INTRODUCTION
Chronic back pain, typically lasting over 12 weeks, reduces the range of motion (ROM) in the joints, decreases core muscle function and flexibility, and leads to pain and movement restrictions that hinder daily activities [1]. Most back pain (BP) arises primarily from weakened and imbalanced core muscles, as the muscles surrounding the spine and pelvis play a crucial role in core stability, and weakness in these muscles increases the risk of BP [2]. BP is generally associated with musculoskeletal injuries caused by simple and repetitive tasks and is strongly correlated with being overweight or obese [3]. Additionally, women show higher prevalence rates of musculoskeletal disorders than men, likely because of lower muscle mass, reduced muscle function, and the influence of factors such as pregnancy, sex hormones, and menstruation, which affect sensitivity to BP [4]. These physiological differences imply that a more effective treatment for BP in women may be necessary with age.
Common treatments for BP include pharmacological, non-invasive conservative, invasive, and surgical interventions. Conservative treatment is the first approach, followed by invasive and surgical treatments, based on pain severity [5]. Various methods such as nonsteroidal anti-inflammatory drugs, physical therapy, and injection therapy—including spinal procedures, manual therapy, behavioral therapy, and exercise therapy— are used in the rehabilitation of chronic BP [6]. However, because treatments such as pharmacotherapy, physical therapy, and manual therapy are generally effective only for temporary pain relief, exercise therapy is primarily utilized for fundamental pain management to strengthen muscles and increase flexibility in the lumbar region and pelvis [7]. To reduce BP through exercise therapy, it is essential to enhance lumbar flexibility and restore the elasticity and function of shortened muscles, ultimately improving muscle strength and related functional abilities such as muscle function [8].
Among the exercise therapies used effectively to improve BP, lumbar stabilization exercises (LSE) are the most common [9,10]. LSE strengthens various deep muscles within the core, enhancing spinal stability and reducing pain in patients with BP [9]. Additionally, exercises performed on a Swiss ball have been investigated to be highly effective in decreasing BP by engaging various core muscles to maintain balance under unstable conditions and improve ROM [11]. However, BP is not only influenced by the stabilization and strength of the lumbar region, which can be improved through LSE, but also by the function of the hip and gluteal muscles and lower extremity strength (LES) [12,13]. Weakness in the hip and gluteal muscles is a major cause of BP and is reported to exacerbate pain and lead to functional impairments [14,15]. Moreover, BP is highly correlated with LES, particularly with decreased strength and imbalance in the quadriceps femoris and hamstring muscles, which have been identified as major causes of BP [16]. Previous studies have emphasized the necessity of various exercise therapies to reduce BP by stretching the hip and gluteal muscles and strengthening the lower extremity muscles [8,17].
Therefore, this study aimed to investigate the effects of a 10-week LSE program combined with passive stretching (PS) and LES exercises on muscle stiffness, pain perception, and physical function factors related to BP in middle-aged women with BP.
METHODS
Participants
The participants of this study consisted of 40 middle-aged women who had been experiencing BP for over six months and had been regularly attending hospitals for treatment and diagnosis. They were randomly assigned to one of two groups: 20 participants in the lumbar stabilization exercise group (LSEG) and 20 in the combined exercise group (CEG), which incorporated both PS and LES exercises. During the 10-week exercise intervention, two participants from the LSEG and three from the CEG dropped out, resulting in 18 participants in the LSEG and 17 participants in the CEG for the final analysis. Participants were excluded if their pain visual analog scale (P-VAS) score was below 3 or above 7, or if they had undergone lumbar surgery in the past year. Additionally, participants were excluded if they experienced pain exceeding a P-VAS score of 7 during the exercise interventions (LSE, PS, and LES).
Before the study commenced, all participants were informed of the Institutional Review Board (IRB) approval and were provided with an information sheet explaining the purpose, procedures, and essential details of the study. Written informed consent was obtained from all the participants before conducting the study. This study was reviewed and approved by the IRB of Konkuk University (7001355-202205-HR-547). Before the experiment, participants were informed of the IRB approval results and familiarized with the purpose, procedures, and details of the study through an approved summary, after which individual written consent was obtained. Following consent, a pre-test was conducted one week before the exercise intervention, and a post-test was conducted within one week after the intervention was completed. The physical characteristics of participants in each group are presented in Table 1.
Exercise program
The exercise program for the LSEG consisted of four movements: plank, pelvic tilting, pelvic bridge, and back crunch (Figure 1). For the LSE, pelvic tilting, pelvic bridge, and back crunch movements were performed for 15 repetitions per movement, for a total of two sets. The plank was performed for 15 s in the first and second sets, and 30 s in the third, making 3 sets. The exercise intensity was set at an OMNI scale of 6-8, as previously mentioned, with a rest period of 60-90 seconds between exercises; thus, the total exercise time for each participant was approximately 30 min.
The exercise program for the CEG consisted of the PS and LES exercises. PS targeted five muscles: the gluteus, psoas, piriformis, hamstring, and tensor fascia lata. LES exercises used resistance bands, including leg extensions, glute kickbacks, clam shells, and standing hamstring curls. The CEG performed PS for the five muscles for two sets of at least 15 seconds each, followed by the four LES exercises. These exercises were performed for 15 repetitions per movement at an OMNI scale intensity of 6-8, with a rest period of 60-90 seconds between each exercise, and a total of two sets were completed. The total exercise time for the complex exercise program was approximately 30 min, similar to that for LSE. LES and PS exercises were performed as shown in Figure 2 and 3. The exercise intensity of all the exercise programs was set by referring to previous studies, and instructors with national qualifications monitored the participants’ exercise intensity.
Measurements
Body composition
Body composition was measured using a bioelectrical impedance analyzer (Inbody 330; Inbody, Seoul, Korea), with the participants dressed in light clothing. All participants removed the metal objects attached to their bodies before stepping barefoot on the footplate electrodes of the device. The height of each participant was entered into the analyzer. Participants were instructed to hold handgrips with both hands and stand upright with their arms and legs slightly apart. The measurements included height, weight, body mass index (BMI), lean body mass, body fat mass, and body fat percentage.
Muscle stiffness
Muscle stiffness was measured using a Myoton PRO device (Myoton AS, Estonia), which is known for its high reliability. Measurements were taken with participants resting comfortably in the prone position. The Myoton PRO device was positioned perpendicular to the skin at measurement sites, which included the quadratus lumborum, gluteus medius, and hamstring muscles.
P-VAS
The P-VAS was used to assess the intensity of BP. The P-VAS is a subjective tool that is easy to score and demonstrates high validity and reliability.
Oswestry disability index (ODI)
The ODI was used to evaluate functional limitations in daily life. The score was calculated using the following formula: Total score / (number of questions answered × 5) × 100% [18]. A score of 0-20% indicates minimal functional disability, suggesting that the individual is capable of performing daily activities with no special treatment required beyond general advice on lifting, sitting, and exercise. A score of 21-40% represents moderate disability, where daily life is minimally affected, but the individual may experience some difficulties and pain that are manageable with conservative therapy. A score of 41-60% indicates that pain is a significant issue that greatly impacts daily life and requires detailed medical examination. A score of 61-80% shows that pain severely affects the individual’s overall life, necessitating active treatment for the symptoms. A score of 81-100% can mean either that the individual is incapable of movement or that they are exaggerating and overstating their symptoms.
Physical function
Balance was assessed by having the participants perform a one-leg stand with their eyes open, which was based on their BP. This test was conducted twice for both the right and left legs and the average time, measured in seconds, was recorded as the result.
Gait speed was evaluated using an item from the Short Physical Performance Battery, that assesses walking speed in relation to daily functional activities. The time taken to walk 4 meters was recorded in seconds.
To assess functional ability, a 30-second sit-to-stand test was performed. Using a stopwatch and a 45 cm highchair, this test measured the total number of complete stands from a seated position within 30 s.
The flexibility of the lumbar region was evaluated using the YMCA sit-and-reach test, with the best result of two attempts recorded as the measurement.
Statistical analysis
Data analysis was conducted using IBM SPSS version 28.0 statistical software, and descriptive statistics for all variables were computed. The assumptions of normality and homogeneity for all variances for parametric statistical analyses were tested using the Shapiro-Wilk test for all dependent variables. To examine the interaction effects of group and measurement time on the primary variables, repeated two-way ANOVA was performed, and effect sizes were calculated using partial eta-squared (ηp²). If significant interaction effects were observed, post-hoc analyses using the Bonferroni test and paired t-tests were conducted to evaluate the efficacy of the exercise interventions within each group. The statistical significance level was set at p < 5%.
RESULTS
Body composition
No significant interactions or main effects were found for any variables related to body composition in this study. Additionally, there were no significant differences in body composition between the LSEG and CEG (Table 2).
Muscle stiffness
The changes in muscle stiffness observed in the LSEG and CEG after the 8-week exercise intervention in middle-aged women are shown in Table 3.
Although no significant interaction effects were found for muscle stiffness measurements in this study, significant main effects of the exercise interventions were observed (p < 0.05). Post-hoc analyses revealed significant improvements in muscle stiffness in the right and left quadratus lumborum, gluteus medius, and hamstring muscles in both the LSEG and CEG (p < 0.05). However, no differences were observed between the two interventions in terms of improvement in muscle stiffness.
P-VAS and ODI
The changes in P-VAS and ODI, for the LSEG and CEG after the 8-week exercise intervention in middle-aged women are shown in Table 4.
Significant interaction effects (p < 0.05) and main effects of treatment (p < 0.05) were observed for both the P-VAS and ODI. Post-hoc analyses revealed that the LSEG and CEG both showed significantly reduced P-VAS and ODI scores (p < 0.05). Furthermore, the CEG demonstrated greater improvement than the LSEG.
Physical function
Significant interaction effects (p < 0.05) and main effects of the treatment (p < 0.05) were observed for all physical function factors, including balance, 4-meter walking speed, the 30-second sit-to-stand test, and the YMCA sit-and-reach test. Post-hoc analyses revealed significant improvements in all physical functional factors in both the LSEG and CEG (p < 0.05). Additionally, CEG showed greater improvements than the LSEG group (Table 5).
Discussion
This study investigated the effects of a 10-week LSE intervention compared to a combined intervention of PS and LES exercises on muscle stiffness, pain perception, and physical functional factors in middle-aged women with BP. It was hypothesized that the combined intervention would result in greater improvements. The results confirmed that both interventions effectively improved muscle stiffness, P-VAS score, ODI, and physical functional factors, with greater improvement in the CEG than in the LSEG.
No significant interaction or main effects on body composition were observed for either intervention, and no significant differences were found between the LSEG and CEG. Previous studies on body composition have reported mixed results. Aksen-Cengizhan et al. reported significant reductions in weight, body fat percentage, and BMI after a 6-week progressive LSE program in women [19]. In contrast, Kaya et al. found no significant changes in body composition among different exercise groups, including cervical, lumbar, and thoracic exercises, in a study of 121 adult women aged 19-24 [20]. Consistent with these findings, this study found no significant changes in body composition, aligning with prior research.
Regarding muscle stiffness, P-VAS, and ODI, the improvements were greater in the CEG group, supporting the hypothesis that the combined intervention of PS and LES exercises is more effective than LSE alone for reducing pain and enhancing functional ability in daily life. Latimer et al. noted higher muscle stiffness in individuals with BP than in those without [21]. Patrick et al. reported that increased stiffness of lumbar muscles contributes to functional impairment in daily activities [22]. This study demonstrated reductions in muscle stiffness in both groups following 10 weeks of intervention, likely contributing to improved pain perception and functional ability [22]. The greater improvements observed in the CEG align with findings by Arab et al. who emphasized the importance of lower extremities strength for managing BP [23]. The enhanced strength and flexibility of the hip and glutes in the CEG likely facilitated muscle relaxation and elasticity, consistent with the findings of Perrier et al. [24]. Furthermore, the close association of LES and PS with daily functional movements further supports their effectiveness in improving physical function [25].
Significant interactions and main effects of treatment were observed for all physical functional factors, including balance, 4-meter walking speed, 30-second sit-to-stand test, and YMCA sit-and-reach test. Post-hoc analysis showed significant improvements in these measures for both the LSEG and CEG, with greater effects observed in the CEG. Rief et al. reported that LSE improved physical function, including the sit-to-stand test [26], while Javadian et al. found that LSE improved lumbar flexion and extension ROM in adults with lumbar segmental instability [27]. Previous research has indicated that enhanced deep muscle strength through exercise contributes to lumbar stability and improves the mobility of the lumbar spine and pelvis [9]. However, this study found that the combined intervention of PS and LES exercises resulted in greater improvements in physical and functional factors. This may be attributed to the higher correlation of these factors with core flexibility and lower extremity muscle function as well as improvements in muscle stiffness, P-VAS, and ODI. Van Dillen et al. reported significant functional improvements in patients with chronic BP following a 6-12 month exercise program, supporting the effectiveness of the combined exercise program in this study [28]. Therefore, for middle-aged women with BP, a combined approach that emphasizes flexibility and strength through PS and LES exercises is more effective in improving physical functional ability than focusing solely on lumbar stability. In conclusion, the 10-week combination of PS and LES exercises and LSE effectively improved muscle stiffness, P-VAS score, ODI, and physical functional factors in middle-aged women. However, the combined intervention demonstrated superior outcomes compared to LSE alone. Future studies should include large sample sizes, longer intervention durations, and consideration of extraneous variables, such as social and psychological factors, to enhance the generalizability of the findings.
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