I finally joined a gym again. This one's close to work and there's plenty of colleagues that attend it too. There should be no lack of motivation, in theory.
I really need to strengthen my back and hips. About a year ago, I hurt my hip playing tennis. Went to a chiro and he treated me for spinal problems: I had a few bulged disks. But that didn't ease the pain. So I went to a GP and physio, who told me it was an SI joint issue, so I got a cortisone injection. That helped for a while, the problem hasn't gone away.
At my previous gym, I used to go swim; which has made the greatest improvement so far. But pools are a bit hard to find, and my current gym doesn't have one. So I'm going to try and get some cardio done, as well as gain overall strength. I have a feeling that once the blood gets flowing and the pressure on my muscles gets distributed more evenly, the hips and back will get heal themselves.