Research published in June 2015 has concluded that average racehorse speed is continuing to increase but that historical improvement has "not been linear".
There was a period of "rapid improvement" from the late 1800s to 1910 and then several decades of "comparative stasis" until 1975.
The rates of improvement in average speed have also varied by race distance and "elite race winners improved more rapidly at shorter distances".
Data from the most recent decades show that "improvement is ongoing":
"Contemporary improvement is low for middle and long distances, but winning speed for elite sprint races actually exceeds estimated historical rates. A similar pattern emerges when all elite finishers are included, and if the wider population of non-elite performers is considered."
The research has been published in the Royal Society's Biology Letters and has been conducted by Patrick Sharman and Alastair Wilson.
http://rsbl.royalsocietypublishing.org/content/11/6/20150310
