INTRODUCTION
Low back pain (LBP) is a condition experienced by 60%-85% of the global population at least once in their lifetime, regardless of age or sex [1]. In addition to causing severe pain, LBP can reduce muscle strength, endurance, mobility, and coordination, thereby limiting daily activities [2]. In severe cases, LBP can result in dependence on others, trigger depression, and lower quality of life, contributing to the rising socioeconomic costs associated with its management [3]. Generally, studies examining sex differences in the prevalence of LBP have reported that women experience LBP more frequently than men. Moreover, the severity of pain associated with LBP increases with age [4]. This is attributable to factors such as weaker and smaller muscles in women than in men, hormonal differences, and increased pain sensitivity associated with menstruation and pregnancy [5].
Tension in the thigh muscles reportedly delays the activation of the transversus abdominis, internal oblique, multifidus, and gluteus maximus muscles, creating a vicious cycle that exacerbates LBP [6]. Furthermore, 50%-70% of patients with chronic LBP exhibit pelvic asymmetry, which is largely influenced by the sacroiliac joint [7]. Patients with LBP exhibit more lumbar movement than hip joint movement when bending forward, leading to abdominal flexor and hip extensor weakness [8,9]. Patients with chronic LBP often experience muscle and joint stiffness because of reflexive inhibition from pain, which decreases physical activity, exacerbates muscle stiffness, and leads to pain recurrence [10]. Core strength and balance control are essential in daily life and are critical for maintaining independence in clinical settings [11]. However, patients with LBP tend to experience lumbar instability owing to weakened deep muscles and impaired proprioceptive function, which can lead to recurrent LBP [12].
Although physical and pharmacotherapies are effective in relieving pain during the acute and subacute phases of LBP, they offer only temporary relief in patients with chronic LBP. Thus, exercise therapy to strengthen the muscles is considered the most effective treatment [13]. Lumbar stabilization exercises (LSE), which induce the contraction of deep muscles contributing to spinal stability, can help prevent and treat pain by reducing spinal instability and improving exercise performance [14]. Additionally, LSE strengthens the lumbar muscles, thereby maintaining the functional stability of the body [15]. Among these exercises, Swiss ball exercises are particularly effective for developing balanced muscle strength across various body parts, maintaining or increasing the range of motion (ROM) in joints, and preventing and treating LBP [16]. However, LBP is closely related to back muscle and lower extremity strength (LES) [17]. Weakness and imbalance in the lumbar muscles, quadriceps femoris muscles, and hamstrings play a significant role in the development of LBP [18].
However, most previous studies have only reported positive effects of LSE on lumbar strength, balance, lumbar joint ROM, and pain improvement. Research on the effectiveness of combined lumbar stabilization and LES exercise is lacking. Therefore, this study aimed to examine the differences in effectiveness between LSE alone and a combined regimen of lumbar stabilization and LES exercises in middle-aged women with chronic LBP who could participate in exercise programs despite not experiencing severe pain.
METHODS
Participants
This study included 20 middle-aged women residing in G City, Gyeonggi Province, Republic of Korea. These individuals had a history of chronic LBP due to persistent symptoms and had experienced continuous LBP for over the past 6 months, during which they had received treatment and diagnosis at a hospital. Participants were excluded if they had a visual analog scale (VAS) pain score of <3 or >7, a VAS score of ≥5 during exercise, or had undergone lumbar surgery within the past year. The 20 selected participants were randomly divided into two groups as follows: the lumbar stabilization exercise group (LSEG, n=10), which performed only LSE (control group), and the combined exercise group (CEG, n=10), which performed both LSE and LES exercises (experimental group). Both groups underwent an 8-week exercise program.
This study was reviewed and approved by the Institutional Review Board (IRB) of Konkuk University (7001355-202009-HR-401). Before the experiment, the participants were informed of the IRB’s review and approval and were briefed on the purpose, procedures, and guidelines of the study through an information sheet. Written informed consent was obtained from all the participants before exercise program implementation and pre- and post-intervention measurements. The physical characteristics of the participants in each group are presented in Table 1.
Exercise program
The lumbar stabilization and LES exercises performed in this study are illustrated in Figures 1 and 2, respectively, and the exercise programs conducted in the LSEG and CEG are shown in Tables 2 and 3, respectively. Each group received pre-exercise training to ensure that they understood the movements and precautions involved in the exercise program.
The program for the LSEG included plank, pelvic tilting, pelvic bridge, and back crunch exercises using a gym ball. Pelvic tilting, pelvic bridge, and back crunch exercises were performed for 15 repetitions per set, for a total of two sets. The plank exercise was performed for 15 s in the first set, 15 s in the second set, and 30 s in the third set, for 3 sets. Exercise intensity was set according to the participants’ fitness and strength levels using the OMNI scale to achieve a rating of perceived exertion (RPE) of 6 (somewhat hard) to 8 (hard). The rest periods between exercises were 1-1.5 min, and the total exercise time was approximately 30 min.
For the CEG participants who performed a combined exercise program of lumbar stabilization and LES exercises, the LSE included pelvic tilting, pelvic bridge, and back crunch exercises, each performed for seven repetitions. The plank exercise was performed for 10 s in the first set, 10 s in the second set, and 20 s in the third set, for 3 sets. The intensity and rest periods were the same as those for the LSEG, with 15 min dedicated to the LSE. Following LSE, the LES exercises involved the use of resistance bands to perform glute kickbacks, clam shells, and standing hamstring curls, with 15 repetitions per exercise for two sets. The exercise intensity was set at an RPE of 6-8, and rest periods between exercises were 1-1.5 min, with a total exercise time of 15 min.
Measurements
Body composition
Before and after the 8-week exercise intervention, the participants’ height, weight, body mass index (BMI), body fat percentage, body fat mass, and lean body mass were measured using a body composition analyzer (Inbody 620, Inbody Co., Ltd., Korea). The participants were instructed to fast for at least 4 h before the measurement and to urinate before the assessment.
Muscle stiffness
Muscle stiffness was measured using a Myoton PRO device (Myoton AS, Estonia), which is known for its high reliability. Measurements were obtained after the patient rested comfortably in the prone position. The Myoton PRO device was placed perpendicular to the skin during the measurement, and the measurement sites included the hamstrings.
VAS
The VAS was used to assess the subjective pain level in patients with knee pain before and after the exercise intervention. The VAS is a widely used method for quantifying pain because scoring is easy and it has high validity and reliability in clinical and research settings. On the VAS, scores of 0 and 10 represent no pain and extreme pain, respectively.
X-ray
Radiographic examinations were performed to assess lumbar spine and pelvic alignment. Imaging was performed by a radiologist at a professional medical institution. The participants changed into comfortable gowns before the measurement and stood still on the measurement platform, holding their breath and remaining still during the imaging process. Anterior pelvic radiographs were used to measure the differences in iliac length, iliac width, and sacral width, whereas lateral lumbar radiographs were used to measure the differences in the lumbosacral and lumbar lordosis angles.
Physical function
The balance test measures the number of seconds a participant can maintain balance in a straight-line stance. The stopwatch was stopped and recorded when the participant’s feet were lifted.
The 4-meter gait speed test assessed how quickly a participant could walk 4 m. Participants were instructed to walk at their usual pace. Scoring was as follows: 0 points for inability to complete the test, 1 point for taking more than 8.9 s, 2 points for taking 6.21-8.70 s, 3 points for taking 4.82-6.20 s, and 4 points for taking <4.82 s. Each participant was tested twice, and the faster time was used for scoring.
The chair-stand test evaluated the time taken to stand up and sit down five times without using the hands. Scoring was as follows: 0 points if it took >60 s or if the participant was unable to complete the task, 1 point for times >16.7 s, 2 points for times between 13.70 and 16.69 s, 3 points for times between 11.2 and 13.69 s, and 4 points for times of <11.19 s.
Flexibility was assessed using the sit-and-reach test. The participants sat on the floor with their legs extended and their feet pressed against a footplate. They then extended both hands forward, and on the “start” signal, leaned their torso forward to reach as far as possible. The distance from the fingertip to the footplate was measured using a ruler. Each participant performed the test twice, and the maximum value was recorded to the nearest 0.1 cm.
Statistical analysis
Data were analyzed using IBM SPSS version 28.0. Descriptive statistics were computed for all the variables. The assumptions of normality and homogeneity of variance for parametric statistical analysis were tested using the Shapiro- Wilk test for all dependent variables. To examine the interaction effects of group and measurement time on the main variables, a repeated-measures two-way analysis of variance was performed, and effect sizes were calculated using partial eta-squared. In cases where significant interaction effects were found, a post hoc analysis was conducted using paired t-tests to evaluate the effectiveness of the exercise interventions within each group. Cohen’s d, which measures the effect size based on data samples and standardized mean differences, was used to evaluate the effectiveness of each exercise intervention. Statistical differences between the means or effect sizes (Cohen’s d) were determined at a significance level (p < 0.05) and 95% confidence intervals (CI). Significant effects were assessed using statistical significance levels and Cohen’s d effect sizes (small effect, d = 0.2; medium effect, d = 0.5; large effect, d = 0.8).
RESULTS
Body composition
The changes in body composition observed in the LSEG and CEG following the 8-week exercise intervention in middle-aged women are shown in Table 4. No significant interactions or main effects were observed for any of the body composition variables. Therefore, no significant differences were observed between the effects of the 8-week lumbar stabilization exercise program alone and the combined lumbar stabilization and LES exercise interventions.
Muscle stiffness and VAS
The changes in muscle stiffness and VAS scores observed in the LSEG and CEG after the 8-week exercise intervention are shown in Table 5.
No significant interaction effects were identified for muscle stiffness across all muscles; however, significant main effects were noted (p < 0.05). Post-hoc analysis revealed a significant reduction in muscle stiffness in both groups. Specifically, in the right hamstring, muscle stiffness decreased significantly in both the LSEG (Cohen’s d = −0.94, 95% CI: −1.78, −0.01, p < 0.05) and CEG (Cohen’s d = −1.31, 95% CI: −2.18, −0.33, p < 0.05). In the left hamstring, significant reductions were observed in the LSEG (Cohen’s d = −0.65, 95% CI: −1.48, 0.24, p < 0.05) and CEG (Cohen’s d = −1.08, 95% CI: −1.93, −0.14, p < 0.05). However, the improvement in muscle stiffness was similar between the two groups.
For the VAS scores, significant interactions and main effects were observed (p < 0.05). The post-hoc analysis showed significant reductions in VAS scores for both the LSEG (Cohen’s d = −2.08, 95% CI: −3.03, −0.95, p < 0.05) and CEG (Cohen’s d = −1.63, 95% CI: −2.53, −0.59, p < 0.05), with a larger decrease in VAS scores observed in the CEG than in the LSEG.
X-ray
The changes in lumbar and pelvic alignment assessed by radiography for the LSEG and CEG after the 8-week exercise intervention in middle-aged women are shown in Figure 3. No significant interaction effects were observed for variables measured using X-rays. However, significant main effects (p < 0.05) were observed for most variables including differences in iliac crest length, iliac width, sacral width, and lumbosacral angle, except for the lumbar lordosis angle. The post-hoc analysis revealed significant reductions only in the CEG for the differences in sacral (CEG: Cohen’s d = −0.92, 95% CI: −1.77, −0.00, p < 0.05) and iliac width (CEG: Cohen’s d = −1.08, 95% CI: −1.93, −0.13, p < 0.05). Significant reductions in the lumbosacral angle were observed in both groups with similar effect sizes (LSEG: Cohen’s d = −0.97, 95% CI: −1.81, −0.04, p < 0.05; CEG: Cohen’s d = −0.96, 95% CI: −1.81, −0.04, p < 0.05). However, no significant changes were noted in the iliac crest length between the two groups.
Physical function
The changes in the physical function assessment for the LSEG and CEG after the 8-week exercise intervention in middle-aged women are shown in Table 6. Among the physical function assessment items, significant interactions and main effects (p < 0.05) were observed only in the 4-meter gait test. The CEG showed a greater improvement compared to the LSEG (LSEG: Cohen’s d = −0.95, 95% CI: −1.80, −0.03, p < 0.05; CEG: Cohen’s d = −1.42, 95% CI: −2.30, −0.42, p < 0.05). Significant improvements in the balance test (LSEG: Cohen’s d = 1.44, 95% CI: 0.44, 2.32, p < 0.05; CEG: Cohen’s d = 1.29, 95% CI: 0.31, 2.16, p < 0.05), chair-stand test (LSEG: Cohen’s d = −1.01, 95% CI: −1.86, −0.08, p < 0.05; CEG: Cohen’s d = −1.37, 95% CI: −2.24, −0.38, p < 0.05), and sit-and-reach test (LSEG: Cohen’s d = 0.21, 95% CI: −0.64, 1.04, p < 0.05; CEG: Cohen’s d = 0.45, 95% CI: −0.42, 1.28, p < 0.05) were observed in both groups, with similar effects between the two interventions.
Discussion
Individuals with LBP often exhibit decreased activation of trunk stabilizing muscles and balance-maintaining muscles compared to healthy individuals, which can impair spinal stability and contribute to LBP. Therefore, interventions targeting muscles around the lumbar region are necessary [12]. Among dynamic LSE, gym ball exercises support the lumbar spine and pelvis; enhance deep muscle strength, endurance, and flexibility; and improve reflexes, perception, balance, and proprioception [19,20]. Similarly, LES exercises using resistance bands are effective in improving gait, movement, balance, and overall physical function [21].
This study aimed to compare and analyze the effects of 8-week LSEG and CEG on body composition, muscle stiffness, VAS score, radiography, and physical function in middle-aged women with chronic LBP. The study included 20 participants who had experienced persistent LBP for >6 months and had received treatment and diagnosis at a hospital. Both the LSEG and CEG showed improvement in most pain-related variables, muscle stiffness, and physical function assessment. The CEG showed more significant improvements in pain, lumbar and pelvic alignment, and gait assessment than the LSEG.
In this study, no changes in body composition were observed in either the LSEG or CEG after the 8-week exercise program. By contrast, Aksen-Cengizhan et al. have reported significant weight, BMI, and percent body fat reduction with progressively increased gym ball volume and resistance band exercises targeting lumbar stabilization [22]. Kaya et al. identified no significant changes in the body composition of women performing LSE [23]. Similarly, we did not observe changes in body composition in either the LSEG or CEG.
Trueblood et al. have demonstrated that LSE can reduce excessive muscle tone by promoting normal movement patterns in patients [24]. The current study’s findings align with these results, showing that the 8-week exercise program improved muscle stiffness in both the LSEG and CEG. Including pelvic exercises in the LSE and LES programs likely facilitated the activation of the gluteus maximus and hip extensors, indirectly increasing the hamstring muscle length [25]. Balakrishnan et al. have noted reduced pain with LSE in individuals with LBP [26]. Arab and Nourbakhsh have reported that the LES was necessary to improve LBP, as differences in the strength of the gluteus medius were observed between individuals with and without LBP [27]. This study showed reductions in VAS scores in both the LSEG and CEG, with CEG exhibiting a more significant improvement. Thus, combined LSE and LES exercises may be more effective for pain relief than lumbar stabilization alone.
Radiographic assessments were performed to evaluate pelvic and lumbar spine misalignments that can cause chronic LBP and exacerbate musculoskeletal disorders [28]. Regular exercise improves the spinal alignment, neural activation, blood flow, oxygenation, and muscle activation [29]. In this study, the CEG program significantly reduced the differences in iliac crest and sacral widths, whereas both lumbar stabilization and combined exercises showed significant improvements in the lumbosacral angle. However, no changes were observed in the iliac crest length difference or lumbar lordosis. The greater improvement observed with the combined exercise program suggests that incorporating LES with LSE may be more effective in correcting body misalignment.
Regarding LSE and LES, MacDonald et al. have reported that using small equipment for LSE improved the ROM and strength in men [30]. Rief et al. have indicated significant improvements in chair-stand tests using the LSE [31]. This study observed significant improvements in all physical function assessment items, including balance, 4-meter gait, chair stand, and sit-and-reach tests in both the LSEG and CEG. However, the CEG showed greater improvement in the 4-meter gait test than the LSEG, and trends toward better improvement were observed in the balance and sitand-reach tests. This aligns with the findings of Hayden et al., who have reported that exercise therapy was more effective in improving function than general treatments such as physical and manual therapy [32]. Strengthening the lower extremities through targeted exercises likely reduces pain and improves function in participants with reduced physical capabilities due to LBP. In conclusion, for middle-aged women with chronic LBP, an 8-week program combining LSE and LES exercises using a gym ball and resistance bands improved muscle stiffness, lumbar pain, and physical function more than LSE using only a gym ball.
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