Introduction
Chronic nonspecific low back pain (CNLBP) is considered a common musculoskeletal system problem that can lead to disability. It entails pain, stiffness, or tightness in the area of the lower part of the spine from below the rib cage to above the buttocks; lasts for more than 12 weeks; occurs without any known cause, and accounts for 90% of LBP.1
Lumbar muscle dysfunction, diminished strength of muscles, neuromuscular control impairment, and changes in movement patterns are among the problems that are linked with CNLBP.1 The problems cause increased muscle fatigue, impaired muscle endurance,2 and diminished lumbar proprioception, which can affect spinal posture and muscle coordination. All of these might lead to increased muscle and spinal demands and thus increase LBP problems.3
Currently, non-pharmacological treatments are prescribed as primary treatments for chronic LBP, which include exercise therapy, multidisciplinary treatment, and acupuncture.4 Exercise can treat back pain, fatigue and endurance, lumbar proprioception, and fear of movement.5,6 In turn, the activation of acupoints, acupuncture, proved effective in pain and disability in CNLBP7 and increases muscle excitability, strength, and endurance.8 At the same time, classic needling acupuncture can be constrained by such disadvantages as needle phobia, pain sensation, bleeding, and risks of infections. That is why laser phototherapy on acupoints became an alternative method that could address these drawbacks.9
Laser acupuncture (LA) is the practice whereby an individual uses lasers to stimulate acupuncture points along with the biological action of photobiomodulation (PBM). The lasers applied in LA differ based on their characteristics and therapeutic use.10 The laser power output exceeds 500 mW, allowing the laser to penetrate into deeper tissues and produce photothermal, photochemical, and photomechanical reactions on them.11
LA may enhance ATP synthesis, control nociceptive, neuromuscular, and inflammatory processes, and facilitate tissue regeneration through PBM.10 A wavelength from 780 to 950 nm can penetrate tissues that are deep, such as the back area.11 Previous studies have reported beneficial effects of high-power lasers on muscle exhaustion, 12 proprioceptive accuracy, 13 pain, muscular power, and physical function. 14
For lower back pain, high-power lasers were used locally rather than activating acupoints, as previously demonstrated.12–14 Unlike conventional local high-power laser irradiation, high-power laser acupuncture (HPLA) combines PBM with targeted stimulation of traditional acupuncture points. This approach was selected to investigate the potential sensory and neuromuscular effects of acupoint stimulation in addition to local photobiomodulatory effects. The rationale is that stimulation of acupuncture points may influence sensory input involved in proprioceptive processing and motor control, potentially contributing to improved joint repositioning accuracy.
However, this proposed mechanism has not been established for HPLA. Luan et al15 reported improvements in proprioception, balance, and self-reported function following acupuncture or similar needling therapy in individuals with chronic ankle instability. These findings suggest that acupuncture-based interventions may influence proprioceptive outcomes, although the underlying mechanisms remain unclear.
Their applicability to lumbar proprioception in patients with CNLBP, particularly following HPLA, remains to be investigated.
Nevertheless, the therapeutic effects of HPLA remain insufficiently investigated in patients with CNLBP. In addition, prior laser studies have predominantly evaluated subjective results such as pain, while objective and clinically relevant outcomes, particularly fatigue and lumbar proprioception, have received limited attention. Pain self-efficacy has also been underexplored, despite its importance in understanding patients’ confidence in performing activities despite pain.
Therefore, the current study sought to examine the effect of HPLA on back muscular fatigue and endurance, proprioception, pain severity, and pain-related self-efficacy in CNLBP patients.
Materials and Methods
Study Design
From November 2025 to June 2026, the prospective double-blind, randomized controlled study had to be carried out at Cairo University’s outpatient orthopedic physical therapy clinic. The Cairo University Faculty of Physical Therapy’s Research Ethics Committee granted ethical permission to conduct this research study (Number: P.T.REC/012/005223), followed by prospective registration in ClinicalTrials.gov (ID: NCT07196709). The methods applied during this study are consistent with the Consolidated Standards of Reporting Trials (CONSORT) regulation, which provides a comprehensive framework to follow when designing studies, collecting data, and presenting findings.
Prior to recruitment into the study, all participants were given complete information on objectives of the research process, treatment processes, advantages anticipated, and risks involved. Also, prior consent was acquired in writing, signed by those taking part in the current investigation. Participant-level data were deemed confidential and treated accordingly.
Study Participants
Participants have been included in the group of patients with CNLBP (duration for at least 3 months), with no identifiable causes for such problems established according to medical data and clinical assessment.16 The referral has been made by an orthopedist who was not a part of the research. The participants (men and women) were aged 20–40 years17 and had a body mass index (BMI) in the range of 18.5 to 24.9 kg/m2 with a pain score equal to or higher than 30 mm based on the Visual Analog Scale (VAS).18 Exclusion was based on the following: presence of a history of spine fracture or surgery during the last 6-month period; use of corticosteroid/anticonvulsant/anti-inflammatory drug therapy; having an implanted pacemaker; having chronic cardiovascular diseases, photosensitivity disorder/injury, and trauma on the targeted area; having cancer/cancer treatment within the previous 1-year period/remission stage; having neurological/infection disease or systematic illness such as rheumatological disorders/lupus erythematous/type I and II diabetes; having a thyroid problem; having spinal stenosis; having any kind of psychiatric or mental disorders; undergoing medical treatment for LBP in the last 3-month duration; being pregnant; and having obese status.
Sample Size
G*Power Software was used to estimate the sample size (Version 3.1.9.4, Germany). The effect size estimate (Cohen’s f) is 0.241, which is computed from partial eta squared (ηp2) of 0.055 from pilot isokinetic fatigue, using F-tests—ANOVA (within-between interaction and repeated measurements) with α set at 0.05, 90% power, 0.5 correlation among repeated measures, and a nonsphericity correction factor of 1. The initial sample size estimate is 48 subjects.
With consideration of a 20% attrition rate and 30 patients in each group, the overall sample size was found to be 60.
Randomization
A 1:1 randomization process was used to assign eligible participants to either the HPLA group, who were given HPLA plus exercises, or the sham group, who were given sham laser plus the same exercises (Figure 1). A block randomization sequence produced by a computer, with blocks of four, was prepared using http://www.randomization.com/ by another person who did not participate in the hiring, assessment, or treatment. To ensure allocation concealment, opaque, sealed envelopes with sequential numbers were utilized.
Outcome assessments were performed before treatment and after six weeks by a blind assessor. Figure 1Participant flow diagram according to CONSORT guidelines.Flowchart sequence: Eligibility screening, enrolment, randomized, allocation, two groups, completed, analyzed.Flowchart sequence: Eligibility screening left parenthesis n equals 75 right parenthesis, Enrolment, Excluded n equals 15, Ineligible n equals 9, Declined participation n equals 6, Randomized n equals 60, Allocation, HPLA Group, HPLA plus Exercise therapy, Allocated left parenthesis n equals 30 right parenthesis, Completed 6 dash Week treatment, n equals 30, Analyzed left parenthesis n equals 30 right parenthesis, Sham Group, Sham Laser plus Exercise therapy, Allocated left parenthesis n equals 30 right parenthesis, Completed 6 dash Week treatment, n equals 30, Analyzed left parenthesis n equals 30 right parenthesis.Abbreviation: HPLA, High-power laser acupuncture.
Intervention
High-Power Laser Acupuncture
To achieve standardization of the treatment protocol, all participants received treatment at predefined acupuncture points in the same order while also using standardized participant positions, skin preparation, perpendicular probe placement, exercises, and treatment times. Furthermore, a single physical therapist conducted all of the laser treatments; the exercise component of each treatment session was administered by only one physiotherapist. The entire treatment was given in a room temperature kept constant at 20°C.
Participant position during treatment was prone, with appropriate padding beneath the head/heels for comfort. Prior to laser application, the skin covering the targeted region was cleansed with an alcohol solution. Both the physiotherapist and the patient wore eyewear for the purposes of safety and blinding.
Additionally, patients were warned that there may be a transient aggravation of symptoms post-treatment.
The laser treatment was administered by an experienced physiotherapist with ten years of clinical experience who was aware of group allocation. Participants, the outcome assessor, and the physiotherapist supervising exercise therapy were blinded to group allocation throughout the study. However, blinding the treating physiotherapist was not feasible because of the need to operate the active and sham laser settings.
The laser device used for treatment had a high power and model number Zimmer Medizin Systeme, Germany (serial numbers: 15200013306 and 4682). This device has a 5 mm probe diameter and a 0.2 cm2 spot area extendable to 3.1 cm2 using a small spacer and a wavelength between 810 and 980 nm. The treatment parameters chosen were 5 Hz and a 50% duty cycle19 with an average power setting of 5 W.
A dose of 60 J per acupuncture point was selected based on the PBM protocol reported by Peserico et al20 applied for 13 seconds and, therefore, 900 J overall for a total time of 195 seconds.
The physiotherapist placed the laser probe on various midline points such as GV3, GV4, and GV5 as well as their bilaterally symmetric counterparts, namely BL20, BL23, BL24, BL25, BL40, and GB30, which had been researched18,21 and localized in accordance with WHO’s recommendations.22 The order of applying the treatments consisted of first applying all the GV3, GV4, and GV5 unilateral points, then proceeding with the points on both sides, namely BL20, BL23, BL24, BL25, BL40, and GB30.
Participants in the sham therapy group had the intervention applied by the same physiotherapist through the same device, in the same position and acupuncture points as those in the active intervention group but without any energy delivered due to setting the laser emission to zero.23 The use of protective glasses facilitated the blinding process in both groups, whereas equal time and therapist touch ensured proper blinding. To reduce the interaction between participants from different groups, each session was conducted on different days for six weeks, three times every week.
Exercise Therapy
All groups underwent identical exercise therapy three times a week for a period of six weeks, under the supervision of another physiotherapist blinded to group allocations and the use of laser therapy.
Stretching exercises were prescribed for the back, hamstrings, and calves;24 these stretches were maintained at one position for thirty seconds and repeated four times.25 In addition, stabilization and strength training for the muscles in the back and abdomen had been given. Ten repetitions of each exercise were completed separated by ten-second rest intervals. Progression according to participants’ tolerance was made accordingly.26
Outcome Measures
Back muscle fatigue was assessed using the 50% torque reduction protocol, which was used to measure back muscle fatigue, where peak torque < 50% of initial maximum for 3 consecutive repetitions was defined as fatigue.27,28 Before the test session, the Biodex isokinetic dynamometer (Biodex Medical Systems, Shirley, NY, USA) got calibrated. Individuals sat on the back extension/flexion attachment such that their trunk remained upright while their hips/knees were maintained at 90°, the floor plane was parallel to the thighs, and the line joining the subjects’ anterior superior iliac spines and the dynamometer axis was collinear, with the anterior tibia, upper trunk, and head/sacrum all supported by cushions. Additionally, the upper trunk/pelvis/thighs were immobilized via Velcro straps.29 Participants performed multiple maximal concentric contractions of the back extensors followed by passive submaximal back flexor contractions with a 60°/s angular velocity, during which they received verbal encouragement28 until reaching the 50% torque threshold.
The number of repetitions needed to achieve this threshold served as their fatiguing score.27
Back muscle endurance was done using the Biering-Sørensen test. This procedure involved positioning the participants in a prone position and keeping their iliac crests in line with the edge of the table The legs of the participants were strapped in place while the arms were placed over the chest. The back muscles were required to keep the body position neutral and horizontal as much as possible.
The test continued until the participant either lost the ability to maintain the position, experienced pain or fatigue, had a trunk drop of more than 10°, or reached a maximum duration of 240 seconds.30
Lumbar proprioception was assessed as lumbar repositioning accuracy using a Biodex System isokinetic dynamometer with a reclining back attachment, which has demonstrated excellent validity and reliability for joint position-sense assessment.31 Participants sat upright with the pelvis, thighs, trunk, and head stabilized, while the actuator axis was in line with the L5/S1 level with the starting position at 0°. The target angle was 30° of lumbar flexion. After two familiarization trials, the dynamometer passively moved the trunk to the target angle32 and held it for 5 seconds for memorization.33 Participants then returned to neutral and actively reproduced the target angle with their eyes closed.
Three trials were performed with 10-second rest intervals. Proprioceptive error was stated as the average absolute inaccuracy, in degrees, of the target angle to the reproduced angle.34
We measured pain level by a 100 mm VAS, with 0 denoting “no pain” and 100 denoting “severe pain.” Participants signed their highest pain level, and we recorded the score in mm from the “no pain” end.35 For self-efficacy in relation to pain, we used the Arabic Pain Self-Efficacy Questionnaire (PSEQ-A), which has 10 parts. Scores from 0 to 60—higher numbers show more confidence in handling daily activities even when in pain.36
Adverse Events
We watched carefully for any side effects and made sure participants knew exactly what to notice—like pain, warmth, swelling, or redness. If anything occurred, they were instructed to inform us immediately. We recorded every detail about these events: what happened, when it started, how bad it got, how long it lasted, and what we did to manage it, utilizing established forms both before and after every treatment.
If someone had a serious reaction, or if their symptoms got worse or just would not go away, their participation was paused until they obtained a full medical evaluation.
Statistical Analysis
All statistical analyses were conducted using IBM SPSS Statistics for Windows, version 25.0 (IBM Corp., Armonk, NY, USA). Following their summary of frequencies and percentages, between-group comparisons of categorical variables were performed using the chi-squared (χ2) test. The normal continuous variables were evaluated by the Shapiro–Wilk test, and Levene’s test was used to evaluate the assumption of homogeneity of variances.
The presentation of continuous variables was mean ± standard deviation (SD). Baseline differences between groups were assessed using an independent samples t-test. The main effects of group and time and their interaction were identified by a mixed repeated-measures ANOVA.
When significant effects were detected, within-group variations through time as well as between-group variations at each evaluation point had been assessed using Bonferroni-adjusted post hoc comparisons. The estimated mean differences and corresponding 95% confidence intervals (CIs) had been reported. Cohen’s d had been used to quantify between-group effect sizes, whereas partial eta squared (ηp2) was reported for the mixed repeated-measures ANOVA.
A two-sided p value < 0.05 was considered statistically significant.
Result
All 60 randomized participants (30 in each group) completed the six-week intervention, with no dropouts or losses to post-intervention assessment (Figure 1). Table 1 presents the participants’ baseline demographic and clinical profile. No significant baseline differences were observed between the two groups in age, sex, weight, height, BMI, marital or employment status, LBP duration, physical activity, isokinetic fatigue, Biering–Sørensen endurance, proprioceptive error, VAS, or PSEQ-A scores with all p values > 0.05.
Table 1Baseline Demographic and Clinical Profile of ParticipantsVariablesHPLA Group (n = 30)Sham Group (n = 30)Test of Significancep-ValueAge (years)33.33 ± 3.6232.82 ± 3.83t = 0.5360.594Gender, N (%)χ2 = 0.0690.793Male13 (43.3)12 (40.0)Female17 (56.7)18 (60.0)Weight (kg)71.32 ± 4.1370.40 ± 3.93t = 0.8900.377Height (cm)170.84 ± 4.36171.13 ± 4.11t = −0.2710.787BMI (kg/m2)24.42 ± 0.5524.03 ± 0.97t = 1.9010.062Marital statusχ2=0.6110.894Single11 (36.7)12 (40.0)Married15 (50.0)14 (46.7)Widowed1 (3.3)2 (6.7)Divorced3 (10.0)2 (6.7)Employment statusχ2=0.1620.688Employment27 (90.0)26 (86.7)Unemployment3 (10.0)4 (13.3)Duration of LBP (months)19.00 ± 3.6118.47 ± 3.27t = 0.6000.551Physical activityχ2= 0.4510.798Low7 (23.3)5 (16.7)Moderate18 (60.0)19 (63.3)High5 (16.7)6 (20.0)Isokinetic fatigue (reps)32.53 ± 5.9233.20 ± 4.48t = −0.4920.625Biering–Sørensen endurance (s)49.30 ± 8.3350.07 ± 5.05t = −0.4310.668Proprioception error (°)6.55 ± 0.726.25 ± 0.68t =1.6530.104VAS (mm)61.07±8.3560.57 ± 8.44t = 0.2310.818PSEQ-A (score)33.57 ± 6.8234.07 ± 6.07t = −0.3000.765Notes: Data are displayed as mean ± standard deviation (SD) for continuous variables and N (%) for categorical variables. t, independent-samples t-test; χ2, chi-square test. Statistical significance was set at p < 0.05.Abbreviations: HPLA, High-power laser acupuncture; BMI, Body mass index; LBP, Low back pain; VAS, Visual Analogue Scale; PSEQ-A, Pain Self-Efficacy Questionnaire.
A statistically significant main effect of time (F(1,58) = 418.17, p < 0.001, ηp2 = 0.878), group (F(1,58) = 5.06, p = 0.028, ηp2 = 0.080), and group × time interaction (F(1,58) = 26.76, p < 0.001, ηp2 = 0.316) was observed in the mixed repeated-measures ANOVA for isokinetic fatigue. Post hoc pairwise evaluations with Bonferroni adjustment revealed a significant increased repetitions to fatigue following the intervention in both the HPLA group (MD = 19.24 reps; 95% CI: 17.11, 21.36; p < 0.001) and the sham group (MD = 11.47 reps; 95% CI: 9.34, 13.59; p < 0.001). The HPLA group also achieved a significantly greater rise than the sham group at post-intervention (MD = 7.10 reps; 95% CI: 3.42, 10.78; p < 0.001; Cohen’s d = 0.996), as Table 2 illustrates.
Table 2Comparison of Isokinetic Fatigue, Biering-Sørensen Endurance, and Proprioception Error at Pre- and Post-Intervention Across the Two GroupsVariablesHPLA Group (n=30)Sham Group (n=30)Difference (95% CI)Between-Group p-ValueEffect Size (Cohen’s d)Time × Group InteractionIsokinetic fatigue (reps)Pre-intervention32.53 ± 5.9233.20 ± 4.48−0.67 (−3.38, 2.05)0.625-F =26.76ηp2 =0.316P <0.001Post-intervention51.77 ± 8.9544.67 ± 4.637.10 (3.42,10.78)<0.0010.996Difference (95% CI)19.24 (17.11, 21.36)11.47 (9.34, 13.59)% change59.15%↑34.55%↑Within-group p-value< 0.001< 0.001Biering–Sørensen endurance (s)Pre-intervention49.30 ± 8.3350.07 ± 5.05−0.77 (−4.33, 2.79)0.668--F =27.93ηp2 =0.325P <0.001Post-intervention76.07 ± 6.9464.40 ± 8.2211.67 (7.74,15.60)<0.0011.534Difference (95% CI)26.77 (23.44,30.10)14.33 (11.00,17.66)% change54.30%↑28.62%↑Within-group p-value< 0.001< 0.001Proprioception error (°)Pre-intervention6.55 ± 0.726.25 ± 0.680.30 (−0.06, 0.66)0.104-F = 76.54ηp2 =0.569P <0.001Post-intervention2.74 ± 0.554.01 ± 0.74−1.27 (−1.60, −0.93)<0.0011.948Difference (95% CI)−3.81 (−4.06, -3.56)−2.24 (−2.50, -1.99)% change 58.17%↓35.84%↓Within-group p-value< 0.001< 0.001Notes: F, Mixed repeated measures ANOVA; ηp2, Partial eta squared; ↑, indicates an increase; ↓, indicates a decrease.Abbreviations: HPLA, High-power laser acupuncture; CI, Confidence interval.
Regarding Biering-Sørensen endurance, there were statistically significant time-related main effects (F(1, 58) = 305.15, p < 0.001, ηp2 = 0.840), group effects (F(1, 58) = 13.96, p < 0.001, ηp2 = 0.194), and interaction between group and time (F(1, 58) = 27.93, p < 0.001, ηp2 = 0.325). Also, both groups demonstrated a significant improvement following the intervention (MD = 26.77 sec, 95% CI: 23.44, 30.10; p < 0.001) for the HPLA group (MD = 14.33 sec, 95% CI: 11.00, 17.66; p < 0.001) for the sham group. Moreover, there was statistically significant greater enhancement in the HPLA treatment group than the sham group at post-intervention (MD = 11.67 sec; 95% CI: 7.74, 15.60; p < 0.001; Cohen’s d = 1.534), as displayed in Table 2.
In terms of proprioception error, there were statistically significant time-related main effects (F(1, 58) = 1142.60, p < 0.001, ηp2 = 0.952), group effects (F(1, 58) = 10.31, p = 0.002, ηp2 = 0.151), and interaction between group and time (F(1, 58) = 76.54, p < 0.001, ηp2 = 0.569). Both groups demonstrated significant reductions following the intervention (MD = −3.81°; 95% CI: −4.06, −3.56; p < 0.001 for the HPLA group and MD = −2.24°; 95% CI: −2.50, −1.99; p < 0.001 for the sham group). Following the intervention, the HPLA treatment group was statistically considerably lower than the sham group, with an MD of −1.27° (95% CI: −1.60, −0.93; p < 0.001; Cohen’s d = 1.948) (Table 2).
Table 3 showed statistically significant time-related main effects (F(1, 58) = 383.21, p < 0.001, partial η2 = 0.869), group (F(1, 58) = 9.22, p = 0.004, partial η2 = 0.137), and interaction between group and time (F(1, 58) = 40.31, p < 0.001, partial η2 = 0.410) for the VAS. A statistically significant decline occurred following the intervention for the HPLA treatment group (MD = −24.57 score; 95% CI: −27.25, −21.88; p < 0.001) and the sham group (MD = −12.53 score; 95% CI: −15.22, −9.85; p < 0.001). Additionally, after the intervention, the HPLA group’s results were statistically substantially lower than the sham group’s (MD = −11.53, 95% CI: −15.38, −7.68 score; p < 0.001; Cohen’s d = 1.549) (Figure 2).
Figure 2Changes in VAS (a) and PSEQ-A (b) at pre- and post-intervention between the two groups. Error bars represent 95% confidence intervals (95% CI). *, Statistically significant at P < 0.05 between groups.A two-plot line graph showing pre and post intervention scores for HPLA group and sham group.Abbreviations: HPLA, High-power laser acupuncture; VAS, Visual Analogue Scale; PSEQ-A, Pain Self-Efficacy Questionnaire.Table 3Comparison of VAS and PSEQ-A Scores at Pre- and Post-Intervention Across the Two GroupsVariablesHPLA Group (n=30)Sham Group (n=30)Difference (95% CI)Between-Group p-ValueEffect Size (Cohen’s d)Time × Group InteractionVAS (mm)Pre-intervention61.07 ± 8.3560.57 ± 8.440.50 (−3.84, 4.84)0.818-F = 40.31ηp2 =0.410P <0.001Post-intervention36.50 ± 6.9748.03 ± 7.89−11.53 (−15.38, −7.68)<0.0011.549Difference (95% CI)−24.57 (−27.25, −21.88)−12.53 (−15.22, −9.85)% change40.23%↓20.70% ↓Within-group p-value< 0.001< 0.001PSEQ-A (score)Pre-intervention33.57 ± 6.8234.07 ± 6.07−0.50 (- 3.84, 2.84)0.765-F =41.30ηp2 =0.416P <0.001Post-intervention46.87 ± 4.3639.90 ± 6.166.97 (4.21, 9.73)< 0.0011.306Difference (95% CI)13.30 (11.66, 14.94)5.83 (4.19, 7.48)% change39.62%↑17.11%↑Within-group p-value< 0.001< 0.001Notes: F, Mixed repeated measures ANOVA; ηp2, Partial eta squared; ↑, indicates an increase; ↓, indicates a decrease.Abbreviations: HPLA, High-power laser acupuncture; VAS, Visual Analogue Scale; PSEQ-A, Pain Self-Efficacy Questionnaire; CI, Confidence interval.
For the PSEQ-A, Table 3 displayed statistically significant time-related main effects (F(1, 58) = 271.18, p < 0.001), group effects (F(1, 58) = 5.22, p = 0.026), and interaction between group and time (F(1, 58) = 41.30, p < 0.001). Pre- and post-intervention PSEQ-A scores increased substantially for both the HPLA treatment group (MD = 13.30 points, 95% CI: 11.66, 14.94; p < 0.001) and the sham group (MD = 5.83 points, 95% CI: 4.19, 7.48; p < 0.001). Following the intervention, the HPLA group’s PSEQ-A results were substantially greater than the sham group, with an MD of 6.97 points (95% CI: 4.21, 9.73; p < 0.001; Cohen’s d = 1.306) (Figure 2).
Adverse Events
No serious AEs or treatment discontinuations occurred. Seven participants in the HPLA group reported mild, transient warmth and flushing at the treatment site, which resolved spontaneously without intervention.
Discussion
The study revealed significant between-group differences across all outcome measures following the intervention (p < 0.05). Participants receiving HPLA combined with exercise therapy showed greater improvements than those receiving sham laser treatment with exercise, indicating an additional treatment effect of HPLA. These findings included large between-group effect sizes for several outcomes, supporting the magnitude of the observed short-term differences.
However, statistical effect sizes should be interpreted alongside clinical relevance and patient-reported outcomes.
The improvement in back muscle fatigue resistance observed in the present study may be partly explained by photobiomodulation-related effects on cellular and mitochondrial metabolism reported in previous research. Following laser irradiation, laser energy can enter tissue and be taken up by cytochrome c oxidase and other mitochondrial chromophores, enhancing ATP production and electron transport and cellular energy availability. Furthermore, decreased lactate buildup and oxidative stress may postpone the beginning of tiredness, while increased intramuscular microcirculation may improve oxygen supply and metabolic waste clearance.37 Due to its relatively powerful output (≥500 mW), which stimulates mitochondrial activity, increases ATP synthesis, and improves cellular metabolism, high-power laser treatment can further boost these effects by providing enough energy to deeper tissues.11 Furthermore, increased regional blood flow may enable the removal of metabolic byproducts, improve the delivery of nutrients and oxygen, and encourage the resorption of edema and interstitial fluid.38 Although these mechanisms provide a plausible explanation for improved muscle fatigue resistance, mitochondrial activity, ATP production, oxidative stress, and microcirculation were not directly evaluated in the present study.
The current study’s improvement in fatigue during repeated isokinetic contractions is consistent with earlier research demonstrating PBM’s ergogenic benefits. When compared to a placebo, pre-exercise 830-nm laser therapy increased biceps repetitions to exhaustion by an average of 4.5,39 whereas 655-nm laser treatment increased repetitions by 8.5 compared to 2.7 under placebo conditions.40 These results suggest that PBM can withstand repeated contractions of the muscles and postpone the onset of fatigue. Elimy et al’s41 recent works further supported PBM’s function in reducing muscular fatigue by demonstrating that HPLA application enhances trunk muscle fatigue.
Unlike that study, which compared high- and low-intensity LA over four weeks, the present trial compared HPLA with sham treatment over six weeks and additionally evaluated back muscle endurance, lumbar proprioception, and pain-related self-efficacy.
The results of Oliveira et al42 agree with the increase in trunk muscles’ endurance and the longer time to fatigue. According to their systematic review, PBM reduced oxidative stress, inflammation, creatine kinase, and other markers linked to fatigue while generally improving maximal voluntary force production, oxygen utilization, and endurance capacity, as well as muscle functional recovery. The trunk-extensor muscles may be capable of sustaining activity for a prolonged duration due to these effects, which may also help maintain muscle contractile capacity.
However, the types, wavelengths, and doses of lasers reported in the previous studies varied significantly.
Larkin-Kaiser et al43 investigated laser class IV with wavelengths comparable to those used in the present study. A 240-J dose prolonged time to task failure during a sustained static contraction by 26% compared with sham treatment and by 7% compared with the 480-J dose. The increase in time to task failure was associated with a smaller decline in maximal voluntary contraction, suggesting that the improvement in fatigue resistance was related to better preservation of muscle strength.
The superior effect of 240 J compared with 480 J may reflect a dose-dependent or biphasic response instead of simple linear correlation between dosage and effectiveness. The authors proposed that the effects may be mediated through intramuscular bioenergetic processes, muscular microcirculation, and peripheral neural modulation, though these processes were not directly assessed. Nevertheless, the findings of Larkin-Kaiser et al43 were obtained from healthy young adults and involved the first dorsal interosseous muscle; therefore, their applicability to lumbar extensor muscles in CNLBP should be interpreted cautiously.
Moreover, the clinical significance of the observed improvement is uncertain due to the lack of an established minimal clinically important difference (MCID) available to back muscle fatigue or endurance in this population. Therefore, although the present study demonstrated substantial improvements in back muscle fatigue and endurance, the clinical importance of these changes cannot be established solely from their statistical significance or effect sizes.
However, Gorgey et al44 found no effect in fatigued muscles with laser application in contrast with the present findings. In their studies, neuromuscular electric stimulation was applied to elicit contractions, and radiation with a laser was performed via scanning the targeted area before exercise. This technique potentially decreased the dose to the intended tissue by spreading the power over a larger surface.45 In this study, laser was applied directly to preset acupoints, which may have allowed more focused delivery of energy and stronger activation of the intended tissues.
Our findings demonstrated greater improvement in lumbar proprioceptive accuracy in the HPLA group than in the sham group, despite both groups receiving identical exercise therapy, suggesting an additional benefit of HPLA. This improvement may be partly attributed to pain reduction following high-power laser therapy,46,47 which could mitigate pain-related alterations in muscle activation and motor control, as proposed by Hodges and Tucker.48 Additionally, this effect may be associated with potential neuromuscular effects, which may modulate sensory afferent input from muscle spindles and mechanoreceptors, potentially enhancing sensorimotor integration and joint repositioning accuracy. Liu et al10 reported that changes in pain were not significantly associated with changes in motor abilities after LA, suggesting that functional recovery may be mediated by primarily neuromuscular and tissue-level mechanisms, rather than analgesia alone.
Therefore, the greater reduction in proprioceptive error may reflect both pain-mediated effects and potential neuromuscular adaptations beyond those achieved with exercise therapy alone. However, the present study assessed lumbar repositioning accuracy rather than the underlying physiological mechanisms; therefore, these explanations remain speculative and require further investigation. However, the clinical significance is unknown, since there is no defined MCID for lumbar proprioception in CNLBP.
Consequently, the large effect size observed for proprioceptive improvement should be interpreted as evidence of a substantial statistical difference rather than definitive proof of clinically meaningful improvement.
Studies show that using high-power lasers along with exercise helped improve proprioceptive accuracy, muscular strength, and range of motion in individuals with osteoarthritis in the knee49 and improve female gymnasts with persistent wrist pain’s awareness of joint position.50
Contradictory results suggest that the improvement of proprioception does not always follow pain reduction. Tangsriwong et al51 concluded that the absolute error decreased initially and increased again after 24 hours post-treatment, despite a reduction in pain. This shows that several sessions of interventions and extended treatment should be administered to the patient to effectively improve the joint position sense.
The current study indicated that the HPLA group’s pain changes were both statistically and clinically meaningful, surpassing the VAS scale’s 20 mm minimum clinically important change (MCIC) for LBP.35 Previous research has proposed several potential mechanisms underlying the analgesic effects of high-power laser therapy, including increased endorphin release, suppression of substance P and mediators of inflammation, and raising the pain threshold. 11 However, these mechanisms were not directly investigated in the present study.
Pain-relieving effects from the use of these laser types have been found through systematic reviews and meta-analyses in patients suffering from chronic lower back pain and musculoskeletal disorders.52,53 Several clinical investigations also prove the clinical efficacy of high-power lasers for persistent LBP12–14 together with a range of other diseases.46,47,49–51,54
LA has been proven to participate in the central pain perception and modulation and thus has the potential to alleviate chronic musculoskeletal pain, as well as the associated movement disorders resulting from pain.10 Recent clinical trials in CNLBP reported that HPLA has proved to be an efficient way of reducing this chronic pain.19,41
In comparison to the sham group, individuals receiving HPLA showed higher levels of pain-related self-efficacy (p < 0.05). Clinically, improvements are indicated by changes in PSEQ-A scores that exceed the minimal detectable change of 5.93 points,36 which suggests that HPLA may improve patients’ confidence in carrying out daily tasks in spite of pain, supporting improved coping skills, engagement in rehabilitation, and functional outcomes in CNLBP. A key psychological component that affects both pain results and functional behavior in people with CNLBP is pain-related self-efficacy, which is defined as a patient’s confidence in their capacity to manage pain and carry out everyday tasks.55 Such improvements show that HPLA may be beneficial for CNLBP recovery on both a psychological and functional level.
It has been stated that the application of whole-body PBM for four weeks can alleviate pain and fear of movement while enhancing quality of life and pain self-efficacy in fibromyalgia.56 In addition, it should be noted that high-power lasers improve the musculoskeletal system’s functionality and lower pain, which enhances performance.54
The concurrent improvements in pain severity and pain-related self-efficacy provide clinical context for the observed gains in muscle fatigue, endurance, and lumbar proprioception. Although established MCID thresholds are lacking for these objective measures, the patient-reported improvements suggest potential clinical benefits. However, the relationship between objective and patient-reported outcomes was not directly investigated.
The impact of core stability workouts on reducing fatigue and pain, alongside improving back muscle endurance in chronic LBP, has been established.5 Core stabilization workouts were also found to improve lumbar proprioception and joint position sense and diminish pain and disability.57 These exercises also enhance the activation of the trunk muscles and motor control, which improve a patient’s movement patterns while decreasing their discomfort.58 Core stabilization and strengthening have also been shown to help individuals with LBP enhance their lumbar proprioception and lessen their pain and movement anxiety.6 Furthermore, they effectively decrease LBP and disability by strengthening trunk muscles.26 Furthermore, training one’s core muscle was associated with increased self-efficacy related to pain, which facilitates confidence in engaging in different activities and tasks while experiencing discomfort and enhances psychological flexibility and commitment to treatment.55 Qaseem et al4 regard exercise as an essential management strategy for chronic lower back pain.
Limitations and Recommendations
Some drawbacks have also emerged. First, the six-week period of the intervention and the lack of subsequent follow-up measurements reduced the opportunity to evaluate the persistence of the effect in the long term. Moreover, the use of only one research center and the narrow scope of ages and BMIs reduce the applicability of the results.
Furthermore, there is no use of other examinations such as electromyography and ultrasonography in the research. Future research needs to focus on longer periods of follow-up and different doses of lasers.
Conclusion
The incorporation of LA with high power into a six-week exercise therapy may increase the ability of back muscles to resist fatigue and enhance endurance, lumbar proprioception, pain severity, and pain-related self-efficacy in the CNLBP population. Clinically, HPLA may be integrated as a short-term adjunct to conventional exercise-based rehabilitation to enhance treatment outcomes. However, these findings are limited to the short-term outcomes, as no follow-up assessment was conducted.
Future research should investigate optimal treatment doses and long-term effects through follow-up assessments.