A new study on treadmill use in conditioning has been released. You can read the full study by clicking here but it is an interesting one as they are using yearlings to two year olds, not older horses as their subjects.
12 Yearlings in Japan from the October of their yearling year were broken into 3 Groups and worked through to April of their 2yo year. The groups were:
Group 1 - Those that had conventional riding alone for the 8 months
Group 2 - Those that had riding plus a 2 month interval (Feb to April) of once per week high intensity treadmill work
Group 3 - Those that had riding plus long 8 month interval of once per week high intensity treadmill work
They tested VO2Max in the October of their yearling year (prior) and then the April of their 2yo year (post). The upshot was that while aerobic capacity increased in all groups, which you would expect, Vo2max was significantly higher in Group 3 than in Group 1 and Group 3 (809 m/s) had much higher running speed at Vo2Max than Group 1 (764 m/s).
Interestingly the running speed to achieve Vo2Max was virtually identical between Group 2 (some treadmill work) and Group 3 (all high speed treadmill work), but V02Max was 8.86% higher (almost statistically significant) in Group 3. They also have some interesting data on relative energy expenditure.
It must be clear that they didn't establish the most effective protocol to do this training. They had the treadmill set at 6% incline and running speed was "set to elicit exhaustion between 2.5-3 mins". If a horse could run over 3 mins the treadmill speed was increased 0.5 m/s the following week. It isn't clear at what speed they started the horses off at either.
They were also using a high-speed treadmill to do the work. These are the expensive kind (~$100,000) and are usually seen in universities, research facilities or veterinary clinics. You would hardly see one in a training yard anywhere. The less expensive (~$20,000) kind are seen quite often in training yards in Europe, Japan and Australia, but less so in North America where for whatever reason they are yet to catch on as an effective training tool. It isn't clear if the latter kind of treadmill would be as effective to use in this protocol.
Maybe if a trainer in North America had a high speed treadmill and developed a protocol for yearlings to two year olds, and he started blowing the doors off the competition with sound 2yo's with superior VO2Max that might change. I could also see a 2yo Pinhooker having quite an advantage with this type of protocol.