>Whoa, huge topic here. I want to start by saying there are a million things to look at in any training program BEFORE even thinking about interval training. Most modern day equine athletes will make huge strides without IT. Most of all, it must be taken into consideration the effect of the IT structure on the psychological fitness of the horse. Not all are tough enough, but by many accounts, some are.
Many trainers these days will automatically tell you: “I tried IT (interval training) years ago, it doesn’t work.” Well, odds are they did it wrong. There are a million ways to implement IT, but only one of them is right, and everyone has a different definition of what interval training actually entails.
First off, if you experimented with IT by first adding another repetition to a breeze, you did it wrong. Similarly, if you are a ‘one breeze every 7-10 days’ guy and you try to add intervals, you are playing with fire – get your breeze frequency down to every 3-5 days first.
Secondly, if you added an IT session to a workout in which you couldn’t quantify recovery HR from the first repetition, you did it wrong.
Thirdly, IT doesn’t mean you train 3 separate sessions per day, necessarily.
IT can work, it can also break down a horse. It’s all in the individual. IT should start with gallops, not breezes.
For instance, when a horse can complete a one mile gallop in 3 minutes and show a recovery heart rate under 100bpm within 2 minutes while walking on the track to cool down, then you can safely add another 1 mile in 3 minutes second interval. When recovery HR after that 2nd interval meets the same criteria, under 100bpm within 2 minutes, you can add a 3rd. When recovery is sufficient for all 3 intervals, then you go back to one mile in 2:45, etc.
Personally, I’ve never gone past 2 reps, but I know Tom Ivers surely did so with great success, unfortunately most conventionally trained horses today don’t possess the foundation to support such a workload. His book, The Fit Racehorse II, gives every detail you could possibly need on IT structure.
So much more goes into the IT question, too much to post here, but surely you get the idea – it’s all about giving the horse enough appropriate stress/recovery cycles to foster development.