Procedures
Participants with nonspecific chronic low back pain will be recruited for the study. The participants will be assessed by a blinded evaluator, with prior training and experience in the field, for confirmation of eligibility criteria. In addition, demographic and anthropometric data will be obtained and other information such as the use of pain medications and the realization of any other treatment for low back pain. Eligible participants will be informed about the objectives and procedures of the study and following, the primary and secondary outcomes will be collected. Written informed consent will be obtained from all participants.
Randomization will be performed by a researcher not involved in the recruitment and treatment of the participants (CMNC), using the random number generation from Microsoft Excel for Windows. The allocation will be concealed by using consecutively numbered, sealed, opaque envelopes. After evaluation, eligible participants will be referred to the physical therapists responsible for the electrotherapy treatment that will randomly distribute the participants in the treatment groups.
The primary and secondary outcomes will be assessed at three different terms: baseline, 6-week follow-up and 6-month follow-up. In addition, at the last two assessments the participants will be instructed to refrain from providing treatment information to the evaluator. Only the pressure pain threshold obtained with the algometry will be performed at baseline and at the 6-week follow-up. This procedure aims at minimizing the loss of participants on returning visits at the 6-month follow-up for assessment, since the algometry requires the physical presence of the participant while the questionnaires and scales can be reapplied over the phone. Due to the nature of the intervention, it will not be possible to blind the participants and the therapists responsible for the implementation of the interferential current. Participant recruitment began in October 2013 and has a target date of February 2015 for completion. Table 1 shows the timeline of the study.