Abstract: BACKGROUND: For post-stroke hemiplegic patients, traditional resistance training, while effective, has application limitations in those unable to tolerate active exercise. As a passive intervention, the efficacy specificity, safety, and feasibility of low-frequency pulsed electromagnetic fields for this vulnerable population remain unclear, particularly lacking objective imaging assessments of morphological changes in post-stroke muscle atrophy.
OBJECTIVE: To evaluate the improving effects of low-frequency pulsed electromagnetic fields on the muscle structure of the vastus lateralis muscle in the lower limbs of post-stroke hemiplegic patients.
METHODS: Twenty-three patients with obvious symptoms of lower limb muscle atrophy after stroke hemiplegia were recruited and randomly divided into an experimental group receiving low-frequency pulsed electromagnetic field stimulation and a control group receiving sham treatment. There were 12 cases in the experimental group and 11 cases in the control group. The trial lasted for a total of 4 weeks. Patients in the experimental group received a 15-minute low-frequency pulsed magnetic field stimulation intervention every 48 hours, while the control group received sham treatment alongside routine medical care, with intervention time points consistent with the experimental group. After 4 weeks, B-mode ultrasound imaging was used as an assessment tool to observe changes in the structural indicators of the vastus lateralis muscle, including pennation angle, muscle thickness, and cross-sectional area, in both the unaffected and affected legs of patients in different groups, as well as changes in the difference values.
RESULTS AND CONCLUSION: (1) After 4 weeks of low-frequency pulsed electromagnetic field stimulation, 18 patients completed the trial, with 9 cases in the experimental group and 9 cases in the control group. In the experimental group, the post -test values of the three indicators of muscle morphology in the affected leg, including muscle thickness, pennation angle, and cross-sectional area, were significantly higher than the pre-test values (P < 0.05). The difference values for muscle thickness, pennation angle, and cross-sectional area in the affected leg were significantly lower than those before the trial (P < 0.05). In the control group, muscle thickness and cross-sectional area of the affected leg were significantly higher than before the trial, and the cross-sectional area of the unaffected leg significantly increased; however, there were no significant changes in the difference values of the three muscle morphology indicators between the unaffected and affected legs. (2) Inter-group comparison revealed that the experimental group had significantly higher values than the control group for the three indicators of muscle morphology in the affected leg, including muscle thickness, pennation angle, and cross-sectional area (P < 0.05). The rate of change in the difference values for muscle thickness, pennation angle, and cross-sectional area between the unaffected and affected legs was significantly higher in the experimental group than in the control group (P < 0.05). These findings confirm that after 4 weeks of low-frequency pulsed electromagnetic field stimulation, indicators related to skeletal muscle structure and morphology in the affected vastus lateralis muscle of the lower limb were significantly improved in post-stroke hemiplegic patients, providing morphological evidence supporting the use of this technology as an exercise alternative and medical strategy for improving muscle atrophy symptoms in post-stroke hemiplegic patients.

Key words: low-frequency pulsed electromagnetic fields, calcineurin, transient receptor potential channel 1, peroxisome proliferator-activated receptor gamma coactivator 1-alpha, skeletal muscle morphological structure, stroke, hemiplegia, muscle atrophy, quadriceps femoris