Effects of Detraining on Physical Capacity and Its Relationship With Depressive Symptoms, Quality of Life and Sedentary Behavior in Community-Dwelling Older Adults: A Longitudinal Study.

BACKGROUND: Detraining is the partial or complete loss of physical training-induced adaptations as a result of exercise interruption or reduction. The COVID-19 pandemic led to the discontinuation of many older adult exercise programs and led to increased depressive symptoms (DS), increased sedentary behavior (SB), and decreased quality of life (QoL). OBJECTIVE: To evaluate the effects of detraining, in the pandemic, on physical capacity and its relationship with DS, QoL, and SB of community-dwelling older adults. METHODS: The physical capacity (static balance, dynamic balance, and lower limb and handgrip strength) of 35 participants was assessed prepandemic and after 18 and 24 months of the pandemic. DS, QoL, and SB were evaluated only at 18-month period. The analysis of variance for repeated measures or the Friedman and Pearson or Spearman tests were used for statistical analysis. RESULTS: There was a decline in dynamic balance (p < .001) and strength in the lower limbs (p < .001) in the first 18 months, as well as maintenance in the following 6 months. The reduction in dynamic balance during the 18 months of the pandemic was associated with greater DS (p = .015; r = .414) and worse QoL (p = .024; r = -.381) in this period. More time spent on SB (p = .024; r = .386) in the 18th month was associated with worse dynamic balance in the following 6 months. CONCLUSION: Detraining in the pandemic setting led to long-lasting harmful effects, which can last for 2 years, on the physical capacity of community-dwelling older adults. IMPLICATION: Our findings highlight how periods of detraining can interfere in physical and mental health of older adults.

On the Validity of Single Regression Strategy for Granger Causality Assessment in Cardiovascular and Cardiorespiratory Control Studies.

Granger causality (GC) analysis is based on the comparison between prediction error variances computed over the full and restricted models after identifying the coefficients of appropriate vector regressions. GC markers can be computed via a double regression (DR) approach identifying two separate, independent models and a single regression (SR) strategy optimizing the description of the dynamics of the target over the full model and, then, reusing some parts of it in the restricted model. The present study compares the SR and DR strategies over heart period (HP), systolic arterial pressure (SAP) and respiration (R) beat-to-beat series collected during a graded orthostatic challenge induced by head-up tilt in 17 healthy individuals (age: 21-36 yrs; median: 29 yrs; 9 females and 8 males). We found that the DR approach was more powerful than the SR one in detecting the expected stronger involvement of the baroreflex during the challenge, while the expected weaker cardiorespiratory coupling was identified by both SR and DR strategies. The less powerful ability of the SR approach was the result of the greater variance of GC markers compared to the DR strategy. We conclude that, contrary to the suggestions present in literature, the SR approach is not necessarily associated with a smaller dispersion of GC markers. Moreover, we suggest that additional factors, such as the strategy utilized to build embedding spaces and metric utilized to compare prediction error variances, might play an important role in differentiating SR and DR approaches.

Changes of the cardiac baroreflex bandwidth during postural challenges.

Baroreflex is commonly typified from heart period (HP) and systolic arterial pressure (SAP) spontaneous variations in the frequency domain mainly by estimating its sensitivity. However, an informative parameter linked to the rapidity of the HP response to SAP changes, such as the baroreflex bandwidth, remains unquantified. We propose a model-based parametric approach for estimating the baroreflex bandwidth from the impulse response function (IRF) of the HP-SAP transfer function (TF). The approach accounts explicitly for the action of mechanisms modifying HP regardless of SAP changes. The method was tested during graded baroreceptor unloading induced by head-up tilt (HUT) at 15°, 30°, 45°, 60°, and 75° (T15, T30, T45, T60, and T75) in 17 healthy individuals (age: 21-36 yr; 9 females and 8 males) and during baroreceptor loading obtained via head-down tilt (HDT) at -25° in 13 healthy men (age: 41-71 yr). The bandwidth was estimated as the decay constant of the monoexponential IRF fitting. The method was robust because the monoexponential fitting described adequately the HP dynamics following an impulse of SAP. We observed that 1) baroreflex bandwidth is reduced during graded HUT and this narrowing is accompanied by the reduction of the bandwidth of mechanisms that modify HP regardless of SAP changes and 2) baroreflex bandwidth is not affected by HDT but that of SAP-unrelated mechanisms becomes wider. This study provides a method for estimating a baroreflex feature that provides different information compared with the more usual baroreflex sensitivity while accounting explicitly for the action of mechanisms changing HP irrespective of SAP.

Correlation between changes in Timed Up and Go performance and cognition in older people with mild cognitive impairment: A longitudinal study.

BACKGROUND: Compare changes in performance on subtasks of the Timed Up and Go test over 32 months in older adults with and without mild cognitive impairment; analyze the correlation between frontal cognitive functions at baseline and changes in Timed Up and Go subtasks over time. METHODS: A longitudinal study was conducted involving 31 older adults (15 with and 16 without cognitive impairment). Functional mobility was assessed at both evaluations using an adapted version of the Timed Up and Go test and the Qualisys motion system. The test was divided into five subtasks: sit-to-stand, walking forward, turn-to-walk, walking back and turn-to-sit. Cognition was assessed at baseline using the Frontal Assessment Battery and the Clock Drawing Test. FINDINGS: Significant differences in changes in the sit-to-stand subtask over time were found between groups. The difference in the time required to conclude this subtask was greater in the older adults with cognitive impairment. However, the difference in kinematic variables (peak trunk speed and range of motion) was greater in the group without cognitive impairment. Strong and moderate correlations were found between frontal cognitive functions and changes in Timed Up and Go subtasks, especially those involving transitions (sit-to-stand, turn-to-walk and turn-to-sit) in both groups. INTERPRETATION: Motor intervention protocols should incorporate the sit-to-stand subtask in older adults with mild cognitive impairment. Moreover, changes in more complex subtasks seem to be related to frontal cognitive performance at baseline. Therefore, treatments that combine motor and cognitive functions should be administered to older adults regardless of cognitive impairment.

Autonomous nervous system modulation in supine and standing postures in children with probable developmental coordination disorder.

BACKGROUND: Children with Developmental Coordination Disorder (DCD) are known to have poor physical fitness and psychosocial problems. The autonomous nervous system (ANS) plays an essential role in the regulation of human neurophysiological processes. Inadequate ANS modulation has been associated with harmful health conditions such as poor aerobic power, high body mass index, and symptoms of stress and anxiety. Modulation of ANS in children with DCD needs to be further investigated taking into consideration variables that may influence its function. For instance, would the level of physical fitness or the symptoms of stress and anxiety affect the ANS modulation of children with DCD? AIMS: To examine the ANS modulation during supine and standing postures, and stress/anxiety with questionnaire data from children with probable-DCD (p-DCD). METHODS: and procedures: Thirty children, 8-12 years old, composed two groups paired by age, gender, peak volume of oxygen uptake (aerobic power), and body mass index (BMI): p-DCD (9 boys, mean age 10.8 y) and typically developing (TD). Both groups were compared for stress/anxiety assessment by questionnaire and spectral, symbolic, and complexity heart rate variability (HRV) analyses during posture changes. OUTCOMES AND RESULTS: p-DCD group showed higher stress symptoms than TD group for stress/anxiety assessment in the questionnaire's data, but HRV analyses showed no differences between the two groups. Both groups showed parasympathetic prevalence during supine posture and sympathetic prevalence during standing posture. CONCLUSIONS AND IMPLICATIONS: Children with p-DCD had similar autonomic control function as TD children during posture change (supine to standing). Symptoms of stress and anxiety demonstrated by p-DCD did not impact their ANS modulation. These results indicate that aerobic power and BMI are probable protective factors of ANS modulation for these children.

Comparison between probabilistic and Wiener-Granger causality in assessing modifications of the cardiac baroreflex control with age.

BACKGROUND: Probabilistic causality (PC) is a framework for checking that the occurrence of a cause raises the probability of the effect by comparing the probability of the effect conditioned and unconditioned to the cause. Even though it is less frequently utilized with respect to the more traditional model-based Wiener-Granger causality (WGC) that is based on the predictability improvement of an effect resulting from the inclusion of the presumed cause in the multivariate linear regression model, PC has the advantage of being model-free. OBJECTIVE: The aim of the study is to apply the PC framework to assess the evolution of cardiac baroreflex control with age from spontaneous fluctuations of heart period (HP) and systolic arterial pressure (SAP) and to compare it to the more common WGC approach. APPROACH: We studied 100 healthy humans (54 males, age: 21-70 years, 20 subjects for each 10 years bin). HP and SAP were extracted on a beat-to-beat basis from 5 min recordings of electrocardiogram and plethysmographic arterial pressure at rest in supine position (REST) and during active standing (STAND) under spontaneous breathing. The WGC ratio (WGCR) was computed as the log ratio of the prediction error variance of the autoregressive model on HP to that on HP with exogenous SAP. The PC ratio (PCR) was computed as the probability of observing an HP ramp given an associated parallel SAP variation divided by the probability of observing an HP ramp. MAIN RESULTS: The WGCR and PCR suggested the gradual impairment of cardiac baroreflex with age, especially during STAND. Moreover, they were significantly associated both at REST and during STAND but the degree of the PCR-WGCR association was weak. SIGNIFICANCE: PC can be effectively exploited to assess modification of the cardiovascular control during senescence even though a limited agreement was observed with WGC.

Influence of age and gender on the phase and strength of the relation between heart period and systolic blood pressure spontaneous fluctuations.

Aging affects baroreflex regulation. The effect of senescence on baroreflex control was assessed from spontaneous fluctuations of heart period (HP) and systolic arterial pressure (SAP) through the HP-SAP gain, while the HP-SAP phase and strength are usually disregarded. This study checks whether the HP-SAP phase and strength, as estimated, respectively, via the phase of the HP-SAP cross spectrum (PhHP-SAP) and squared coherence function (K2HP-SAP), vary with age in healthy individuals and trends are gender-dependent. We evaluated 110 healthy volunteers (55 males) divided into five age subgroups (21-30, 31-40, 41-50, 51-60, and 61-70 yr). Each subgroup was formed by 22 subjects (11 males). HP series was extracted from electrocardiogram and SAP from finger arterial pressure at supine resting (REST) and during active standing (STAND). PhHP-SAP and K2HP-SAP functions were sampled in low-frequency (LF, from 0.04 to 0.15 Hz) and in high-frequency (HF, above 0.15 Hz) bands. Both at REST and during STAND PhHP-SAP(LF) showed a negative correlation with age regardless of gender even though values were more negative in women. This trend was shown to be compatible with a progressive increase of the baroreflex latency with age. At REST K2HP-SAP(LF) decreased with age regardless of gender, but during STAND the high values of K2HP-SAP(LF) were more preserved in men than women. At REST and during STAND the association of PhHP-SAP(HF) and K2HP-SAP(HF) with age was absent. The findings points to a greater instability of baroreflex control with age that seems to affect to a greater extent women than men. NEW & NOTEWORTHY Aging increases cardiac baroreflex latency and decreases the degree of cardiac baroreflex involvement in regulating cardiovascular variables. These trends are gender independent but lead to longer delays and asmaller degree of cardiac baroreflex involvement in women than in men, especially during active standing, with important implications on the tolerance to an orthostatic stressor.

Separating arterial pressure increases and decreases in assessing cardiac baroreflex sensitivity via sequence and bivariate phase-rectified signal averaging techniques.

Cardiac baroreflex (cBR) is activated by both arterial pressure (AP) increases and decreases. Sequence method, a widely utilized tool assessing cBR sensitivity (cBRS) from spontaneous heart period (HP) and systolic AP (SAP) variations, allows the separated computation of cBRS from positive and negative SAP variations. The recently proposed phase-rectified signal averaging (PRSA) method has the same feature but it has been applied so far solely to positive SAP variations. We adapted the PRSA method to compute cBRS over negative SAP variations and we compared the results with those derived from sequence method over two protocols: (i) graded head-up tilt (HUT) at 15, 30, 45, 60, and 75° in 19 healthy subjects and (ii) general anesthesia induction in 118 patients undergoing coronary artery bypass graft surgery. Regardless of the sign of SAP changes and method, cBRS moved toward 0 during HUT. Only sequence method detected the cBRS decrease after general anesthesia induction. In both protocols, the correlation between the PRSA-based cBRSs derived from positive and negative SAP changes was higher than that obtained from analogous sequence-based cBRSs and correlation between equivalent cBRSs derived from different methods might be absent. We conclude that the two methods are not interchangeable in assessing cBRS. Graphical abstract Graphical representation of the baroreflex sensitivity (BRS) estimation procedures carried out using sequence (SEQ) and phase-rectified signal averaging (PRSA) techniques over spontaneous fluctuations of heart period (HP) and systolic arterial pressure (SAP). BRSSEQ and BRSPRSA was separately computed over positive (+) and negative (-) SAP variations.

Gait, dual task and history of falls in elderly with preserved cognition, mild cognitive impairment, and mild Alzheimer's disease.

BACKGROUND: Studies with functional and applicable methods and new cognitive demands involving executive function are needed to improve screening, prevention and rehabilitation of cognitive impairment and falls. OBJECTIVE: to identify differences in gait, dual task performances, and history of falls between elderly people with preserved cognition, mild cognitive impairment and mild Alzheimer's disease. METHOD: A cross-sectional study was conducted. The sample consisted of 40 community-dwelling older adults with preserved cognition, 40 older adults with mild cognitive impairment, and 38 older adults with mild Alzheimer's disease. The assessment consisted of anamneses, gait (measured by the 10-meter walk test), dual task (measured by the Timed Up and Go Test associated with the motor-cognitive task of calling a phone number), and history of falls in the past year. RESULTS: There were no differences among all groups for all variables. However, the Alzheimer's disease Group performed significantly worse in the dual task than the other groups. No item of dual task could distinguish people with preserved cognition from those with mild cognitive impairment. The groups with cognitive impairment included more fallers, and specific characteristics in history of falls between groups were identified. CONCLUSION: Dual task could distinguish Alzheimer's disease patients specifically from other cognitive profiles.

Quantifying Net Synergy/Redundancy of Spontaneous Variability Regulation via Predictability and Transfer Entropy Decomposition Frameworks.

Objective: Indexes assessing the balance between redundancy and synergy were hypothesized to be helpful in characterizing cardiovascular control from spontaneous beat-to-beat variations of heart period (HP), systolic arterial pressure (SAP), and respiration (R). Methods: Net redundancy/synergy indexes were derived according to predictability and transfer entropy decomposition strategies via a multivariate linear regression approach. Indexes were tested in two protocols inducing modifications of the cardiovascular regulation via baroreflex loading/unloading (i.e., head-down tilt at -25° and graded head-up tilt at 15°, 30°, 45°, 60°, 75°, and 90°, respectively). The net redundancy/synergy of SAP and R to HP and of HP and R to SAP were estimated over stationary sequences of 256 successive values. Results: We found that: 1) regardless of the target (i.e., HP or SAP) redundancy was prevalent over synergy and this prevalence was independent of type and magnitude of the baroreflex challenge; 2) the prevalence of redundancy disappeared when decoupling inputs from output via a surrogate approach; 3) net redundancy was under autonomic control given that it varied in proportion to the vagal withdrawal during graded head-up tilt; and 4) conclusions held regardless of the decomposition strategy. Conclusion: Net redundancy indexes can monitor changes of cardiovascular control from a perspective completely different from that provided by more traditional univariate and multivariate methods. Significance: Net redundancy measures might provide a practical tool to quantify the reservoir of effective cardiovascular regulatory mechanisms sharing causal influences over a target variable.Objective: Indexes assessing the balance between redundancy and synergy were hypothesized to be helpful in characterizing cardiovascular control from spontaneous beat-to-beat variations of heart period (HP), systolic arterial pressure (SAP), and respiration (R). Methods: Net redundancy/synergy indexes were derived according to predictability and transfer entropy decomposition strategies via a multivariate linear regression approach. Indexes were tested in two protocols inducing modifications of the cardiovascular regulation via baroreflex loading/unloading (i.e., head-down tilt at -25° and graded head-up tilt at 15°, 30°, 45°, 60°, 75°, and 90°, respectively). The net redundancy/synergy of SAP and R to HP and of HP and R to SAP were estimated over stationary sequences of 256 successive values. Results: We found that: 1) regardless of the target (i.e., HP or SAP) redundancy was prevalent over synergy and this prevalence was independent of type and magnitude of the baroreflex challenge; 2) the prevalence of redundancy disappeared when decoupling inputs from output via a surrogate approach; 3) net redundancy was under autonomic control given that it varied in proportion to the vagal withdrawal during graded head-up tilt; and 4) conclusions held regardless of the decomposition strategy. Conclusion: Net redundancy indexes can monitor changes of cardiovascular control from a perspective completely different from that provided by more traditional univariate and multivariate methods. Significance: Net redundancy measures might provide a practical tool to quantify the reservoir of effective cardiovascular regulatory mechanisms sharing causal influences over a target variable.

Assessing the evolution of redundancy/synergy of spontaneous variability regulation with age.

OBJECTIVE: We exploited a model-based Wiener-Granger causality method in the information domain for the evaluation of the transfer entropy (TE) and interaction TE (ITE), the latter taken as a measure of the net balance between redundancy and synergy, to describe the interactions between the spontaneous variability of heart period (HP) and systolic arterial pressure (SAP) and the effect of respiration (R) on both variables. APPROACH: Cardiac control was typified via the genuine TE from SAP to HP, that from R to HP, and the ITE from SAP and R to HP, while vascular control was characterized via the genuine TE from HP to SAP, that from R to SAP, and the ITE from HP and R to SAP. The approach was applied to study age-related modifications of cardiac and vascular controls in a cohort of 100 healthy humans (age from 21 to 70 years, 54 males) recorded at supine rest (REST) and during active standing (STAND). A surrogate approach was exploited to test the significance of the computed quantities. MAIN RESULTS: Trends of the genuine information transfer with age, already present in literature, were here confirmed. We originally found that: (i) at REST redundancy was predominant over synergy in both vascular and cardiac controls; (ii) the predominance of redundancy of the cardiac control was not affected by postural challenge, while STAND reduced redundancy of vascular control; (iii) the net redundancy of the cardiac control at REST gradually decreased with age, while that of vascular control remained stable; (iv) during STAND net redundancy of both cardiac and vascular controls was stable with age. SIGNIFICANCE: The study confirms the relevance of computing genuine information transfer in cardiovascular control analysis and stresses the importance of evaluating the ITE to quantify the degree of redundancy of physiological mechanisms operating to maintain cardiovascular homeostasis.

Cardiovascular coupling during graded postural challenge: comparison between linear tools and joint symbolic analysis.

BACKGROUND: A joint symbolic analysis (JSA) is applied to assess the strength of the cardiovascular coupling from spontaneous beat-to-beat variability of the heart period (HP) and the systolic arterial pressure (SAP) during an experimental protocol inducing a gradual baroreflex unloading evoked by postural change (i.e. graded head-up tilt). METHOD:: The adopted JSA can quantify the degree of association between the HP and SAP variabilities as a function of the time scale of the HP and SAP patterns. Traditional linear tools assessing the HP-SAP coupling strength, such as squared correlation coefficient, squared coherence function, and percentage of baroreflex sequences, were computed as well for comparison. RESULTS:: We found that: i) JSA indicated that the strength of the cardiovascular coupling at slow temporal scales gradually increased with the magnitude of the orthostatic challenge, while that at fast temporal scales gradually decreased; ii) the squared correlation coefficient and percentage of baroreflex sequences did not detect this behavior; iii) even though squared coherence function could measure the magnitude of the HP-SAP coupling as a function of the time scale, it was less powerful than JSA owing to the larger dispersion of the frequency domain indexes. CONCLUSION:: Due to its peculiar features and high statistical power, JSA deserves applications to pathological groups in which the link between HP and SAP variabilities is lost or decreased due to the overall depression or impairment of the cardiovascular control.

Cardiovascular coupling during graded postural challenge: comparison between linear tools and joint symbolic analysis

ABSTRACT Background A joint symbolic analysis (JSA) is applied to assess the strength of the cardiovascular coupling from spontaneous beat-to-beat variability of the heart period (HP) and the systolic arterial pressure (SAP) during an experimental protocol inducing a gradual baroreflex unloading evoked by postural change (i.e. graded head-up tilt). Method: The adopted JSA can quantify the degree of association between the HP and SAP variabilities as a function of the time scale of the HP and SAP patterns. Traditional linear tools assessing the HP-SAP coupling strength, such as squared correlation coefficient, squared coherence function, and percentage of baroreflex sequences, were computed as well for comparison. Results: We found that: i) JSA indicated that the strength of the cardiovascular coupling at slow temporal scales gradually increased with the magnitude of the orthostatic challenge, while that at fast temporal scales gradually decreased; ii) the squared correlation coefficient and percentage of baroreflex sequences did not detect this behavior; iii) even though squared coherence function could measure the magnitude of the HP-SAP coupling as a function of the time scale, it was less powerful than JSA owing to the larger dispersion of the frequency domain indexes. Conclusion: Due to its peculiar features and high statistical power, JSA deserves applications to pathological groups in which the link between HP and SAP variabilities is lost or decreased due to the overall depression or impairment of the cardiovascular control.

Maximal expiratory pressure and Valsalva manoeuvre do not produce similar cardiovascular responses in healthy men.

NEW FINDINGS: What is the central question of this study? This is the first study to evaluate and describe the cardiovascular responses during maximal expiratory pressure compared with the Valsalva manoeuvre, and whether those responses are similar. What is the main finding and its importance? This study showed that the duration of the manoeuvres appears to be responsible for the different physiological mechanisms involved in the cardiovascular responses to each manoeuvre and that the intensity of expiratory effort was related to the response in maximal expiratory pressure. These results are important to identify the risks to which subjects are exposed when performing these manoeuvres. The main purpose of this study was to compare the cardiovascular responses between the Valsalva manoeuvre (VM) and maximal expiratory pressure (MEP) and to evaluate the effect of age on these responses. Twenty-eight healthy men were evaluated and divided into two groups, younger (n = 15, 25 ± 5 years) and middle aged (n = 13, 50 ± 5 years), and they performed the VM and MEP measurement. The VM consisted of an expiratory effort (40 mmHg) against a manometer for 15 s, and the MEP was performed according to American Thoracic Society guidelines. The cardiovascular responses were analysed at rest, isotime (3 s), peak, nadir and recovery, and the cardiovascular variations (Δ) were calculated as peak or isotime minus resting values. For the statistical analysis, we used two-way ANOVA (P < 0.05). We observed that MEP and the VM generate similar changes in cardiac output (P > 0.05), but MEP presents higher values for mean arterial pressure (MAPPeak , MAPIsotime , ΔMAP and ΔMAPIsotime ) than those observed in the VM (P < 0.05). The execution time of the manoeuvres (VM ∼15 s and MEP ∼5 s) appears to be largely responsible for the activation of different physiological mechanisms involved in the cardiovascular control for each manoeuvre, and the intensity of expiratory effort is related to the higher response of MAP and peripheral vascular resistance (PVRIsotime and ΔPVRIsotime ) during MEP (P < 0.05). Moreover, it appears that age affects only the heart rate and PVR responses (P < 0.05), which were higher in the young and middle-aged group, respectively. Based on these findings, we can conclude that MEP and the VM do not generate similar cardiovascular responses, except for cardiac output.

Effect of variations of the complexity of the target variable on the assessment of Wiener-Granger causality in cardiovascular control studies.

We hypothesized that Wiener-Granger causality (WGC) indexes might have different abilities in coping with modifications of the complexity of the target variable in the context of the assessment of the cardiovascular control from spontaneous fluctuations of heart period (HP), systolic arterial pressure (SAP) and respiratory activity (R). After having defined the universe of knowledge as the set Ω = {HP, SAP, R} and the unpredictability decrement (UPD) as the difference between the prediction error variances of the target signal computed in Ω after excluding the presumed cause (i.e. the restricted Ω) and in Ω, we computed the following frequently utilized WGC indexes: (i) the plain UPD; (ii) the fractional UPD (FUPD) by dividing UPD by the prediction error variance in the restricted Ω; (iii) the normalized UPD (NUPD) by dividing UPD by the prediction error variance in Ω; (iv) the log-unpredictability decrement (LUPD) by applying the logarithm transformation to the prediction error variances before computing the UPD. The hypothesis was tested over two experimental protocols known to produce modifications of the complexity of HP variability: graded head-up tilt (HUT) inducing a gradual decrease of the HP complexity with tilt table inclination and head-down tilt (HDT) inducing the opposite trend. We demonstrated that: (1) when the strength of the causal relations from SAP to HP during HUT and from R to HP during HDT is assessed in Ω, WGC indexes reach different conclusions; (2) UPD is biased by modifications of the complexity of HP dynamics; (3) FUPD, NUPD and LUPD are less sensitive to changes of the complexity of the target dynamic, even though they have slightly different statistical power, being the NUPD the weakest one and FUPD and LUPD the strongest ones. We conclude that UPD should be avoided when assessing WGC and FUPD and LUPD should be privileged over NUPD.

Eccentric Torque-Producing Capacity is Influenced by Muscle Length in Older Healthy Adults.

Considering the importance of muscle strength to functional capacity in the elderly, the study investigated the effects of age on isokinetic performance and torque production as a function of muscle length. Eleven younger (24.2 ± 2.9 years) and 16 older men (62.7 ± 2.5 years) were subjected to concentric and eccentric isokinetic knee extension/flexion at 60 and 120° · s(-1) through a functional range of motion. The older group presented lower peak torque (in newton-meters) than the young group for both isokinetic contraction types (age effect, p < 0.001). Peak torque deficits in the older group were near 30 and 29% for concentric and eccentric contraction, respectively. Concentric peak torque was lower at 120° · s(-1) than at 60° · s(-1) for both groups (angular velocity effect, p < 0.001). Eccentric knee extension torque was the only exercise tested that showed an interaction effect between age and muscle length (p < 0.001), which suggested different torque responses to the muscle length between groups. Compared with the young group, the eccentric knee extension torque was 22-56% lower in the older group, with the deficits being lower in the shortened muscle length (22-27%) and higher (33-56%) in the stretched muscle length. In older men, the production of eccentric knee strength seems to be dependent on the muscle length. At more stretched positions, older subjects lose the capacity to generate eccentric knee extension torque. More studies are needed to assess the mechanisms involved in eccentric strength preservation with aging and its relationship with muscle length.

Conditional Self-Entropy and Conditional Joint Transfer Entropy in Heart Period Variability during Graded Postural Challenge.

Self-entropy (SE) and transfer entropy (TE) are widely utilized in biomedical signal processing to assess the information stored into a system and transferred from a source to a destination respectively. The study proposes a more specific definition of the SE, namely the conditional SE (CSE), and a more flexible definition of the TE based on joint TE (JTE), namely the conditional JTE (CJTE), for the analysis of information dynamics in multivariate time series. In a protocol evoking a gradual sympathetic activation and vagal withdrawal proportional to the magnitude of the orthostatic stimulus, such as the graded head-up tilt, we extracted the beat-to-beat spontaneous variability of heart period (HP), systolic arterial pressure (SAP) and respiratory activity (R) in 19 healthy subjects and we computed SE of HP, CSE of HP given SAP and R, JTE from SAP and R to HP, CJTE from SAP and R to HP given SAP and CJTE from SAP and R to HP given R. CSE of HP given SAP and R was significantly smaller than SE of HP and increased progressively with the amplitude of the stimulus, thus suggesting that dynamics internal to HP and unrelated to SAP and R, possibly linked to sympathetic activation evoked by head-up tilt, might play a role during the orthostatic challenge. While JTE from SAP and R to HP was independent of tilt table angle, CJTE from SAP and R to HP given R and from SAP and R to HP given SAP showed opposite trends with tilt table inclination, thus suggesting that the importance of the cardiac baroreflex increases and the relevance of the cardiopulmonary pathway decreases during head-up tilt. The study demonstrates the high specificity of CSE and the high flexibility of CJTE over real data and proves that they are particularly helpful in disentangling physiological mechanisms and in assessing their different contributions to the overall cardiovascular regulation.

The relationship between dual-task and cognitive performance among elderly participants who exercise regularly.

BACKGROUND: The dual-task performance is associated with the functionality of the elderly and it becomes more complex with age. OBJECTIVE: To investigate the relationship between the Timed Up and Go dual task (TUG-DT) and cognitive tests among elderly participants who exercise regularly. METHOD: This study examined 98 non-institutionalized people over 60 years old who exercised regularly. Participants were assessed using the TUG-DT (i.e. doing the TUG while listing the days of the week in reverse order), the Montreal Cognitive Assessment (MoCA), the Clock Drawing Test (CDT), and the Mini Mental State Examination (MMSE). The motor (i.e. time and number of steps) and cognitive (i.e. number of correct words) data were collected from TUG-DT. We used a significance level of α=0.05 and SPSS 17.0 for all data analyses. RESULTS: This current elderly sample featured a predominance of women (69.4%) who were highly educated (median=10 years of education) compared to Brazilian population and mostly non-fallers (86.7%). The volunteers showed a good performance on the TUG-DT and the other cognitive tests, except the MoCA, with scores below the cutoff of 26 points. Significant and weak correlations were observed between the TUG-DT (time) and the visuo-spatial/executive domain of the MoCA and the MMSE. The cognitive component of the TUG-DT showed strong correlations between the total MoCA performance score and its visuo-spatial/executive domain. CONCLUSIONS: The use of the TUG-DT to assess cognition is promising; however, the use of more challenging cognitive tasks should be considered when the study population has a high level of education.

The relationship between dual-task and cognitive performance among elderly participants who exercise regularly

BACKGROUND: The dual-task performance is associated with the functionality of the elderly and it becomes more complex with age. OBJECTIVE: To investigate the relationship between the Timed Up and Go dual task (TUG-DT) and cognitive tests among elderly participants who exercise regularly. METHOD: This study examined 98 non-institutionalized people over 60 years old who exercised regularly. Participants were assessed using the TUG-DT (i.e. doing the TUG while listing the days of the week in reverse order), the Montreal Cognitive Assessment (MoCA), the Clock Drawing Test (CDT), and the Mini Mental State Examination (MMSE). The motor (i.e. time and number of steps) and cognitive (i.e. number of correct words) data were collected from TUG-DT . We used a significance level of α=0.05 and SPSS 17.0 for all data analyses. RESULTS: This current elderly sample featured a predominance of women (69.4%) who were highly educated (median=10 years of education) compared to Brazilian population and mostly non-fallers (86.7%). The volunteers showed a good performance on the TUG-DT and the other cognitive tests, except the MoCA, with scores below the cutoff of 26 points. Significant and weak correlations were observed between the TUG-DT (time) and the visuo-spatial/executive domain of the MoCA and the MMSE. The cognitive component of the TUG-DT showed strong correlations between the total MoCA performance score and its visuo-spatial/executive domain. CONCLUSIONS: The use of the TUG-DT to assess cognition is promising; however, the use of more challenging cognitive tasks should be considered when the study population has a high level of education. .

Complexity analyses show two distinct types of nonlinear dynamics in short heart period variability recordings.

Two diverse complexity metrics quantifying time irreversibility and local prediction, in connection with a surrogate data approach, were utilized to detect nonlinear dynamics in short heart period (HP) variability series recorded in fetuses, as a function of the gestational period, and in healthy humans, as a function of the magnitude of the orthostatic challenge. The metrics indicated the presence of two distinct types of nonlinear HP dynamics characterized by diverse ranges of time scales. These findings stress the need to render more specific the analysis of nonlinear components of HP dynamics by accounting for different temporal scales.