In the first part of this series, we discussed “substantial equivalence” and how the FDA approves medical devices. The FDA is currently reviewing the MyoCycle to determine if it is substantially equivalent to the RT300. When the FDA clears the MyoCycle for sale, they are agreeing with our claim that the MyoCycle is at least as safe and effective as the RT300, despite differences in the technology. In this part of the series, we discuss the differences between the RT300 and the MyoCycle in terms of the therapeutic modalities they both employ: FES and stationary cycling.
Therapy with a MyoCycle vs. RT300
An FES bike combines two therapeutic modalities into a single system: FES and cycling. Let’s explore how the MyoCycle and the RT300 implement each of these modalities.
Functional electrical stimulation (FES) uses small amounts of electrical current to cause targeted muscles to contract, enabling people with weakened or paralyzed muscles to perform functional movements. Ultimately, the effects of FES depend on the stimulation parameters and the stimulation pattern. The stimulation parameters boil down to frequency (stimulation pulses per second, usually in Hz), intensity (combination of pulse amplitude in mA and pulse width in µs), and waveform (the shape of the stimulation pulses).
The stimulation parameters on the MyoCycle and the RT300 are very similar. Both devices use rectangular, charge-balanced waveforms, and the frequency and intensity between devices are close. The table below compares the stimulation parameters for each device.
|Waveform||Biphasic, charge-balanced||Monophasic, charge-balanced|
|Amplitude||0 – 126 mA||0 – 140 mA|
|Pulse width||0 – 500 µs||50 – 500 µs (default 250 µs)|
|Frequency||60 Hz||10 – 100 Hz (default 33 Hz)|
The stimulation pattern determines which muscle groups are stimulated and how the stimulation changes over time. For FES-cycling, the stimulation pattern is linked to the pedal position, so a particular muscle group is ideally stimulated when that muscle group can help the pedaling motion. Stimulation patterns are typically depicted as in the figures below. In the top figure, LQ and RQ denote the left and right quadriceps while LH and RH denote the left and right hamstrings.
From the figures, you can see that there are three basic characteristics of a stimulation pattern: muscle groups, on/off angles, and shape. The table below details the stimulation pattern for the MyoCycle vs. the RT300. Note that the muscle group comparison only applies to the RT300-SL with six stimulation channels.
| Muscle groups
||Quadriceps, hamstrings, and glutes on both legs||Quadriceps, hamstrings, and glutes on both legs (more optional)|
| On/off angles
||Automatically determined for each rider based on geometry||Manually adjustable by a specialist|
|Shape||Automatically determined for each rider based on geometry||Trapezoid (as in the figure above), manually adjustable by a specialist|
One of the most important distinctions between the MyoCycle and the RT300 is MYOLYN’s proprietary algorithms for determining when and how much to stimulate the rider’s muscles. MYOLYN’s proprietary algorithms were developed by co-founder Matthew Bellman, PhD, to automatically customize the stimulation pattern for each rider. This customization is based on the rider’s geometry and optimizes the power output and efficiency of stimulating the rider’s muscles. The RT300 uses the traditional trial-and-error approach, relying on a trained specialist to tune the stimulation pattern manually, which can result in a sub-optimal stimulation pattern.
Cycling is characterized by cadence (pedaling speed), time/distance, and work/power. Both the RT300 and the MyoCycle utilize motorized, recumbent, wheelchair-accessible, stationary cycle ergometers (powered exercise bikes that can be used from a wheelchair).
The RT300 uses an off-the-shelf ergometer called the THERA-Trainer tigo, manufactured by a German company (Medica Medizintechnik GmbH). The THERA-Trainer is an “active-passive” exercise bike designed to assist riders in pedaling if they pedal below a target speed or resist them if they pedal above the target speed. The RT300 adds FES to the THERA-Trainer, stimulating the riders’ muscles more or less depending on how fast they pedal (more stimulation if pedaling slower, less if faster). The target speed and the behavior of the FES are pre-programmed by a trained specialist (patients cannot change the settings).
The MyoCycle ergometer is custom-designed and manufactured in the USA by MYOLYN, and it was designed specifically for isokinetic FES-cycling. The MyoCycle’s motor always maintains a constant 35 rpm, providing only the amount of assistance or resistance necessary to maintain that speed (isokinetic). FES is applied based on the Level selected by the rider and the rider’s geometry – it doesn’t change with speed or resistance – so the rider can control the amount of work generated by the muscles.
Both the RT300 and the MyoCycle display workout time, distance, power output, and calories burned. The only differences between the two here is how power and calories burned are calculated. The RT300 calculates positive net power output, whereas the MyoCycle calculates active power output. This means that the MyoCycle takes the power the rider needs to produce just to move their legs into consideration and not just the force being applied to the pedals. This also affects the calculation for calories burned. The RT300 only counts calories burned when the rider actively pedals faster than the target speed (net positive power output), and the calculation is based on calibration of the motor and an equation programmed into the THERA-Trainer. The MyoCycle includes both passive and active power output in the equation for calories burned, based on the research done by Ken Hunt.
To conclude, the RT300 and the MyoCycle both apply FES to the rider while a motorized ergometer assists or resists the pedaling, as appropriate. While the technological means for achieving this behavior differs between devices, the therapeutic effect is substantially equivalent, as both devices keep the legs moving while exercising the muscles. By doing so, both the MyoCycle and the RT300 are able to provide the following therapeutic benefits:
- Relaxation of muscle spasms
- Prevention or retardation of disuse atrophy
- Increasing local blood circulation
- Maintaining or increasing range of motion
Therefore, the RT300 and the MyoCycle achieve substantially equivalent therapeutic effects, though the technological characteristics are different.
The next post in this seris will focus on the features of the MyoCycle that differentiate it from the RT300 in terms of ease-of-use. While both devices have similar therapeutic effects, most people agree that the MyoCycle is much easier to use than the RT300. Stay tuned to find out why!