What (vet issues) could cause a horse to be stiff under saddle?

[fredflop]

After some ideas really...

with me on the ground, my horse responds well to pressure, asking for lateral flexion (like carrot stretched) both sides, as well as vertical (lowering head down). Under saddle is a completely different matter, the horse is totally wooden.

I’m not asking about training/saddle, bridle or bit fit/teeth/back... purely veterinary issues that may be contributing towards the problem

 

[Goldenstar]

Kissing spines hock issues Sacroiliac issues PSD sore front feet issues with the thoracic sling there’s an almost endless list of things .

 

[Midlifecrisis]

fredflop have you a biomechanics type riding instructor near you...it’s possible that once in the saddle there is a imbalance or rider stiffness which the horse is compensating for and therefore feeling stiff when ridden. I have used a centred riding trainer and small corrections to me really helped my mare move..GS is right the list of veterinary possibilities is huge....