These are really good, try making them less sketchy (or choppy looking) and show more confiedence with your linework.

I hope to work on that either today or later in the week.

Soda!

I agree with  youandme, you need a little more confidence in your strokes. No matter if you're doodling, sketching or drawing for real, you need to put more soul into every line. Even if you're using skeleton techniques like these, you've gotta be more sure of what it is you're doing. That way, you'll be ready when you actually start the drawing itself.

Keep at it, I can tell that, when you're done with your challenge, you'll be bit better than you were before. Not to mention all the nifty poses you're picking up will come in handy.