For therapeutic purposes magnetic fields come from static magnets or from electrically generated pulsed magnetic fields, however it is the characteristics of the magnetic field rather than actual magnet strength that seem to be the important factor. The change in polarity of the field then creates electrical currents in the body that in turn interact with cells and trigger changes in the way the body cells operate. Structures in the cells detect the presence of a magnetic field, and processes such as protein, hormone or enzyme synthesis are then affected. Experiments with thermography have shown an increase in blood flow with the use of magnets. Therefore conditions which benefit from improvements in circulation are highly likely to respond positively to the use of a magnet. There is also evidence that the magnetic field influences ionic exchange across the cell membrane thus influencing metabolism of waste products left behind by injury. With the use of scintigraphy scanning (that measures the metabolic uptake of an injected substance) researchers have found a 30% increase in the rate of substance uptake in the soft tissue and in the bone of the leg treated with magnetic field. It is likely that this also assists in the reduction of medication resistant pain. In a double blind placebo controlled study patients were treated with magnets applied to the skin. A statistically significant reduction in lower back pain was observed. The pain relief was significantly greater than the placebo group where unmagnitized pads were used. Magnets are increasingly being used to replace non-steriodal anti-inflammatory drugs for arthritic pain. The use of magnetic field can replace many embrocations and poultices that have been traditionally used. Because the magnetic field penetrates to the bone it can therefore affect tissues that are not reached by topical applications.