Effects of an eight-week physical exercise program on low back pain and function in fruit workers: A randomized controlled trial

1. Introduction

Low back pain is one of the most common skeletal disorders and the most prevalent work-related musculoskeletal disorder (WMSD), responsible for approximately 568.4 million cases worldwide in 2019 and reaching an annual prevalence of more than 50% in adults in Brazil [1, 2]. More recent data shows that low back pain prevalence rates increased by 26.8% between 1990 and 2017, being the leading cause of years lived with disability [3]. Low back pain can affect individual, physical, social, and psychological aspects, contributing to increased healthcare costs and work incapacity [4, 5, 6, 7, 8]. This condition was responsible for total social costs which totaled US$2.2 billion in Brazil between 2012 and 2016, and productivity losses accounted for 79% of these costs [4].

Low back pain in workers has shown a high prevalence and a strong relationship with absenteeism and presenteeism rates, being considered the leading cause of disability [7]. However, the prevalence rates vary according to the different branches of work, with values between 44 and 64% reported in health professionals, teachers, factory, and office workers [9, 10, 11, 12]. The reported prevalence of low back pain among agricultural workers can reach up to 86% [13, 14], and disability due to it is higher in low- and middle-income countries, where there are few possibilities for modifying work activities [7].

It is believed that a complex combination of factors causes low back pain. Among occupational factors, the type of work activity, maintenance of postures, repeated movements, and exposure to loads are considered important risk factors for low back pain [15, 16].

Agricultural workers perform activities which involve manual tasks performed in open environments and are often exposed to high temperatures [17, 18]. In addition to these factors, viticulture workers have greater overload in the upper limbs and trunk region, including twisting movements and repetitive lifting of excessive loads [19, 20]. The combination of these tasks and factors imposes a physical and functional demand related to the high prevalence rates of musculoskeletal complaints [21].

Different strategies for preventing and treating low back pain in workers have been researched in recent decades [22]. In this context, the practice of physical exercise has gained prominence due to its potential effects on reducing signs and symptoms of pain and improving the functional status of individuals [23]. In addition, the recent American Physical Therapy Association Clinical Practice Guidelines for low back pain strongly recommend using physical training interventions to treat chronic low back pain [24].

On the other hand, a recent systematic review with meta-analysis seeking to investigate the effect of physical exercise applied in the work environment on workers with low back pain, demonstrated that exercise was not superior to other pain management strategies, such as guidelines and booklets [25]. The studies included in this review [25] evaluated office and industry workers with acute and chronic low back pain.

Considering that agricultural workers have specific occupational demands [19, 20] and that acute and chronic conditions have different prognoses [26], the present study aimed to investigate the effect of an eight-week strength, endurance, and flexibility exercise program compared to guidance on pain and disability outcomes in fruit workers with chronic low back pain. The study hypothesized that the group submitted to physical exercise in the workplace would present a more significant reduction in their pain and disability levels.

2. Materials and methods

3. Results

The first recruitment phase was completed in September 2020, and the second in January 2021. The intervention period for the first phase was between October and December 2020, and between January and March 2021 for the second phase. It was necessary to carry out two entries, given the many farm layoffs due to the COVID-19 pandemic.

A total of 90 workers were initially evaluated. However, only 63 were randomized into the experimental and control groups. Finally, 44 participants effectively participated in the study and received the intervention. The assessment, allocation, reassessment, and analysis processes are shown in Fig. 1.

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The sample consisted of 32 women (72.7%) and 12 men (27.3%), with a mean age of 37 years, body mass of 72.71 kilograms, a height of 1.62 meters, Body Mass Index of 27.68 and mean of pain of 6.79 points on the Numerical Pain Scale. Descriptive characteristics of participants in the total sample and stratified by group are presented in Table 1.

Table 2 presents the mean values, standard deviation, and differences within and between groups for pain intensity, disability, kinesiophobia, and Global Perceived Effect. The results indicated that pain and disability symptoms improved with both interventions ( 0.01). The EG showed a mean decrease of 4.55 points on the numeric pain scale and 4.45 points on the Roland-Morris. The CG showed mean reductions of 3.81 points for pain and 4.43 for disability. The interventions had no effect on the kinesiophobia outcome ( p = 0.81).

No differences were found between groups ( $p>$ 0.99) for all analyzed outcomes. The analysis of the Global Perceived Effect showed no difference between the control and experimental groups ( p = 0.118). Both groups had scores ranging from 0 (no difference) to 5 (fully recovered) points. Only one participant in the EG responded that he had not felt a difference in low back pain before and after the intervention, and 12 participants reported feeling fully recovered. Two participants in the CG reported no difference in low back pain before and after the intervention, and eight reported feeling fully recovered. No adverse events were recorded in either group throughout the interventions.

This randomized clinical trial aimed to evaluate the effect of a resistance and stretching exercise program on pain intensity and function of the lumbar spine in fruit farming workers in the São Francisco Valley. The results found in this study demonstrated that both groups presented similar changes in the reduction of low back pain intensity and disability after eight weeks of intervention, with no significant differences between groups. Thus, it was possible to observe that supervised exercise in the work environment was not superior to orientation for carrying out exercises through a booklet in the home environment, rejecting our initial hypothesis.

A recent Cochrane systematic review of 249 studies [39] concluded that physical exercise is more effective in treating chronic low back pain, significantly reducing pain symptoms and functional limitations compared with no treatment, usual care, or placebo. On the contrary, our results demonstrated that the group that performed the supervised exercise program at the workplace did not present better results than the control group. However, our control group reported having completed the structured program of stretching exercises performed at home. In this sense, both groups may have benefited from the practice of exercises, considering that the literature recognizes that the different types or modalities of exercises have positive effects in managing musculoskeletal pain through different mechanisms [39].

Resistance exercises in the case of the experimental group may have resulted in increased muscle strength and function, gain in the range of motion, and improved neuromuscular control and stabilization. In addition to the physical benefits, the workers may have benefited from the emotional and psychological effects of physical exercise, which are strongly associated with improving pain and disability [39]. Furthermore, resistance exercise may have reduced pain perception, as it contributes to activating central pain inhibition and modulation mechanisms, increasing the concentration of β -endorphins and catecholamines, and altering sensitivity to painful stimuli [40, 41]. The workers in the control group performed ten muscle stretching and joint mobility exercises. Evidence demonstrates that this exercise also promotes benefits in the pain symptoms of different disorders that affect the musculoskeletal system. Muscle stretching has the hypothesized mechanism of reducing pain by decreasing muscle tension and stiffness, decreasing the viscoelasticity of the tissues, increasing the range of motion, and improving blood flow in the capillaries adjacent to the stretched structures [42, 43].

These findings seem to corroborate the conclusions of Bernardelli et al. [44], who observed that a regular physical exercise program at home or the workplace was equally effective in improving disability and kinesiophobia related to low back pain in workers with low back pain. In this context, training guidelines for a home exercise program can be promising in improving outcomes related to low back pain, which are less costly for the company in terms of lost work hours and are more cost-effective [44].

On the other hand, Jakobsen et al. [45, 46] demonstrated that ten weeks of supervised physical exercise at work was more effective than home exercises for reducing the intensity of low back pain in health professionals. However, methodological differences such as the characteristics of the workers and their work demands, the duration of the intervention, and the lack of monitoring of the home group explain the divergence in the results. In addition, whether there was a control or selection of volunteers about the initial intensity of pain and duration (acute or chronic) was not reported. These factors directly influence the size of the effect observed for the outcomes of pain and disability since most episodes of acute low back pain have a favorable course, with resolution within 6 to 8 weeks, even in the absence of active treatment [47]. The conclusion of previous studies [45, 46, 47] indicating the superiority of exercises performed in the workplace is based on statistical differences (difference between groups of 0.7 [CI95% - 1.0 to - 0.3]). In this case, it is possible to verify that the change of 0.7 points in the intensity of low back pain does not reach clinically important values, making the superiority of supervised exercise in the workplace questionable. Thus, the reported results or original studies must be interpreted with caution, considering the clinical relevance of the findings, the follow-up time, the natural course of the disease, and especially the external validity of these studies.

The decrease in the intensity of low back pain observed in the present study in both the experimental group of 4.55 points, and in the control group of 3.81 points, is above the established value for a minimal important clinical difference (MICD) for chronic low back pain, which is 1.7 points [31]. Similarly, a decrease of 4.45 points was observed for disability in the experimental group and 4.43 points in the control group assessed by the Roland-Morris questionnaire, with these reductions being greater than the MICD of this instrument, which is 3.5 points [48]. The reduction of pain and incapacity of the lumbar region in both groups above the predetermined MICD values [31] is confirmed by the volunteers’ Global Perceived Effect (GPE). Although no significant differences were observed between the experimental and control groups in the analysis of the workers” GPE, both reported mean values greater than three points, close to the upper limit of “total recovery” indicated by the scale, which is five points. These data have a meaningful clinical significance, as none of the workers reported worsening the clinical condition throughout the intervention, and almost half of the assessed sample reported feeling fully recovered.

Another relevant aspect to be analyzed regarding low back pain concerns kinesiophobia due to its relationship with disability and the perpetuation of symptoms. Lack of activity due to fear of movement can induce changes in muscle tropism and function and worsen symptoms [49]. When analyzing the Tampa Scale of Kinesiophobia (TSK) score, no significant difference was found between time and group. The results in the literature are divergent regarding the effects of different exercise modalities on kinesiophobia [49, 50, 51, 52]. However, our findings corroborate studies which evaluated more physically active participants with lower indicators of kinesiophobia in the baseline assessment [50, 51, 52]. This finding can be explained by the fact that even with a pain level above three points on the Numerical Pain Scale, all workers continued their activities normally on the grape farm. Gregg et al. [53] found that the changes in TSK scores after a rehabilitation program in patients with low back pain did not strongly correlate with pain scores, functional levels, or return to work results. Therefore, constructs such as kinesiophobia may or may not develop regardless of the intensity of symptoms and perceived disability.

Finally, the scarcity of clinical trials with intervention in the work environment involving fruit workers makes this study very relevant. However, the results of this study have some limitations. Our small, even though significant sample size and participant characteristics made it challenging to analyze possible moderating effects, such as gender differences. This fact is related to many layoffs due to the COVID-19 pandemic and the fear of employees that involvement in the intervention could harm productivity. Another limitation was using subjective instruments that required the participants’ recall to be answered, which could lead to a memory bias.

The clinical relevance of the current findings is that eight weeks of supervised exercise at the workplace do not offer different results in reducing the low back pain intensity or disability in fruit workers compared to home exercise guidelines using booklets. Future studies should be carried out to investigate whether a particular exercise modality is more effective than another in reducing low back pain and disability. In addition, it should be explored whether some interventions with exercise would be superior among workers with different occupational activities.

5. Conclusions

The results of the present study demonstrate that the intervention with a physical exercise program performed in the work environment was not superior to the intervention with home exercises guided by a self-explanatory booklet. However, both interventions showed important clinical improvements in pain intensity and disability. These findings reinforce that employers can use both strategies to mitigate the impact of low back pain on the health and functional and work performance of fruit workers.

Funding

This study was financed in part by the Coordenação de Aperfeiçoamento de Pessoal de Nível Superior – Brasil (CAPES) – Finance Code 001.

Author contributions

Conceptualization, M.H.P.P., S.P.B.P., G.A.B., A.C.R.P., R.C.A.; formal analysis, M.H.P.P., S.P.B.P., G.A.B., A.C.R.P., R.C.A.; investigation, M.H.P.P., S.P.B.P., V.Y.S.N., F.A.S.O.; data curation, M.H.P.P., S.P.B.P., V.Y.S.N., F.A.S.O.; writing – original draft preparation, M.H.P.P., V.Y.S.N.; writing – review and editing, F.L., A.C.R.P., R.C.A.; supervision, F.L., R.C.A.; project administration, A.C.R.P., R.C.A.; All authors have read and agreed to the published version of the manuscript.

Ethical considerations

This study was approved by the Research Ethics Committee of the University of Pernambuco (protocol CAAE 17386919.6.0000.5207).

Informed consent

All participants read and signed the consent form, which contained all information regarding the study.

Data availability statement

The data supporting this study’s findings are available on request from the corresponding author.

Supplementary data

The supplementary files are available to download from https://dx-doi-org.web.bisu.edu.cn/10.3233/BMR-230201.