Your posture (static, trasitional, dynamci) says a lot about your past exercise program. Among other things, posture shows the strenght of your core and whether certain muscles are tight or weak. The first picture is an example of bad posture and the second is obviously good. It makes a difference in your daily functioning and exercising to practice good posture---standing, sitting, walking, running and exercising. Bad posturing causes dysfunctions to happen in other parts of your body, and will eventually lead to injuries (if left uncorrected).
Poor and good sitting posture.
Good running posture.
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Perhaps it is not so obvious that functional strength training is not synonymous with "working out", "weight lifting", or "body building". Functional strength training has a mission, as I understand it, of working strength in order to do the things one needs to do in life - lifting a child from the floor, chasing food or a mate, opening a door, etcetera.
Just as there are well trained, proficient yoga teachers (my profession) there are also well trained, proficient strength trainers. And of course the corollary is also true in both (all) fields - there are less trained, less skilled personnel.
The same is true of those who do these things. There are people working with weights - no matter how I may feel about it personally or professionally - who do so in a way that supports their body's integrity and there are those who do not and wind up with radical imbalance in the physical body, at very least.
I do not use the words "good" and "bad" when I teach so I would not take to good posture and bad posture just as I would not take to a good sun salutation and a bad one. That sort of labeling tends to do two things. One, it creates a state of inferiority in the student and two, it tends to make the teacher rigid and dogmatic. That may be perfectly fine for strength training but it is not for yoga.
The pictures above which outline wellbeing by way of posture are very important. I would add only that a healthy neck is never straight just as a healthy spine is never straight as each has curvature built in for proper weight bearing.
I know I've seen in my class very strong men who can't straighten their arms fully because the muscles are so tight. They look nice, but I wonder about the functionality of working out to that extreme. Of course the same with the hamstrings, but that seems to be more common.
one other thing-overbuilding of the traps can cause the neck to jut forward, especially in very athletic men, and can cause all kinds of havoc in the shoulder girdle, collar bones and neck and causing "poor posture." It's a pretty good example of how overworking and underworking the body can create all kinds of imbalances.