Sore forearm

Am I doing something wrong?
My fretting hand forearm gets sore - the outer side of the forearm and
closer to elbow. Or is it just lack of practice?

BTW it begins to look like the bass guitar is not so much a musical instrument but
a sports equipment, and the warm-ups and cool-downs needs to be taken seriously.
I wonder what off-season jogging could do...

Stop. Now. Make sure you don't have any pain before you play, and if it hurts, stop.

I got mild tendonitis and it had the same symptoms as you described and I couldn't play for a month or two... I'm better now but it completely threw off my habit of practising

yeah definatly stop
that could get serious

make sure you definatly warm up and stretch properly before you start playing, even if is just for a couple of minutes

also watch dmans tendon/hand exercises video if you havnt already

If it doesnt get better then definatly go and see a doctor

Darn! I was just getting some further understanding about slapping.