I'm not exactly sure when physios became the posture nazis, but somewhere along the way the Catholic matron with her yard stick has been replaced by us; physiotherapists. Instead of wrapping knuckles, we gracefully demonstrate how the perfect posture looks and expect our patients to dutifully adopt it forever...
Okay, so on every account, that is a massive exaggeration; but there is this idea that there is an ideal posture, but like most things, it isn't that simple. There is no perfect posture that is best for all 7 billion of us on this planet; with all of the normal and healthy variability in the forms of human beings, how could there be a single posture for us all.
This isn't to say that if you sit in front of a computer screen, slumped in half for most of the day, that you'll be fine; you might be, but more than likely, it will cause you pain sooner than later. And it's these types of examples that do indeed give credence to posture improvement exercises because anything that gets you out of the continuous slumping will show an improvement.
What do I think is the best posture? The next posture!
The human body was meant to move, and varying our positions and posture is likely more important that adopting a single, 'best' posture.
How do we apply this to our lives, especially when our livelihood depends upon our ability to complete work-related tasks?
If you work at a desk, setting an alarm to remind you to stand up and stretch for 1 minute, is a good start. Sit-stand desks are another option, though they are expensive, it is worth asking your employer if that is an option they would look into (it IS in their best interest to keep you healthy, pain free and functioning at a high level). An ergonomic assessment of your work station can help to reduce strain, but even holding the 'optimal' posture for 8 hours is too much, so you will still need to get up and move and stretch regularly.
Let's say you work in manufacturing and you have to stand at a line for 8+ hours a day; it may not be feasible to stop your work when you want. Prevention in this case is key, outside work hours, you should be strengthening the muscle groups that have the biggest demands. If your muscles and body are stronger than the demand at work, as well as having some varied movement, then they will be able to cope with the work load much better.
In sports training, cross-training is an excellent way of increasing the tolerance our body has, as well as improving fitness. The same is important for work; cross-training your body on the evenings and/or weekends will do wonders for increasing your body's tolerance of the work load. So take up a recreational sport, do a Pilates or yoga class a few times a week, do some strengthening work 1-2 times a week, etc.
The worst thing you can do is nothing, so don't let things sneak up on you, get out and get active.