What's the difference between TENS and FES?
TENS aims to relieve pain by stimulating nerves and encouraging the body's healing process. The muscles are only gently stimulated if at all. They may gently twitch but often don't even do that as the currents are so low.. The currents needed to stimulate nerves are quite low, much lower than needed to stimulate muscles..
FES stimulates muscles enough to make them contract. So if your biceps is stimulated your elbow will bend. FES strengthens muscles, relaxes then and improves their function. This needs higher currents than TENS and feels more like exercise.
In technical terms TENS uses a pulse width between 150 and 200 microseconds, frequencies above 80 Hz or between 2-20 Hz, currents typically up to 15mA maximum and the current is usually constantly on.
FES uses pulse widths between 240 and 300 microseconds, frequencies between 10 and 70 hz, currents up to 50mA and the currents alternates between on and off.
It sounds confusing but DON'T WORRY. Modern machines often have preset programmes so all you need to do is choose the programme and start. Using machines with preset programmes all you have to alter is the current which makes then ideal for home use.
As an example if you have a sore knee due to arthritis you'll use TENS on the thigh muscles and knee to get pain relief but not move the leg, only get perhaps a gentle twitch of thigh muscle. Using FES on the thigh muscles makes them contract, bending and straightening your knee to build strength.
Can I use my TENS machine for FES?
Not really as the current you would need is very high and would be painful. Also you can't set work and rest times so the results would be poor and might rapidly exhaust your muscles.
Can I use my FES machine for TENS
Yes, as long as you can input your own settings. It would certainly be possible to use the FES machine for conventional TENS and with a bit of creative setting of work and rest times you could mimic modulated TENS but again the results would not be a patch on using a TENS machines with proper programmes.
Do any machines have both TENS and FES programmes?
Yes. The Rehab stimulator has 8 TENS and 8 FES programmes as well as a hand switch for an even better response. It's easy to use and means you don't have to buy 2 machines.
A brief outline of the science behind electrical stimulation
TENS and FES machines deliver current to your body. The current is not constant, it's made up of lots of little 'pulses' . Each pulse only lasts for a few millionths of a second. (known as microseconds). The time each pulse lasts is known as the pulse width. The number of pulses per second is the frequency. The current is measured in milliamps or mA.
Pulse widths less than 200 microsecond stimulate nerves but not muscles. Pulse widths over 240 microseconds stimulate both nerves and muscles.
Frequencies below 20-25 pulses per second can be felt as twitches or taps on your skin.. Above this you just feel constant. Frequencies above 40 cause smooth muscle movements which feel natural and not jerky.
Currents at low levels below 8 mA often can't be felt. Currents above 50 mA can be quite painful.
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