I’m just starting yoga and I was trying to do the downward dog but my back wouldn’t stay straight. It always curves after a certain angle and it hurts my leg muscles if I try to keep my back straight. Is there any way to work my way down to downward dog or is it impossible?
You may have a deviation of the spine. If that is the case keep the posture until the point before it starts curving.
Focus your attention on lifting the buttocks up vs. getting closer to the floor.