Effects of different ON/OFF time ratios of cycling pulses on the analgesic effect of motor-level transcutaneous electrical nerve stimulation (TENS)

Abstract

Purpose: Motor-level transcutaneous electrical nerve stimulation (TENS) provides greater analgesic effects than sensory-level TENS. However, it may also cause muscle fatigue and psychological discomfort. To mitigate these issues, the concept of intermittent duty cycle (ON/OFF time) in motor-level TENS was proposed. This study investigated the relationship between different ON/OFF time ratios in motor-level TENS and its analgesic effects.

Methods: Twenty healthy volunteers participated in five experimental conditions over 5 days: 1) conventional motor-level TENS without ON/OFF time, (2–4) motor-level TENS with ON/OFF time ratios of 1:1, 1:2, or 2:1, and (5) a control condition without motor-level TENS. All motor-level TENS interventions were applied to the left tibialis anterior muscle for 30 min, with intensity adjustments made at 10 and 20 min to counteract muscle contraction weakening due to fatigue. Pain thresholds were measured at baseline and at 3, 10, 20, and 30 min after the of motor-level TENS onset. Psychological anxiety was assessed using the state-trait anxiety inventory (STAI), while muscle fatigue was evaluated by changes in the current intensity required to maintain muscle contraction during motor-level TENS.

Results: Significant increases in pain threshold were observed with both conventional motor-level TENS and all motor-level TENS with ON/OFF time ratios compared to the control. No significant differences were found in STAI scores across conditions. Notably, all motor-level TENS interventions with ON/OFF time ratios required significantly lower current intensity compared to conventional motor-level TENS.

Conclusion: This study suggests that motor-level TENS maintains its analgesic effects even with the inclusion of ON/OFF time. Additionally, motor-level TENS with ON/OFF time may be recommended over conventional motor-level TENS.