TENS Under the Hood: Stimulation Frequency
This is the fourth in a series of posts that explore how TENS devices work. Our intention is to go “under the hood” of these valuable pain relief devices to help you understand their operation. We will explore key technical specifications and operating principles. We hope this information is useful when deciding on a TENS device for your particular needs.
In this post we will discuss stimulation frequency, which is an important but misunderstood attribute of TENS therapy.
What is Stimulation Frequency?
As we have covered in the first three posts of this series (TENS Under the Hood: Maximum Voltage, Stimulation Pulse, Intensity Control), TENS produces pain relief by passing an electric current between electrodes separated on the skin to stimulate nearby nerves. This current is usually generated as individual pulses at a certain rate, called stimulation frequency. For example, a device stimulating at 80 Hertz (abbreviated Hz) generates 80 pulses per second. A device stimulation at 2 Hz outputs far fewer pulses; only 2 per second. TENS stimulation frequency is labeled “low” if it is below 10 Hz and “high” if it is above 50 Hz. High frequency stimulation has a buzzing sensation. Low frequency stimulation feels like a strong tapping. See the figure below for a visual comparison of high and low frequency stimulation.
Does Stimulation Frequency Matter?
This question has vexed researchers, and despite studies on the topic, remains unresolved. On balance, high frequency or both low and high frequency stimulation is preferred when using TENS at a strong but comfortable intensity. One reason is that low and high frequency stimulation have distinct pain relief mechanisms. Low frequency stimulation increases endorphins, an endogenous pain-relief molecule, while high frequency stimulation increases enkephalins, a different pain-relief molecule. Most prescription pain medications mimic endorphins, so individuals currently (or recently) taking these drugs may not experience pain relief from low frequency stimulation. Another reason is that high frequency stimulation is usually more comfortable than low frequency stimulation for regular TENS users.
Most TENS devices stimulate at a single frequency. Some devices offer options such as frequency sweeps, alternating frequencies, high frequency bursts and random frequencies. Although unique benefits have been proposed for these patterns, they have not been proven in clinical studies.
In many TENS devices, stimulation intensity decreases at high frequencies, which may lead to reduced pain relief. Due to its novel electronic design, Quell® exhibits stable stimulation at all frequencies. Another issue is that TENS devices have poor battery life when used at high frequency. Every stimulation pulse consumes the same amount of battery charge. So, for example, stimulating at 80 Hz will drain the battery much faster than stimulating at 8 Hz. Quell’s battery technology is designed to provide 20-30 hours (3-5 days of typical use) of high frequency stimulation before having to recharge the battery.
If you would like to read more posts in the TENS Under the Hood series, please click here.
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