-so i think the problem is that the pose look too stiff and does not have the natural flow, you can try adding those construction you did on top of my gesture sketch to understand it. -and as @pifalo said you can use cubes for ribcage ---If you want to learn about gesture, you should watch gesture drawing lecture by Michael Hampton.its free on youtube and more on his channel. - he is the guy if you want to learn about gesture and you should also read his book "figure drawing design and invention"

