2025, Vol. 29 ›› Issue (8): 1634-1642

Effects of chronic exposure to low-frequency pulsed magnetic fields on contractility and morphology of the quadriceps muscle in healthy adults

Wang Xuanqiang1, Zhang Wenyang2, Li Yang3, Kong Weiqian4, Li Wei4, Wang Le1, Li Zhongshan5, 6, Bai Shi4   

Abstract: BACKGROUND: Changes in skeletal muscle mass have been indicated in studies addressing the effects of low-frequency pulsed magnetic fields on the structure and morphology of the skeletal muscle, but no relevant studies have been conducted on the morphologic changes that occur after chronic exposure to the low-frequency pulsed magnetic field.
OBJECTIVE: To observe the effects of chronic exposure to low-frequency pulsed magnetic fields on the maximal voluntary contraction and morphologic indicators of the quadriceps muscle of the leg, thereby providing a reference of muscle morphologic changes for the use of this technique as a strategy for muscle function improvement.
METHODS: Seventy healthy subjects were recruited and randomly divided into a test group that received magnetic field stimulation and a control group that underwent sham treatment, with 35 subjects in each group, and the total duration of the trial was 4 weeks. The test group underwent low-frequency pulsed magnetic stimulation for 15 minutes every 48 hours, while the control group underwent sham treatment, with the same intervention interval and duration as the test group. After 4 weeks of intervention, changes in the maximum voluntary contraction value of the quadriceps muscle in different groups were observed, and B-mode ultrasonography was utilized as a means of assessment to observe changes in muscle thickness, muscle cross-sectional area, and pinnation angle indexes.
RESULTS AND CONCLUSION: After 4 weeks of chronic exposure to low-frequency pulsed magnetic fields, 68 subjects completed the test. The maximum voluntary contraction value of the quadriceps muscle in the test group increased significantly (P=0.000), and the increment was significantly higher than that of the control group (P=0.008). Three indexes related to muscle morphology in the test group were significantly higher than the pre-test values (P=0.000), while in the control group, muscle thickness showed a significant reduction (P=0.020), there was no significant change in the pinnation angle, but a significant increase in the cross-sectional area (P=0.000). Intergroup comparisons revealed that the three indicators related to muscle morphology, including muscle thickness (P=0.012), pinnation angle (P=0.003), and cross-sectional area (P=0.049), were significantly higher in the test group than in the control group. The above data confirmed that the maximum voluntary contraction of the quadriceps muscle was significantly increased in healthy adults after 4 weeks of chronic exposure to the low-frequency pulsed magnetic field, and significant increases in the three muscle morphometric indices of muscle thickness, cross-sectional area, and pinnation angle were observed in the test group, providing a basis of muscle tissue morphology for the use of this technique as an exercise alternative and medical treatment strategy for muscle improvement.
Key words: low-frequency pulsed magnetic field, chronic exposure, transient receptor potential channel 1, TRPC1, skeletal muscle morphologic structure, maximal voluntary contraction, musculoskeletal ultrasound, muscle thickness, muscle cross-sectional area, pinnation angle, double-blind trial