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Static magnetic field influence on human nerve function
Abstract
In an attempt to understand the possible neural mechanism mediating the effects of a static magnetic field (SMF), nerve conduction velocity (NCV) and excitability index (EI), measured as the ratio of the amplitude of the submaximally evoked compound muscle action potential during or after magnetic exposure to that before exposure from the same intensity of stimulation of the motor nerve, were studied on ten normal volunteers (aged 17 to 39), when the nerve was exposed to an SMF of 1 tesla (T) for 15 seconds. NCV and EI were measured before, during (5, 10, and 15 sec) and three minutes after magnetic exposure. Both NCV and EI were measured on median nerve in all ten subjects, the peroneal nerve in seven subjects, while the ulnar nerve was measured for only EI in eight subjects. There was no significant change in NCV over the segment exposed to the magnetic field. However, EI was significantly increased during the magnetic exposure in all three nerves. The effects were observed as early as five seconds after exposure and disappeared by three minutes after exposure. It is concluded that the excitability of the motor nerve is increased when it is exposed to an SMF with a density of 1T.
... 7 However, it has since been concluded that it may not be alterations in nerve conductivity that result in pain relief, but rather a change in the nerve excitability. 8 In respect of therapy, however, there are two parameters that still need to be clarified: the duration of the application, magnetic field strength and orientation. With respect to orientation, the negative (north) side of the magnet apparently should be directed towards the patient's skin in order to have an increased ability to achieve pain relief. ...
... Results from various studies have suggested that increasing either the duration of magnet therapy or the frequency of the treatment might lead to an increased therapeutic effect. 5,8,9 Therefore, it is considered that long periods of use per day would be appropriate in order to optimize the effectiveness of the magnets. ...
... Therefore, with respect to the use of static bipolar magnets, 0.5 T appears to produce minimal, if any, activity in low back pain, 9 whereas 1 T was reported as being capable of affecting proximal axonal action potential conduction time. 7,8 On the basis of this, it was decided to use the higher value (greater than or equal to 1 T) for the active treatment magnets. In addition, due to the public awareness of magnets, it was deemed appropriate and necessary to use a magnetised placebo. ...
Introduction: Chronic low back pain (CLBP) is one of the most common pain states seen in general medicine today. However, there are currently few, if any, reliable modalities that can be used in its treatment. Magnets are in common use as a therapeutic modality in the relief of a number of pain states. However, the validity of this use is relatively untested, with the effects of magnets on CLBP having not been studied previously. Objective: To investigate the potential usefulness of static magnetic field therapy in the relief of CLBP. Design: A prospective, blinded, randomised, controlled clinical trial. Settings/location: Welsh Institute of Chiropractic, University of Glamorgan. Subjects: Twelve CLBP patients (symptoms for more than 3 months) who were participating in a spinal rehabilitation clinic at the Welsh Institute of Chiropractic (WIOC). None of the subjects had any neurological deficit, or any known underlying pathological problems. Interventions: A belt containing two small 'Neomax' disc magnets (either 1.20 ± 0.05 T in the active or 0.5 ± 0.05 T in the inactive group) was given to each patient. This was applied continually for the 4 weeks of the trial. Outcome measures: Oswestry disability questionnaire, a visual analogue pain scale (VAS), as well as left and right lateral lumbar flexion. Results: Ten subjects completed the study. VAS scores showed a strong trend (p = 0.05) towards a decrease in pain in the active magnet group. However, no significant change was seen in either the Oswestry or lumbar flexion results. Conclusions: Although the numbers in this study were small, they illustrate the possibility that VAS could be decreased in these patients. This suggests that there may be some worth in using magnets to symptomatically relieve CLBP. The results support a larger scale study of static magnetic field application in chronic low back pain. © 2004 The College of Chiropractors. Published by Elsevier Ltd. All rights reserved.
... Altered action potential and excitatory postsynaptic potential 56;66;67 Enhanced nerve excitability 67 ...
... In a study of 10 healthy human volunteers, the nerve conduction velocity and excitability index (measured as the ratio of the amplitude of the submaximally evoked compound muscle action potential during or after magnetic exposure to that before exposure) was measured when the nerve was exposed to a static magnetic field of 1T for 15 sec 67 . In this study, there was no significant change in the nerve conduction velocity over the nerve segment exposed to the magnetic field. ...
This review examines the molecular, cellular and physiological effects of magnetic fields with particular reference to the possible effects of magnetism on athletic performance. Magnetic fields have been shown to alter sub-atomic, molecular and cellular parameters, including the hydrogen bonding and solubility of water, enzyme activity, gene expression, ion transport, membrane permeability and mitochondrial function. Each of which could possibly have an effect on athletic performance, by enhancing the transport of substrates in and out of cells, up-regulating enzyme activity and enhancing the production of ATP. Magnetism has also been shown to affect the central nervous system altering neurotransmitter and hormone levels as well as altering the excitability of peripheral nerves. This could affect athletic performance by enhancing the neuromuscular control, as well as having a central effect altering the perception of pain and fatigue which, in turn, could result in an athlete being able to train harder. Human and animal studies indicate that magnetic fields may have an effect on the cardiovascular system altering the haematocrit, haemoglobin concentration, micro-vascular and vascular tone. This may affect athletic performance by enhancing the oxygen-carrying capacity of blood, as well as the perfusion to active tissue. The musculoskeletal effects of magnetic fields have been well studied and have been shown to up-regulate the growth factors associated with increased bone growth, as well as enhancing the orientation of collagen and bone. This could have important implications for athletes in the prevention and treatment of stress fractures, as well as to enhance bony union following surgery. Today magnetic fields are used to successfully treat fractures, depression, pain, wounds and other medical conditions. Exposure to magnetic fields appears to be safe with very few reported side effects, even after long-term exposure to very strong magnetic fields. Despite these molecular, cellular and physiological changes induced by magnetic fields, there has, however, been little documented research on the possible effects of magnetism on athletic performance
... Although some investigators have attempted to delineate a neural mechanism related to pain reduction after wearing static magnets, 14,15,33 the results have been inconsistent. Hong et al 14 investigated the effects of magnetized necklaces or placebos on neurological indices in 101 volunteers, approximately half of whom were currently experiencing chronic neck and shoulder pain. ...
... Again, data supporting the notion that static magnets have an effect on local neurological function are inconclusive. 14,15,33 In contrast to the studies by Vallbona et al 32 and Weintraub, 33 Collacott et al 7 recently conducted a double-blind, placebo-controlled study involving 20 individuals with chronic low back pain. Each participant had lumbosacral range of motion and subjective pain evaluated before and after wearing either a magnet or placebo for 6 consecutive hours, 3 days per week. ...
Prospective, randomized, double-blind, placebo-controlled crossover design.
To examine the effects of static magnets on resting forearm blood flow and vascular resistance.
Despite little scientific evidence indicating benefits of wearing static magnets, recent reports have indicated a dramatic increase in the usage of magnets to treat a variety of medical conditions. Magnet manufacturers have proposed that one mechanism for pain reduction involves magnet-related blood flow alterations to the affected area.
Twenty young, healthy men (mean age +/- SD = 25 +/- 2 years) wore commercially available static magnets and placebos for 30 minutes on 2 separate occasions. Resting forearm blood flow was assessed in triplicate at minutes 10, 20, and 30, using venous occlusion plethysmography. Forearm vascular resistance was estimated by dividing mean arterial pressure by blood flow.
The average blood flow over the 30-minute measurement period was not significantly different between the magnet and placebo sessions (mean +/- SD for magnet session = 1.40 +/- 0.63 ml blood x 100 ml tissue(-1) x min(-1); mean +/- SD for placebo session = 1.36 +/- 0.46 ml blood x 100 ml tissue(-1) x min(-1); P = 0.66). Blood flow measurements at minutes 10, 20, and 30 were also not significantly different between the magnet and placebo sessions, and forearm vascular resistance was not different between the magnet and placebo sessions at any time (P > 0.05).
Exposure to static magnets for up to 30 minutes had the same effect on resting forearm blood flow and vascular resistance as placebo magnets. These data suggest that static magnets do not result in significant alterations in resting blood flow.
... The 2 main fields under study have been the nervous and cardiovascular systems and, in both cases, the results regarding direct effects of magnetic fields on human physiology are somewhat confusing (for a review, see Saunders 2005). In the nervous system, several studies (Gaffey and Tenforde 1983; Hong et al. 1986; Hong 1987) have failed to show any effect of fields as high as 1.5 T on action potential conduction velocity. In fact, the necessary intensity for varying the conduction velocity was estimated to be 24 T (Wikswo and BarachFigure 7. (A) Scheme representing the arrangement of the different elements during the experiment. ...
Noninvasive brain stimulation techniques have been successfully used to modulate brain activity, have become a highly useful
tool in basic and clinical research and, recently, have attracted increased attention due to their putative use as a method
for neuro-enhancement. In this scenario, transcranial static magnetic stimulation (SMS) of moderate strength might represent
an affordable, simple, and complementary method to other procedures, such as Transcranial Magnetic Stimulation or direct current
stimulation, but its mechanisms and effects are not thoroughly understood. In this study, we show that static magnetic fields
applied to visual cortex of awake primates cause reversible deficits in a visual detection task. Complementary experiments
in anesthetized cats show that the visual deficits are a consequence of a strong reduction in neural activity. These results
demonstrate that SMS is able to effectively modulate neuronal activity and could be considered to be a tool to be used for
different purposes ranging from experimental studies to clinical applications.
... In vitro studies have also revealed a variable impact of SMF on neurophysiological mechanisms. While some studies reported no effects of up to 2 T SMF exposures on action potential conduction velocity [12][13][14], others found alteration of the activation time-constant of voltagegated sodium and calcium channels which may reduce nerve discharge (120 mT [15,16]. Exposures to intense static fields (7-14 T) were found to affect the vestibular system [17,18]. ...
Primary objective:
Occupational exposure to static magnetic fields (SMF) increases, in particular due to the widespread use of Magnetic Resonance Imaging (MRI) for medical diagnosis, thus raising health concerns. This study investigated the behavioural effects of 128 mT SMF in rats and examined the hypothesis that iron supplementation (3 mg kg(-1) for 5 days) potentiate the effects of SMF.
Methods:
Spatial learning abilities in the water maze, motor co-ordination in the rotarod and motor skills in the stationary beam and suspending string tests were assessed in iron-treated, SMF-exposed and co-exposed SMF-iron rats.
Results:
Acquisition of the water maze navigation task was unaffected in all groups. SMF-exposed and iron-treated rats showed a deficit in the 7-day retention test. No deficit was found in the rotarod and suspended string tests in all groups. Only iron-treated rats were impaired in the stationary beam test. A combination of iron and SMF treatments did not produce additional degradation of performance in all tests.
Conclusion:
SMF exposure had no massive effect but affected long-term spatial memory. Iron supplementation and 128 mT SMF had no synergistic effects.
... We have found that exposure to a SMF (1.0 mT, 30 min) modified the hemodymamic responses in a Ca 2þ channel blocker, nicardipine-induced hypotension or a nitric oxide synthase antagonist, L-NAMEinduced hypertension to buffer BP swings in unanesthetized rabbits [Okano and Ohkubo, 2001]. In addition, a number of other experimental studies have demonstrated that the effects of SMFs act as a trigger for microcirculatory relevant biochemical pathways: acetylcholine release [Rosen, 1992], action potentials [Azanza, 1989;Balaban et al., 1990;Rosen and Lubowsky, 1990;Rosen, 1993Rosen, , 1994Ayrapetyan et al., 1994;Cavopol et al., 1995;McLean et al., 1995;Trabulsi et al., 1996;Wieraszko, 2000;Reina and Pascual, 2001], Ca 2þ -ATPase activity [Itegin et al., 1995], calcium channel function [Rosen, 1996], phosphorylation of myosin light chain [Markov et al., 1993;Markov and Pilla, 1997;Engström et al., 2002;Liboff et al., 2003], nerve excitability [Hong et al., 1986;Hong, 1987;Rosen and Lubowsky, 1987], muscle tension [Satow et al., 2001], cellular immune parameters [Flipo et al., 1998], blood-brain barrier permeability [Prato et al., 1990], inhibition of apoptosis [Fanelli et al., 1999;Teodori et al., 2002], and baroreflex sensitivity [Gmitrov and Ohkubo, 2002a,b]. These actions of SMFs are predicted to involve alternations in Ca 2þ fluxes [Azanza, 1989;Rosen, 1992Rosen, , 1996Markov et al., 1993;Ayrapetyan et al., 1994;Itegin et al., 1995;Markov and Pilla, 1997;Flipo et al., 1998;Wieraszko, 2000;Reina and Pascual, 2001;Satow et al., 2001;Gmitrov and Ohkubo, 2002b;Liboff et al., 2003]. ...
Effects of static magnetic fields (SMFs) on development of hypertension were investigated using young male, stroke resistant, spontaneously hypertensive rats (SHRs) beginning at 7 weeks of age. SHRs were randomly assigned to two different exposure groups or an unexposed group. The SHRs in the exposure groups were constantly exposed to two different types of external SMFs of 3.0-10.0 mT or 8.0-25.0 mT for 12 weeks. The SMFs were generated from permanent magnetic plates attached to the rat cage. The blood pressure (BP) of each rat was determined at weekly intervals using indirect tail-cuff method. The SMFs suppressed and retarded the development of hypertension in both exposed groups to a statistically significant extent for several weeks, as compared with an unexposed group. The antipressor effects were related to the extent of reduction in plasma levels of angiotensin II and aldosterone in the SHRs. These results suggest that the SMFs of mT intensities with spatial gradients could be attributable to suppression of early BP elevation via hormonal regulatory system.
During the performance of magnetic resonance imaging (MRI) the patient is exposed to three different forms of electromagnetic radiation: a static magnetic field, gradient magnetic fields, and radiofrequency (RF) electromagnetic fields. Each of these may cause significant bioeffects if applied at sufficiently high exposure levels.
It has long been assumed that equilibrium models of cellular excitation that focus on depolarization of the membrane potential and associated massive changes in ionic equilibria across the cell membrane also offer an adequate basis for an understanding of the first events in cell membrane transductive coupling of molecular and electrochemical stimuli at the cell surface. For nervous tissue, it has been generally accepted that the Hodgkin-Huxley (1952) model appropriately describes both sequence and energetics of excitatory events. However, this brilliant thesis from relatively limited biological data was originally offered only in the context of a mathematical description of major perturbations in Na+ and K+ ionic equilibria that occur at a certain epoch in the course of excitation in giant nerve fibers of the squid.
Superconducting magnetic energy storage (SMES) is discussed as a
developing technology for storing electric energy. Its efficiency is
significantly greater than any existing energy storage method. Most of
the environmental concerns associated with present-day energy storage
devices do not exist with SMES: it does not use or produce harmful
chemicals, no dams or other radical changes to the landscape are
required, and it is silent in its operation. The author explores the
current state of knowledge on magnetic-field effects upon animals
(including man) and electronic devices and communications
Developing valid control groups that generate similar perceptions and expectations to experimental complementary and alternative (CAM) treatments can be challenging. The perceived credibility of treatment and outcome expectancy often contributes to positive clinical responses to CAM therapies, thereby confounding efficacy data. As part of a clinical feasibility study, credibility and expectancy data were obtained from subjects suffering from migraine who received either CranioSacral therapy (CST) or an attention-control, sham, and low-strength magnet (LSSM) intervention.
The objective of this study was to evaluate whether the LSSM intervention generated similar levels of subject credibility and expectancy compared to CST.
This was a two-arm randomized controlled trial.
Sixty-five (65) adults with moderate to severe migraine were the subjects of this study.
After an 8-week baseline, subjects were randomized to eight weekly treatments of either CST (n=36) or LSSM (n=29). The latter involved the use of a magnet-treatment protocol using inactive and low-strength static magnets designed to mimic the CST protocol in terms of setting, visit timing, body positioning, and therapist-subject interaction.
A four-item, self-administered credibility/expectancy questionnaire, based on a validated instrument, was completed after the first visit.
Using a 0-9 rating scale, the mean score for perceived logicality of treatment was significantly less for LSSM (5.03, standard deviation [SD] 2.34) compared to CST (6.64, SD 2.19). Subject confidence that migraine would improve was greater for CST (5.94, SD 2.01) than for LSSM (4.9, SD 2.21), a difference that was not statistically significant. Significantly more subjects receiving CST (6.08, SD 2.27) would confidently recommend treatment to a friend than those receiving LSSM (4.69, SD 2.49).
Although LSSM did not achieve a comparable level of credibility and expectancy to the CST, several design and implementation factors may have contributed to the disparity. Based on analysis of these factors, the design and implementation of a future study may be improved.
An amputee (traumatic) experienced increased phantom limb pain when exposed to the magnetic fields of two magnetic resonance imagers. With a visual analog scale used to measure pain, electric stimulation studies demonstrated that the residual limb was unusually sensitive to subthreshold (for muscle twitch) levels of current. The painful symptoms produced mimicked those experienced in the presence of the imagers.
The literature is contradictory regarding the effect of static magnetic fields on the function of the central nervous system of mammals. Since human subjects are exposed to intense static magnetic fields during magnetic resonance imaging, it is important to determine if the static magnetic field adversely affects the nervous system of man. Therefore, somato-sensory evoked potentials (SEPs) elicited from median nerve stimulation were measured in 11 normal subjects before and during short-term exposure to a 1.5 Tesla static magnetic field. Specially modified instrumentation was used to record SEPs that were unperturbed by the static magnetic field. There were no statistically significant differences in the N20 or P25 latencies or in the amplitude from N20 negative peak to P25 positive peak of the SEPs obtained before compared to those recorded during exposure to the static magnetic field. In addition, there were no changes in the waveforms associated with exposure to the static magnetic field. We conclude that short-term exposure to a 1.5 Tesla static magnetic field does not affect SEPs (i.e., nerve conduction and synaptic transmission were within normal limits) in normal human subjects.
The study was performed to examine the influence of the exposure to magnetic fields in the potrooms of an electrolysis plant on the occurrence of musculoskeletal symptoms among the employees. The study was performed after much discussion and worry in the aluminium industry about this issue.
A retrospective cohort study was performed at an aluminium plant. The occurrence of musculoskeletal symptoms registered at health controls performed by the occupational health care unit in 1986 and 1991 was assessed from employees exposed to magnetic fields in the potrooms (n = 342) and from a control group (n = 277). The data were collected before the discussion about the effects of magnetic fields started. The exposure to static magnetic fields was found to be 3-20 mT inside the potrooms. Ripple components (alternating currents (AC fields)) were registered as well.
No difference between the exposed and unexposed groups was found for the reported musculoskeletal symptoms in 1986 or in 1991.
There seems to be no relation between work in potrooms with exposure to static magnetic fields and the occurrence of musculoskeletal symptoms.
In this study, we aimed to clarify the effects of chronically applied static magnetic field (200 Gauss) on specific ATPase activities and bioelectrical and biomechanical responses in isolated rat diaphragm muscle. The mean activities of Na(+)-K+ ATPase and Ca2+ ATPase determined from the diaphragm homogenates were significantly higher in the magnetic field exposed group (n = 20), but that of Mg2+ ATPase was nonsignificantly lower compared to the control group (n = 13). Resting membrane potential, amplitude of muscle action potential, and overshoot values (mean +/- SE) in the control group were found to be -76.5 +/- 0.6, 100 +/- 0.8, and 23.5 +/- 0.6 mV, respectively; these values were determined to be -72.8 +/- 0.4, 90.3 +/- 0.5, and 17.2 +/- 0.4 mV in the magnetic field-exposed group, respectively. The latency was determined to increase in the experimental group, and all the above-mentioned bioelectrical differences between the groups were significant statistically. Force of muscle twitch was found to decrease significantly in the magnetic field-exposed group, and this finding was attributed to the augmenting effect of magnetic field on Ca2+ ATPase activity. These results suggest that magnetic field exposure changes specific ATPase activities and, thence, bioelectrical and biomechanical properties in the rat diaphragm muscle.
To determine if the chronic pain frequently presented by postpolio patients can be relieved by application of magnetic fields applied directly over an identified pain trigger point.
Double-blind randomized clinical trial.
The postpolio clinic of a large rehabilitation hospital.
Fifty patients with diagnosed postpolio syndrome who reported muscular or arthritic-like pain.
Application of active or placebo 300 to 500 Gauss magnetic devices to the affected area for 45 minutes.
Score on the McGill Pain Questionnaire.
Patients who received the active device experienced an average pain score decrease of 4.4 +/- 3.1 (p < .0001) on a 10-point scale. Those with the placebo devices experienced a decrease of 1.1 +/- 1.6 points (p < .005). The proportion of patients in the active-device group who reported a pain score decrease greater than the average placebo effect was 76%, compared with 19% in the placebo-device group (p < .0001).
The application of a device delivering static magnetic fields of 300 to 500 Gauss over a pain trigger point results in significant and prompt relief of pain in postpolio subjects.
Therapeutic modalities are useful adjuncts in the rehabilitation of many patients commonly seen by hand surgeons. Therapeutic heat, cold, electrical stimulation, and laser and magnetic field treatments are evaluated for their respective mechanisms of action, indications, contraindications, and clinical results. The majority of therapeutic modalities have been extensively investigated and relevant basic science and randomized well-controlled clinical studies addressing the efficacy of therapeutic modalities are emphasized.
Static or electromagnetic fields have been used for centuries to control pain and other biologic problems, but scientific evidence of their effect had not been gathered until recently. This article explores the value of magnetic therapy in rehabilitation medicine in terms of static magnetic fields and time varying magnetic fields (electromagnetic). A historical review is given and the discussion covers the areas of scientific criteria, modalities of magnetic therapy, mechanisms of the biologic effects of magnetic fields, and perspectives on the future of magnetic therapy.
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.
Despite anecdotal reports, rigorous scientific evidence of the effectiveness of magnetic insoles for the pain of plantar fasciitis is lacking.
To determine whether magnetic insoles provide greater subjective improvement for treatment of plantar heel pain compared with identical nonmagnetized insoles.
Randomized, double-blind, placebo-controlled trial conducted from February 12, 2001, to November 9, 2001, of a volunteer sample of 101 adults with diagnoses of plantar heel pain for at least 30 days from a multispecialty group practice clinic in Rochester, Minn. Daily pain diaries were kept for 8 weeks.
Cushioned insoles, with either active bipolar magnets or sham magnets, which were worn daily by the participants for 8 weeks.
Reported average daily foot pain (by metered visual analog scale [VAS] and by categorical response of change from baseline) at 4 and 8 weeks, and impact of insoles on employment performance and enjoyment.
No significant between-group differences were found on any outcome variables studied when comparing active vs sham magnets. Both the nonmagnetic and magnetic groups reported significant improvements in morning foot pain intensity, with mean (SD) VAS scores improving from 6.9 (2.3) and 6.7 (2.0), respectively, at baseline to 3.9 (2.6) for each group at 8 weeks (P =.94). At 8 weeks, 33% of the nonmagnetic group and 35% of the magnetic group reported being all or mostly better (P =.78). At baseline, foot pain interfered moderately with participants' employment enjoyment (mean VAS, 4.2) and improved in both groups by 8 weeks (1.3 and 1.5, respectively; P =.68).
Static bipolar magnets embedded in cushioned shoe insoles do not provide additional benefit for subjective plantar heel pain reduction when compared with nonmagnetic insoles.
Various experimental studies carried out over the last 30-40 years have examined the effects of the chronic or acute exposure of laboratory animals to static magnetic fields. Many of the earlier studies have been adequately reviewed elsewhere; few adverse effects were identified. This review focuses on studies carried out more recently, mostly those using vertebrates, particularly mammals. Four main areas of investigation have been covered, viz., nervous system and behavioural studies, cardiovascular system responses, reproduction and development, and genotoxicity and cancer. Work on the role of the natural geomagnetic field in animal orientation and migration has been omitted. Generally, the acute responses found during exposure to static fields above about 4 T are consistent with those found in volunteer studies, namely the induction of flow potentials around the heart and the development of aversive/avoidance behaviour resulting from body movement in such fields. No consistently demonstrable effects of exposure to fields of approximately 1T and above have been seen on other behavioural or cardiovascular endpoints. In addition, no adverse effects of such fields on reproduction and development or on the growth and development of tumours have been firmly established. Overall, however, far too few animal studies have been carried out to reach any firm conclusions.
To determine whether magnetic insoles are effective for relieving nonspecific subjective foot pain in the workplace, resulting in improved job satisfaction.
A prospective, randomized, double-blind, placebo-controlled study of health care employees who experienced nonspecific foot pain for at least 30 days, which occurred more days than not, was conducted between February 2001 and January 2002 at the Mayo Clinic in Rochester, Minn. Participants were asked to wear either magnetic or sham-magnetic cushioned insoles for at least 4 hours daily, 4 days per week for 8 weeks. The primary outcome variable was reported foot pain (by categorical response of change from baseline and by visual analog scale) at 4 and 8 weeks. Secondary outcome variables included graded intensity of pain experienced during various daily activities and the effect of insoles on job performance and enjoyment.
Among 89 enrolled participants, 6 either withdrew before wearing insoles or were noncompliant with follow-up questionnaires; 83 participants remained for full statistical analysis. Participants in both treatment groups reported improvements in foot pain during the study period. No significant differences in categorical response to pain or pain intensity were seen with use of magnetic vs sham-magnetic insoles.
The magnetic insoles used in this study by a heterogeneous population with chronic nonspecific foot pain were not clinically effective. Findings confirmed that nonspecific foot pain significantly interferes with some employees' ability to enjoy their jobs and that treatment of that pain improves job satisfaction.
Static and pulsed magnetic fields have been reported to have a variety of physiological effects. However, the effect of static magnetic fields on pain perception and sympathetic function is equivocal. To address this question, we measured pain perception during reproducible noxious stimuli during acute exposure to static magnets. Pain perception, muscle sympathetic nerve activity, mean arterial pressure, heart rate, and forearm blood velocity were measured during rest, isometric handgrip, postexercise muscle ischemia, and cold pressor test during magnet and placebo exposure in 15 subjects (25 +/- 1 yr; 8 men and 7 women) following 1 h of exposure. During magnet exposure, subjects were placed on a mattress with 95 evenly spaced 0.06-T magnets imbedded in it. During placebo exposure, subjects were placed on an identical mattress without magnets. The order of the two exposure conditions was randomized. At rest, no significant differences were noted in muscle sympathetic nerve activity (8 +/- 1 and 7 +/- 1 bursts/min for magnet and placebo, respectively), mean arterial pressure (91 +/- 3 and 93 +/- 3 mmHg), heart rate (63 +/- 2 and 62 +/- 2 beats/min), and forearm blood velocity (3.0 +/- 0.3 and 2.6 +/- 0.3 cm/s). Magnets did not alter pain perception during the three stimuli. During all interventions, no significant differences between exposure conditions were found in muscle sympathetic nerve activity and hemodynamic measurements. These results indicate that acute exposure to static magnetic fields does not alter pain perception, sympathetic function, and hemodynamics at rest or during noxious stimuli.
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