Midweek Moleskine: Muscle Study (Patreon)

A half-hour study of muscles.

One thing I found that helps when doing art studies is using both photos and drawings as references. Photos are good for learning proper perspective, anatomy and proportions, but drawings and studies that other people have done can help you get an idea of how to render them well on paper. Photos should always be your main source of reference of course, but looking at how other people have drawn things can help too (so long as they're not too stylized).