Medium work

using poles is a good way to start. Put them at the normal length you use for your horse for trotting and then gradually make them wider - making sure you keep the supplness, rhythm and tempo the same whilst riding over them - but so your horse just stretches out more over them.

What ideas does your trainer have for medium work? Perhaps its worth getting advice from him/her aswell.
 
There are probably many (better) ways to do it, but the way I have been taught is to start increasing and decreasing the pace within the trot/canter e.g slowing the trot down, then asking for a bigger trot again while at the same time working on keeping the horse straight, and asking for more engagement.

Once he's learnt that there's more than one gear in trot, he's as straight as you can get him, and fairly well engaged, it just kind of happens. Then you give loads of praise, and generally they think it's all quite good fun.

The other thing I do is to play around with it on hacks, when they're out in the open and usually nice and free and forward - sometimes you need more space than you get in a school, especially if they're big. I'll pick a nice long bridleway with good going, and play around with the trot, slowing down, asking for more, seeing what they offer.

Good luck!
 
working on a fairly large circle can also be helpful as the medium work needs plenty of hind leg engagement , with a bit of luck your horse should be stepping under well on a circle so you are already part way there with the engagement
 
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