Product Comparison
Number of Channels
Why it Matters:
The number of channels on an electrotherapy device determines how much area can be treated, how efficient the therapy is and how well patients adhere to treatment.
With 4 channels, patients can place up to 8 electrodes at once – covering larger treatment areas or multiple pain sites – in a single session without needing to reposition pads. This makes therapy more effective and convenient, supporting better compliance and ultimately better outcomes when compared to a 2-channel device.
To be specific, a 2-channel device can cover a 3.5-inch by 7-inch treatment area, whereas a 4-channel device can cover 7-inches by 14-inches – double the treatment size.
Devices marketed as 4-channel but with only 2 outputs are still limiting because the channels are not truly independent. Instead of customizing intensity, frequency or waveform for each pair of electrodes, these devices split the current – restricting flexibility and sometimes creating uneven stimulation. In practice, these devices function more like a 2-channel unit with extra leads, rather than providing the full benefits of a true 4-channel electrotherapy device.
Premodulation
Why it Matters:
The RS-4i Plus can pre-mix – that is, premodulate – Interferential signals inside the unit instead of the patient’s body. This results in a larger treatment area because the “sweet spot” of the therapy isn’t limited to where the two signals intersect. Rather, the area of therapeutic interference spans the entire distance between the electrodes – which for many patients can mean covering an area of 7 or 8 inches instead of an area that’s closer to 2 inches.
Additionally, premodulation allows the RS-4i Plus to transition between Interferential treatments and NMES treatments without repositioning the electrodes, which is required for devices without this technology. The added ease-of-use for patients can increase treatment compliance and in turn, improve effectiveness. It is also what enables the RS-4i Plus to utilize patented Intersperse technology, which intermixes IFT and NMES treatments into a single session.
Intersperse
Why it Matters:
Most electrotherapy devices provide either pain relief (through IFT or TENS) or muscle stimulation (through NMES), but they don’t combine the two therapies in a way where they amplify each other. Because the RS-4i Plus can premodulate – that is, pre-mix – Interferential signals inside the unit instead of the patient’s body, it is able to transition between IFT and NMES treatments without the patient having to reposition the electrodes.
Additionally with premodulation, the RS-4i Plus can utilize patented Intersperse technology to intermix these therapies in a single session – delivering IFT pain relief signals during the relaxation phase of NMES muscle contractions. This creates a repeating cycle of contraction, relief, contraction and relief that maximizes both comfort and effectiveness.
The unique intermixing of IFT pain treatment and NMES muscle therapy during Intersperse sends a sequence of signals up both the neo and paleo spinothalamic tracts into the brain, provoking a beta-endorphin release. These are long-chain peptides (endogenous opiates) that provide pain relief lasting up to 8 hours. Intersperse is why so many patients report relief that lasts hours after they complete a treatment with the RS-4i Plus.
Pain Relief Type
Why it Matters:
While both TENS and Interferential (IFT) Therapy are designed to relieve pain, IFT is more effective because of how the stimulation is delivered.
Traditional TENS units use an electrical signal at a single, low frequency, which can’t penetrate deep into tissue, provides only temporary relief and is less comfortable for the patient. In contrast, IFT uses two slightly different high-frequency signals, for instance 5000 Hz and 5100 Hz. These signals intersect within the body to create an area of interference – a “sweet spot” where the therapeutic benefit is strongest.
This intersection of signals results in a new frequency – the beat frequency – which is able to recruit the maximum number of A-beta nerve fibers for treatment. These high-frequency signals also trigger the body’s production of enkephalins, short-chain peptides (endogenous opiates) that provide pain relief lasting about 1 hour. This deeper-reaching stimulation is not only more comfortable for patients, but also more effective at targeting pain pathways.
Pain Relief Waveform Frequency
Why it Matters:
Resistance and frequency have a linear relationship – as frequency increases, resistance decreases. Traditional TENS units operate at frequencies around 50 Hz. At 50 Hz, the skin presents significant electrical resistance of 3,200 ohms. As a result, low-frequency stimulation can only affect surface-level tissues and cannot penetrate into deeper layers. When the frequency is increased to 5,000 Hz, the skin’s resistance drops dramatically – to 32 ohms. This reduction in resistance enables the signal to travel deeper and more comfortably into the tissue, reaching the area proximal to the nerves causing pain. The RS-4i Plus has a 5,000 Hz frequency therefore, is able to penetrate 1.75 inches into the skin, whereas a 50 Hz device can only reach 0.0175 inches into the skin – 100 times less depth.
Pain Relief Mechanism of Action
Why it Matters:
Most traditional TENS units rely on distraction for pain relief. This is akin to running your hand under cold water after burning it, and it’s why most patients report their pain returning quickly after using a traditional TENS unit.
Other higher-powered electrotherapy devices rely solely on the Gate Control Theory for pain relief, which works by hyper-stimulating A-beta nerve fibers to trigger the release of short-chain peptides – enkephalins – that block the transmission of pain signals to the brain. While effective, this mechanism typically provides only about an hour of relief before pain returns.
The RS-4i Plus also relies on Gate Theory and yet takes pain relief a step further with patented Intersperse technology, which intermixes premodulated IFT and NMES. This combined hyper-stimulation of both A-delta and C nerve fibers sends a sequence of signals up both the neo and paleo spinothalamic tracts into the brain, provoking a beta-endorphin release. These endogenous opiates are long-chain peptides that provide pain relief lasting up to 8 hours, and it’s why patients report relief that lasts hours after they complete a treatment with the RS-4i Plus.
NMES Waveform
Why it Matters:
The shape of a waveform is determined by its height (amplitude) and width (pulse width). The pulse width, commonly expressed in microseconds, is the time it takes for a signal to complete its cycle. The wider the pulse width, the longer the stimulation. This matters for muscle fiber recruitment because slower-twitch fibers, like in the lower back and upper legs, take longer to fire. Therefore, if the pulse width isn’t wide enough, the duration of stimulation will not be long enough to cause a contraction in these big muscles.
The RS-4i Plus NMES waveform is an adjustable, custom square/asymmetrical spiked waveform. The square portion of the waveform has a wide pulse width to recruit slow-twitch muscle fibers, and the spiked portion has a narrow pulse width to recruit fast-twitch muscle fibers, like in the arms and lower legs. The RS-4i Plus is one of the few devices to offer pulse width control, which allows the patient to widen the pulse width when they turn up the device, recruiting more slow-twitch fibers as they increase the intensity, eliciting a maximal muscle contraction.
By contrast, devices with a spike/spike waveform can only recruit fast-twitch muscle fibers because the pulse width is not wide enough – meaning the stimulation is not long enough – to recruit slow-twitch muscle fibers.
NMES Frequency
Why it Matters:
At low NMES frequencies (about 1–20 Hz), stimulation produces isolated muscle twitches rather than sustained contractions. These twitches do not generate high force but are less fatiguing, which can be useful for patients with severely atrophied muscles. Moderate frequencies (20–60 Hz) begin to produce tetany – smooth, sustained contractions as individual twitches overlap. High frequencies (80–100 Hz and above) can yield strong, powerful contractions, but they tend to cause rapid fatigue and may increase patient discomfort.
The RS-4i Plus uses a frequency of 71 Hz, which is high enough to produce a strong tetanic contraction recruiting both slow- and fast-twitch fibers, while still below the threshold that typically leads to intolerable fatigue or discomfort. This makes 71 Hz particularly effective and well-tolerated for NMES therapy.
Number of Programs
Why it Matters:
Having 82 programs on the RS-4i Plus matters because it gives practitioners the ability to match therapy to each patient’s specific condition, while still keeping the device simple for patients to use at home. With 82 pre-programmed treatments covering IFT, NMES and Intersperse, practitioners can easily select protocols based on the type and location of pain as well as the muscle stimulation needed – whether that’s progressive stimulation for atrophy or sequential stimulation for muscle spasms. This level of customization ensures treatment is clinically appropriate while reducing trial-and-error for patients.
While the RS-4i Plus has advanced features, it’s still easy for patients to use. Once the preferred program is identified, the device automatically defaults to it – so patients can simply “turn it on and turn it up” for repeat sessions. For more advanced needs, practitioners can create fully customized programs that are saved to memory and just as easy to re-use. This balance of flexibility and simplicity makes the RS-4i Plus both a powerful clinical tool and a patient-friendly solution, increasing the likelihood of consistent use and better outcomes.