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I would like to measure muscle tension with a sensor. When I'm sleeping sometimes a shoulder muscle cramps and I would like to make something (for example with an Arduino board) to wake me up. The problem is to measure the muscle tension.

A EMG sensor uses three pads. The Myoware EMG board can be used for DIY projects. I have not tried it yet. I think it is not easy to attach it every evening and I don't known where to attach the three pads to select a specific shoulder muscle. But so far this is the only thing that comes close.
[ADDED] I wonder what happens if I attach the pads to a muscle that has already a high tension. Would the EMG be able to measure the absolute tension ?

A ultrasonic liquid density sensor is big, they can not stay attached while sleeping. It could also be a safety risk. Perhaps the ultrasonic could harm tissue and blood cells.

The best way to measure muscle tension is to pinch or press it. Perhaps something small that mechanically pushes into the muscle and measures the strength could work. I have no idea how to make this.

With dry needling, a relaxed muscle does not react, but with a muscle that cramps or has a high tension, then the muscle reacts a lot. However, I can't push needles into my body while sleeping, that would be silly.

If you know a way to measure muscle tension in a practical way, please let me know.
A similar question was asked in the Health section as well: How can I quantify muscle tightness?

[Update] First tests with a EMG sensor.
I have been testing a EMG sensor. The Myoware 4th generation EMG sensor is easy to use for DIY project. To prevent grounding or noise, I used a battery and it is not connected to the computer.
Sadly, it is not near to what I want.
With my fingers I can feel how much tension a (shoulder)muscle has, when I move my back/head/shoulder a little I can feel what is going on. The EMG sensor is more like a lie detector. It detects the tension of a muscle, but that is mostly relative tension and it depends a lot on where the pads are located an how well they are attached. When I use it the next day, I want the same tension to result into the same numbers. That is not possible.

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    \$\begingroup\$ hm, I'd pretty much say EMG is exactly what you want. \$\endgroup\$ Jul 8, 2017 at 15:16
  • \$\begingroup\$ Thank you ! It will take some time to buy the Myoware to do some experiments, since the board is available in shops, but not the pads. I'm a Arduino enthusiast but not a physiotherapist, so I don't know about muscles. \$\endgroup\$
    – Jot
    Jul 8, 2017 at 15:21
  • \$\begingroup\$ haven't used it myself, but my guess is that you can get EKG pads instead. Ask your friendly apothecary! \$\endgroup\$ Jul 8, 2017 at 15:44
  • \$\begingroup\$ @MarcusMüller, do you know if they all have the same size connector click metal knob ? FranckDernoncourt, no sorry, not near Boston. \$\endgroup\$
    – Jot
    Jul 8, 2017 at 15:54
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    \$\begingroup\$ One possible cause of muscle cramps is magnesium deficiency. Try taking a teaspoon of magnesium citrate before you sleep. \$\endgroup\$ Jul 22, 2017 at 19:12

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Although my answer goes against being electrical engineering in nature I have to say you are going about this all wrong. Even if you could somehow make a gadget how can you be sure that trying to measure tension in one muscle is even going to be the right one when the next time it may be in completely different area.

What you need to consider instead is a holistic approach. If you are having muscle seizures and cramps while you sleep be assured that is almost always caused by something going on in your life or physical self. It could be stress from any one of dozens of factors. It could be the condition and environment you put yourself through during the day and reflecting that in through the night.

I would suggest that even trying to hook yourself up to a gadget that wakes you when these conditions happen will make things even worse. There will be added tension and stress due to the anticipation of being awakened and will certainly lead to less sleep and lower quality sleep when and if you do get to sleep.

You may want to try some of these things to try to being more calm and reduced stress and tension in your being:

  1. Try to reorganize your day - get up earlier - do your most energetic activities early and then by evening make sure there is a quiet wind down time for a couple of hours before trying to go to sleep.
  2. Try learning yoga and take a class. The benefits to overall body stress relief can be amazing.
  3. Consider a treatment of whole body acupuncture. Even one session will show you what total relaxation can be like.
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  • \$\begingroup\$ (detecting muscle seizures and cramps while you sleep is one use case but more generally quantifying muscle tension with a sensor would be extremely important, e.g. prevention of injuries) \$\endgroup\$ Jul 8, 2017 at 15:49
  • \$\begingroup\$ @MichaelKaras, Well said, and I totally agree with you. It is exactly the same in electrical engineering: Find the cause, then fix the cause instead of fumbling into something to reduce the resulting troubles. However, in my situation I know the cause. It is my spine which troubles me for a few decades. \$\endgroup\$
    – Jot
    Jul 8, 2017 at 15:49
  • \$\begingroup\$ @jot, I agree with Michael. It is not sustainable even if EMG application is succesfull. But you may still need it. Because I would try to find a correlation with the seizures and unconscious behaviours like snoring while sleeping. This is primarily to find results indicating the seisure as a cause and capturing them as an alarm but maybe you would even find some causes resulting as seisures. \$\endgroup\$
    – Ayhan
    Jul 17, 2017 at 14:10
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I agree with Michael.

Although you could probably use any metal foil that is compatible with your skin would work. The gap between the epidermis dielectric and electrodes creates a galvanic skin voltage and any gap modulation also changes capacitance so when moving, a false reading can occur, which may be what you want ir if not and just muscle tension, it will be a pulse noise envelope < 1kHZ BW.

So special low-k dielectric constant partially-conductive adhesive gel pads work best as perhaps provided with that instrument. But you will need extra pads which normally use snap buttons.

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  • \$\begingroup\$ Thanks. The Myoware that I'm testing recognizes the muscle signals and is not influenced too much by other things. I'm using the 'evelope' signal, not the raw EMG. But I found that the signal level for a certain tension depends on many things. I have a conductive fabrics and different pads to try. \$\endgroup\$
    – Jot
    Jul 18, 2017 at 1:54
  • \$\begingroup\$ gold plated or ENIG FPC pads could be good too ;) \$\endgroup\$ Jul 18, 2017 at 4:14
  • \$\begingroup\$ Thanks, I will try more things, but those are hard to find. \$\endgroup\$
    – Jot
    Jul 18, 2017 at 14:29
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You might try a piezo strip sensor taped to the skin. The are inexpensive and don't require an external power source, but generate an electrical signal when flexed which could be used to trigger your Arduino or measured by the Arduino ADC. You could poll the ADC and look for voltage and keep a log or initiate some other action like the alarm you suggest.

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    \$\begingroup\$ Thanks. I think it can work with a larger muscle. For a smaller shoulder muscle the skin-surface does not really bend. Thank you for thinking about it an providing an new idea. There is also conductive rubber stretch sensor cord. Using the Arduino and writing log files is no problem for me. \$\endgroup\$
    – Jot
    Jul 23, 2017 at 4:50

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