So I've been working on more complicated songs, and I've been having a problem that's preventing me from getting through whole songs. It seems that when I play things like chords, or move up and down the fretboard quickly, my wrist bends at a near 90 degree angle. Once I start playing a more difficult song, my left wrist becomes sore and tired fairly quickly, but that feeling wears off very fast if I stop playing for like a minute.

I do have really tiny hands, but it hasn't prevented me from playing a lot of songs up until now. Is there anything I can do about this?

Here's a video demonstrating my issue:

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I use a 6 string bass in the video, but the issue still occurs with a 4 string.
Last edited by dking3211 at May 15, 2017,
It might feel kind of weird at first but it helps a fair bit. Try switching from having the guitar sitting on your right leg, to having it sit on your left leg, and rotate it slightly clockwise so the headstock is higher than usual. This angle allows your hand to wrap around the frets much more easily and doesn't crank your wrist. 

Also, if anyone has ever heard of or experienced swelling in the strumming wrist after about 5 hours of playing (while used to playing for long periods of time), swelling that doesn't fully go away for about or over 7 weeks... I would love to hear about it... I'm getting really worried.
Practice standing up. This will allow you to pull your elbow back and up a bit, should shift your wrist angle to a much better position.

And other poster, if it's swelling for that long, go to a doctor. That is the only worthwhile advice for you to take.
I also recommend you practice while standing up. When you feel your wrist is tired, stop practicing for 30 seconds of one minute. It is all about training, so the intervals between your wrist become tired should be still longer and longer.
Ice your upper neck, no not the Bass.

You might be stressing in your neck at the nerve paths to your hand.

I have done this as well as using Arnica Gel on my wrist, and an anti-inflammatory seems to be helping the neck and the subsequent wrist and numb hand issues.
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Played with an older bass player a while back, and when he showed up the rest of us were sniffing the air; it had suddenly become redolent with the odor of BenGay. Turns out he has a routine preventative system of applications of anti-inflammatories and pain salves and salon pas patches followed by a couple of ibuprofen when he gets home.

Playing bass horizontally and low-slung may look good and it may work for some folks, but playing it with the headstock high seems to work for more. It may also explain the growing acceptance of multi-scale basses and guitars; the frets point in the direction your wrist does naturally, and they may actually be more comfortable than playing a fixed-scale bass.