Effect of repeated exercise and recovery on heart rate variability in elite trotting horses during high intensity interval training.
BACKGROUND
Interval training is a commonly used training method for trotting horses. In addition, trainers are provided with efficient and inexpensive heart rate monitor devices for the management of training.


OBJECTIVE
Since the high frequency (HF) frequency peak (fHF) of heart rate variability (HRV) corresponds to the breathing frequency in combination with stride frequency during trotting, it is hypothesised that modifications of breathing and stride frequencies induced by repeated exercise could be detected from fHF.


METHODS
RR interval time series of 7 trotting horses were recorded during an interval training session. Interval training was made up of 5 successive 800 m high-velocity trotting runs (H1, H2...H5) separated by 1 min recovery bouts at low speed (R1, R2...R5). Fast Fourier transform (FFT) and Poincaré plot analysis techniques were applied to RR series.


RESULTS
Repeated exercise had significant effects on HRV components during interval training. Despite constant trotting velocities during high-speed and recovery, repetition induced a decrease in mean RR interval (H1: 295 +/- 19 vs. H5: 283 +/- 15 msec, P<0.05) and in the root mean square of successive differences in RR series (RMSSD; H1: 6.31 +/- 1.28 vs. H5: 5.31 +/- 1.31 msec, P<0.05). Furthermore, high-speed and recovery repetitions induced an increase in fHF (H1: 1.37 +/- 0.35 vs. H5: 1.62 +/- 0.40 Hz and R1: 0.22 +/- 0.02 vs. R4: 0.64 +/- 0.38 Hz, P<0.05). Hence, recovery induced a decrease in the s.d. of the successive RR series (SDRR; R3: 10.5 +/- 3.96 vs. R5: 6.17 +/- 2.65 msecs, P>0.05) and in the long term index of Poincaré plot (SD2; R1: 43.29 +/- 28.90 vs. R5: 18.19 +/- 9.35 msecs, P<0.05).


CONCLUSIONS
The observed increase in fHF during the interval training could be induced by alterations of the coupling between breathing and stride frequency linked to the emergence of fatigue. The decrease in SD2 and SDRR during successive recovery bouts could be linked with a deterioration of the recovery pattern.


CONCLUSIONS
HRV can provide breathing frequency data of Standardbreds during training without any respiratory device. Furthermore, HRV could provide useful makers of the emergence of fatigue states during training.
Cottin
F
F
Laboratory of Exercise Physiology (LEPHE), University of Evry, E.A. 3872, Genopole, Boulevard F Mitterrand, F-91025 Evry cedex, France.
Barrey
E
E
Lopes
P
P
Billat
V
V
D000818:Animals; D004562:Electrocardiography / Q000662:veterinary; D005221:Fatigue / Q000175:diagnosis / Q000662:veterinary*; D005583:Fourier Analysis; D006339:Heart Rate / Q000502:physiology*; D006736:Horses / Q000502:physiology*; D010805:Physical Conditioning, Animal / Q000379:methods* / Q000502:physiology*; D012119:Respiration; D013997:Time Factors