in individuals with Attention-deficit/hyperactivity disorder (ADHD). Psychostimulant medications, used to treat ADHD symptoms, may improve balance performance in this population as demonstrated by a growing literature; however, there has not been a systematic investigation to understand the effects of psychostimulant medications on balance performance in individuals with ADHD. This systematic review examined the existing evidence to determine if psychostimulant medications improve balance performance in this population. METHODS: We searched PubMed, CINAHL, SPORTDiscus, Scopus, Embase and Cochrane in March 2021 and in January 2022 to locate articles relevant to the topic. Two reviewers evaluated the methodological quality of included articles using the Study Quality Assessment Tools and the PEDro scale. The reviewers rated articles for the level of evidence based on the American Academy of Neurology (AAN) criteria. The reviewers further offered recommendations for research and clinical practice based on the strength of the reviewed articles using the AAN criteria. Additionally, the reviewers gleaned important characteristics from each article, such as study design, balance domain and study results. RESULTS: Nine articles addressed the role of psychostimulant medications on balance outcomes. These articles included two Class II studies, two Class III studies and five Class IV studies. Based on study quality, this systematic review indicated low confidence in the use of psychostimulant medications for improving balance performance based on AAN criteria. CONCLUSION: Psychostimulant medications trends to enhance balance performance in individuals with ADHD. However, the lack of well-designed studies and heterogeneity of balance measures warrant additional research.

Joint specificity of stretch shortening cycle potentiation at propulsion onset during jump test performance.

BACKGROUND: Joint specific stretch-shortening cycle (SSC) potentiation of lower extremity joints at propulsion onset during jump test performance (JTP) can temporally affect SSC potentiation. However, joint-specific SSC potentiation at propulsion onset during JTP is unknown. METHODS: Twenty-two healthy young adults, 12 men and 10 women, performed: vertical jumps (1) with a preliminary countermovement (CMJ), 2) from a squat position held isometrically for 2-3 seconds at the same knee angle of CMJ (SJ), and (3) after landing from a 15 cm high platform (DJ). Kinetics and kinematics of lower extremity joints were collected. The propulsion onset was calculated uniquely for the hip, knee, and ankle joints and defined as the first positive data point (after the eccentric phase) of the joint angular velocity for each respective joint. SSC potentiation was calculated as the ratio of jump height (JH) and joint extensor moments for CMJ/SJ, DJ/SJ, and DJ/CMJ. RESULTS: JH ratio for CMJ/SJ, DJ/SJ, and DJ/CMJ were >1 (all P< 0.01). Hip, knee, and ankle extensor moment ratio was >1 (all P<0.01) for CMJ/SJ and DJ/SJ, while for DJ/CMJ, extensor moment ratio was >1 only for the ankle (P<0.03). SSC potentiation was greatest at the ankle followed by the hip and knee for CMJ/SJ and DJ/SJ (all P<0.05). CONCLUSIONS: SSC potentiation at propulsion onset was largest at the ankle followed by hip and knee. Our findings emphasize the importance of the ankle versus hip and knee joints regarding SSC potentiation at the very beginning of JTP.

Sensitivity of dynamic stability to changes in step width during treadmill walking by young adults.

Recent experimental findings support theoretical predictions that across walking conditions the motor system chooses foot placement to achieve a constant minimum "margin of stability" (MOSmin)--distance between the extrapolated center of mass and base of support. For example, while step width varies, similar average MOSmin exists between overground and treadmill walking and between overground and compliant/irregular surface walking. However, predictions regarding the invariance of MOSmin to step-by-step changes in foot placement cannot be verified by average values. The purpose of this study was to determine average changes in, and the sensitivity of MOSmin to varying step widths during two walking tasks. Eight young subjects walked on a dual-belt treadmill before and after receiving information that stepping on the physical gap between the belts causes no adverse effects. Information decreased step width by 17% (p = .01), whereas MOSmin was unaffected (p = .12). Regardless of information, subject-specific regressions between step-by-step values of step width and MOSmin explained, on average, only 5% of the shared variance (ß = 0.11 ± 0.05). Thus, MOSmin appears to be insensitive to changing step width. Accordingly, during treadmill walking, step width is chosen to maintain MOSmin. If MOSmin remains insensitive to step width across other dynamic tasks, then assessing an individual's stability while performing these tasks could help describe the health of the motor system.