It’s also the case that in a ‘live’ figure, either human, other animal, or fish, muscles always work in groups. People and animals come lean, moderately or grossly fat, or very skinny with not enough to eat. For me it was slowly coming to understand the bones [anybody’s] are profoundly three-dimensional in nature, and evolved on staggeringly complex geometry, all their own, while remaining stable no matter what happens, excluding disasters likes fractures or arthritis, so if the places they show become integrated into your thinking [when working from the model], whether ‘revealed’ as knobs, or dimples, in an obese individual, they’ll ‘tell’ you a lot. Elbows, wrists and fingers all are bearers of these characteristics, as are knees and backbones. I hope that’s helpful, for a start.