Elsevier

Physiology & Behavior

Volume 227, 1 December 2020, 113145
Physiology & Behavior

Behavior of the muscle quality index and isometric strength in elderly women

https://doi.org/10.1016/j.physbeh.2020.113145Get rights and content

  • Muscle quality index (MQI) is a clinical and practical tool to assess the muscular power of the lower extremities.

  • Older women presented a lower peak force in hip flexion, extension and external rotation regardless of the method of normalization.

  • No significant differences were found in the MQI between older and younger women.

  • The MQI was negatively correlated with the time in the STS in older women.

Abstract

This study aimed (I) to compare the muscle quality index (MQI) and the isometric hip strength between younger and older women, and (II) to determine the relationship of the MQI with the sit-to-stand test (STS) and isometric hip strength in younger and older women. Twenty-eight elderly women (age= 66.2 ± 5.6 years) and twenty younger women (21.2 ± 2.2 years) participated in the study. The following dependent variables were measured: MQI, STS, body composition, and the peak isometric strength of the hip (PF) which was also normalized using three different methods (PF/Body Mass, PF/Fat-Free Mass, and PF/Body Mass0,335). Older women presented a lower PF in hip flexion, extension and external rotation regardless of the method of normalization (p < 0.001), but the PF of hip abductors and internal rotators was higher for older women (p < 0.05). No significant differences were found in the MQI between older and younger women (p = 0.443). The MQI was negatively correlated with the time in the STS in older women (r = -0.706, p < 0.001) and younger women (r = -0.729, p < 0.001), while the correlations of MQI with isometric hip strength were weaker in older women (r range: -0.082 – 0.556) and younger women (r range: -0.020 – 0.309). MQI is a clinical and practical tool to assess the muscular power of the lower extremities.

Introduction

The demographic evolution and proportion of older adults is increasing at an unprecedented rate generating a profound impact on global public health [9]. The progressive loss of neuromuscular function with aging entails degrees of disability and reduction of independence during everyday activities [15], fragility [35], risk of falling [18], reduction in physical fitness [33], and even the presence of pathologies [2]. The decrease in muscular strength has also been associated with the loss of functionality in everyday activities, such as walking [27].

Previous studies have described the importance of the hip muscles for function, stability and pain in adults and healthy subjects [26,36,38]. Possessing high levels of isometric strength in hip muscles has been associated with clinical and functional improvements in healthy subjects and also in subjects with musculoskeletal conditions [19,20,29]. On the contrary, the weakness and atrophy of hip muscles is evident in subjects with osteoarthritis, and the weakness of hip abductors has been associated with a higher prevalence of injury in healthy subjects and athletes [28,32]. Clinically, the evaluation of the strength of hip muscles can be performed by manual muscle testing [12], isokinetic dynamometers [44], functional electromechanical dynamometer (FEMD) [10], and handheld dynamometry [1]. It is also important to consider that certain variables might influence the expression of muscle strength such as body mass and muscle mass, so it is recommended to normalize strength data to avoid the influence of these variables [4,22]. In this context, different methods have been validated to normalize hip muscle strength according to sex, with specific values for both strength and torque [4].

On the other hand, the intramuscular changes associated with aging have led to the generation of muscle quality measurement strategies in the elderly [3,16,17]. Conceptually the muscle quality is defined in two different ways: (I) the relationship between strength and muscle mass, and (II) the functional physiological characteristics of muscle tissue, including muscle composition, architecture, and ultrastructure [14,17]. In this context, body size and lower-body muscle strength and power are frequently evaluated to explain changes in muscle quality associated with age [13]. In recent years the muscle quality index (MQI) has been proposed as a tool to evaluate the muscle power of lower extremities through anthropometric measurements and the time needed to complete the sit-to-stand test (STS) [3,40]. Low levels of MQI have been associated with a higher probability of dying, low physical function and poor muscle strength [7,16,24].

In this context, the MQI has been positively correlated with the strength and cross-sectional area of the knee extensors [40], but there is no evidence of the relationship that may exist between the MQI and the isometric strength of the hip muscles. Therefore, the present study aimed (I) to compare the MQI and the isometric hip strength using different normalization methods between younger and older women, and (II) to determine the relationship of the MQI with the STS test and isometric hip strength in younger and older women. It was hypothesised that (I) younger women would present a higher MQI and isometric hip strength compared to older women, and (II) the MQI would be positively correlated with isometric hip strength and negatively correlated with the time needed to complete the STS test.

Section snippets

Study design

A cross-sectional study was designed to compare the MQI and maximal hip strength between younger and older women. Two familiarization sessions separated by 48–72 h were conducted before the main experimental session to explain testing procedures and minimize potential learning effects. Each familiarization session lasted 30 min. Anthropometric measurements (height, body mass, fat mass, fat-free mass, and leg length) were collected in the first familiarization session. The third session (i.e.,

Results

Older women presented a higher BM and fat mass compared to younger women (p < 0.001) (Table 1).

Regardless of the method of normalization, older women presented a lower PF in hip flexion, extension and external rotation compared to younger women (p < 0.001). The PF (p = 0.024, ES = -0.06) and PF/FFM (p = 0.035, ES = -0.63) of hip abductors were higher for older women compared to younger women. In turn, the PF of hip adductors was higher for older women compared to younger women (p = <0.001,

Discussion

This study was designed to compare the MQI and the isometric hip strength using different normalization methods evaluated by means of a FEMD between younger and older women and to determine the relationship of the MQI with body composition, STS, and hip muscles strength. The primary finding of this study revealed that older women presented a lower isometric peak force in hip flexion, extension and external rotation compared to younger women. Our data showed a higher MQI for younger women

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