Is there an effect of the time elapsed between heart rate measurements on the cardiac recovery index score in endurance competitions?

Mira Monica (Speaker), Williams, J. (Speaker), David Marlin (Speaker)

Activity: Talk or presentation typesOral presentation at Conference


Cardiac recovery index (CRI) is currently a key component of the veterinary inspections to assess endurance horses metabolically. It was first described by Ridgeway in 1991. A resting heart rate (HR0) is taken when the horse is initially presented for examination. The veterinarian then starts a stop-watch when the horse starts the 40m out and back trot to assess gait. A further HR (HR1) is taken exactly 1 minute after the stop-watch was started. HR1 is subtracted from HR0 to obtain the CRI. It is widely believed that a difference of more than 4bpm might be an indicator of fatigue. The FEI rules instruct the veterinarians to start the stop-watch exactly one minute after the HR0 count instead of trot start as described previously. CRIs are anecdotally observed to be recorded after more than one minute has elapsed. This study aimed to assess if variations in the timing of the stages of the veterinary inspection influenced horses’ CRI results. The time taken for horses from entering the VG to be presented for inspection (T1), between HR0 and the start of HR1 (T2), and from the start of the trot-up to HR1 (T3) were recorded for 187 horses competing in 78 km free speed (n = 47) and 19-78 km controlled speed (n = 140) FEI endurance races. HR0 and HR1 values were noted from horses’ veterinary cards and CRI were calculated to divide horses into one of two groups: A: CRI > 4, abnormal (n = 43) and B: CRI < 4, normal (n = 97) in accordance with method advocate by Gillespie et al. (2015). Horses were also allocated into groups according to T3 length: Group 1 T3 < 1 minute (n = 112) and Group 2: T3 > 1 minute (n=68). Data met non-parametric assumptions, therefore a series of Mann Whitney U analyses examined if the duration of T1, T2 and T3 differed between horses in Groups A and B, and if T1 and T2 length varied between horses in Groups 1 and 2. The average time between entering the vet gate and presenting a horse to the official veterinarian was 1 minute (m) 42 seconds (s) ± 2m27s (s.d.) in the free speed competitions. The mean time between HR0 and HR1 was 13 ± 19s and 56 ± 262s between the start of the trot and HR1 across all competitions. T1 was significantly shorter in Group B horses (P = 0.02; T1: Group A mean: 34s, Group B mean: 12s) but the duration of T2 and T3 was not different between the groups (P > 0.05). No significant differences were found between the length of T1 and T2 and Groups 1the length of T3, the CRI phase, (P > 0.05). These results suggest that timings at vet gates do not influence CRI reliability. However more data are needed to further corroborate this finding.
PeriodJun 2019
Held at26th Equine Science Symposium
Event typeConference
LocationAsheville, United States, North Carolina


  • enhance
  • cardiac recovery index