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Synopsis: Flexible therapeutic magnets did not affect skin or deep tissue temperatures.
Source: Sweeney KB, et al. Therapeutic magnets do not affect tissue temperatures. Journal of Athletic Training. 2001;36(1):27-31.
Competitive and recreational athletes use therapeutic magnets to treat the pain arising from all types of musculoskeletal injuries. Sweeney and associates sought to determine if the application of therapeutic magnets increased skin and deep tissue temperatures in comparison to sham and control treatments. The basis for the study was the suggestion that therapeutic magnets increase blood flow by increasing tissue temperature.
Subjects for the study were 13 healthy university students. The treatments included the application of a single 5 ´ 11 commercially available magnet, a silicone rubber and cork sham treatment identical in size, thickness, and mass to the magnet, and a control consisting of temperature measurement only. Quadriceps tissue temperatures were measured 1 cm below the fat layer with implantable fine-wire thermocouples interfaced with a 16-channel electronic thermometer. Skin and ambient temperatures were measured with copper/constantan thermocouples. Temperature measurements were taken every 30 seconds for 60 minutes. The skin and intramuscular temperatures under the 3 treatment conditions were analyzed at 0, 20, 40, and 60 minute time points.
The magnet used in this study was advertised as having field strength of 700 G (0.07 T). To confirm this field strength, Sweeney et al used a gauss meter at arbitrarily selected points on the treatment surface to measure magnet field strength and uniformity.
Sweeney et al found no differences in skin or intramuscular temperatures across the 3 treatments at any time. Intramuscular and skin temperatures had a tendency to rise slightly for both the magnet and sham groups over time. Sweeney et al attributed these clinically insignificant increases to the insulating properties of the magnet and sham treatments. The field strength of the magnet ranged from 6 G to 537 G.
Comment by David H. Perrin, PhD, ATC
As with many alternative therapies, little scientific evidence exists to explain or document efficacy of treatment. It has been estimated that more than $500 million has been spent on magnet products in 1 year alone. Therapeutic magnets are purported to increase blood flow from the Hall effect, which causes charged particles to accumulate with like charges in the presence of a magnetic field. Manufacturers suggest the resistance of these particles to accumulate against their normal direction of flow produces heat that in turn results in blood vessel dilation.
Sweeney et al found no difference in intramuscular or skin temperatures among the magnet, sham, and control treatments. Although the design of this study did not measure blood flow, one would expect an increase in tissue temperature in the presence of increased blood flow. It would be interesting to measure blood flow in future studies on the efficacy of magnet therapy.
Magnet therapy has also been associated with reductions in pain and improvements in range of motion and strength. As with tissue temperature, the scientific evidence for these claims is scant. Borsa and Liggett examined the effects of magnets on pain, range of motion, and strength after muscle micro-injury and also failed to find a therapeutic effect.1
This study also found that the field strength of the magnet was variable and did not attain advertised levels. It is possible that the lower levels of field strength might have accounted for the failure of the magnet to increase tissue temperature. However, this would seem unlikely as no trends toward increased temperatures from the magnet treatment in comparison to the sham treatment were observed. Continued study and oversight of the purported field strength and treatment efficacy of magnet therapy by the Food and Drug Administration appears to be indicated.
1. Borsa PA, Liggett CL. Flexible magnets are not effective in decreasing pain perception and recovery time after muscle microinjury. Journal of Athletic Training. 1998;33:150-155.