I really like the three finished bodies you drew on the right. They look pretty good.
I like the red one in the middle best because it has the best construction and the pose is also represented clearly.
For the other bigger sketches I think you tried to figure out the spine hips and head working together. And the basic understanding of it looks correct. The spine seems to bend like a spine would normally so thats good.
Now to your goal of understanding human anatomy. I think you already understand the most important party of human anatomy. For example you know how the hips are the brodest part of the upper body, then get thiner as the move uf to the shoulders and are the broadest at the shoulders. You know that arms and legs get thinner going down the body an the proportions of Arms, upper body, legs and head to each other are pretty accurate. Based on these observations I think that you know enough human anatomy, except maybe the hands and feet, which are drawn pretty rough ( but also in correct shape and size ). Maybe you could add the thumb on the hand and the ankle at the foot more clearly.
What I think you could instead improve on is your 3 dimensional thinking and your lines. Those two things will help you, once you understand them better, to also understand anatomy better.
Lets start with the lines: I think you should use less lines. We have all been there, using too many lines. But it's just something we do if we are not 100% sure of how the line should be. So we first draw a line and then improve on that line using more lines. The problem with that is, that the drawing gets very cluttered with lines and everything gets a bit messy und unclear. Now a strategy to help avoid this ( especially digitally ) is to use different layers, on one layer you draw the sketchy messy part and on top you draw the clean correct line using the sketchy construction underneath as a guide. But avoiding too many lines all together can help us especially with quick drawings such as gesture drawings. And to practice using less lines will also help alot when drawing 3 dimensional objects using perspective.
Which brings us to 3 dimensional thinking. I like that you are using a simplified human figure for sketching. That's the best trick to understand the 3 dimensionality of the body better ( to simplify it). Now you're doing the right thing using this method, but the simplified human figure you are using could be easier to understand. It helps alot to construct the body using cylinders, spheres and cubes, because those are 3dimensional objects. A line or a shape is not 3 dimensional. So for the chest you should use a cube (with the correct proprtions of the chest of course, that means a bit flat), for the hips you shoud also use a cube and to connect the chest cube with the hip cube use a sphere. Then for the neck use a cylinder and for the head use a cube, as this helps define the front ( where the face is). You used a cylinder or sphere for the head which doesn't help you see how the head is oriented. For the arms and legs use a cylinder for the upper arm then a sphere for the elbow and another cylinder for the lower arm. Using cylinders helps because they point into a specific direction with their flat surface wgich also helps the 3dimensionality. For feet and hands you can use a cube again. You can check out numerous constructions of the body on the internet. Just be sure to use one for yourself that uses 3 dimensional objects ( sphere cylinder cube) not lines and flat shapes. And also make sure the shapes they are using are not too complex which is why using cubes and cylinders is better than some kind of rounded sphere shapes.
It got a bit long but I hope some of this helps you improve :)
I really like the three finished bodies you drew on the right. They look pretty good.
I like the red one in the middle best because it has the best construction and the pose is also represented clearly.
For the other bigger sketches I think you tried to figure out the spine hips and head working together. And the basic understanding of it looks correct. The spine seems to bend like a spine would normally so thats good.
Now to your goal of understanding human anatomy. I think you already understand the most important party of human anatomy. For example you know how the hips are the brodest part of the upper body, then get thiner as the move uf to the shoulders and are the broadest at the shoulders. You know that arms and legs get thinner going down the body an the proportions of Arms, upper body, legs and head to each other are pretty accurate. Based on these observations I think that you know enough human anatomy, except maybe the hands and feet, which are drawn pretty rough ( but also in correct shape and size ). Maybe you could add the thumb on the hand and the ankle at the foot more clearly.
What I think you could instead improve on is your 3 dimensional thinking and your lines. Those two things will help you, once you understand them better, to also understand anatomy better.
Lets start with the lines: I think you should use less lines. We have all been there, using too many lines. But it's just something we do if we are not 100% sure of how the line should be. So we first draw a line and then improve on that line using more lines. The problem with that is, that the drawing gets very cluttered with lines and everything gets a bit messy und unclear. Now a strategy to help avoid this ( especially digitally ) is to use different layers, on one layer you draw the sketchy messy part and on top you draw the clean correct line using the sketchy construction underneath as a guide. But avoiding too many lines all together can help us especially with quick drawings such as gesture drawings. And to practice using less lines will also help alot when drawing 3 dimensional objects using perspective.
Which brings us to 3 dimensional thinking. I like that you are using a simplified human figure for sketching. That's the best trick to understand the 3 dimensionality of the body better ( to simplify it). Now you're doing the right thing using this method, but the simplified human figure you are using could be easier to understand. It helps alot to construct the body using cylinders, spheres and cubes, because those are 3dimensional objects. A line or a shape is not 3 dimensional. So for the chest you should use a cube (with the correct proprtions of the chest of course, that means a bit flat), for the hips you shoud also use a cube and to connect the chest cube with the hip cube use a sphere. Then for the neck use a cylinder and for the head use a cube, as this helps define the front ( where the face is). You used a cylinder or sphere for the head which doesn't help you see how the head is oriented. For the arms and legs use a cylinder for the upper arm then a sphere for the elbow and another cylinder for the lower arm. Using cylinders helps because they point into a specific direction with their flat surface wgich also helps the 3dimensionality. For feet and hands you can use a cube again. You can check out numerous constructions of the body on the internet. Just be sure to use one for yourself that uses 3 dimensional objects ( sphere cylinder cube) not lines and flat shapes. And also make sure the shapes they are using are not too complex which is why using cubes and cylinders is better than some kind of rounded sphere shapes.
It got a bit long but I hope some of this helps you improve :)
Have fun!