I know there might not be a solution, and probably one of the best choices might just be to get a full suspension ( I might be wrong) but I have a hardtail. I'm just wondering, do you guys do lower back exercises to strengthen the muscles and cope with the pain better. I ride only trails (nothing DW or FR) and I'm just wondering if you could share tips from your own experiences. Thank you!

1. make sure your fit is right. too much or too little reach can hurt your back.
a. too little reach gives you a cramped posture and puts more weight on your saddle, and thus your lower back.
b. too much reach makes you bend over farther. it generally does reduce weight on your saddle, though. so maybe you shouldn't do this and instead...

2. increase your flexibility
a. do some light, gentle stretching before rides.
b. if you stop for more than 2 minutes mid-ride, more gentle stretching.
c. when you're totally done riding, do some GOOD stretching. do not wait until after you drive home. even if you don't see anyone else stretching, do it. who gives a crap what anyone else thinks.. it's your body.

3. get out of the saddle when going over rough terrain like roots and rock gardens. I bet you're doing this one already. don't stand rigidly, use your legs and arms as shock absorbers.

Good advice from Colin. Just some stuff to add on the stretching front, don't stretch before you warm up. Stretching cold muscles is bad. I don't usually do any stretching beforehand, but if you choose to, keep it light and dynamic (not static stretching...save that for afterward). And when Colin says GOOD stretching, he means it. In order to see muscle length changes, you need to stretch for a while...like a total of 3 minutes at a time (go with say 6x30 seconds).

Do some searches on the net for core work. Abs and mid body connectors keep your back in place and happy.

Planks, raised bird dogs, kettlebell get ups, and all kinds of stuff you wish you didn't know about till your back hurts.

Also pics of good stretching and Zephyr is right on about length, timing.

I had some lower back pain for a while there.

Went and saw a physio, etc for it. I wrote up all the advice he gave me in another post. But basically the physio told me to strengthen my core...lots of weird little exercises over a number of months fixed me up. I still do them every other day along with stretching my left gluteus medius...which was the main culprit in my case...and in most others from what Im told.

Google gluteus medius stretch and try one. Odds are it'll hit the spot thats hurting.

Thanks for all your tips, its until last week that I actually decided to start training my core. Never been a fan but now that I really want to get fit ( I know I'll never look like a pro bodybuilder since I put more time riding than resistance training) the core will help out. As for the stretching you are absolutely right. Thank you for reaffirming my thoughts. @Lexi01 you might also be right, My left knee always gives me some problem but that is mostly because I am prone to getting a tight IT band often so I guess I need to take out my foam roller and work on the stretching. Thank you all for your tips and help!

Graston technique works wonders for IT band dysfunction, if you can find a chiropractor who does it.

Core is very important, but please don't overlook bike fit. Go back and reread Colin's post. Then see if your bike shop does fittings. They may be able to help you swap out your stem, adjust your bar height, adjust your saddle position, etc.

You may want to check out thudbuster seat posts, which would be much cheaper than a new fs bike.

Probably -- your seat is a little too low. Impossible to say for sure with info given however. Raise your seat to the proper ergonomic position for pedaling just as you would on a road bike. If you feel you want more control for descents get a dropper post or 1980s-era Hite-Rite.

Update: Core workout it helped a lot but one thing that helped tremendously and maybe you can try it yourself is to try to keep your core activated while you ride. I raised my seat because I wasn't confident on certain things but got over that now. But I noticed that if I ride without keeping my tight core I start to get a lower back ache. Once I have it I also notice that when I go back to tightening it, it slowly starts to disappear.

So yeah, thanks again. On the bright side I started p90x2 and the firt phase, half of each week is a core workout so i'll be ripping the benefits hand in hand. So in 90 days you guys shall see my results! XD

That's great to hear.. stick with it!