"We don't have replication crisis in exercise science because nobody expects any of the studies to replicate" - paraphrased joke from Eric Trexler. PhD, >30 publications in the field, pro bodybuilder, professional coach

So, a lot studies related to health&fitness are horrible. Without funding they are run on 20 random college students for the duration of a single semester. Measuring what they actually want to measure is usually expensive to impossible, so usually a proxy will be chosen without any formal proof that the proxy is accurate. In general everyone in every health and fitness study is unhealthy and almost any intervention will help them so there are a lot of studies showing that ~miracle training~ works but really it's because literally anything would have helped.

But if I flail around in the space of possible exercise interventions for my musculoskeletal problems I honestly expect that to go pretty well.

A lot of bone things can't really be fixed with exercise, only worked around. Most muscle things are made better by getting stronger. People achieve world class deadlifts with scoliosis because they've strengthened everything else so much that the scoliosis can be compensated for. Rarely your shoulder bones are in a shape where you're basically guaranteed to get rotator cuff damage if you work in certain planes. So some bone things are just impossible to fix, that person will never be able to do the volume of overhead work as someone else. But like, when your tendon gets inflamed and starts to hurt you can just stop doing overhead work and avoid injury. Even if you push through it and get a small tear, most people over 40 have scar tissue in their rotator cuff and experience 0 negative symptoms. And the scoliosis dude is better than where he started. Sure he might need some surgery to make it go away for good, but he needed that beforehand too.

So don't worry about doing the best thing. Cardio probably won't help any skeletal issue, but is good for general health. Warmups are good but don't need to be long. A lot of warmups are just a chance for your body to settle back into good form. For muscular issues, you generally want to work on the muscle+synergists+antagonists. The muscle that hurts, the ones that move with it, and the muscle that does the opposite motion all three need to be strengthened to allow that plane of movement to be painless. Lifting with a proper progression scheme is many many times better at strengthening muscles than the next best thing. Yoga type things are nice for old tendon injuries. Just doing movements all through the range of motion can help you learn to compensate. Also sometimes a muscle isn't activating right causing other muscles to have to compensate for that muscle. That's a bit harder to explain in a short post (at least, at my current skill level) but it's worth looking into if you have range of motion issues that isn't solved with training that area specifically.

Note that this is assuming you have some normal back pain. I used to have lordosis that was bad enough that it hurt to walk >5min. Through the power of deadlifts I have fixed it and now I have medals from powerlifting meets. But for "oh god, I spent a month writhing in agony level" issues please disregard my advice that was aimed at the general public and see a physical therapist who works with athletes and those are usually the best. They will be able to give you advice specific to your situation, including possibly saying "above my paygrade, get surgery". Also nutrition and medication are harder, this applies more to physical interventions than other types.

We are evolved animals. Set your expectations reasonably. Don't expect miracle cures, esp. if you're past the usual age of reproduction. Be skeptical of those promising miracle cures.

Esp. as we get older, there are lots of things we need to learn to live with, and suffer with. Embrace mild ameliorations, like ibuprofen and (small doses of!!) opiates.

Our bodies are reasonably well adapted to the kinds of things our ancestors in the state of nature had to do on a daily basis. Try to do more of those (lots of mild exercises like walking, some occasional strenuous exercise, very exceptional extreme physical efforts) and less of the modern unnatural stuff we do a lot of (sitting and staring at computer screens, eating sugar).

Be skeptical of programmes that tell you to diverge too much from the ancestral behavior patterns.

Be skeptical of fads and "breakthrus".

Appreciate that if one approach were obviously and clearly better than the others, this would likely be pretty clear to everyone by now.

Since that isn't the case, don't expect too much. There is probably no one approach that is a whole lot better than the others (tho some may be far worse than the median).

This is a very hard problem. I really have no answer other than learning as much as you need to know. Keep asking "what is the evidence for this?", and learn statistics deeply. I read lots of books and read the FAQs and watched the debates on /fit/ etc.

Most of the fitness advice you will hear is bad. But this is not unique; the same applies to financial advice and to medical advice, including from doctors and specialists. Conflicts of interest play a role but incompetence is rife. [Conflicts of interest: I commented to a General Practitioner here that surgeons often have a conflict of interest - they recommend surgery and also profit from. His comment was that there was no conflict - they are in it for the money!. Perhaps slightly too cynical but not bad as a first approximation. Incompetence: Anyone who has read the medical literature or looked deeply into their own medical issues and then spoken to doctors and specialists will be appalled. This post is too short to go into details but if at all possible and you have a serious medical issue - read up both on statistics and on the particular problem.] Also worth noting that, far more than most other scientific fields, medicine is a 'status' model not a 'knowledge and evidence' model. Pernicious and wrong ideas can live for decades because the people who hold them are powerful and have high status.

I think part of the problem is government enforced licensing of medical people. if you can do a better job that current endocrinologists for example and start doing that, the government will put you in jail. Add to this the fact that membership of the esteemed order of endocrinologists is at the whim of the current endocrinologists. For example in my country having seen at least a dozen endocrinologists I have yet to find one who has even an elementary grasp of medically relevant statistics, nor have I found one who seems to be able to think of the endocrine system as a complex non-linear feedback system. Usually you don't get much beyond "your blood level is normal therefore there cannot be a problem". And how is 'normal' defined ...

Having gotten into fitness myself thanks to a back problem, I do agree with the proposition that lack of strength is behind many but not all such problems. But hormonal issues are important too - if you have low testosterone (which many young males do, and by low I mean < 450ng/dl USA or < 15nM/L everywhere else). High cortisol can also nuke any fitness program.

I also agree with warm-ups. Not with stretching. Warm up for me = a few minutes of walking and then reps of the target exercise at low weights, gradually building up 10X10kg, 5X30, 3X50, 2*65...

On the other hand I found machines to be of limited value in producing real world strength because the unnatural movements only trained a very specific set of muscles and did not train proprioception and bodily intelligence. I switched to barbells.

On cardio I think that it is good if intense and in small doses i.e. HIIT. Long moderate cardio only put up my stress hormone levels and left me debilitated. Cool down from intense cardio is important I think to restore normal blood flow and avoid staving the heart of oxygen. Again just walk a few minutes. At this time you can stretch if flexibility is a goal - now, not before exercising.

For burning calories long slow walks are best IMHO. You can use the time for 'diffuse mode' thinking which is important. If you are very young you might be able to get away with slow running.