Bottom line, even if you don't want to go for the spiritual side of it, the physical stuff is pretty awesome too. Back in the day, there were kinda two schools of thought - one, no point doing meditation and practicing a moral life if your physical body was too out of shape to persist or your mental life was too all over the shop to concentrate - so, do physical asana so that you can prepare for it. The other school was like, nahhhh, you don't need the asana, just concentrate on the meditation. BUT - once people started doing the physical stuff, the other stuff just came along anyway, so I'm on the side of getting bendy and stretchy! I've met so many people that started with the physical stuff and learnt all these yogic lessons without a guru at all - one being that 'this too shall pass' - it might be painful as you are doing it, but you persist and get the benefits, right? So surely that's true in all areas of life? And that the body is different on different days - we can't expect everything to go as planned.
I just read a post on HIVE about a guy who got his 75 year old grandma to start doing yoga, so that's pretty cool! I used to do Bikram, very hot and sweaty in a super heated room, and you'd get all these footy dudes coming in. They'd think they were really hard and end up in a puddle on the floor - but they'd come back, because there was something in it that was different to gym, or running, and they'd get the benefits from it.
Ah, I could talk about it for ever - both the physical side of it and the spiritual side of it! One door opens, another twelve open...