Effect of blood flow restriction training with core stabilization exercise on muscle activity and muscle thickness in subjects with nonspecific chronic low back pain

Abstract

Background

Blood flow restriction (BFR) is considered an alternative method for increasing muscle activity and thickness to reduce Nonspecific Chronic Low back pain (NSCLBP).

Objectives

This study aimed to evaluate the effects of BFR with core stabilization exercise (CSE) on muscle activity, muscle thickness, and disability in individuals with NSCLBP.

Methods

A total of 38 individuals with NSCLBP aged 18–45 years were included in this study. The participants were randomly divided into the BFR + CSE and CSE groups (n = 19 each). All participants underwent supervised rehabilitation sessions three times per week over a period of four consecutive weeks. Muscle activity, muscle thickness, and disability were assessed before and after the four-week intervention.

Results

The BFR + CSE group showed significant within-group improvement in muscle activity of the transversus abdominis (TrA), multifidus (MF), and gluteus maximus (Gmax), muscle thickness at rest and during contraction, and disability (p < 0.05). The CSE group showed a significant increase in electromyography activity of the MF muscle (p < 0.05), a significant increase in muscle thickness at rest for the TrA, MF, and Gmax muscles (p < 0.05), and only a significant increase in muscle thickness during contraction for the TrA muscle (p < 0.05). Additionally, the BFR + CSE group exhibited superior benefits compared to the CSE group across all variables.

Conclusion

BFR combined with CSE over four weeks is more effective in improving TrA, MF, and Gmax muscle strength, muscle thickness, and disability.

Keywords

chronic low back pain blood flow restriction core stabilization exercise hypertrophy muscle activity

Introduction

Chronic low back pain (CLBP) is localized between the costal margins and inferior gluteal folds and persists for 12 weeks or more.¹ In approximately 85% of CLBP cases, the precise cause is often unknown but frequently associated with pelvic, abdominal, and back muscular dysfunction. More than 90% of LBP cases are classified as non-specific low back pain (NSLBP) because the exact cause is unknown.^2,3 Multifidus (MF) and transversus abdominis (TrA) muscle activity imbalance may cause decreased muscle thickness and trunk stability and exacerbated back pain. The gluteus maximus (Gmax) muscle stabilizes the pelvis during trunk rotation and weight-bearing. The Gmax contributes to spinal extension and is coactivated with the contralateral MF muscle during lifting activities. Muscle weakness can increase the risk of LBP and diminish thoracolumbar fascia tension and lumbar spine stability through the mechanism of force closure.^4–6

Core stabilization exercises (CSE) aimed to reeducate the synchronic activity of the TrA, MF, and Gmax muscles and help reduce the risk of NSCLBP.^7,8 Additionally, gluteal muscle strengthening exercises, when combined with lumbar stabilization, are more effective than lumbar stabilization alone in improving lumbopelvic balance and reducing disability.⁹ A recent study on individuals with NSCLBP showed great thickness of the TrA and Gmax muscles and reduced disability after CSE for four weeks.¹⁰ CSE can reduce pain and disability while retraining the essential functions of local trunk muscles to enhance neuromuscular control of spinal stability.¹¹ Several CSE programs have been developed for managing NSCLBP and have been shown to increase MF and TrA muscle thickness.^12,13 However, little is known about their influence on TrA, MF, and Gmax muscle electromyography (EMG) activity and muscle thickness. However, CSE programs are performed at low loads for NSCLBP rehabilitation. Clinicians often discourage heavy-load or resistance exercises due to concerns about the mechanical and compressive stress on the spine, as well as the associated potential risks.¹⁴ This biomechanical constraint presents a therapeutic challenge, as many individuals with LBP are unable to tolerate the loading intensities necessary to induce meaningful activation and adaptation of the trunk musculature. Furthermore, existing low-load exercise protocols currently lack strong empirical support for their effectiveness in eliciting neuromuscular adaptations in key deep trunk stabilizers, such as the transversus abdominis and multifidus muscles essential for maintaining spinal stability and motor control.¹⁵ Therefore, determining a new rehabilitation strategy to effectively maximize trunk, abdominal, and lower extremity muscle activation and adaptation is necessary for managing individuals with NSCLBP.¹⁶

Blood flow restriction (BFR) training is a technique utilized in bodybuilding to enhance muscle hypertrophy and strength.^17–19 BFR training involves performing low-load exercises while partially occluding blood flow to the working muscles using a pressure cuff. This novel exercise strategy involves the application of pneumatic cuffs proximally around the limb, which reduces arterial inflow while concurrently causing total venous occlusion. This process results in local hypoxia due to the accumulation of deoxygenated blood during cuff inflation.^20–22 The mechanisms contributing to the benefits of blood flow restriction (BFR) training are not yet fully understood. However, Blood flow restriction (BFR) training can enhance muscle strength and hypertrophy by inducing local hypoxia, creating metabolic stress, and recruiting high-threshold motor units or type 2 muscle fibers. Additionally, it enhances mammalian target of rapamycin (mTOR) signaling and stimulates muscle protein synthesis. A previous study indicated that the hypoxia and metabolic accumulation resulting from BFR training combined with exercise can recruit fast-twitch motor units. This recruitment may occur through the stimulation of group III and IV afferents, which helps to maintain force production and consequently increases electromyographic (EMG) activity.²² Previous study demonstrated that BFR exercises enhanced back muscle endurance and increased the cross-sectional area of the trunk extensor muscles following a five-week intervention in individuals with low back pain (LBP).²³ A recent study found that low-load BFR significantly reduced pain and functional disability while producing strength gains similar to high-load resistance training in male collegiate athletes with CNLBP.²⁴ The cuffs were applied to the limbs, yet we observed a significant increase in core muscle strength, likely due to the remote muscle strength adaptations resulting from BFR training. This improvement is attributed to a cross-transfer of therapeutic effects to the lumbar musculature, affecting muscles that are not directly engaged during BFR exercises.^23,24 Furthermore, evidence suggests that this novel exercise approach establishes a cost-effective and easily implementable rehabilitation strategy that surpasses existing paradigms in its ability to promote muscle adaptation in individuals with LBP.

To the best of our knowledge, no study has investigated the effects of BFR with CSE on clinical outcome measures, including muscle activity, muscle thickness, and back disability, in individuals with NSCLBP. Therefore, this study aimed to evaluate the effect of BFR with CSE on muscle activity, muscle thickness, and back disability in individuals with NSCLBP. The hypothesis of this study is that, compared with CSE alone, BFR with CSE can produce systemic effects that enhance muscle activation and thickness of the back, abdominal, and hip muscles and back disability in individuals with NSCLBP.

Methods

Participants

A total of 40 individuals with NSCLBP aged 18–45 years were recruited from outpatients of Burapha hospital and the Physical Therapy clinic in the Faculty of Allied Health Sciences, Burapha university, Thailand. To evaluate NSCLBP, a qualified physician performed diagnostic assessments, including radiographic, to verify the presence and characterize the nature of lumbar spine pathology.

The inclusion criteria consisted of individuals with a history of low back pain (LBP) lasting more than three months, those experiencing pain localized between the costal margin and the gluteal fold without radiation to the lower extremities prior to study enrollment, and individuals exhibiting a disability score of 19% or higher as determined by the Modified Oswestry Disability Questionnaire (MODQ). The exclusion criteria were individuals with a history of pregnancy, those with surgery of the spine or lower extremity, those with a history of spine or lower extremity fractures or injuries within six months, those with a body mass index >30 kg/m², those with neurological deficit, those with nerve root compression, those who underwent physical therapy of the spine within one month, those with uncontrolled hypertension, those with diabetes mellitus, and those with cardiovascular disease. All participants were provided with comprehensive information regarding the study procedures, benefits, and risks. Written informed consent was obtained from each participant prior to enrollment. Additionally, all participants were assured of their right to withdraw from the study at any time, and their full anonymity was maintained. Participants were randomly assigned to either the BFR training combined with CSE group or the CSE-only group using block randomization at a 1:1 ratio, with block sizes of 2, 4, and 6. Each participant had been assigned a number in a sealed, opaque envelop.

Study design

This study was designed as a single-blinded, parallel, randomized clinical trial, following the guidelines specified in the CONSORT 2010 flow diagram (Figure 1). Participants were blinded to their group allocation. The study protocol was registered with the Thai Clinical Trials Registry under the identification number TCTR20240608006. This study was conducted in accordance with the principles outlined in the Declaration of Helsinki and received approval from the Research and Innovation Administration of Burapha University's Ethics Committee (IRB1-049/2566). Data were collected from May to November 2023 at Physical Therapy Laboratory, Burapha University, Thailand.

Figure 1.

The study flowchart.

Sample size calculation

The sample size was calculated using G*Power software, employing the effect size derived from previous study data on electromyographic (EMG) activity of the transversus abdominis (TrA) at the 8-week follow-up.²⁵ With a significance level (α) of 0.05, a power of 0.8, an effect size of 1.06, and an anticipated attrition rate of 20%, a total sample size of 38 participants was determined, comprising 19 participants per group.

Intervention

BFR training

A pneumatic occlusion cuff (Large STRAIGHT Cuffs: HS1003, H Plus cuff, Santa Barbara, CA, USA) measuring 10 cm in width and 75 cm in length was utilized for BFR training. Participants lay in a supine position and rested for 5 min before an appropriately sized cuff was applied to their left proximal thigh. The posterior tibial artery of the dominant or nondominant limb was assessed using a handheld portable Doppler probe (SD3 Vascular, Edan Instrument, Inc., Shenzhen, China) by inflating the cuff to 80% of each participant's individualized arterial occlusion pressure.²⁶

CSE

The CSE program began with a 5 min warm-up before the exercise using a stationary bicycle.

All CSE programs for levels 1–3 were previously described^10,27 (Table 1). Participants in the CSE group wore a BFR cuff similar to that used in the experimental group; however, the cuff in this group was not inflated.

Table 1.

Outline of core stabilization exercise.

Level/Week	1/Week 1	2/Week 2–3	3/Week 4
Program	Stationary bicycle for 5 min
	Abdominal drawing (Held 10: 10 repetitions/set, 3 sets, rest 60 s)	Unilateral bridging (Held 10:10 repetitions/set, 3 sets, rest 60 s)	Bridging on swiss ball (Held 10: 10 repetitions/set, 3 sets, rest 60 s)
	Abdominal bracing (Held 10: 10 repetitions/set, 3 sets, rest 60 s)	Quadruped contralateral arm and leg lift (Held 10: 10 repetitions/set, 3 sets, rest 60 s)	Diagonal curl up with elastic band (Held 10: 10 repetitions/set, 3 sets, rest 60 s)
	Alternative arm and leg lifts (Held 10: 10 repetitions/set, 3 sets, rest 60 s)	Curl up (Held 10: 10 repetitions/set, 3 sets, rest 60 s)	Trunk extension on swiss ball (Held 10: 10 repetitions/set, 3 sets, rest 60 s)
		Diagonal curl up (Held 10: 10 repetitions/set, 3 sets, rest 60 s)	Unilateral bridging with weight cuff (Held 10: 10 repetitions/set, 3 sets, rest 60 s)
		Sit back (Held 10: 10 repetitions/set, 3 sets, rest 60 s)
		Prone hip extension (Held 10: 10 repetitions/set, 3 sets, rest 60 s)

Participants completed a supervised BFR training program combined with the CSE program, or only the CSE program, for 30 min, three days per week, over four consecutive weeks. All training sessions were conducted in a laboratory setting under the supervision of the same registered physical therapist.

Outcome measurements

EMG activity

Electromyographic (EMG) activity of the multifidus (MF), transversus abdominis (TrA), and gluteus maximus (Gmax) muscles was assessed using TELEMyo DTS telemetry (Noraxon Inc., Scottsdale, AZ, USA). EMG signals were recorded at a sampling rate of 1500 Hz via MyoResearch-XP 3.8.2 software. Surface electrodes were placed parallel to the muscle fibers over the midsection of each muscle belly, following the guidelines outlined by the Surface Electromyography for the Non-Invasive Assessment of Muscles (SENIAM). Prior to electrode placement, the skin over the electrode sites was shaved (if necessary), debrided, and cleaned with an alcohol pad. Disposable standard Ag/AgCl electrodes, 10 mm in diameter (Blue-Sensor, Ambu A/S, Ballerup, Denmark), were attached to each muscle. For electrode placement, the MF electrode was positioned along a line extending from the posterior superior iliac spine to the first lumbar vertebra, aligned with the fifth lumbar spinous process. The TrA electrode was placed 2 cm medial and inferior to the anterior superior iliac spine, while the Gmax electrodes were positioned midway between the greater trochanter and sacrum. To prevent electrode slippage and minimize movement artifacts during testing, electrodes and EMG sensors were secured using flora tape. Muscle activity was normalized to the maximum voluntary isometric contraction (MVIC) for each muscle. Participants were positioned prone for the Gmax muscle assessment, with the tested knee flexed to 90°, the opposite knee extended, and the hip extended against the resistance of a belt.²⁸ For the TrA muscle, participants were positioned supine with knees flexed while drawing in the abdomen.¹⁰ For the MF muscle, participants were positioned prone on a table with a belt secured around the upper thoracic spine and their trunk elevated to the level of the xiphoid process.²⁸ Participants were instructed to avoid explosive contractions and gradually increase their effort to maximum upon hearing the signal “Go.” They held the maximum contraction for 5 s, with two repetitions and a 30-s rest period between sets. Standardized verbal encouragement was provided to all participants throughout the testing procedure.

EMG data were processed using MyoResearch-XP 3.8.2 software. A digital band-pass filter (Lancosh FIR) was applied between 20 and 500 Hz. Raw EMG signals were full-wave rectified and smoothed using a root-mean-square (RMS) algorithm with a time constant of 50 ms. Muscle activation was quantified by averaging 3 s of the 5-s recording period, excluding the initial and final 1-s intervals to minimize variability. EMG signals were then normalized to the maximum voluntary isometric contraction (MVIC) for each muscle and expressed as a percentage of the MVIC (%MVIC).

Muscle thickness

Muscle thickness at rest and during maximal isometric contraction (for 10 s) was assessed using a B-mode diagnostic ultrasound system (M5 series, Shenzhen Mindray Bio-Medical Electronics Co., Shenzhen, China) equipped with a 3.5–13 MHz linear transducer, a linear array probe with a 38 mm surface, and a frequency of 5–7.5 MHz (7L4s, Shenzhen Mindray Bio-Medical Electronics Co., Shenzhen, China). Three measurements were taken with a 30-s rest between repetitions. The thickness of the transversus abdominis (TrA) muscle was measured at rest and during the abdominal drawing-in maneuver while participants were in a supine crook position. The probe was positioned along the midaxillary line, just above the iliac crest, following the method of Zheng et al.²⁵ and Teyhen et al.²⁹ All images were captured at the end of normal exhalation to account for respiratory effects. To measure the multifidus (MF) muscle, participants lay prone with a pillow under the abdomen. The probe was placed at the L4/5 interspinous space, as described by Kiesel et al.,¹³ with images taken at rest and during trunk extension while the contralateral arm was raised by 5 cm, holding a 0.5 kg weight, with the arm fully extended and abducted at 120°. For the gluteus maximus (Gmax), muscle thickness was measured with participants in a prone-lying position, the hip extended, and the knee flexed to 90°. The probe was positioned at the midpoint between the posterior superior iliac spine and ischial tuberosity, following the described landmarks. Images were captured at rest and while participants lifted their leg 5 cm from the table, maintaining this position for 5 s. The average muscle thickness from three measurements was recorded for analysis. Image processing and analysis were conducted using ImageJ version 1.51 (Wayne Rasband, NIH, Bethesda, MD, USA) by tracing muscle borders. Muscle thickness at rest and the percentage change during contraction [(contraction – rest)/rest × 100] for the TrA, MF, and Gmax were calculated and analyzed.

An intra-examiner reliability test was previously carried out using 10 individuals. Image acquisition for each muscle in both resting and maximal contraction conditions was performed three times by a single examiner. All data were collected within one day, across two sessions, with a 30-min interval between each session. The examiner was blinded to her own previous measurements to prevent potential assessment bias. Excellent reliability was demonstrated for the thickness measurements of the TrA (ICC_3,1 = 0.93), MF (ICC_3,1 = 0.91), and Gmax (ICC_3,1 = 0.92).

MODQ

The MODQ includes 10 sections, each addressing a specific domain of functional limitation: pain intensity, personal care, lifting, walking, sitting, standing, sleeping, sexual activity, social life, and traveling. Each item was rated on a scale from 0 to 5, with 0 indicating the lowest level of disability and 5 indicating the highest. The total score is multiplied by two and expressed as a percentage, with higher scores indicating greater levels of disability.³⁰

Data analysis

Descriptive statistics for demographic data were presented as mean and standard deviation. Data normality was assessed using the Shapiro–Wilk test. Mean differences in all dependent variables were compared between and within groups using the independent sample t-test and paired t-test. Differences between the means were considered significant at p-value < 0.05, and the confidence interval (CI) was set at 95%. All data were analyzed using SPSS version 26 (SPSS Inc., Chicago, IL, USA).

Results

Characteristic variables

Of the 40 individuals enrolled in this study, two were excluded because one had a history of spine surgery, and one refused to participate. Finally, 38 participants with NSCLBP were included in the analysis: the BFR + CSE group (n = 19) and the CSE group (n = 19) (Figure 1). No significant differences in participant characteristics at baseline were observed between the groups (p > 0.05) (Table 2).

Table 2.

Baseline characteristics of the participants.

	Group		P-value
	BFR + CSE (n = 19)	CSE (n = 19)	P-value
Sex, men:women, n(%)	5:14(26.3:73.7)	3:16(31.6:68.4)	0.218
Age, years	20.33 ± 1.33	19.83 ± 0.98	0.208
Weight (kg)	57.47 ± 14.17	56.31 ± 9.07	0.770
Height (cm)	165.67 ± 8.66	163.28 ± 7.92	0.394
Body mass index, kg/m²	20.89 ± 4.48	21.04 ± 2.41	0.904
MODQ scores	25.17 ± 15.22	25.06 ± 9.59	0.979

Values were presented as percentage (%) or mean ± standard deviation.

Abbreviations: BFR: blood flow restriction; CSE: core stabilization exercise; Kg: kilograms; cm: centimeters; m: meter; MODQ: Modified Oswestry Low Back Pain Disability Questionnaire.

The primary outcomes

EMG activity

The BFR + CSE group showed significant improvements in the EMG activity of the TrA, MF, and Gmax muscles after the 4-week intervention compared with the baseline (p < 0.05). However, the CSE group showed a significant increase in the EMG activity of the MF muscle only (p < 0.05). The BFR + CSE group showed significantly greater TrA (p = 0.038, 95% CI, −33.14 to −0.98), MF (p = 0.039, 95% CI, −23.36 to −0.65), and Gmax (p = 0.044, 95% CI, −42.46 to −0.26) activation after the 4-week intervention than the CSE group (Figure 2).

Figure 2.

Mean and standard deviation of the EMG activity of the transversus abdominis (TrA), multifidus (MF), and gluteus maximus (Gmax) between the BFR + CSE (black bar) and CSE (open bar) groups.

The secondary outcomes

Muscle thickness

The BFR + CSE group showed a significant increase in the mean value of TrA, MF, and Gmax muscle thickness at rest and during contraction after intervention compared with the baseline (p < 0.05) and the CSE group (p < 0.05). However, the CSE group showed a significant increase in TrA, MF, and Gmax muscle thickness at rest (p < 0.05) and a significant increase in TrA muscle thickness only during contraction (p < 0.05) (Figure 3) (Table 3).

Figure 3.

Ultrasound imaging of TrA muscle at pre-intervention (a) rest (b)contraction and post BFR + CSE at 4 weeks (c) rest (d)contraction.

Table 3.

Mean (standard deviation) values and mean difference (95% confidence interval) of outcome measures during pre- and postintervention among groups.

Variables	BFR + CSE group (n = 19)			CSE group (n = 19)			Difference among groups (95% confidence interval)
Variables	Pre	Post	Difference (95% confidence interval)	Pre	Post	Difference (95% confidence interval)	Difference among groups (95% confidence interval)
Muscle thickness (mm²)
TrA
Rest	2.42 ± 0.43	3.17 ± 0.56*	−0.74 (−1.06, −0.42)	2.49 ± 0.50	2.76 ± 0.63*	−0.27 (−0.53, −0.01)	−0.40^† (−0.79, −0.01)
Contracted	2.81 ± 0.49	3.30 ± 0.60*	−0.68 (−1.02, −0.34)	2.75 ± 0.49	3.00 ± 0.64*	−0.25 (−0.48, −0.02)	−0.49^† (−0.90, −0.08)
Percent change	17.10 ± 8.52	11.94 ± 9.41	5.15 (−5.99, 16.31)	11.41 ± 4.82	12.40 ± 27.64	−0.99 (−15.44, 13.46)	0.46 (−14.74, 15.66)
MF
Rest	22.74 ± 3.06	29.60 ± 8.38*	−6.87 (−11.20, −2.53)	23.10 ± 2.62	25.39 ± 2.59*	−2.29 (−3.17, −1.40)	−4.21^† (−8.29, −0.13)
Contracted	31.41 ± 4.99	38.74 ± 5.68*	−7.32 (−11.66, −2.99)	31.16 ± 2.52	33.31 ± 4.05	−2.15 (−4.42, 0.10)	−5.42^† (−8.67, −2.17)
Percent change	36.23 ± 14.44	35.92 ± 15.43	0.31 (−15.06, 15.69)	36.14 ± 5.57	31.84 ± 9.57	4.31 (−7.20, 0.79)	−12.80 (−29.76, 5.58)
Gmax
Rest	21.18 ± 2.40	29.12 ± 9.25*	−7.93 (−12.55, −3.32)	21.73 ± 2.72	23.95 ± 3.50*	−2.22 (−3.73, −0.71)	−5.16^† (−9.77, −0.56)
Contracted	38.51 ± 8.93	49.95 ± 10.35*	−11.43 (−16.79, −6.07)	38.95 ± 7.26	41.21 ± 14.78	−2.26 (−10.39, 5.86)	−8.73^† (−17.13, −0.34)
Percent change	81.63 ± 10.28	76.80 ± 11.50	−4.17 (−26.11, 35.77)	78.67 ± 7.69	82.23 ± 17.69	−3.56 (−41.94, 34.82)	5.42 (−36.97, 47.82)
MODQ	25.17 ± 15.22	12.679 ± 9.21*	4.83 (6.69, 18.331)	25.06 ± 9.59	20.78 ± 8.69	4.28 (−0.13, 8.69)	8.11^† (0.13, 16.09)

Values were presented mean ± standard deviation.

Abbreviations: BFR: blood flow restriction; CSE: core stabilization exercise; mm: millimeters; TrA: transversus abdominis; MF: multifidus; Gmax: gluteus maximus; MODQ: Modified Oswestry Low Back Pain Disability Questionnaire.

*Significantly different between pre- and postinterventions, p < 0.05.

^†Significantly different from the R group, p < 0.05.

MODQ

The BFR + CSE group showed significant improvement in back disability after the 4-week intervention compared with the baseline (p < 0.001) and the CSE group (p < 0.05) (Table 3).

Discussion

This randomized controlled trial aimed to examine the effects of BFR training combined with a core stabilization exercise (CSE) program on muscle activity, muscle thickness, and back-related disability in individuals with NSCLBP. In this study, the BFR cuff was applied to the participants’ left proximal thigh, a protocol that differs from those used in previous studies, making direct comparisons challenging. The present study differs from previous study in both the exercise protocol and duration of intervention. Prior research predominantly employed resistance-based exercises such as leg extensions and arm curls over a five-week period, reporting that blood flow restriction (BFR) training improved back muscle endurance and increased the cross-sectional area (CSA) of trunk extensor muscles in individuals with low back pain (LBP).²³ In contrast, the current study implemented a four-week core stabilization exercise (CSE) program, with and without BFR, targeting muscle activity and thickness. Our findings revealed that both BFR + CSE and CSE alone led to significant improvements in muscle activity and muscle thickness compared to baseline. Furthermore, BFR combined with CSE was more effective in improving muscle activity and thickness at rest and during contraction than CSE alone.

This study demonstrated that the EMG amplitude of the transversus abdominis (TrA), multifidus (MF), and gluteus maximus (Gmax) muscles was significantly higher in the group performing blood flow restriction (BFR) combined with core stabilization exercises (CSE) than in the CSE-only group. It is plausible that this may have occurred through increased fatigue of the thigh muscle, as it is placed under direct BFR, thus causing greater stress on the back and abdominal musculature to compensate for the loss of strength. Although increased stress was placed on the thigh due to the BFR stimulus, the increased EMG activity in the back, abdominal, and gluteus maximus muscles suggests that their relative contributions during BFR training with CSE were maintained, despite these muscles not being directly restricted. This finding supports our initial hypothesis and aligns with previous literature, suggesting that the neuromuscular effects of BFR are not limited to the muscles directly under occlusion, but may also influence proximal muscle groups involved in stabilization and postural control. Although the BFR cuffs were applied to the proximal thigh, increased EMG activity was observed in the trunk musculature. This suggests that BFR may induce systemic neuromuscular responses that enhance motor unit recruitment beyond the occluded region. Prior studies have proposed that BFR training can lead to enhanced activation of core stabilizing muscles, including the TrA and MF, possibly through increased central motor drive and compensatory mechanisms during load-compromised movement patterns.^20,21,31 Furthermore, the increased activity in the Gmax, despite its location distal to the site of occlusion, may reflect the muscle's role in stabilizing the pelvis and facilitating movement during CSE tasks. Supporting this, Werasirirat and Yimlamai³² reported that BFR combined with rehabilitation significantly increased the EMG activity of the Gmax, gluteus medius, and tibialis anterior in athletes with chronic ankle instability, highlighting the systemic influence of BFR on muscle recruitment patterns. Although the precise physiological mechanism behind these adaptations remains unclear, the elevated EMG amplitude in the back and abdominal muscles may be indicative of greater type II muscle fiber recruitment, a factor critical for hypertrophic responses. One plausible explanation is that the muscular fatigue induced by occlusion in the thigh muscles necessitated greater compensation by the trunk and gluteal musculature to preserve movement efficiency and postural control. The engagement of these muscles may thus serve as a response to the localized metabolic and mechanical stress imposed by BFR. This systemic response is further supported by findings from Takarada et al.,^33,34 Bowman et al.,³⁵ and Dankel et al.,³⁶ who observed enhanced activation in both distal and proximal muscles in response to BFR. Theoretically, distal occlusion (e.g., at the proximal thigh) may lead to muscle fatigue below the cuff and subsequent recruitment of synergistic proximal muscles above the occlusion zone to compensate for reduced force production.^37–39 This neuromuscular redistribution could explain the increased EMG signals in core musculature during BFR-CSE protocols.

The results of this study showed that the BFR + CSE group demonstrated a more significant improvement in TrA, MF, and Gmax muscle thickness at rest and during contraction than the CSE group. These findings indicate that BFR combined with CSE enhances muscle activity, partly by increasing muscle thickness. These findings are consistent with those of a recent study that investigated the effect of BFR exercises after five weeks of intervention and showed improved back muscle endurance and increased cross-sectional area in trunk extensor muscles in individuals with LBP, indicating a cross-transfer of therapeutic effects to the lumbar musculature, even extending to muscles not directly targeted by the BFR regimen. BFR training may stimulate the production of anabolic hormones and proteins that promote muscle growth and circulate throughout the body.^23,24,40 This could be due to the fact that BFR combined with CSE relies on principles of motor learning, prioritizing the activation of muscles such as TrA and MF.⁴¹ Additionally, several studies have documented notable muscle hypertrophy resulting from BFR training, primarily attributed to elevated levels of metabolic stress. According to current theories, metabolite-induced fatigue and cellular swelling are considered the primary mechanisms that underlie the benefits of BFR training.⁴² Metabolite-induced fatigue involves the buildup of substances such as lactate, inorganic phosphate, and hydrogen ions during ischemic exercise conditions. This biochemical environment may enhance neuromuscular activation by increasing afferent feedback to the central nervous system, thereby promoting greater recruitment of fast-twitch motor units.⁴³ These motor units, which are typically activated only under high-load conditions, can be stimulated under low loads when metabolic stress is sufficiently high, contributing to muscle development in both the occluded and non-occluded regions. Cellular swelling, resulting from fluid shifts into muscle fibers during BFR, is another proposed stimulus for muscle growth. The increase in intracellular pressure may act as a mechanosensory signal, initiating anabolic signaling cascades such as the mTOR pathway, which promotes protein synthesis and reduces protein breakdown.⁴⁴ This response may help explain how muscle hypertrophy can occur in regions not directly affected by occlusion.

This study showed a statistically significant decrease in the MODQ scores after the BFR training combined with the CSE program for four weeks compared with before exercise, with a remaining decrease of only 12.7 points, indicating a significant improvement in the ability to perform activities. These findings are consistent with those of Amano et al.'s study,²³ which examined the effects of general exercise with BFR compared with general exercise alone in individuals with LBP and found that the group undergoing general exercise with BFR demonstrated a significant reduction in disability after exercise.²³ There is no clear explanation for this, but it may be related to increased TrA, MF, and Gmax muscle activity and thickness, resulting in a better ability to perform activities. The TrA, MF, and Gmax muscles, when contracted, assist in enhancing the stability of the lumbar spine and pelvis. The core muscles are engaged in motor learning, involving coordinated activity between the TrA and MF muscles, which are deep stabilizing muscles attached to the thoracolumbar fascia and enhance spinal stability by increasing intra-abdominal pressure. Moreover, it is possible to modify structures related to pain through brain commands, adjust muscle function, and train specific trunk muscles responsible for controlling the nervous system and muscles. This can lead to disability reduction, increased awareness of joint movement, and correction of posture deficiencies, thereby enhancing spinal stability.^42,45

This study has some limitations. One of the limitations of this study is the lack of a control group without BFR, which would have allowed for a better evaluation of the BFR-induced effects in each training protocol. Another limitation is the lack of a follow-up design. Therefore, the long-term benefits of BFR combined with CSE in individuals with NSCLBP remain unknow.

Conclusions

This study showed that BFR training combined with the traditional CSE program over four weeks is more effective in improving TrA, MF, and Gmax muscle activity and thickness and back disability in individuals with NSCLBP than the traditional CSE alone. The findings of this study can help physiotherapists design exercise programs to reduce exercise intensity, decrease forces on the joints and muscles, and alleviate pain resulting from high joint loading during resisted exercise in individuals with NSCLBP.

Footnotes

Acknowledgements

The authors would like to thank all participants and Wareeporn Tongtidram, Kanokwan Chatnguen, and Pathitta Chananan who hardly worked and supported the project. PW was supported by a grant from the Faculty of Allied Health Sciences, Burapha University.

Ethical considerations

This study was conducted in accordance with the principles outlined in the Declaration of Helsinki and received approval from the Research and Innovation Administration of Burapha University's Ethics Committee (IRB1-049/2566).

Informed consent

Informed consent has been obtained from all individuals included in this study.

Author contributions

All authors contributed to the study conception and design, reviewed the results, and approved the final manuscript.

Funding

The author(s) disclosed receipt of the following financial support for the research, authorship, and/or publication of this article: The present study was financially supported by the Faculty of Allied Health Sciences, Burapha University (AHS03/2566).

Declaration of conflicting interests

The author(s) declared no potential conflicts of interest with respect to the research, authorship, and/or publication of this article.

Data availability statement

The data used to support the findings of this study are included within the article.

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