There is a difference between LSD for a new horse and LSD for an
experienced horse. After the base is in place, then a hour at 10 mph on
flat good trail I would consider LSD. I prefer to use heart rate to define
LSD rather than speed. For an experienced horse I prefer to use 45 minutes
to an hour at a heart rate of 120 to define LSD. This can be maintained
independent of terrain and footing. For example going up a steep climb 120
might be a walk. In deep sand 120 may be a slow trot.