Alternating frequencies of transcutaneous electric nerve stimulation: Does it produce greater analgesic effects on mechanical and thermal pain thresholds?

Objective: To determine whether alternating frequency transcutaneous electric nerve stimulation (TENS) at 2 and 100Hz (2/100Hz) has a more potent hypoalgesic effect than a fixed frequency at 2 or 100Hz in healthy participants. Design: A single-blind randomized controlled trial with a convenience sample. Setting: University physiotherapy department. Participants: Sixty-four healthy volunteers (32 men [mean age, 28.1 +/- 5.9y], 32 women [mean age, 27.7 +/- 5.6y]) were recruited and randomly divided into 4 groups. Interventions: The 4 groups received TENS delivered at (1) 2Hz; (2) 100Hz; (3) 2/100Hz alternating frequency; and (4) no treatment (control group), respectively. Electric stimulation was applied over the anterior aspect of the dominant forearm for 30 minutes. Main Outcome Measures: Mechanical pain thresholds (MPTs) and heat pain thresholds (HPTs) were recorded before, during, and after TENS stimulation. The data were analyzed using linear mixed models, with group treated as a between-subject factor and time a within-subject factor. Results: During and shortly after electric stimulation, HPT increased significantly in the alternating frequency stimulation group (P=.024). MPT increased significantly in both the 100Hz (P=.008) and the alternating frequency groups (P=.012), but the increase was substantially larger in the 100Hz group. Conclusions: Alternating frequency stimulation produced a greater elevation in the HPT, but a greater increase in the MPT was achieved using 100Hz stimulation.