The effects of training on ventilation and blood gases in exercising thoroughbreds

Comparison of ventilatory and oxygen consumption measurements of yearling Thoroughbred colts and fillies exercising unridden on an all-weather track

Sex effects on ventilatory and oxygen consumption (V̇O2) measurements during exercise have been identified in humans. This study's aim was to evaluate the hypothesis that there are sex effects on ventilatory and V̇O2 measurements in exercising, untrained yearling Thoroughbreds (Tb). Forty-one Tbs (16 colts, 25 fillies; 19.8 ± 1.4 months old) were recruited. Physiological, ventilatory and exercise data were gathered from horses exercising unridden at high intensity on an all-weather track from a global positioning-heart rate unit and a portable ergospirometry system. Data were analysed with an unpaired Student's t-test and the Benjamini-Hochberg correction for multiple testing (P ≤ 0.05 significant). Mean bodyweight (BW, P = 0.002) and wither height (P = 0.04) were greater for colts than fillies. There were no differences in physiological and exercise data and absolute peak V̇O2 between groups. However, fillies had a higher mass specific peak V̇O2 (P = 0.03) than colts (121.5 ± 21.6 mL/kg.min vs. 111.9 ± 27.4 mL/kg.min). The peak breathing frequency was greater for fillies (P < 0.001) while the peak inspiratory (P < 0.001) and expiratory air flow (P < 0.001), peak expiratory tidal volume (VTE; P < 0.001) and peak minute ventilation (V̇E; P = 0.01) were greater for colts; there were no differences for peak VTE and V̇E when adjusted for BW. Differences in BW explain the differences in mass specific peak V̇O2 between groups. Given their morphological differences, it is likely that lung volumes and airway diameters are smaller for fillies, resulting in greater resistance and lower air flows and volumes. Further research is required to investigate the ventilatory differences and how they may change with maturation and impact performance.

Inspiratory muscle training in young, race-fit Thoroughbred racehorses during a period of detraining

Although inspiratory muscle training (IMT) is reported to improve inspiratory muscle strength in humans little has been reported for horses. We tested the hypothesis that IMT would maintain and/or improve inspiratory muscle strength variables measured in Thoroughbreds during detraining. Thoroughbreds from one training yard were placed into a control (Con, n = 3 males n = 7 females; median age 2.2±0.4 years) or treatment group (Tr, n = 5 males, n = 5 females; median age 2.1±0.3 years) as they entered a detraining period at the end of the racing/training season. The Tr group underwent eight weeks of IMT twice a day, five days per week using custom-made training masks with resistance valves and an incremental threshold of breath-loading protocol. An inspiratory muscle strength test to fatigue using an incremental threshold of breath-loading was performed in duplicate before (T₀) and after four (T₁) and eight weeks (T₂) of IMT/no IMT using a custom-made testing mask and a commercial testing device. Inspiratory measurements included the total number of breaths achieved during the test, average load, peak power, peak volume, peak flow, energy and the mean peak inspiratory muscle strength index (IMSi). Data were analysed using a linear mixed effects model, P≤0.05 significant. There were no differences for inspiratory measurements between groups at T₀. Compared to T₀, the total number of breaths achieved (P = 0.02), load (P = 0.003) and IMSi (P = 0.01) at T₂ had decreased for the Con group while the total number of breaths achieved (P<0.001), load (P = 0.03), volume (P = 0.004), flow (P = 0.006), energy (P = 0.01) and IMSi (P = 0.002) had increased for the Tr group. At T₂ the total number of breaths achieved (P<0.0001), load (P<0.0001), volume (P = 0.02), energy (P = 0.03) and IMSi (P<0.0001) were greater for the Tr than Con group. In conclusion, our results support that IMT can maintain and/or increase aspects of inspiratory muscle strength for horses in a detraining programme.

Conditioning equine athletes on water treadmills significantly improves peak oxygen consumption

Equine water treadmills (WT) were initially designed for rehabilitation of musculoskeletal injuries, but are also commonly used for conditioning sport horses, however the effects are not well documented. The purpose of this study was to test the effect of an 18-day WT conditioning programme on peak oxygen consumption (V̇O2peak). Nine unfit Thoroughbreds were used in a randomised controlled trial. Six horses worked daily for 18 days in stifle-height water (WT group), while 3 control horses worked without water (dry treadmill group (DT)). Preconditioning and postconditioning maximal exercise racetrack tests (800 m) were performed using a portable ergospirometry system. Measured outcomes were V̇O2, tidal volume, minute ventilation, breathing frequency, heart rate, blood lactate and instantaneous and average speed. The workload as assessed by V̇O2 was 21.7 per cent of preconditioning V̇O2peak values for WT horses. V̇O2peak on the racetrack increased by 16.1 per cent from preconditioning to postconditioning in the WT horses (P=0.03), but did not change in the DT horses. Therefore, exercising horses in high water heights may improve conditioning.

Assessment of high-intensity over-ground conditioning and simulated racing on aerobic and anaerobic capacities in racehorses

A prospective, randomised study assessed the impact of high-intensity racetrack conditioning on aerobic and anaerobic capacities in seasoned Thoroughbred racehorses. The effect of 10 weeks race conditioning and two simulated races on V̇O2maxand maximum accumulated oxygen deficit (MAOD) were evaluated. An incremental treadmill test to determine V̇O2max, followed by three supramaximal runs to fatigue (at speeds (V105%, V115%, V125%) corresponding to oxygen requirements 105%, 115% and 125% of V̇O2max, in randomised order) were performed at each timepoint (T1 [pre-conditioning] and T2 [post-conditioning]). Prior to T1, racehorses were briefly de-trained for four-six weeks and given low-level treadmill conditioning to prepare them for the more strenuous race conditioning after T1. Paired variables between T1 and T2 were analysed using a paired t-test. A 2-way RM ANOVA compared variables with >1 measurement. Speed at V̇O2max(P=0.04) and V̇O2max(P=0.01) increased with conditioning. Calculated speeds for the supramaximal runs increased for V105% (P=0.02) and V115% (P=0.03) but not for V125% (P=0.08). There was no conditioning effect on time to fatigue (P=0.34), although it was different between all intensities (2.8, 2.2 and 1.4 mins at V105%, V115% and V125% respectively at T2). O2demand increased with conditioning (P=0.02) for each supramaximal intensity. On average, horses’ aerobic capacity improved 4.43% after conditioning. MAOD was unchanged with conditioning (P=0.25) and unaffected by exercise intensity. Fit racehorses that have undergone repeated intensive training programs, experience smaller, incremental improvement than completely unfit horses. The anaerobic capacity of previously trained racehorses is relatively stable, despite brief periods of de-training.

Reduced high intensity training distance had no effect on VLa4 but attenuated heart rate response in 2-3-year-old Standardbred horses

BACKGROUND

Training of Standardbred race horses aims to improve cardiovascular and metabolic functions but studies on the effects of different training strategies from breaking till racing are lacking. Sixteen horses with the goal to race as 3-year-olds were studied from breaking (1-year-olds) to December as 3-year-olds. Horses were allocated to either a control (C) or reduced (R) training program from 2 years of age. The aim was to evaluate the effect of reducing the distance of high intensity exercise by 30% with respect to velocity at lactate concentration 4 mmol/l (VLa4), blood lactate and cardiovascular response. All training sessions were documented and heart rate (HR) was recorded. A standardized exercise test of 1,600 m was performed 10 times and a VLa4 test was performed five times.

RESULTS

C horses initially exercised for a longer time with a HR >180 beats per minute compared to R horses (P < 0.05) but after 6-9 months, time with HR >180 bpm decreased in C and were similar in the two groups (P > 0.05). Over the 2-year period, recovery HR after the 1,600 m-test decreased in both groups but was within 2 months lower in C than in R (P < 0.05). C horses also had lower resting HR as 3-year-olds (P < 0.01) than R horses. In C, post exercise hematocrit was higher than in R (P < 0.05). There was a tendency (P < 0.1) towards a larger aortic diameter in C as 3-year-olds (C: 1.75 ± 0.05, R: 1.70 ± 0.05 cm/100 kg BW). Left ventricle diameter and blood volume (in December as 2-year-olds) did not differ between groups. There were no differences between groups in post exercise blood lactate concentration or in VLa4. Both groups were equally successful in reaching the goal of participation in races.

CONCLUSIONS

Horses subjected to a reduced distance of high intensity training from the age of 2 showed an attenuated heart rate response, but were able to maintain the same VLa4 and race participation as horses subjected to longer training distances.