Exercise combined with magnetic stimulation improves muscle strength and gait speed in patients with disuse-induced muscle atrophy of the lower limbs

Abstract

BACKGROUND: In recent years, magnetic stimulation therapy can activate the classical transient receptor potential channel 1, triggering the calcium-mitochondrial axis to enhance myogenesis and mitochondrial biogenesis in vivo, thereby recapitulating physiological adaptations related to exercise-induced metabolic responses. As an emerging technique for promoting muscle function, magnetic stimulation has gained widespread attention and validation in the rehabilitation of muscular diseases due to its advantages of being non-invasive, passive, and safe. However, there is a lack of clinical studies on the therapeutic efficacy of this technique in the treatment of disuse-induced muscle atrophy. OBJECTIVE: To investigate the therapeutic effect of exercise therapy combined with magnetic stimulation on the recovery of muscle strength and locomotor ability in patients with disuse-induced muscle atrophy of the lower limbs. METHODS: Sixteen patients with lower limb disuse muscle atrophy caused by prolonged bed rest after unilateral Achilles tendon rupture surgery were recruited and randomly divided into control group and experimental group, 8 cases in each group. The control group received traditional exercise rehabilitation therapy, including joint range of motion training, muscle strength training, and soft tissue stretching training, 3 times a week. The experimental group additionally received medical magnetic physical factor stimulation (intensity 1.5 mT, frequency 3 300 Hz, 48 h per session, 10 min each time) on this basis, with a total trial duration of 4 weeks. All subjects underwent maximum voluntary contraction (MVC) test of the lower limbs and gait speed measurements including Timed Up and Go test (TUG), 5-times sit-to-stand test (5STS), and 6 m normal walking speed test before and after intervention. RESULTS AND CONCLUSION: After 4 weeks of intervention, all 16 subjects completed the trial. In the experimental group, the maximum voluntary contraction of the affected lower limb (P=0.001) and the difference rate of MVC between affected and healthy sides (P=0.001) significantly decreased, and the improvements were superior to those in the control group. In terms of gait speed indicators, the experimental group showed significant improvements in TUG (P=0.038), 6 m normal walking speed (P=0.025), and 5STS (P=0.050) compared with baseline. Between-group comparison revealed that the experimental group had significantly greater improvements in MVC of the affected leg (P=0.003), difference rate of MVC between affected and healthy sides (P=0.004), TUG (P=0.019), and 6 m normal walking speed (P=0.011) than the control group. These data confirm that after 4 weeks of low-frequency pulsed magnetic field (1.5 mT, 3 300 Hz) combined with exercise therapy, patients with disuse muscle atrophy after Achilles tendon rupture showed significantly better improvements in MVC of the affected and healthy legs, TUG, and 6 m normal walking speed than the control group, demonstrating that magnetic stimulation combined with exercise therapy has an auxiliary synergistic effect on isometric muscle strength and lower limb motor function. Therefore, magnetic stimulation combined with exercise therapy can be used as a new means for rehabilitation of disuse muscle atrophy.

1. Introduction

Disuse muscle atrophy is a pathological change in skeletal muscle caused by mechanical unloading, characterized by decreased muscle fiber cross-sectional area, loss of myofibrillar protein, and decline in muscle function [1], significantly increasing the risk of falls and secondary injuries [2-4]. The pathogenesis involves an imbalance in multi-pathway molecular regulatory networks. At the molecular level, inhibition of the insulin-like growth factor 1-protein kinase B-mammalian target of rapamycin (IGF1-Akt-mTOR) signaling pathway leads to reduced ribosomal biogenesis efficiency [5], imbalance in calcium release and reuptake [6], and activation of the ubiquitin-proteasome system [7]. Current intervention strategies focus on antioxidant defense system reconstruction, mitochondrial function optimization, and regulation of protein metabolism dynamic balance.

Walking limitation caused by disuse muscle atrophy is an important trigger for the continuous deterioration of patients' health. To improve muscle function, early clinical treatment plans have used active and passive exercise therapy as an important means of rehabilitation [8], with its therapeutic mechanism involving dual regulation of mechanical signal transduction and mitochondrial function [9-10]. Mechanical load promotes muscle regeneration and enhances mitochondrial respiratory function by activating mTOR, satellite cells, and peroxisome proliferator-activated receptor-γ coactivator-1α (PGC-1α) [11], thereby inhibiting the progression of muscle atrophy [12]. Postoperative pain leading to inability to bear exercise load is a major limiting factor for exercise therapy, affecting muscle function and walking ability recovery. In this context, magnetic physical factor therapy based on muscle function enhancement shows important clinical translational value. Low-frequency pulsed magnetic field, as an emerging non-invasive physical factor intervention, has gained widespread attention in the rehabilitation of muscle diseases due to its advantages of being non-invasive, passive, and safe.