shadow

Your attempt at making your work dynamic is clear, and you're getting there! You showed a good sense of gesture in these, especially the bottom figure.

Learning about anatomy (where muscles are, how they stretch, etc.) is extremely helpful with posing and just making everything look smoother in general. You don't have to learn about every single one in the body, but the main ones that are mostly seen. Getting a good grasp about how the body works will help you with proportions. It will also help you work a little faster, which will make your stuff less stiff.

I would also discourage you from using the line-and-circle skeleton method. Building your drawing from basic shapes is fine, but don't rely too heavily on guildelines like that, it tends to make things turn out stiff.

Great work! Keep it up :)