**1. Introduction**

Fibromyalgia (FM) is a chronic disease that is characterized by chronic widespread, diffuse, and persistent musculoskeletal pain, often accompanied by other symptoms, such as fatigue, sleep disorders, mood disturbance, anxiety, depression, cognitive problems, low physical activity, and balance problems [1–3]. All these symptoms have an important influence on the activities of daily living [4] and tend to reduce the health-related quality of life in this population [5]. It is estimated that FM affects 0.2% to 6.6% of the general population and mainly women over 50 years old [6].

One of the ten most debilitating symptoms of FM is balance impairments, which is experienced by 45% of this population [7]. Moreover, people with FM usually report nonspecific postural balance disorder, an increased prevalence of falls [8], a reduced performance in mobility [9–11], a higher risk of falling [12–14], and, therefore, a lower performance on balance tests [12,14]. In addition, gait disturbances [15] that are influenced by attention and executive function [16] have been also detected.

One of the most important objectives that a rehabilitation or training program should follow is to increase the individual's performance to minimize the risks associated with

**Citation:** Leon-Llamas, J.L.; Villafaina, S.; Murillo-Garcia, A.; Domínguez-Muñoz, F.J.; Gusi, N. Test–Retest Reliability and Concurrent Validity of the 3 m Backward Walk Test under Single and Dual-Task Conditions in Women with Fibromyalgia. *J. Clin. Med.* **2023**, *12*, 212. https://doi.org/10.3390/ jcm12010212

Academic Editors: Carmen María Galvez Sánchez, Casandra I. Montoro Aguilar and Markus W. Hollmann

Received: 14 November 2022 Revised: 20 December 2022 Accepted: 24 December 2022 Published: 27 December 2022

**Copyright:** © 2022 by the authors. Licensee MDPI, Basel, Switzerland. This article is an open access article distributed under the terms and conditions of the Creative Commons Attribution (CC BY) license (https:// creativecommons.org/licenses/by/ 4.0/).

the condition. Therefore, previous studies have evaluated the physical fitness of people with FM using different tests to assess flexibility [17], endurance [10], strength [10,17–19], balance [9], or mobility [11,17]. Among the physical fitness tests used to assess functional mobility, the Timed Up and Go test (TUG) has been used in different populations [20,21], including FM [9,11,17]. This test involves walking forward, balance, and turning tasks. Nevertheless, walking backward, which is not contemplated in the TUG test, is more complex and requires higher neuromuscular and proprioceptive control [22]. Moreover, it is a task that can occur in everyday life situations, such as opening a door, avoiding an obstacle, or backing up to a chair [23]. Additionally, walking backward is considered a more sensitive measure for assessing mobility and balance deficits [24,25]. In this regard, Carter et al. [23] proposed the 3 m walking backward test (3MBWT). This is a clinical tool developed in healthy older adults to identify the risk of falling that appears to be more accurate or equal to other existing tests such as TUG, Five Times Sit-to-Stand, and Four Square Step Test. Regarding the 3MBWT, it has shown high test–retest reliability and validity in the stroke population [26], community-dwelling older adults [27], multiple sclerosis [28,29], and patients with advanced knee osteoarthritis [30]. However, this test has yet to be studied in people with FM. Interestingly, it could become an important clinical tool due to the characteristics of this population since it is essential to perform a functional assessment of mobility and balance to aid in diagnosing and managing the disease.

Due to the similarities to real-life conditions and activities of daily living requirements [31], previous studies have included a simultaneous cognitive task (dual-task paradigm). Therefore, assessing these activities is essential in clinical and ecological settings since they require significant attention and executive processes [31]. In this regard, people with FM have exhibited a considerable impairment in dual-task performance compared to healthy controls [32–34]. Furthermore, the reliability of the chair stand test [18], 10-m walking test [11], TUG [11], and arm curl test [18] under dual-task conditions have been explored for people with FM. Nevertheless, the reliability of walking backward while performing a cognitive task has yet to be assessed. This issue is crucial since healthcare professionals and researchers can better understand an individual's symptoms and develop a more effective treatment plan to address their specific needs.

To our knowledge, previous investigations have not explored the reliability and validity of the 3MBWT in people with FM. Therefore, this study aimed to analyze the test–retest reliability of the 3MBWT under single and dual-task conditions. As a secondary objective, we also aimed to evaluate the test–rest reliability using different instruments (stopwatch and Chronopic). Lastly, we also aimed to assess the concurrent validity of the TUG and 3MBWT as well as the relationship between the 3MBWT test and the impact of the disease. We hypothesized that good test–retest reliability values would be obtained with both Chronopic and stopwatch, with higher scores when using a Chronopic, as previous studies suggested [9,11]. Additionally, a high concurrent validity between the 3MBWT and TUG test would be obtained considering the results reported in previous research [26–29], and a significant correlation between the 3MBWT and the impact of the disease would be observed.
