Traditional drawings done by Vitaly Ekleris, our life drawing mentor - https://www.instagram.com/vitaly_yekleris 
We released a new pose reference pack with over 450+ high quality pictures and it's pretty epic, check it out! https://grafit.artstation.com/store/ejD9/450-epic-ancient-warrior-pose-reference-pictures 
We use it in our illustration pipeline, so all poses are carefully curated by our art-directors to help make the process more efficient.