Elsevier

Brazilian Journal of Physical Therapy

Volume 24, Issue 1, January–February 2020, Pages 30-38
Brazilian Journal of Physical Therapy

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

https://doi.org/10.1016/j.bjpt.2018.12.004Get rights and content

Highlights

  • •

    Knee extensor torque complexity is reduced in the presence of frailty syndrome.

  • •

    Frail participants showed a reduction in body mass, peak knee extensor torque and decreased physical performance.

  • •

    The relationship between complexity and force levels was similar in all groups.

Abstract

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.

Introduction

Frailty syndrome is considered a different process from normal physiological aging. This syndrome is characterized by a marked reduction in physiological reserves, making the individual more vulnerable to adverse outcomes, including the risk of falls, institutionalization, hospitalization, disability, and death.1, 2, 3 Some researchers describe frailty as a clinical state of vulnerability to stress, due to decreased resilience, with a progressive decline in the capacity to maintain homeostasis.1, 3 Additionally, frailty syndrome is associated with changes in the complexity of biological signals, such as, heart rate4 and oscillation of pressure center.5, 6 However, the effect of frailty on the neuromuscular system has not yet been investigated from this perspective. Measurements of physiological complexity are useful for early identification and preclinical degeneration, as well as for evaluating the effects of strategies rehabilitation and prevention.7

The neuromuscular system consists of multiple components: excitatory drive from supraspinal centers, α-motoneuron excitability, antagonistic muscle activity, motor unit recruitment and rate coding, neuromuscular transmission, muscle mass, excitation-contraction coupling processes, and muscle morphology and architecture.8 The interaction of these components results in force fluctuations with irregular and non-linear behavior, which is more appropriate to evaluate using non-linear measurements, such as the complexity of the force output.9

Therefore, non-linear methods can be used to analyze the torque complexity, such as entropies. These are mathematical algorithms that quantify the degree of predictability of the isometric torque fluctuations over time. Entropies evaluate the predictability and regularity of a signal, and they are an indirect measure of the complexity of the force output.10, 11, 12 Lower values of torque complexity indicate a less adaptive response to internal or external demands and may cause gait instability and increase the risk of falls.13 This torque complexity reduction could be related to the loss of structural components, such as a reduction in the number of motor units, or changes in the coupling between them, for example in the reduction of the simultaneous action of motor unit recruitment.14

In this context, the primary aim of this study was to evaluate the complexity of submaximal isometric knee extensor torque in frail, pre-frail, and non-frail older adults. In addition, a secondary aim was to analyze the torque complexity behavior at different force levels in each group. It was hypothesized that frail older adults would exhibit a reduction in knee extensor torque complexity compared with pre-frail and non-frail older adults.

Section snippets

Study design

A cross-sectional study was conducted. According to the sample calculation using G*Power 3.1.3 program, based on ANOVA repeated measures, considering group factors (non-frail, pre-frail and frail) and force levels (15%, 30% and 40% of maximal isometric voluntary contraction), it was observed that in order to reach a power of 80%, with an effect size of 0.25 and a significance level of 5%, 36 volunteers would be required, equally distributed among the groups.

Potentially eligible participants

Results

A total of 61 older adults were evaluated. Nineteen subjects were excluded due to the presence of a cognitive impairment (3), a history of stroke (5), or did not finalize the evaluations, and did not return for the second evaluation day (11). The final sample consisted of 42 individuals, divided into three groups: non-frail group (n = 15), pre-frail group (n = 15), and frail group (n = 12) (Fig. 1).

The baseline characteristics of participants are described in Table 1. All groups were homogeneous for

Discussion

The major novel findings of this investigation were: (a) torque complexity was reduced in the presence of frailty syndrome; (b) all groups showed an increased torque complexity with increased force levels.

Regarding the clinical and anthropometric data, there were no significant differences between the groups for age and sex. The frail group presented lower body mass and stature than the non-frail group. This finding is in accordance with Ferriolli et al.41, who affirmed that older adults

Conclusion

To the best of our knowledge, this is the first study to investigate the relationship between torque complexity and force levels in frailty syndrome. In conclusion, torque complexity was reduced in the presence of frailty syndrome although the relationship between torque complexity and force levels remained similar in all groups. Lipsitz47 suggested that physical exercise could potentially restore the dynamics of biological systems, thus improving health and preventing frailty. In this way,

Conflicts of interest

The authors declare no conflicts of interest.

Acknowledgements

This study was supported by the Coordination for the Improvement of Higher Education Personnel (CAPES).

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