Approximate entropy based on attempted steady isometric contractions with the ankle dorsal- and plantarflexors: reliability and optimal sampling frequency

Complexity of knee extensor torque in patients with frailty syndrome: a cross-sectional study

BACKGROUND

Frailty syndrome is characterized by a marked reduction in physiological reserves and a clinical state of vulnerability to stress. Torque complexity analysis could reveal changes in the musculoskeletal systems that are the result of having the syndrome.

OBJECTIVE

The aim of this study was to evaluate the complexity of submaximal isometric knee extensor torque in frail, pre-frail, and non-frail older adults. A secondary aim was to analyze the torque complexity behavior in different force levels in each group.

METHODS

A cross-sectional study was conducted. Forty-two older adults were divided into three groups: non-frail (n=15), pre-frail (n=15), and frail (n=12). The data collected included body composition, five times sit-to-stand test, walking speed, and isometric knee extensor torque at 15, 30, and 40% of maximal voluntary contraction. The knee extensor torque variability was evaluated by coefficient of variation, and the torque complexity was evaluated by approximate entropy and sample entropy.

RESULTS

The frail group presented a reduction in body mass and peak torque value compared to the non-frail group. Also, the frail group showed worse physical performance (on the five times sit-to-stand test and walking speed) compared to the pre-frail and non-frail groups. In addition, the frail older adults showed reduced torque complexity compared to the non-frail group. Finally, the association between torque complexity and force levels remained similar in all groups.

CONCLUSION

Torque complexity is reduced in the presence of frailty syndrome.

Joint Moment-Angle Properties of the Hip Extensors in Subjects With and Without Patellofemoral Pain

Strength deficits of hip extension in individuals with patellofemoral syndrome are commonly reported in literature. No literature to date has examined these deficits with variable positions of the knee and hip; altering knee angle alters the length and therefore potentially the force produced by the biarticular muscles. Beyond strength, neuromuscular control can also be assessed through the analysis of isometric joint moment steadiness. Subjects consisted of a group of individuals with patellofemoral syndrome (n = 9), and a group of age- and size-matched controls with no symptoms (n = 9). Maximum isometric joint moments for hip extension were measured at 4 points within the joint's range of motion, at 2 different knee positions (0° and 90°) for each group. The joint moment signals were analyzed by computing signal Coefficient of Variation (CV). The results indicate that no significant differences were found between the groups of subjects for the hip extension moments when the knee was extended. However, there was a significant difference between the groups for the joint moments of hip extension with the knee flexed at all 4 hip positions. Results also showed hip extension CV values to be significantly higher in the patellofemoral group compared with the control group, indicating greater signal noise and therefore poorer neuromuscular control of the hip extensor musculature. This study demonstrated that individuals with patellofemoral syndrome have reduced hip extension strength and reduced neuromuscular control with the knee flexed compared with a control group. These results have implications for the etiology of patellofemoral syndrome and its rehabilitation.

Quality and structure of variability in children during motor development: a systematic review

Variability has been perceived to be beneficial to movement organization and execution, being essential to selection of movement patterns during motor development, to obtain flexible patterns and adaptability to different task demands. Human movement variability can be measured by linear and nonlinear tools. Recently, nonlinear techniques have been used successfully to give insight into motor skills control in children, and be able to discriminate pathologic and non-pathologic children. For that, this paper is the first to review systematically studies that used nonlinear measures in children. We intend to describe which mathematical tools are utilized to analyze quality and structure of variability, the factors that influence this variability and methodological procedures which are considered for its analysis, and how they are interpreted in child motor development field. A search was performed by one reviewer in relevant databases and the quality appraisal was conducted independently by two reviewers. In all, 27 articles were identified and 20 were selected for the present review. It was detected a large variation in sample characteristics and methodological issues among studies. In fact, the main importance of this review was due to the attempt to define some parameters and standardize some values for typical children and children with disabilities. It is noted that the results from nonlinear techniques depend on the task being analyzed, the age and the type of mathematical technique chosen. The presence of disability is associated to decreases in complexity and nonlinear tools were considered sensible to investigate the effectiveness of practice and intervention in typical children and children with cerebral palsy. Furthermore, future studies should be more careful in standardizing selection, recruitment and explaining missing data. Future reports also should present details of their results and limitations to favor comparisons and helping in formulating new research questions.

The appropriate use of approximate entropy and sample entropy with short data sets

Approximate entropy (ApEn) and sample entropy (SampEn) are mathematical algorithms created to measure the repeatability or predictability within a time series. Both algorithms are extremely sensitive to their input parameters: m (length of the data segment being compared), r (similarity criterion), and N (length of data). There is no established consensus on parameter selection in short data sets, especially for biological data. Therefore, the purpose of this research was to examine the robustness of these two entropy algorithms by exploring the effect of changing parameter values on short data sets. Data with known theoretical entropy qualities as well as experimental data from both healthy young and older adults was utilized. Our results demonstrate that both ApEn and SampEn are extremely sensitive to parameter choices, especially for very short data sets, N ≤ 200. We suggest using N larger than 200, an m of 2 and examine several r values before selecting your parameters. Extreme caution should be used when choosing parameters for experimental studies with both algorithms. Based on our current findings, it appears that SampEn is more reliable for short data sets. SampEn was less sensitive to changes in data length and demonstrated fewer problems with relative consistency.