• K C Tong, Sing Kai Lo, and Gladys L Cheing.
• Department of Rehabilitation Sciences, The Hong Kong Polytechnic University, Hong Kong SAR, China.
• Arch Phys Med Rehabil. 2007 Oct 1;88(10):1344-9.

ObjectiveTo 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.DesignA single-blind randomized controlled trial with a convenience sample.SettingUniversity physiotherapy department.ParticipantsSixty-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.InterventionsThe 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 MeasuresMechanical 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.ResultsDuring 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.ConclusionsAlternating frequency stimulation produced a greater elevation in the HPT, but a greater increase in the MPT was achieved using 100Hz stimulation.

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