Physical activity level and physical fitness in subjects with chronic musculoskeletal pain: a cross-sectional study

Design

This study used an analytical, cross-sectional design and a convenience non-probabilistic sample. The study measures were carried out at the University of Talca Physiotherapy Clinic and in the Physiotherapy Care Center of Lircay Clinic, Talca, Chile. This study followed the recommendations for the reporting of cross-sectional studies contained in Strengthening the Reporting of Observational Studies in Epidemiology- STROBE (von Elm et al., 2007). STROBE checklist can be reviewed in Supplemental file 1.

Participants

The sample selection process is illustrated in a flow diagram (Fig. 1). Sixty-two potentially eligible subjects were selected from 184 active patients who attended the outpatient rehabilitation centers of the University of Talca and the Lircay Clinic between October and December 2022. Of these, 41 subjects were examined for eligibility based on the IASP clinical decision-making tree (Nijs et al., 2021). A sample size calculation for independent groups was performed (power = 0.8, alpha = 0.05) based on the mean and standard deviation of previous studies (Moseng et al., 2014), and considering a 50% loss rate. Based on the calculation, 30 participants were randomly recruited for the NP (n = 6 men, 9 women) and NNP (n = 6 men, 9 women) groups.

The participants included in the study met the following inclusion criteria: (1) age between 30 and 65 years, (2) medical diagnosis of chronic musculoskeletal condition or pathology without surgical intervention, (3) pain lasting ≥3 months, (4) independent walking, and (5) the ability to go up and down stairs independently. The exclusion criteria were: (1) a medical diagnosis of sensory or vestibular alterations, (2) a medical diagnosis of heart disease, and (3) a physiotherapy-patient relationship with the researchers. All the participants read and signed the informed consent form approved by the scientific ethics committee of the University of Talca (approval number 24-2022).

Measures

Clinical interview and categorization of nociplastic pain

Subjects examined for eligibility underwent a clinical interview process that included general questions such as age, sex, body mass index (BMI), diagnosis (the compromised anatomical region), and evolution time of the symptoms, and specific questions to detect the type of pain, corresponding to the IASP clinical decision-making tree and classification system (based on; Nijs et al., 2021), which was applied by a single blind investigator during the initial evaluation session. This tool contains questions that, according to the answers of the subject, allow the categorization of pain as nociceptive pain, neuropathic pain, or NP (Fig. 2). Moreover, it allows differentiating between possible NP (no comorbidities) and probable NP (at least one comorbidity) (Kosek et al., 2021). The participants were categorized as NNP or NP, regardless of the subcategorization of each one.

Statistical analysis

The Shapiro-Wilk test was used to determine whether the variables followed a normal distribution. The mean and standard deviation are reported for the total IPAQ-SF survey (METs/min/week), the 5R-STS (s), the HGS test (kg), and the YMCA 3MST (peak VO₂ [mL/kg/min]). An independent samples t-test was used to compared between the groups. Finally, Cohen’s d (Cohen, 2013) was calculated to determine the effect size of the differences. Statistical analyzes were performed using SPSS Version 26.0 software (IBM Corp., Armonk, NY, USA). The statistical significance level was set at p < 0.05.

Physical activity level

The NP group reported a significantly lower level of vigorous PA compared with the NNP group (p = 0.0009): 0.0 and 645.87 METs/min/week, respectively. In the moderate PA dimension, the NP group reported 0.0 METs/min/week, significantly lower (p = 0.0002) than the NNP group, which reported 348.0 METs/min/week. In the light PA dimension, there was no significant difference between the groups (p = 0.08). Total PA was significantly lower for the NP group (p = 0.005): 652.86 METs/min/week compared with 1486.66 METs/min/week for the NNP group. Considering the PA level categorization, more subjects with NP (53.3%) were characterized at the low PA level, while the NNP group had the highest proportion of subjects (66.6%) characterized at the moderate level (Table 3).

Physical fitness

The NP group had a significantly longer execution time in the 5R-STS test (p = 0.000), taking 6.94 s longer (65%) than the NNP group; the effect size was large (d = 1.87). In addition, the NP group presented significantly lower HGS (p = 0. 002), generating 20.43 kg (54.8%) less than the NNP group; the effect size was large (d = 1.28). Finally, the difference in the estimated peak VO₂ between the NP and NNP groups was 1.05 mL/kg/min. This difference was not significant (p = 0.635), and the effect size was small (d = 0.17) (Table 4).

Discussion

The present study aimed to compare the levels of PA and PF in subjects with NP and NNP. The main results showed that compared with the NNP group, the NP group reported a significantly lower level of PA—specifically the vigorous PA, moderate PA, and total PA dimensions of the IPAQ-SF—and also presented worse PF, characterized by significantly lower upper limb strength and lower limb strength and power. There was not a significant difference in peak VO₂ between the NP and NNP groups.

The PA level was measured using the IPAQ-SF, which estimates this value based on the amount of time each week that an individual dedicates to vigorous, moderate, or low activity. This information was used to the total METS of PA. In this study, the NP group reported a lower level of moderate, vigorous, and total PA compared with the NNP group. This difference may be explained by the characteristics of pain and comorbidities associated with NP symptoms reported by the participants (Nijs et al., 2021). The subjected with NP presented pain of non-neuropathic or nociceptive origin as main symptom, with the presence of evoked hypersensitivity phenomena, and reported sleep deprivation (n = 5), general fatigue (n = 4), or both symptoms (n = 6). These comorbidities increase pain sensitivity, which could explain the avoidance of movements that involvepowerful or sustained muscle contractionsand vigorous PA, and lead to a maladaptation of the neuromuscular and cardiovascular systems (Fitzcharles et al., 2021).

Based on the literature, subjects with classic chronic pain have much lower PA levels based on the IPAQ-SF compared with healthy controls (Ezeukwu et al., 2019). However, no studies have categorized pain as nociplastic or non-nociplastic according to the IASP criteria. Previous studies have related PA to pain comorbidities, avoidance behaviors, and central sensitization symptoms in subjects with chronic low back pain. Huijnen et al. (2011) evaluated the PA level by using the Beacke Physical Activity Questionnaire in subjects with chronic low back pain. The authors categorized the participants according to their behaviors, observing that subjects with avoidance behaviors and fear of movement presented lower levels of self-reported PA. More recently, Zheng et al. (2023) compared the PA level measured by accelerometry between subjects with chronic low back pain and with and without symptoms of central sensitization; they observed different PA patterns between both groups. Although total PA was not different between the groups, subjects with central sensitization showed more inactive time compared with subjects without sensitization. While avoidance behaviors and central sensitization could represent an indirect relationship to the clinical categorization of NP, more studies that subclassify pain according to the IASP criteria are necessary to corroborate the results of the present study. Longitudinal studies are required to establish a better relationship between the PA level and NP. In addition, studies are needed that assess the PA level with accelerometry as well as self-reported questionnaires.

The NP group presented a lower PF level compared with the NNP group—specifically, lower limb strength and power based on the 5R-STS test and HGS. The HGS test can be a reliable method for assessing total muscle strength, and indirectly the level of muscle sarcopenia (Gonçalves et al., 2018). The 5R-STS has been validated as an objective test to measure functional impairment related to lower limb power and strength in subjects with various chronic pathologies such as non-specific low back pain (Klukowska et al., 2021).

Previous studies have reported that subjects with chronic pain perform worse in PF tests such as the HGS test, the 5R-STS, the 6-Min Walk Test, and the Astrand test, among others (Choi et al., 2021; Klukowska et al., 2021). These results are consistent with the present findings, which could be explained by neural adaptations of processing and modulation of nervous system signals generated by subjects with NP (Fitzcharles et al., 2021; Chimenti, Frey-Law & Sluka, 2018). NP is related to central sensitization processes, which implies changes in the representation of sensory and motor areas. The poor differentiation of afferent pain pathways causes an inhibition of motor efferent stimuli, which results in lower muscle recruitment, and decreased ability to generate force and muscle power (Hodges et al., 2013). This causes catastrophizing and avoidance behaviors that lead to disuse, disability, and altered neuromuscular activity during functional movements (Lund et al., 1991; Vlaeyen et al., 1995), contributing to worse test performance, muscle weakness, and lower PF. This could also explain the lower levels of vigorous PA (i.e., aerobics, running, and fast bicycling) reported by subjects with NP, because these require both the recruitment of a greater number of motor units and more muscle groups in a shorter amount of time.

Peak VO₂ of the YMCA 3MST test was not significantly different between the NP and NNP groups. Previous studies have reported that subjects with chronic pain have worse cardiorespiratory performance in submaximal and maximal tests compared with healthy controls (Smeets et al., 2006; Duque, Parra & Duvallet, 2009; Doury-Panchout et al., 2012). However, no studies have analyzed differences between different pain subgroups. The absence of difference between the groups in the YMCA 3MST test could be explained by the submaximal characteristics of this test; hence, it may not be the best tool to estimate peak VO₂ in subjects with pain. In the present study, the NP and NNP groups did not show differences in activities with a low metabolic cost (light PA) categorized with the IPAQ-SF, which includes tasks such as walking or up and down stairs. If the level of adaptation of subjects with NP and NNP is similar for the task performed, it may not be demanding enough to show differences in the estimated peak VO₂. Although direct measurement of VO₂ could be an alternative to represent PF, it would not be recommended given the limitation of subjects with NP to perform vigorous PA, as observed with the PA measurements. Due to the characteristics of NP, it would be difficult to determine whether a difference in VO₂max is due to their cardiorespiratory performance or to exercise-induced pain. Other representative variables of PF should be considered in future studies.

This study has some limitations that need to be mentioned. The sample size is small relative to the high prevalence of chronic pain. Moreover, this study used a convenience sample of people attending health centers. It is important to increase the sample size and to recruit a random sample. Regarding the data analysis, there was a significant 9.5-year age difference between the NP and NNP groups, which could have influenced the differences found in upper limb strength and lower limb strength and power. However, the literature shows that the decrease in strength in both men and women occurs after the age of 60 years (Mancilla, Ramos & Morales, 2016). Given that the mean age of the entire sample was 44.85 years, age can be ruled out as a confounding variable. Regarding the measurements, using the IPAQ-SF to determine the PA level implies a subject bias as it is self-reported and depends exclusively on the subject’s understanding of the tool (Hagstromer et al., 2010). Nevertheless, it is widely used to assess PA and has been validated for the Chilean population (Palma-Leal et al., 2022). In addition, an indirect peak VO₂ test was used in the present study. Although sufficient methodological safeguards were taken to validate the procedure, it is advisable to carry out laboratory tests that allow measuring VO₂max objectively, which provides a better characterization of PF. Finally, the present study measured the differences in the levels of PA and PF in subjects with NP and NNP; however, some characteristics of the population must be taken into consideration. First, unlike other studies, a broad spectrum of diagnoses rather than a single pathology (i.e. low back pain) was considered. Although this approach does not influence the IASP categorization of NP, future studies should consider a larger sample to allow differentiation between the diagnosis, subtypes of pain, and comorbidities. On the other hand, other psychosocial factors, such as depression (Codella & Chirico, 2023) could affect the level of PA The IASP decision-making tree considers specific comorbidities, such as sleep deprivation and general fatigue, ignoring other conditions that may affect the level of PA and PF. It would be recommended that future studies conduct a comprehensive clinical interview and integrate other evaluations associated with pain experiences (i.e., Tampa Kinesiophobia Scale) in order to identify other factors associated with nociceptive pain and central sensitization processes.