Dirt vs Synthetic surfaces and training intensity

Sorry for the lack of posting recently, but still fighting off the effects of the flu.

I have to preface what follows by stating I only have limited data on polytrack training sessions at Keeneland, but the findings seem to be startling.

Concerning horses yet to break their maidens, I've charted many half mile breezes on dirt during training and heart rate recoveries are typically around 80%. Heart rate recovery is defined as how closely the profile hits 120bpm and 80bpm and 2 and 5 min post breeze. 

However, I see the same HR recovery profile for maidens on polytrack at 6 furlongs! What that tells me is horses going over the polytrack are stressed as much as 50% less than going on dirt.

Anecdotally, it seems west coast based trainers do more 6F and longer breezes compared to east coast trainers. But with the intro of more polytrack training tracks to the KY area, local trainers might need to consider lengthening their breeze sesssions in order to get the same conditioning effect.