Peripheral Magnetic Stimulation of Foot Muscles: Effects on Medial Longitudinal Arch Height and Foot Muscle Strength in Adults With Flat Feet (rPMS-Foot)

University of Ljubljana

Status: Not yet enrolling

Conditions: Pes Planus; Posterior Tibial Tendon Dysfunction; Flatfoot

Treatments: Device: Repetitive Peripheral Magnetic Stimulation (rPMS)

Study type: Interventional

Funder types: Other

Identifiers

NCT07237321

P5-0124, P3-0043 (Other Identifier)

rPMS, 0124-0043

Details and patient eligibility

About

This study examines the effects of repetitive peripheral magnetic stimulation (rPMS) on foot invertor muscle strength, morphology, and the height of the medial longitudinal arch (MLA) in individuals with flat feet. The rPMS will be applied non-invasively to the extrinsic and intrinsic foot muscles three times per week for twelve weeks. The experimental group will receive rPMS targeting the invertor muscles of the foot, while the control group will not receive stimulation but will follow the same measurement schedule.

Assessments will be performed at baseline, after 6 weeks, and after 12 weeks of intervention. The primary outcome will be the change in the height of the MLA, evaluated using dynamic navicular drop assessment during gait. Secondary outcomes will include changes in the isometric inversion torque of the foot invertors and morphological adaptations of the tibialis posterior muscle assessed by ultrasound imaging.

This study seeks to determine whether rPMS can improve the height of the MLA, foot invertor muscle strength and structural stability in adults with flat feet. The findings may contribute to developing new, non-invasive therapeutic approaches for improving foot function and preventing musculoskeletal imbalances related to flat foot deformity.

Full description

During movement, the role of the foot muscles is often overlooked. Through their strength and stabilizing function, foot muscles play an important role in maintaining balance, posture, and force transmission throughout the body. Proper activation of these muscles also helps preserve the stability of the medial longitudinal arch (MLA), thereby influencing the overall biomechanics of human movement.

The foot muscles are classified as extrinsic (originating outside the foot) and intrinsic (originating and inserting within the foot). Extrinsic muscles, primarily stabilize the ankle joint and control larger movements, whereas intrinsic muscles store and release elastic energy within the foot, contributing to arch support and movement efficiency.

A lowered height or collapsed arch of the foot, known as flat foot (pes planus), is characterized by arch flattening during weight-bearing and affects approximately 13-27% of the adult population. This deformity alters force distribution and shock absorption, increasing mechanical load on the joints and muscles of the lower kinetic chain. Consequently, flat feet are often associated with foot pain, tendinopathies, and different musculoskeletal disorders in the knees, hips, and lumbar spine.

One of the main causes of flat foot deformity is dysfunction of the tibialis posterior (TP) tendon. This dysfunction leads to reduced muscle strength, decreased neuromuscular activation of the foot invertors and plantar flexors, and subsequent lowering of the navicular bone, resulting in a reduced MLA height. Strengthening the m. TP not only maintains arch position but also improves gait efficiency by reducing compensatory activation of other muscles. This muscle is considered as the strongest foot invertor and has the largest moment arm along the subtalar axis.

Recent research highlights that strengthening foot invertor muscles, particularly m. TP, can effectively increase height of the MLA. Conventional interventions include specific exercise programs and proprioceptive neuromuscular facilitation techniques. However, neuromuscular electrical stimulation used in previous studies did not showed significant increases in MLA height, partly due to pain and discomfort during deep muscle stimulation.

Repetitive peripheral magnetic stimulation (rPMS) has emerged as a promising non-invasively alternative, capable of stimulating deep neuromuscular structures. Several studies have shown that high-frequency rPMS can induce muscle activation, transient swelling, and potential hypertrophy indicators. Nevertheless, there is limited evidence on the long-term (multi-week) effects of rPMS on deep muscles such as the m. TP.

Aim of this research is to implement a 12-week rPMS protocol targeting both extrinsic and intrinsic foot invertor muscles, and to examine whether rPMS induces changes in the height of the MLA. Additionally, the study aims to determine whether 12-week rPMS protocol contributed to increased strength and cross-sectional area of the m. TP.

Enrollment: 30 estimated patients

Sex: All

Ages: 18 to 50 years old

Volunteers: No Healthy Volunteers

Inclusion criteria

• Age between 18 and 50 years,
• functionally flat feet of participants.

Exclusion criteria

• Acute leg injuries,
• diabetes,
• vascular disorders of the lower limbs,
• open wounds or skin lesions on the lower leg or foot,
• participants with metal implants near the stimulation site,
• cardiac pacemaker,
• other orthopedic or neurological conditions that could affect the study results or pose a health risk to the participants.

Trial design

Primary purpose: Treatment

Allocation: Randomized

Interventional model: Parallel Assignment

Masking: Single Blind

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30 participants in 2 patient groups

rPMS Stimulation Group

Experimental group

Description:

Subjects in this group will receive repetitive peripheral magnetic stimulation (rPMS) of the foot invertor muscles three times per week for 12 weeks. Stimulation will be applied to the upper third of the anteromedial side of the shin. Intrinsic foot muscles will be simultaneously stimulated using a foot stimulator, with the nondominant foot placed on the stimulation platform. Participants in the experimental group will complete ultrasound imaging, navicular drop assessment, clinical evaluation of the plantar arch index, and isometric strength testing of the foot invertor muscles at three time points: before the intervention (baseline), after 6 weeks, and after 12-week stimulation period.

Treatment:

Device: Repetitive Peripheral Magnetic Stimulation (rPMS)

Control Group (no stimulation)

No Intervention group

Description:

Subjects in control group will not receive any stimulation but will undergo the same measurement procedures as the experimental group, including ultrasound imaging, navicular drop assessment, clinical evaluation of the plantar arch index, and isometric strength testing of the foot invertor muscles before and after the 6- and 12-week period.