Conditioning horses for eventing’s cross-country phase is critical, especially for upper-level athletes. That’s why French researchers recently developed a way to look at horses’ individual fitness levels by monitoring heart rate and blood lactate levels during exercise. They recently investigated a broad range of eventing horses to determine how those measures changed between training and competition and across difficulty levels (in this study, the 1* to 4* levels).

They found that, in training, the higher the difficulty level, the lower the heart rates and lactate readings. However, in competition, the results were the opposite. As difficulty increased from 1* to 4*, so did heart rates and lactate readings, said Didier Serteyn, PhD, of the University of Liège, in Belgium, during a presentation at the 2017 French Equine Research Day.

“This study describes the intensity of the efforts the horses produced during training and competition and showed that different levels of exercise intensity induced varying changes in heart rate and blood lactate values,” he said. The research was part of Katharina Kirsch’s PhD thesis; she studies at the University of Liège and serves as a German Olympic Committee for Equestrian Sports veterinarian.

While the horse’s individual capacity to carry out the task played a major role in those measurements, so did environmental factors, he added. “The impact of the terrain and of the climatic conditions must not be overlooked,” he said.

In their preliminary study, Kirsch, Serteyn, and Charlotte Sanderson, DVM, PhD, Dipl. ECEIM, ECVAA (also of the University of Liège), monitored heart rates and measured blood lactate on 159 horses on the German cross-country team over a five-year period. They studied the animals during 293 training sessions and 524 competitions (1* to 4*). They also followed the horses’ speeds and distances using GPS technology during these same sessions.

In training sessions, 4* horses had average heart rates of 161 beats per minute (BPM). But in competition, the average heartbeat was 210 with a maximum of 233. Meanwhile, 1* horses had average heart rates of 184 BPM in training and 194 in competition (with a maximum of 214). They also showed increasing lactate levels with increasing heart rate.

“Our results indicated that higher competition levels induced higher intensities, which is not really surprising,” Kirsch said. “Previous researchers have concluded that horses competing at higher levels were fitter and, therefore, able to offset the higher absolute exercise intensity. But our results show that this was not the case, as horses competing at higher levels had higher values and were consequently not able to offset the increase of exercise intensity.”

Whether the horses had been trained appropriately for their respective levels, however, is “difficult to answer,” as there is currently no recognized lactate limit that shouldn’t be exceeded, she said.

“But we also noted that there were discrepancies between competition and training,” said Kirsch. “Additionally, we observed very high variability between horses, which was probably due to different fitness levels and not only to different velocities.”

The results shed light on the amount of effort a horse must exert when competing at particular levels, which can be useful when designing a training program, she said.

The researchers did not aim to understand cause and effect to explain the various differences in the scope of this particular study. However, they hope to investigate those aspects further, they said.

In the meantime, scientists can begin to develop methods that will help riders and trainers evaluate their own horses’ fitness.

“Close monitoring of physiological responses to exercise during training and competition allows us to evaluate the intensity of the efforts the horse is providing,” Serteyn said. “Thanks to the data we’ve collected, it’s now possible for researchers to estimate the efficacy of training for competition preparation.”

Even so, he said scientists must keep additional factors, such as age, experience, and environmental influences, in mind. “To obtain a more precise evaluation of the horse’s aptitude and the influence of training on physical fitness, it’s necessary to take a great number of factors, which can influence the results, into consideration,” he said.