Nice work. Accurate proportions and lines, you seem to be able to find the correct curves very quickly.
Regading the impression of stiffness: I'm getting the same feeling from your drawings than from academic illustrations.
Very realistic, but somehow missing a bit of a "spark of life".
That can be a direction for your drawings, and I can think of several comics authors who draw this way (Edgar P. Jacobs, Jean Giraud, ...).
If you want to get your drawings more flexible, what i would suggest is to try the 30s drawings: This way you can focus only on the main lines, the ones carrying movement.
I guess you need to go down to 30s, seeing the quality of what you draw in 2min!
