As a young person, I remember being reminded to stand up straight. That was good advice. Not only do I look different when I sit up straight and stand straight, I feel better.
To improve posture, a young girl might walk through her home with a stack of books on her head. In that upright position, it is impossible to look down or to the left or to the right without toppling the books. Her gaze must be forward. Her concentration is straight ahead.
The expression, “He is no slouch,” means he is not lazy and doesn’t mind working. Slouching gives the appearance of laziness.
Slouching is not good for your health. Slouching while standing or sitting can cause spine alignment issues. Office workers are particularly susceptible. Every inch you hang your head forward can add ten pounds of pressure on your spine.
If you work at a computer for several hours a day, you know what I’m talking about. Your chair and your sitting position are very important. As back pain is a common work-related injury, many companies have found it necessary to make sure their working environment is ergonomically correct.
I spent a few years working in a chair I loved but it was giving me a backache. My husband bought me a better chair and the problem went away.
Standing erect is not only good for your posture. It is imperative for your spiritual life. Those who are upright are disciplined in righteousness, justice and integrity. Upright is defined as an object that is 
vertical or erect or a person that is honorable or honest. In the Amplified Bible, the word upright is often translated as consistently or uncompromisingly righteous, one who walks uprightly, in right standing with God, or moral and spiritual rectitude in every area and relation.
An upright person is not perfect, but focused. Occasionally the books will fall. The posture of a focused Christian will improve with time and practice. The more determined one is to love God and please Him, the more disciplined he will be.
The upright godly person walks with wisdom, looking forward, considering the steps of the path before him and is determined not to let distractions turn him aside from the path God has chosen for him.
...His secret counsel is with the upright (Proverbs 3:32 NKJV). …His confidential communion and secret counsel are with the [uncompromisingly] righteous [those that are upright and in right standing with Him] (Proverbs 3:32 Amplified).
One Focus Ministries 