Therapeutic Magnets Do Not Affect Tissue Temperatures

OBJECTIVE: Manufacturers of commercially available "therapeutic" magnets claim that these magnets cause physiologic thermal effects that promote tissue healing. We conducted this study to determine if skin or intramuscular temperatures differed among magnet, sham, and control treatments during 60 minutes of application to the quadriceps muscle. DESIGN AND SETTING: A 3 x 3 mixed-model, factorial design with repeated measures on both independent variables was used. The first independent variable, application duration, had 3 random levels (20, 40, and 60 minutes). The second independent variable, treatment, had 3 fixed levels (magnet, sham, and control). The dependent variable was tissue temperature ( degrees C). Measurement depth served as a control variable, with 2 levels: skin and 1 cm below the fat layer. Data were collected in a thermoneutral laboratory setting and analyzed using a repeated-measures analysis of variance. SUBJECTS: The study included 13 healthy student volunteers (8 men, 5 women; age, 20.5 +/- 0.9 years; height, 176.8 +/- 10.4 cm; weight, 73.8 +/- 11.8 kg; anterior thigh skinfold thickness, 16.9 +/- 6.5 mm). MEASUREMENTS: Temperatures were measured at 30-second intervals using surface and implantable thermocouples. Temperature data at 20, 40, and 60 minutes were used for analysis. Each subject received all 3 treatments on different days. RESULTS: Neither skin nor intramuscular temperatures were different across the 3 treatments at any time. For both skin and intramuscular temperatures, a statistically significant but not clinically meaningful temperature increase (less than 1 degrees C), was observed over time within treatments, but this increase was similar in all treatment groups. CONCLUSIONS: No meaningful thermal effect was observed with any treatment over time, and treatments did not differ from each other. We conclude that flexible therapeutic magnets were not effective for increasing skin or deep temperatures, contradicting one of the fundamental claims made by magnet distributors.