背筋をしゃんと伸ばして歩きなさい。の英語

Carry your head high.

Please keep your back straight and relax your body.

sitting with one's back straight

Don't slouch! Sit up straight [Straighten you back]!

jump vertically, with legs stiff and back arched

to spin one's body rapidly with one leg raised

Take care not to fail to fall over and skin your knee.

Take care not to fall down and skin your knee.

to stretch one's legs out and lie on one's stomach

sit bolt upright

Keep your back [legs] straight.

Bend your knees and look in front of you.

bump and grind

stand ramrod straight

Swing your arm back and forth.

to make a person stoop by having him/her bend his lower body

dip a curtsy

bend one's back forward from the waist on down

Turn onto your back.

of a person, to bend forward, rounding the back

to make one's posture in a low position by bending over at the waist or by bending one's legs

He sits up straight.

a muscle that flexes and supinates the forearm

a position lying on your back with knees bent and thighs apart

slow down by moving the tail sideways

to crawl on one's hands and knees

to stride over something

to make someone sit down

I do push-ups and sit-ups.

She says “No” and nods assent.