Trot to COLLECTED Canter dressage transition (movie)
The aid for canter is given with the inside leg (left leg) at the time of the left hind toe-down (begins stance phase for that leg) supported by the outside rein. This is a diagonal aid for the transition. Hands have the function only to complete the connection through the horse so the aid can be answered in balance.
Preparation for a transition can be a half-halt. Half-halts can be strong or subtle but should be a clear, tactful request for the horse to understand rebalancing or adjusting for "what comes next." I prefer a half-halt with a combined stretch of upper body (avoids driving with the seat and "extra noise" from rein to bit) combined with a soft, definite touch of the calf that will ask for the transition itself. Thus there is a "library" of half-halts that go with dressage movements. Some riders will include a positioning of the poll or hindquarters with the half-halt. I prefer to separate the two and adjust the horse's spine prior to the half-halt. Whatever the choices, horse and rider should practice together until there is confident understanding of this communication by touch.
I am riding bareback in order that a saddle and pad do not hide the horse's shoulder and back muscles. In Frame 4 above, Max is showing a positively dissassociated left canter diagonal where the hind leg of the pair (LH-RF) lands fractionally before the right front leg. This reflects the lowered hindquarters of this collected canter, which converts to the canter of pirouettes.
By stepping through the movie, you can observe a frame by frame understanding of the transition, which occurs slightly past its first third. Max makes this transition to LEFT CANTER on the RH-LF diagonal pair in response to the outside calf aid. This is a little understood feature of leg-swapping in transitions: the prompt, fluent, balanced DRESSAGE transition to canter in this movie takes place on a diagonal pair opposite to that of the canter lead.
The UNBALANCED "on the forehand transition" looks like a "lurch" because the horse rocks forward onto the inside fore and accomplishes only a partial swap of the other three legs completed before taking an unbalanced canter stride into the lead. If you make your own digital video movies, you can observe your own horse's response to your aids.
A balanced canter transiton from trot with less collection is HERE.