if one wants to see if a smooth horse won't jiggle or hurt ones back but will condition your abdomens so well somehow that back pain or seat pain is not an issue then ride a Paso Fino; I do as Truman recommends mix up gaits to rest ones muscle groups in the extreme sport of endurance/Paso Finos can very well gait as fast as larger Arabs can canter but they can also canter and gallop and as fast as QHs. I will not make things like this up but maybe someone that rides with my little 14/1 hh. Paso Fino Obi may verify that we fly at gait and canter and gallop and if terrain is easy he may even trot if sure footedness is not called for. I am around 800 miles LD on him so I would listen to someone like Julie Suhr about gaited horses also who is happy to set things straight on ridecamp about this non issue. The fitness & balance and riding ability of riders is also a factor whether on gaited or trotting horses, have been fit and unfit have been balanced and unbalanced, and have suffered on gaited and trotting horse as well on long rides of many hours but now I hope I will not regress for my horses sake.
