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

Официальное название

Peripheral Magnetic Stimulation of Foot Muscles

Обзор

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.

Подробное описание

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.

Вмешательства

• Устройство Repetitive Peripheral Magnetic Stimulation (rPMS)
  Repetitive peripheral magnetic stimulation (rPMS) will be applied to the foot invertor muscles three times per week for 12 weeks. Stimulation will target the upper third of the anteromedial side of the shin, near the tibia, using an oval magnetic coil. To ensure correct coil placement, visible muscle contraction and ankle inversion will be monitored. Intrinsic foot muscles will be simultaneously stimulated using a foot stimulator, with the nondominant foot positioned on the stimulation platform.

Первичные конечные точки

• Change in medial longitudinal arch height [Срок оценки: Baseline (Day 1), Week 6, Week 12]

Вторичные конечные точки (1)

• Change in isometric inversion torque of the stimulated foot [Срок оценки: Baseline (Day 1), Week 6, Week 12]

Критерии участия

Критерии включения

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

Критерии исключения

• 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.

Критерии приведены из реестра в оригинале (на английском). Окончательную оценку соответствия проводит исследовательский центр.

Здоровые добровольцы: Нет

Дизайн исследования

Распределение

Рандомизированное

Модель

Параллельные группы

Маскирование

Простое слепое

Основная цель

Лечение

Центры проведения

Словения · 2 центра

• Faculty of Sport, University of Ljubljana — Ljubljana
• Faculty of Sports — Ljubljana

Публикации

• Zschorlich V, Yamaguchi T, Schneider C. Editorial: The use of repetitive peripheral magnetic stimulation (rPMS) in neurological disorders and neurorehabilitation. Front Neurol. 2023 Nov 20;14:1324882. doi: 10.3389/fneur.2023.1324882. eCollection 2023. No abstract available. PMID 38053798
• Hirono T, Ikezoe T, Taniguchi M, Nojiri S, Tanaka H, Ichihashi N. Acute effects of repetitive peripheral magnetic stimulation following low-intensity isometric exercise on muscle swelling for selective muscle in healthy young men. Electromagn Biol Med. 2021 Jul 3;40(3):420-427. doi: 10.1080/15368378.2021.1907402. Epub 2021 Mar 25. PMID 33764250
• Masse-Alarie H, Flamand VH, Moffet H, Schneider C. Peripheral neurostimulation and specific motor training of deep abdominal muscles improve posturomotor control in chronic low back pain. Clin J Pain. 2013 Sep;29(9):814-23. doi: 10.1097/AJP.0b013e318276a058. PMID 23370067
• Neugebauer R. [Surgical treatment of colon cancer. 4. Preoperative preparation of the colon]. Aktuelle Probl Chir Orthop. 1979;(10):38-40. No abstract available. German. PMID 32789
• Baek J, Park N, Lee B, Jee S, Yang S, Kang S. Effects of Repetitive Peripheral Magnetic Stimulation Over Vastus Lateralis in Patients After Hip Replacement Surgery. Ann Rehabil Med. 2018 Feb;42(1):67-75. doi: 10.5535/arm.2018.42.1.67. Epub 2018 Feb 28. PMID 29560326
• Yang SS, Jee S, Hwang SL, Sohn MK. Strengthening of Quadriceps by Neuromuscular Magnetic Stimulation in Healthy Subjects. PM R. 2017 Aug;9(8):767-773. doi: 10.1016/j.pmrj.2016.12.002. Epub 2017 Jan 8. PMID 28082179
• Aenumulapalli A, Kulkarni MM, Gandotra AR. Prevalence of Flexible Flat Foot in Adults: A Cross-sectional Study. J Clin Diagn Res. 2017 Jun;11(6):AC17-AC20. doi: 10.7860/JCDR/2017/26566.10059. Epub 2017 Jun 1. PMID 28764143
• Kelly LA, Farris DJ, Cresswell AG, Lichtwark GA. Intrinsic foot muscles contribute to elastic energy storage and return in the human foot. J Appl Physiol (1985). 2019 Jan 1;126(1):231-238. doi: 10.1152/japplphysiol.00736.2018. Epub 2018 Nov 21. PMID 30462568

Идентификаторы

NCT: NCT07237321 · rPMS, 0124-0043 · P5-0124, P3-0043

Первоисточники (государственные реестры)

• ClinicalTrials.gov (NIH, США)

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