Hey there! I had some issues finding the link you had posted so I fixed the message for you. :)
Your gestures are looking pretty solid to me. What goal do you have in mind for improvements?
My one current piece of critique is to try and do shorter gestures in less but more confident strokes. Instead of smaller, repeated 'scratches' to get the figure down, it helps to minimize the short gestures by capturing motion and/or proportions in a couple of 'swoops' of lines. Being confident and bolder with your lines to capture the essence of motion and proportion has more benefits than to try and get an accurate figure down with some scribbling. Can you give that a try and see how it works out for you?
That's exactly what I was going to say. Shorter lines might be ok for longer drawings and details, but when you only have 30sec to get the gesture right, long bold lines are the best option available.
I advice you to remember this: only use C curve, S curve, or I straight line for your gesture. I should help you improve.