The Effect of Cognitive Resource Competition Due to Dual-Tasking on the Irregularity and Control of Postural Movement Components
ABSTRACT: Postural control research suggests a non-linear, n-shaped relationship between dual-tasking and postural stability. Nevertheless, the extent of this relationship remains unclear. Since kinematic principal component analysis has offered novel approaches to study the control of movement components (PM) and n-shapes have been found in measures of sway irregularity, we hypothesized (H1) that the irregularity of PMs and their respective control, and the control tightness will display the n-shape. Furthermore, according to the minimal intervention principle (H2) different PMs should be affected differently. Finally, (H3) we expected stronger dual-tasking effects in the older population, due to limited cognitive resources. We measured the kinematics of forty-one healthy volunteers (23 aged 26 ± 3; 18 aged 59 ± 4) performing 80 s tandem stances in five conditions (single-task and auditory n-back task; n = 1–4), and computed sample entropies on PM time-series and two novel measures of control tightness. In the PM most critical for stability, the control tightness decreased steadily, and in contrast to H3, decreased further for the younger group. Nevertheless, we found n-shapes in most variables with differing magnitudes, supporting H1 and H2. These results suggest that the control tightness might deteriorate steadily with increased cognitive load in critical movements despite the otherwise eminent n-shaped relationship.
Project description:Sample entropy (SaEn), calculated for center of pressure (COP) trajectories, is often distinct for compromised postural control, e.g., in Parkinson, stroke, or concussion patients, but the interpretation of COP-SaEn remains subject to debate. The purpose of this paper is to test the hypotheses that COP-SaEn is related (Hypothesis 1; H1) to the complexity of the postural movement structures, i.e., to the utilization and coordination of the mechanical degrees of freedom; or (Hypothesis 2; H2) to the irregularity of the individual postural movement strategies, i.e., to the neuromuscular control of these movements. Twenty-one healthy volunteers (age 26.4 ± 2.4; 10 females), equipped with 27 reflective markers, stood on a force plate and performed 2-min quiet stances. Principal movement strategies (PMs) were obtained from a principal component analysis (PCA) of the kinematic data. Then SaEn was calculated for the COP and PM time-series. H1 was tested by correlating COP-SaEn to the relative contribution of the PMs to the subject specific overall movement and H2 by correlating COP-SaEn and PM-SaEn. Both hypotheses were supported. This suggests that in a healthy population the COP-SaEn is linked to the complexity of the coordinative structure of postural movements, as well as to the irregularity of the neuromuscular control of specific movement components.
Project description:Dual-tasking charges the sensorimotor system with performing two tasks simultaneously. Center of pressure (COP) analysis reveals the postural control that is altered during dual-tasking, but may not reveal the underlying neural mechanisms. In the current study, we hypothesized that the minimal intervention principle (MIP) provides a concept by which dual-tasking effects on the organization and prioritization of postural control can be predicted. Postural movements of 23 adolescents (age 12.7 ± 1.3; 8 females) and 15 adults (26.9 ± 2.3) were measured in a bipedal stance with eyes open, eyes closed and eyes open while performing a dual-task using a force plate and 39 reflective markers. COP data was analyzed by calculating the mean velocity, standard deviation and amplitude of displacement. Kinematic data was examined by performing a principal component analysis (PCA) and extracting postural movement components. Two variables were determined to investigate changes in amplitude (aVark) and in control (Nk) of the principal movement components. Results in aVark and in Nk agreed well with the predicted dual-tasking effects. Thus, the current study corroborates the notion that the MIP should be considered when investigating postural control under dual-tasking conditions.
Project description:Leg dominance has been reported as one potential risk factor for lower-limb injuries in recreational downhill skiers. The current study proposed and tested two possible mechanisms for a leg dominance effect on skiing injuries-imbalance of the knee muscle strength and bilateral asymmetry in sensorimotor control. We hypothesized that the knee muscle strength (Hypothesis 1; H1) or postural control (Hypothesis 2; H2) would be affected by leg dominance. Fifteen well-experienced recreational downhill skiers (aged 24.3 ± 3.2 years) participated in this study. Isometric knee flexor/extensor muscle strength was tested using a dynamometer. Postural control was explored by using a kinematic principal component analysis (PCA) to determine the coordination structure and control of three-dimensional unipedal balancing movements while wearing ski equipment on firm and soft standing surfaces. Only H2 was supported when balancing on the firm surface, revealing that when shifting body weight over the nondominant leg, skiers significantly changed the coordination structure (p < 0.006) and the control (p < 0.004) of the lifted-leg movements. Based on the current findings, bilateral asymmetry in sensorimotor control rather than asymmetry in strength seems a more likely mechanism for the previously reported effect of leg dominance on lower-limb injury risk in recreational downhill skiers.
Project description:In sports, postural balance control has been demonstrated to be one of the limiting factors of performance and a necessary component to achieve any sport technique. Team players (TP) must process and react to multiple external stimuli while executing at the same time the skills of the game. By contrast, endurance athletes (END) must perform the same gesture repetitively without a concurrent coordination of continuous stimuli-related actions. However, END are used to facilitate their physical performance by adopting cognitive strategies while performing their sport gesture. Therefore, we aimed to investigate static and dynamic balance performance in these two types of athletes, both in single and dual-task conditions. Nineteen END and sixteen TP underwent a static and a dynamic balance assessment on a dynamometric platform and an instrumented oscillating board, respectively. Among TP static but not dynamic postural balance performance was negatively affected by dual-tasking considering the area of the confidence ellipse (p < 0.001; d = 0.52) and the sway path mean speed (p < 0.001; d = 0.93). Conversely, END unaltered static balance performance but showed an overall improvement in the dynamic one when dual-tasking occurred. The limited human processing capacity accounted the worsening of the cognitive performance in both TP (p < 0.05; d = 0.22) and END (p < 0.001; d = 0.37). Although TP are more used coping dual tasking, the better performance of END could be accounted for by the employment of the external attentive focus (i.e. counting backward aloud) that called into play a strategy close to those adopted during training and competitions. These surprising results should be considered when driving and developing new trainings for team players in dual-tasking conditions.
Project description:BACKGROUND:In 2014, the American Association of Cardiovascular and Pulmonary Rehabilitation Quality of Care Committee was asked to develop performance measures (PMs) to assess program quality and aid in program improvement and certification. METHODS:A 3-step process was used to prioritize, develop, and then validate new PMs for both cardiac and pulmonary rehabilitation programs. First, we surveyed national leadership, medical directors, and program directors to identify and rank various American Association of Cardiovascular and Pulmonary Rehabilitation potential PM topics. Then, the face validity of the drafted PMs was assessed in a second national survey. Finally, we assessed the inter- and intrarater reliability and feasibility of each PM by abstracting patient charts at programs throughout the United States. At each step, modifications were made to refine and improve the measures for clarity, reliability, and consistency. RESULTS:Through survey answers received from 302 people (19% response rate), we identified 5 categories for PM development: optimal blood pressure control, tobacco use cessation, and improvement in functional capacity, depression, and sensation of dyspnea. After drafting the PMs, a second survey with 82 respondents (57% response rate), found that the proposed PMs had good face validity. Finally, we found excellent inter- and intrarater reliability for the blood pressure, functional capacity, depression, and dyspnea measures (? generally >0.80.) However, validity concerns were raised about the tobacco intervention PM as written, and it continues to undergo further refinement and testing. CONCLUSIONS:We developed and validated 5 new PMs for use in cardiac and pulmonary rehabilitation program quality assessment, improvement, and certification.
Project description:An inversion polymorphism of approximately 900 kb on chromosome 17q21, which includes the microtubule-associated protein tau (MAPT) gene defines two haplotype clades, H1 and H2. Several small case-control studies have observed a marginally significant excess of the H1/H1 diplotype among patients with Parkinson's disease (PD), and one reported refining the association to a region spanning exons 1 to 4 of MAPT. We sought to replicate these findings.We genotyped 1,762 PD patients and 2,010 control subjects for a single nucleotide polymorphism (SNP) that differentiates the H1 and H2 clades. We also analyzed four SNPs that define subhaplotypes within H1 previously reported to associate with PD or other neurodegenerative disorders.After adjusting for age, sex, and site, we observed a robust association between the H1/H1 diplotype and PD risk (odds ratio for H1/H1 vs H1/H2 and H2/H2, 1.46; 95% confidence interval, 1.25-1.69; p = 8 x 10(-7)). The effect was evident in both familial and sporadic subgroups, men and women, and early- and late-onset disease. Within H1/H1 individuals, there was no significant difference between cases and control subjects in the overall frequency distribution of H1 subhaplotypes.Our data provide strong evidence that the H1 clade, which contains MAPT and several other genes, is a risk factor for PD. However, attributing this finding to variants within a specific region of MAPT is premature. Thorough fine-mapping of the H1 clade in large numbers of individuals is now needed to identify the underlying functional variant(s) that alter susceptibility for PD.
Project description:Pyridoxamine (PM) is a prospective drug for the treatment of diabetic complications. In order to make zwitterionic PM more lipophilic and improve its tissue distribution, PM derivatives containing medium length alkyl groups on the hydroxymethyl side chain were prepared. The synthesis of these alkylpyridoxamines (alkyl-PMs) starting from pyridoxine offers high yields and is amenable to bulk preparations. Interestingly, alkyl-PMs were found to react with methylglyoxal (MGO), a major toxic product of glucose metabolism and autoxidation, several orders of magnitude faster than PM. This suggests the formation of nonionic pyrido-1,3-oxazine as the key step in the reaction of PM with MGO. Since the primary target of MGO in proteins is the guanidine side chain of arginine, alkyl-PMs were shown to be more effective than PM in reducing the modification of N-?-benzoylarginine by MGO. Alkyl-PMs in the presence of MGO also protected the enzymatic activity of lysozyme that contains several arginine residues next to its active site. Alkyl-PMs can be expected to trap MGO and other toxic 1,2-carbonyl compounds more effectively than PM, especially in lipophilic tissue environments, thus protecting macromolecules from functional damage. This suggests potential therapeutic uses for alkyl-PMs in diabetes and other diseases characterized by the elevated levels of toxic dicarbonyl compounds.
Project description:The influence of attention on the dynamical structure of postural sway was examined in 30 healthy young adults by manipulating the focus of attention. In line with the proposed direct relation between the amount of attention invested in postural control and regularity of center-of-pressure (COP) time series, we hypothesized that: (1) increasing cognitive involvement in postural control (i.e., creating an internal focus by increasing task difficulty through visual deprivation) increases COP regularity, and (2) withdrawing attention from postural control (i.e., creating an external focus by performing a cognitive dual task) decreases COP regularity. We quantified COP dynamics in terms of sample entropy (regularity), standard deviation (variability), sway-path length of the normalized posturogram (curviness), largest Lyapunov exponent (local stability), correlation dimension (dimensionality) and scaling exponent (scaling behavior). Consistent with hypothesis 1, standing with eyes closed significantly increased COP regularity. Furthermore, variability increased and local stability decreased, implying ineffective postural control. Conversely, and in line with hypothesis 2, performing a cognitive dual task while standing with eyes closed led to greater irregularity and smaller variability, suggesting an increase in the "efficiency, or "automaticity" of postural control". In conclusion, these findings not only indicate that regularity of COP trajectories is positively related to the amount of attention invested in postural control, but also substantiate that in certain situations an increased internal focus may in fact be detrimental to postural control.
Project description:OBJECTIVE:To examine minimum sample sizes and follow-up times required for patient-reported outcome-based performance measures (PMs) to achieve acceptable reliability as PMs. PARTICIPANTS:We used 2 groups of patients age 65+ with at least 2 of 13 chronic conditions. The first was a sample of Medicare Advantage beneficiaries, who reported health-related quality of life (HRQoL) at baseline and 2 years. The second was a sample of primary care patients, who reported HRQoL at baseline and 6 months. MEASURES:Medicare Advantage beneficiaries completed the Veterans RAND 12-Item Short Form (VR-12), while the primary care sample completed the Patient-Reported Outcomes Measurement Information System 29-Item Profile Measure (PROMIS-29). We constructed binary candidate PMs indicating stable or improved physical or mental HRQoL at follow-up, and continuous PMs measuring mean change over time. RESULTS:In the Medicare Advantage sample, with a sample size per entity profiled of 160, the most promising PM achieved a reliability of 0.32 as a PM. A sample size of 882 per entity would have been needed for this PM to achieve an acceptable reliability of 0.7. In the prospective sample, with a sample size of 27 per clinic, the most promising PM achieved a reliability of 0.16 as a PM. A sample size of 341 patients (at the clinic level) would have been needed for this PM to achieve a reliability of 0.7. CONCLUSIONS:Achieving acceptable reliability for these PMs and conditions would have required minimum sample sizes of 341 at the clinic level or 880 at the health plan level. These estimates can guide the design of future patient-reported outcome-based PMs.
Project description:Optimal feedback control theory suggests that control of movement is focused on movement dimensions that are important for the task's success. The current study tested the hypotheses that age effects would emerge in the control of only specific movement components and that these components would be linked to the task relevance. Fifty healthy volunteers, 25 young and 25 older adults, performed a 80s-tandem stance while their postural movements were recorded using a standard motion capture system. The postural movements were decomposed by a principal component analysis into one-dimensional movement components, PMk, whose control was assessed through two variables, Nk and ?k, which characterized the tightness and the regularity of the neuro-muscular control, respectively. The older volunteers showed less tight and more irregular control in PM2 (N2: -9.2%, p = 0.007; ?2: +14.3.0%, p = 0.017) but tighter control in PM8 and PM9 (N8: +4.7%, p = 0.020; N9: +2.5%, p = 0.043; ?9: -8.8%, p = 0.025). These results suggest that aging effects alter the postural control system not as a whole, but emerge in specific, task relevant components. The findings of the current study thus support the hypothesis that the minimal intervention principle, as described in the context of optimal feedback control (OFC), may be relevant when assessing aging effects on postural control.