There have been many questions about the lower back pain, but I do not think I read about the kind of lower back pain that I have. I do not experience any pain while cycling or after a training session. But I feel pain in the back when I try to bend down after I wake up, e.g. - to put my socks on. I used to think that this was because of weight training or maybe due to my aging. But recently I had more than a month when I stopped training completely and the morning back pain disappeared. When I resumed training on a cycling trainer (not going to the gym yet), I noticed that the morning back pain returned. So clearly there is a connection with cycling training, not with weight training or anything. The morning back pain completely disappears after I warm up, after breakfast. I am not sure what is it - muscle fatigue or a disk problem? I am guessing it could be muscle fatigue, but how can I improve?
That’s a whole can of worms that could be any one of many issues that the Internet cannot properly diagnose, from as simple as sleeping in the wrong position to degenerative/herniated disc issues to something like spondylitis. I’ve dealt with lower back pain for years, and like you, mine is worse in the morning and gets better with some exercise/movement. I got a Teeter Dex II machine a couple of years ago that I try and hang on every morning for at least 5-10 minutes, and it does seem to make a good difference in how long my morning pain bothers me. Good luck!
I have a long history of on and off back pain due to disc, muscle and facet joint problems. The only thing that has helped me long term is PT focusing on core stability. If even small stabilizer muscles are not doing their job (not firing) it’s just a matter of time before either disc, muscle, ligament, facet joint issue etc…will flare up.
More than likely attributed to degenerative aspects such as osteoarthritis. I get about 4 days a year when I wake up without back pain. Take a look at the strength training recommendations for maintenance, and to minimise the slide.
As the first thing to do I have good experience with googling muscles that could be tightened up and responsible for the pain and then using youtube PT videos to relax them. It is for sure not the final solution in many cases but in this way I could clearly identify the psoas as my main problem. That saved me from getting unnecessary MRTs or other time consuming examinations and I got it under control with PT. As usual this is not advice not to see a doctor but just to say that some things you can check yourself in a fairly easy way.
See a professional.
Any individuals recommendation is based off their own experience and without a thorough clinical exam it could make your issue worse.
When you lie down for many hours overnight, the discs in your spine absorb water and get bigger. So when you wake up in the morning, you might have pain if the increase in disc size is causing them to press on nerves or something. After you’ve been up for a couple of hours, the discs compress and lose water from the force of gravity, so this is why you probably feel better after a few hours.
- How old are you?
- What is your BMI?
- Does the pain disappear within an hour?
- Does the pain get better with activity? (eg, doing things around the house like using the bathroom, making your coffee, etc.) Do those things make it worse?
- Have you ever had this before?
I used to have this exact symptom/pain. I went to a chiropractor and she told me the issue was my hip flexors. I spend two minutes stretching them out after every ride (see: couch stretch) and it all but cured the issue for me.
Many people have exacerbated hip flexor issues due to Covid and sitting in their homes working without moving around much more than Covid. Plus, cycling is not friend of the hip flexor.
I would recommend seeing a physio or a chiropractor, but if you want to focus on your flexors it’s never a bad idea.
My post-ride/trainer stretch routine is as follows:
- Couch stretch with each leg for 15-20 seconds (technique matters)
- Downward dog for 15-20 seconds
- Repeat
- Plank for 60-90 seconds
Whole thing takes less than 5 mins. Good luck.
x2 on hip flexor stretches, and in particular the couch stretch, fixing low back pain.
But it took me several attempts at self treatment over a couple year period to stumble onto my cure. So, with 20-20 hindsight, I’d advise the OP to see some sort of PT. I’m fairly sure a pro could have sized me up and fixed me in a visit or two 
A further n=1 for the OP - the one amazing secret to no back pain for me is the 90/90/90 hip stretch. A few minutes a day seems to keep the pain away. I think Jonathan referenced this one in his comprehensive guide to dealing with knee pain.
I suspect back pain (like knee pain) has many possible underlying causes, maybe you just have to find the right exercise(s) for your body.
This is all proves my point.
The OP has pain with lumbar FLEXION. the hip flexors origin is the anterior aspect of the lumbar spine and insert on the lesser trochanter of the hip.
So when we (all of us) bend forward it places our hip flexors on slack. Not stretch. Stretching a muscle that hurts when in a shortened position will have no affect.
“We’ll maybe stretching them will cause them to relax or work better when he flexes.” Doesn’t work like that. When you bend forward you use your glutes eccentrically and your hip flexors are literally relaxed due to reciprocal inhibition.
All of these posts prove my point. See a professional. Please. I could regale you all with my patients who have hurt themselves worse trying exercises they learned in Dr. Google.
I have ZERO affiliation with the doc or the foundation group…
I highly recommend Dr. Eric Goodman’s Foundation training. I’ve had position induced sciatic issues, lower back issues from sitting weird in the cockpit and various injuries from surfing. Foundation work always gets things back on track in a matter of days. Not weeks, days. I should do it religiously, but I don’t. I have recommended it to a bunch of people for various posterior chain issues and all of them have been successful with it. It is great stuff and for hybridized movement patterns like cycling, the posterior chain work is just great. Hope this helps you and gets you on the right path.