It's awesome that you're looking into this!
Equine biomechanics is a really important topic for anyone who's a rider to understand. Being knowledgeable about the way a horse's body works can help prevent injuries and unneeded stress down the road.
The basis of it all comes from impulsion. If a horse is not pushing correctly from behind they can't carry themselves properly or lift the front end, so you have more force coming down on the front legs which leads to further injury. Rolkur is an extreme example of this, but most dressage today is completely incorrect and trains the horse to put their face on the vertical without any proper push from behind.
Look up videos of the Spanish Riding School and Paul Belasik - they're the most contemporary examples of how correct horses should travel. Haunches down, back legs reaching under to the girth. They're on the vertical, but their bodies are moving properly and with correct way of travel.
Then watch a horse like Totilas - a complete disgrace to dressage - and see how incorrectly and stunted his movement looks. At no point does he really reach under himself with his hind legs and lift the front end.
If you really are interested in this sort of thing and want to learn - Gerd Heuschmann has written amazing books on the subject that I would highly recommend reading.