Thank you Dusty this is very helpful information and visual context. I used to think there was no wrong way to play the dulcimer until the way I was doing it started to hurt. Now I know of at least one wrong way lol. 

I am 6'3 with long legs that tend to cause my knees to be higher than my hips on most chairs and couches, which is something I was never cognizant about until Strumelia pointed it out. When I do sit on something that lets my legs dangle, it is very comfortable to use a strap and let the dulcimer rest across my legs at a downward angle.

In being more aware about my wrist position and posture, I'm already noticing an improvement in strain.

Thanks folks

I'm only a tad taller than Wally, but when I have to sit in a chair that doesn't allow my legs to make a perfectly flat support for the dulcimer, I position the dulcimer comfortably by using a strap.  The strap not only provides some flexibility in sitting positions, but also enables me to angle the dulcimer a little bit so that it is not sitting flat on my lap.

That slight angle of the dulcimer also helps create a more natural angle for both left and right hand. When I first started on the dulcimer I laid the instrument flat on my lap and developed pretty painful tendonitis in the elbow of my strumming hand. Using a strap and changing the angle of the dulcimer cleared that up right away.

For your fretting arm, your entire forearm and hand should make a straight line pointing slightly down, with no angle at the wrist.

Take a look at Aaron O'Rourke here and notice both the way the dulcimer is propped up a bit off his lap and also the straight line of his fretting arm: https://youtu.be/EPClQt6v0Z0?si=08QnvmAx6vM0v60-&t=118 .

They always say there is no wrong way to play the dulcimer, but when I first started and developed tendonitis, and when you found you were straining your wrist, well those are clear signs that we were doing something wrong (at least for us) and needed to alter our approach.

As to seating position, I'm only about 5' 6" tall, with short legs. My lap is horizontal when I sit in a 1950s vintage wooden folding chair, but on more modern chairs for table use my lap slopes down in the wrong direction. I carry a piece of hard urethane packing foam about 3" thick and 12" square to use as a foot rest. (That beats trying to find and carry a Sears catalog or city phone book, or hauling my own chair around.) My elbows are above the dulcimer in my lap and my forearms about horizontal.

Some short folks put their heels on the front cross bar of steel chairs and achieve about the same effect.

Time spent on working out your seating is a good long-term investment.

Thanks folks for these useful tips. Clearly I need to hold my arm at a better angle. I think also paying attention to the level my knees are at will also be very helpful. In general, should my wrist be flat with my forearm, or curved slightly downward?

Nate, I agree with the consensus here.  And I know you responded to my post elsewhere about exercises I'm doing to strengthen my fretting fingers.  Basically  the way you are fretting the strings, you are using your arm to push down on the strings rather than your fingers themselves. If you strengthen your fingers, you won't need your wrist or arm and can just have a relaxed hand, letting the fingers do all the work.  My daughter's old piano teacher (well, I mean ex-piano teacher; she's no older than I am ) used to tell her to imagine that a delicate egg was under her hand.  The hand should be curved to protect the egg while her fingers hit the keys. I think the same principle works on the dulcimer.

Contact me by PM and I'll send you a sticker that should help:

I must agree with KenL. From watching your video here , your wrists are lower than your fretting fingers. It's actually the very same advice for computer ergonomics- elbows and wrists should not be lower than the hands/fingers when typing or mousing. This is to avoid wrist pain and carpal tunnel syndrome over time.
In that video, I see you are sitting on a couch that seems to put your seated hips lower than your knees. That positions the dulcimer on your knees higher up... which in turn causes you to have your wrists & forearms lower than the fretboard. I do recommend that wrists be higher than the fretting fingers, and elbows either at or higher than fretting fingers.
Perhaps this does not apply to your situation Nate, but I did a blog post that might have some useful thought in it about this. I wrote more about fingertip angles than arm or wrist angles, but they are related to each other.
If you are having wrist pain, you may want to examine your computer/device/phone ergonomics as well- they might be a contributing factor.

From your avatar photo you appear to be chording and your wrist is lower than the fret board. I find it much easier to chord if I raise my wrist and come down on the fret board with my fingers. I try to maintain contact with the strings using the tips of my fingers. I don't know if this will help you, but it works for me.

Ken

"The dulcimer sings a sweet song."

Given the wide variety of playing styles used on the dulcimer, I don't think there is any "proper form."

Noter-drone playing puts a very different stress on the wrist than any form of chording. Some people I have met who have hand issues find it the only way they can play. It is part of the reason I play almost exclusively in that style. I use a noter which is about 3/8 inch in diameter and about 6 inches long with my forefinger on top and the heal on the noter at my wrist.

You appear in your photo to be playing chords, so that probably won't helpyou at the present, but of your problem becomes severe, consider the noter-drone tradition before giving up.

Hey folks, can anyone recommend any good videos, articles, or just general advice on proper form for fretting a dulcimer. The way that I fret can put a lot of strain on my wrist at times, so I need to improve my technique, but I don't actually know the correct way to fret ergonomically. Can anyone offer advice or direct me toward content that will help me to learn how to practice good form that puts less stress on my fretting wrist.
I am hesitant to just trust whatever comes up from a google search since I know so little on the topic, so Id be grateful if anyone could share any good resources or tips.
Thanks,
Nate