Racehorses are getting faster, according to new research that has overtaken notions of them reaching the limit of their galloping ability.

A study of 616,084 race times run by more than 70,000 horses shows that winning speeds have increased greatly since 1850.

And more recent data from 1997-2012 confirms that the finish line is not in sight yet. Improvements in performance are still on-going, despite heavier handicap weights, it is claimed.

Scientists are not sure whether the quickening pace, largely driven by sprinters, is due to breeding, better training, jockey tactics, or a combination of factors.

Earlier research had indicated that thoroughbred racehorses may have reached a barrier preventing them from becoming any quicker.

But these studies only focused on a small number of middle and long distance elite races and did not take into account factors such as ground softness, according to experts from the University of Exeter.

Dr Patrick Sharman, from the university's Centre for Ecology and Conservation, said: "There has been a general consensus over the last 30 years that horse speeds appeared to be stagnating.

"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."

Slower middle and long distance speed improvements could indicate that horses are reaching a performance limit over these distances, say the researchers.

Alternatively, it might mean that breeders are focusing on speed rather than endurance.

The scientists, whose findings appear in the Royal Society journal Biology Letters, used data from flat races run in the UK.

Included in the analysis was the year of race, speed, timing method - whether by hand or automatic - race distance, race course, official going, the number of runners, and the name, age, and sex of every horse running.

The results revealed improvement spurts over certain periods, with rapid increases in speed occurring in the early 1900s and again from 1975 to the early 1990s.

Performance gains in the early 1900s have previously been attributed to an altered riding style, with jockeys assuming the now-familiar crouched position with shorter stirrups.

Improvement through the 1970s and 1980s may be due to jockeys emulating Lester Piggott and shortening their stirrups even further, said the researchers.

However, they also point out that racehorse breeding became more commercialised during this period, which may have had genetic benefits.