'stiff posture' is correct and usable in written English.
You can use it to describe someone's body language, especially in a figurative sense. For example, "She held a stiff posture as she listened to the unpleasant news."
When alarmed in daylight they slowly flatten their plumage and stretch their bills upward in a stiff posture with the eyes nearly closed and the bill slightly open.
Mr. Bedford's stiff posture and serene bustling suggest a woman bearing her rectitude like a suit of armor and her trials with the surety of the righteous.
Mr. McCain, as many Republicans acknowledge, looks his age, with his shock of bright-white hair, a face scarred by skin cancer and a stiff posture that is a reminder of the torture he suffered in a Hanoi prison.
From an acknowledging flick of the arm to a slightly forced nod in time to the singing, the German Chancellor retains a stiff posture until the end, when she manages a carefree laugh before shuffling her papers.
We also had unusually stiff posture.
Retired now, balding and trim, he still has a trooper's stiff posture.
How quaint and self-conscious they look, frozen in stiff postures and solemn expressions.
So, the next time you want to improve your posture, skip the stiff stance and focus on your spine, pelvic region, and feet.
With the progression of the disease, the mice showed an abnormal phenotype, with decreased body weight, a hunched stance, severe contraction of hind limbs and a stiff walking posture.
With its tiny legs and stiff, upright posture, a penguin has a waddle that's more than a little ungainly.
With its tiny legs and stiff, upright posture a penguin has a waddle that's more than a little ungainly.
