I see a lot of "chicken scratch-ing" here. Especially since this was in 1 minute, your lines read as indecisive and nervous. I definetely think you should be working with longer times. Maybe start with 10 or 5 minute poses, and gradually work your way down. This way, you'll be more familiar with the anatomy of a pose and your line quality should improve! Best of luck :)
I think your first gesture studies are great! They do capture and give an idea of what the image you referenced looked like. As for your contours problem, I do have a similar issue. I think what's working for me to improve might help. Instead of doing quick studies when trying to put down muscular and countoured forms, give yourself time to really study the body instead. That way when you do quicker drawings, you'll feel more confident in what you are putting down and spend more time on the actual gesture.
Hope this helps, and best of luck!
Love them! Honestly a bit jealous. The line quality and shading looks great. The only criticism I think I have is that the arm on the far right corner looks a bit flat, and could use more curves of muscle contour like the rest. Other than that, they're great!
