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INTRODUCTION
The university period is characterized by heavy academic demands, irregular daily routines, and prolonged sedentary behaviors, all of which increase the risk of musculoskeletal problems. Among these, low back pain (LBP) is common, and up to 80% of adults experience LBP at least once in their lifetime.1 Previous studies reported that the prevalence of LBP among university students is high and is closely associated with prolonged sitting, excessive use of digital devices, low physical activity, core muscle weakness, and postural imbalance.2 Spending more than 6 hours per day seated induces repeated compression on the lumbar spine and fatigue in trunk muscles, overloading the intervertebral discs and negatively affecting daily activity and even psychological status.3 When LBP appears early and remains untreated, it may progress to chronic LBP and lead to long-term functional limitation; therefore, prior research emphasized that early intervention in younger adults is important.4
LBP in young adults can reduce trunk stability and neuromuscular control, which is reflected in gait.5 Trunk instability alters the recruitment and coordination of lower-limb muscles and produces inefficient gait strategies.6 Previous research indicated that individuals with LBP often show abnormal or asymmetric activation in the rectus femoris, tibialis anterior, gastrocnemius, soleus, biceps femoris, and popliteus during gait.7 These neuromuscular deficits typically manifest as slower walking speed, shorter stride length, stance-time asymmetry, and increased energy expenditure.8 In some cases, excessive co-contraction of the hamstrings or gastrocnemius was observed as a compensatory strategy to stabilize the trunk when trunk control is insufficient.9-11
Trunk stabilization exercise (TSE) is a representative non-surgical, non-pharmacological intervention designed to activate deep stabilizers such as the transversus abdominis and multifidus, thereby enhancing lumbopelvic stability and redistributing mechanical load.12,13 Previous studies demonstrated pain reduction, improved postural control, and reorganization of neuromuscular coordination after stabilization training.14-16 However, a clear research gap exists in the current literature. Most previous studies concerning trunk stabilization have focused on older adults or patients with structural degeneration. Unlike degenerative LBP in older adults, LBP in university students is primarily driven by functional instability and lifestyle factors (e.g., prolonged sitting), yet research integrating gait analysis with electromyography to evaluate rehabilitation outcomes in this specific demographic is scarce. Investigating this population is crucial because their functional impairments are often reversible if addressed early, preventing the transition to chronic pathology.
Establishing an effective intervention for this population is clinically important to prevent chronicity and restore functional movement patterns. Therefore, the purpose of this study was to investigate the effects of a 4-week trunk stabilization exercise program on spatiotemporal gait parameters, lower-limb muscle activation during gait, and functional disability in university students with LBP. We hypothesized that the 4-week intervention would improve gait efficiency, optimize neuromuscular activation patterns, and reduce functional disability scores.
METHODS
This study was conducted with university students in their 20s enrolled at a university in Busan, Republic of Korea. The required sample size was calculated using G*Power 3.1 based on an effect size of 0.5, α=.05, and power=0.80; the minimum required sample size was 27, and 27 students who completed both pre- and post-intervention assessments were included. Inclusion criteria were: (1) chronic (lasting>3 months) or recurrent LBP within the last year, (2) moderate disability (21–40%) on the Korean version of the Oswestry Disability Index (K-ODI), and (3) a pain intensity score of ≥ 3 on Visual Analog Scale (VAS). Exclusion criteria were marked pain due to limited lumbar flexibility, inflammatory disease, spinal tumor or infection, history of lumbar surgery, or current pharmacological/physical/exercise therapy. All participants were informed about the study and signed written informed consent. The study was approved by the Bioethics Committee of Daegu University (Approval No.: 1040621-202509-HR-073) and conducted in accordance with the Declaration of Helsinki.
A pressure-based gait analysis system (Gait Checker, GHW-1100, GHiWell, Korea) was used to obtain spatiotemporal parameters. Prior to data collection, partici-pants performed 3 minutes of practice walking on the walkway to familiarize themselves with the experimental environment. Participants then walked at a self-selected speed across the walkway; three trials were performed and averaged. Stance phase, single-limb stance, and stride length were selected as main variables. Single-limb stance was defined as the period from contralateral toe-off to ipsilateral toe-off.17
An 8-channel wireless surface EMG system (TeleMyo DTS, Noraxon Inc., USA) was used to measure activation of the rectus femoris, tibialis anterior, gastrocnemius, soleus, biceps femoris, and popliteus during gait. Electrode placement followed standardized locations.18 EMG signals were band-pass filtered (20–450 Hz), rectified, and smoothed (50 ms RMS). Each muscle’s activation was normalized to its maximal voluntary isometric contraction (%MVIC), obtained from three trials in standardized manual muscle testing positions. To synchronize EMG with gait events, gait was recorded using a smartphone (60 fps), and participants tapped the floor twice at the start and end of the trial to create synchronization markers.19 Heel-strike and toe-off were identified frame by frame, and mean %MVIC in the stance phase was used for analysis.
Functional disability was assessed with the Korean version of the Oswestry Disability Index (K-ODI), which has shown high reliability and validity in Korean populations.20
INTERVENTION
Participants performed a 4-week trunk stabilization exercise program once daily for about 40 minutes, 5 days per week, following an instructional video. The program consisted of 16 flexibility and stabilization exercises organized from supine/frog positions to bridge, plank, side plank, squat, and standing single-leg raises, based on previous studies (Table 1).21,22 A rest period of 30–60 seconds was allowed between exercises, and intensity was adjusted using the Modified Borg Scale to avoid excessive fatigue. Before gait reassessment, treadmill walking was performed until a fatigue level of 4 (“somewhat strong”) was reached.23 To ensure adherence and accuracy, participants were required to record their daily performance, difficulty level, and pain intensity in an exercise log. The researcher monitored their progress once a week via mobile messages and requested short exercise videos if necessary to provide feedback on posture.
Data were analyzed using SPSS Statistics 29.0 (IBM Corp., Armonk, NY, USA). Descriptive statistics were used for general characteristics. The normality of the data distribution was confirmed using the Shapiro–Wilk test. To investigate the overall changes in muscle activity and gait parameters, Repeated Measures ANOVAs (Time × Muscle; Time × Variable) were performed. Upon observing significant interaction effects, paired t-tests were conducted as post-hoc analyses to identify specific pre-post differences for each muscle and gait variable. The significance level was set at $\alpha$=.05. Effect sizes were calculated using partial eta squared (ηp2).
RESULTS
General Characteristics A total of 27 participants (17 males, 10 females) completed the study. All 27 participants completed the 4-week program with an attendance rate of 100%. The mean age was 26.24±3.93 years, height 169.90±7.74 cm, and weight 74.71±12.41 kg. The baseline K-ODI score was 29.4±5.6, indicating a moderate level of disability, and the mean duration of LBP was greater than 3 months (Table 2).
To determine the effects of the intervention on gait, a repeated measures ANOVA was performed. The results revealed a significant interaction effect between time and gait variables (F=362.01, p<.001, ηp2=.933). Post-hoc analysis indicated significant improvements in all measured parameters. Specifically, the stance phase significantly decreased from 63.57±3.31% to 60.96±2.79% (p<.01). The single-limb stance phase significantly increased from 29.96±1.86% to 32.91±2.29% (p<.01). Furthermore, stride length showed a substantial increase from 77.16±22.21 cm to 96.71±7.05 cm (p<.01) (Table 3).
A significant interaction effect between time and muscle type was observed (F=3.23, p=.047, ηp2=.111), indicating that the intervention had differential effects on individual muscles. Post-hoc paired t-tests revealed significant changes in specific muscles. The %MVIC of the soleus increased significantly from 73.40±19.10% to 78.40±24.87% (p<.01), and the biceps femoris increased from 80.00±31.81% to 83.00±31.49% (p<.01). Conversely, significant decreases were observed in the rectus femoris (80.00±21.81% to 77.00±28.23%, p<.05), tibialis anterior (92.00±26.09% to 84.00±25.07%, p<.01), and popliteus (75.00±23.85% to 74.00±21.60%, p<.05). The gastrocnemius showed a slight increase (89.17±19.44% to 92.17±32.92%), but this change was not statistically significant (p>.05) (Table 4).
The K-ODI score decreased significantly from 29.40±5.60 to 23.62±5.01 (p<.01), indicating a meaningful improvement in functional status (Table 5).
| Variables | Pre-test (Mean±SD) | Post-test (Mean±SD) | t | p |
|---|---|---|---|---|
| K-ODI (score) | 29.40±5.60 | 23.62±5.01 | 7.180 | <.001* |
DISCUSSION
This study aimed to investigate the effects of a 4-week trunk stabilization exercise program on spatiotemporal gait parameters, lower-limb muscle activation, and functional disability in university students with chronic LBP. The results demonstrated that the intervention significantly improved gait efficiency, reorganized neuromuscular control patterns, and reduced functional disability. Notably, the Repeated Measures ANOVA revealed significant interaction effects for both gait variables and muscle activation, indicating that the trunk stabilization exercise produced differential, function-specific adaptations rather than a generalized increase or decrease in all parameters.
Gait analysis showed that the stance phase significantly decreased, while the single-limb stance and stride length significantly increased following the intervention. Individuals with LBP typically adopt a "defensive gait strategy" characterized by a shortened stride length and prolonged stance phase to minimize trunk motion and pain.17 The increase in stride length and single-limb stance observed in this study suggests a reversal of this protective mechanism. By enhancing lumbopelvic stability, the participants likely gained the confidence to transfer weight onto a single limb more effectively, leading to a more dynamic and efficient gait pattern consistent with previous reports.24
The EMG results provide further insight into the mechanism of these gait improvements. The significant interaction effect found in our analysis supports the hypothesis of "selective neuromuscular reorganization." Specifically, the activation of the soleus and biceps femoris significantly increased, whereas the rectus femoris, tibialis anterior, and popliteus significantly decreased. The increased activity of the soleus and biceps femoris suggests an enhancement of the posterior chain, which is crucial for generating propulsion (push-off) and maintaining pelvic stability during the stance phase.25-27 This aligns with the observed increase in stride length. Conversely, the significant reduction in rectus femoris and tibialis anterior activity indicates a decrease in excessive anterior-chain co-contraction. In LBP populations, excessive co-contraction is often a compensatory strategy to artificially stiffen the spine.28 The reduction of this unnecessary muscle tension suggests that as intrinsic trunk stability improved, the reliance on superficial global muscle guarding diminished, allowing for more economical movement.29
Functional improvements were confirmed by significant reductions in K-ODI scores. These findings align with previous studies reporting that core stabilization reduces mechanical load on the lumbar spine, thereby improving daily function.30,31 The improvement in functional status likely contributed to the normalization of gait and muscle activation patterns.
There are several limitations to this study. First, the single-group pre–post design limits the ability to draw definitive causal inferences; future randomized controlled trials are needed to control for placebo effects and natural history. Second, the relatively high %MVIC values observed in the soleus muscle warrant cautious interpretation. This finding may be attributed to "pain inhibition" or fear-avoidance mechanisms common in LBP populations. According to the pain adaptation theory, individuals with pain often fail to exert true maximum force during MVIC testing due to neural inhibition, leading to an underestimation of the MVIC reference value.32,33 Consequently, normalized gait EMG values may appear numerically inflated. Therefore, interpretations should focus on the relative pre-post changes rather than absolute magnitudes. Third, the sample consisted of young university students, which may limit the generalizability of the findings to older adults or clinical populations with structural spinal pathologies.
CONCLUSIONS
A 4-week trunk stabilization exercise program improved gait efficiency (shorter stance phase, longer stride length), optimized lower-limb muscle activation through selective reorganization, and reduced functional disability in university students with LBP. These findings suggest that trunk stabilization is an effective intervention for restoring neuromuscular control and function in young adults with lifestyle-related LBP.
