Nice overall flow, but there is absence of structure. For 30 min pose you could integrate some structure flow to the piece. Shading is allover the place, you could devide light and shadow more.
Have a nice day
Try creating a base tone using warm and cool yellow before layering the red and blue. The cool yellow is great for highlights.
Layer hatch marks or wrapping lines over your shadow areas to enhance value contrast and volumes.
The knee is nicely drawn! Use sharper marks to emphasize bone structure or landmarks in other areas such as: the clavical, elbow and wrist.