Further research is required to determine whether the increased speeds have a genetic basis or are the result of improved training, jockey tactics or other environmental factors, researchers said.
It had appeared that racehorse speeds were not improving and previous studies concluded that thoroughbred racehorses may have reached the limits of their abilities.
However these studies only analysed the winning time of a small number of middle and long distance elite races and did not take factors such as ground softness into account.
The full data set of 616,084 race times run by 70,388 horses shows that race winning speeds have improved greatly since 1850, and increases in speed have been greatest in shorter distance races.
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Data from 1997-2012 shows that the improvements in performance are on-going, despite increases in handicap weight, and continue to be driven largely by increases in speeds of sprinters, especially at the elite level.
"There has been a general consensus over the last 30 years that horse speeds appeared to be stagnating," Patrick Sharman from the Centre for Ecology and Conservation at the Exeter's Penryn Campus in Cornwall said.
"Our study shows that this is not the case and, by using a much larger dataset than previously analysed, we have revealed that horses have been getting faster.
"Interestingly, both the historical and current rate of improvement is greatest over sprint distances. The challenge now is to find out whether this pattern of improvement has a genetic basis," said Sharman.
The year of race, horse speed, timing method (hand-timed or automatic), race distance, racecourse, official going (ground softness), number of runners and name, age and sex of every horse were included in the analysis.
The results showed that historical improvement has not been linear. Rapid improvement occurred in the early 1900s and then again from 1975 to the early-1990s.
The research was published in the Royal Society journal Biology Letters.