I am not an expert, I just like to draw, so may be I'm not the right person for advice. It's nice how you capture difficult moves, like the moving feet or a hand heading towards a viewer. It seems to me you are not really interested how arms connect to your hands, may be it would look more natural if you seen hands beeing influenced by forces of arms.
Good morning to you, Hyebinpark, and nicest works on your range of the simplest forms and forces of your hands and feet, but I'm not getting too much flow and fluidity of the shorthands of your hands and feet drawings, so how would you kindly like to go for 10 more minutes of 30 second hands and feet poses? As a result, your hands and feet will become somewhat least stiffest and the most boldest, confident and spontaneous in your memories, ideations, and executions for your character concepts, designs, and styles. My hat's off to you, and have the greatest day!!
You give these studies a lot of life with your quick sketchy lines. A lot of the lines add to the over all form.
I think you are being a little to frantic in getting all the toes and fingers on each piece. You are not taking the time to understand the basic forms and proportions of the fingers. You seem to draw the details and add the shade and form lines afterwards and a lot of the fingers seem flat despite having a ton of details.
Try breaking the figures down into simple shapes. Depict the feet and hands as if they were PS1 polygonal figures. FOr the hands, if the fingers are close together, it is sometimes easier to quickly draw them as if they were one shape. Make sure the palm and the fingers proportions are correct before adding wrinkles and shading.
The feet came out wonderfully all that is left is the obvious shading but needless to day that wasn't the goal on this particular excercise. My only criticism is for the hands, the fingers in particular. They sure can be annoying can they? While the linework is quite great, the fingers, as far as i see at least, seem to lack.. Volume, and a better visual implication of its form, you know? my suggestion is to break down the fingers into a series of segmented rectangular shapes. Take note of the skeletal structure of the hand to get an idea of how you'd like to best deconstruct the hand so you may better portay its likeness in respect to its three dimenional nature. Give it a show and the fingers will look must less flat for you, contour lines are also a HUGE help in identifying form, and needlesss today, assist singificantly in mapping out value. Keep up the good work!! Best of luck to you in your improvement.