This is a randomized double-blind crossover study. The investigators applied ELF with a device named "LIMFA Therapy®" to 48 fibromyalgic patients, assigned in two groups (true-sham and sham-true). Fibromyalgia severity was assessed with the Fibromyalgia Impact Questionnaire (FIQ), quality of sleep with the Pittsburgh Sleep Quality Index (PSQI) questionnaire and global quality of life with Short Form-12 of Physical and Mental Health Summary (SF-12) questionnaire.

In the first part of the protocol the group true-sham received 6 twice a week sessions of true ELF therapy of 1 hour, following the antinflammatory, analgesic and biorhythm settings of the device "LIMFA Therapy®". The sham-true group patients received 6 twice a week sessions of sham therapy (no therapy).

During the second part of the protocol, the true-sham group received the sham therapy twice a week for 3 weeks and the sham-true group received the actual true therapy twice a week for 3 weeks.

For the assessment of pain, sleep quality and global quality of life, a set of questionnaires were administrated at specific stages of the protocol. Questionnaires were administrated every three weeks: before the first therapy, after the first course of therapy, after the washout period, after the second course of therapy, and 3 weeks after the end of treatment.

Inclusion Criteria:

• patients with an established fibromyalgia diagnosis of at least three months according to American College of Rheumatology 2010 modified criteria and no responsive to their current therapy.
• patients were not responsive to amitryptiline, selective serotonin reuptake inhibitor (SSRI) or duloxetine and pregabalin (with a pain reduction below 50% compared to pre-therapy or intolerant to these drugs)
• patients with a pain level measured with Visual Analogue Scale for Pain (VAS) > 50/100.
• patients that had been taking other drugs or food supplements for the treatment of fibromyalgia for at least 6 months.

Exclusion Criteria:

• patients that completed either physiotherapy or acupuncture or behavioral treatment in the last 6 months
• patients that were affected by other painful syndromes or potentially painful syndromes other than fibromyalgia.
• pregnant women
• pace-maker carriers
• oncologic patients
• tuberculotic patients.

Participant and care provider were unaware of the treatment as the machine does not make any sound or heat during the session. Only the nurse that physically connect the cable to the generator knows if the patient recieve or not the therapy but she was not involved in clinical evaluation.