Multiple sclerosis (MS) is a chronic neurological disease associated with reduced muscle strength, impaired mobility, increased fatigue, and deterioration in muscle morphology. Rectus femoris muscle atrophy and reduced muscle quality have been linked to functional limitations and decreased mobility in individuals with MS.

Blood flow restriction (BFR) training is a rehabilitation strategy that combines low-load exercise with partial vascular occlusion, enabling muscular adaptations comparable to those achieved with higher exercise loads. Although BFR has demonstrated promising results in several clinical populations, evidence regarding its effects on muscle morphology in individuals with relapsing-remitting multiple sclerosis (RRMS) remains limited.

The purpose of this randomized controlled trial is to investigate the effects of low-load BFR exercise on rectus femoris muscle morphology in individuals with RRMS. Thirty participants with RRMS (EDSS 2.5-3.5) will be randomly assigned to one of three groups: a BFR exercise group, a sham-BFR exercise group, or an exercise-only control group. All participants will complete the same supervised exercise program twice weekly for eight weeks.

The primary outcome will be rectus femoris muscle thickness assessed by ultrasonography. Secondary outcomes will include rectus femoris echo intensity, knee extensor muscle strength, Timed 25-Foot Walk performance, Nine-Hole Peg Test performance, Symbol Digit Modalities Test scores, and Modified Fatigue Impact Scale scores.

This study aims to determine whether the addition of blood flow restriction to a standardized low-load exercise program results in superior morphological and functional adaptations compared with sham-BFR and exercise-only conditions in individuals with RRMS.

Multiple sclerosis (MS) is a chronic inflammatory and neurodegenerative disease of the central nervous system characterized by demyelination, axonal degeneration, and progressive functional impairment. Individuals with relapsing-remitting multiple sclerosis (RRMS) frequently experience reductions in lower-extremity muscle strength, impaired walking performance, fatigue, and decreased physical function. Among lower-extremity muscles, the rectus femoris (RF) plays a critical role in knee extension, gait performance, and functional mobility. Previous studies have demonstrated associations between RF muscle morphology, muscle performance, and mobility outcomes in individuals with MS.

Blood flow restriction (BFR) exercise involves the application of external pressure to the proximal portion of a limb during low-load exercise. By partially restricting arterial inflow and substantially reducing venous return, BFR creates a hypoxic and metabolically stressful environment within the exercising muscle. This physiological stimulus promotes early recruitment of fast-twitch motor units and may enhance anabolic signaling pathways despite the use of relatively low exercise loads. Consequently, BFR has emerged as a promising rehabilitation strategy for populations that may not tolerate high-intensity resistance training.

Although preliminary evidence suggests that BFR is feasible and safe in people with MS, existing studies have primarily focused on functional outcomes, and the effects of BFR on muscle morphology remain unclear. Furthermore, no randomized controlled trial has investigated rectus femoris muscle morphology as a primary outcome using a three-arm design incorporating both sham-BFR and exercise-only control conditions.

This study is designed as a prospective, parallel-group, three-arm randomized controlled trial. Thirty individuals with RRMS aged 18-65 years and an Expanded Disability Status Scale (EDSS) score between 2.5 and 3.5 will be recruited. Participants will be randomly allocated in a 1:1:1 ratio to one of three groups:

1. Low-load exercise with blood flow restriction (BFR).
2. Low-load exercise with sham blood flow restriction.
3. Low-load exercise without blood flow restriction (control).

All groups will participate in an identical supervised exercise program twice weekly for eight weeks (16 sessions total). Exercise sessions will include a standardized warm-up period, quadriceps-focused strengthening exercises, cycling exercise, and cool-down/stretching activities. The only systematic difference between groups will be the cuff condition applied during the strengthening component.

In the BFR group, individualized arterial occlusion pressure (AOP) will be determined using a pneumatic cuff system, and exercise will be performed at 50-60% of AOP. In the sham-BFR group, cuffs will be applied in the same location but inflated to a pressure insufficient to produce meaningful vascular occlusion. The control group will perform the same exercise program without cuff application.

Outcome assessments will be conducted at baseline and after completion of the intervention. The primary outcome will be rectus femoris muscle thickness measured by ultrasonography. Secondary outcomes will include rectus femoris echo intensity, knee extensor muscle strength, Timed 25-Foot Walk performance, Nine-Hole Peg Test performance, Symbol Digit Modalities Test scores, and Modified Fatigue Impact Scale scores.

The study is expected to provide novel evidence regarding the effectiveness of low-load BFR exercise for improving muscle morphology and related functional outcomes in individuals with RRMS. In addition, the inclusion of a sham-BFR condition will allow differentiation between the physiological effects of blood flow restriction and potential placebo or expectancy effects associated with cuff application.

Inclusion Criteria:* Age 18-65 years

• Diagnosis of relapsing-remitting multiple sclerosis according to revised McDonald criteria
• EDSS score between 2.5 and 3.5
• Clinically stable disease
• No relapse within the previous 3 months
• No corticosteroid treatment within the previous 3 months
• Ability to participate in exercise training
• Written informed consent

Exclusion Criteria:* Deep vein thrombosis or pulmonary embolism history

• Peripheral vascular disease
• Uncontrolled hypertension
• Severe cardiovascular disease
• Pregnancy
• Recent lower extremity surgery or injury
• Musculoskeletal or neurological conditions interfering with exercise participation
• Contraindications to blood flow restriction training
• Participation in another structured exercise trial during the study period

Individual participant data will not be made publicly available because the informed consent obtained from participants does not include permission for public data sharing and institutional policies restrict release of participant-level data.

Outcome assessments will be performed by evaluators who are blinded to group allocation. Ultrasonographic and clinical outcome measurements will be conducted by assessors who are not informed of participants' intervention assignments. Participants and treating therapists will not be blinded because of the nature of the intervention.