If your back hurts after doing yard work or lifting things, try this exercise.
It sometimes works better than the traditional press up because it allows the joints to fall into extension instead of being pushing into it.
Do 2-3 sets of 10 reps.
Keep your low back relaxed throughout.
Perform two breath cycles at the end of the last rep (in the cobra position).
It should decrease soreness down your legs and ease the back pain.