SEARCH

SEARCH BY CITATION

Keywords:

  • horse;
  • warm-up;
  • inline image kinetics;
  • supramaximal exercise;
  • aerobic power

Summary

  1. Top of page
  2. Summary
  3. Introduction
  4. Materials and methods
  5. Results
  6. Discussion
  7. Acknowledgement
  8. Manufacturers' addresses
  9. References

Reasons for performing study: Several studies have indicated that even low-intensity warm-up increases O2 transport kinetics and that high-intensity warm-up may not be needed in horses. However, conventional warm-up exercise for Thoroughbred races is more intense than those utilised in previous studies of equine warm-up responses.

Objectives: To test the hypothesis that warm-up exercise at different intensities alters the kinetics and total contribution of aerobic power to total metabolic power in subsequent supramaximal (sprint) exercise in Thoroughbred horses.

Methods: Nine well-trained Thoroughbreds ran until fatigue at 115% of maximal oxygen consumption (inline image) 10 min after warming-up under each of 3 protocols of equal running distance: 400 s at 30% inline image (LoWU), 200 s at 60% inline image (MoWU) and 120 s at 100% inline image (HiWU). Variables measured during exercise were rates of O2 and CO2 consumption/production (inline image,inline image), respiratory exchange ratio (RER), heart rate, blood lactate concentration and accumulation rate and blood gas variables.

Results:inline image was significantly higher in HiWU than in LoWU at the onset of the sprint exercise and HR was significantly higher in HiWU than in LoWU throughout the sprint. Accumulation of blood lactate, RER, Paco2 and inline image in the first 60 s were significantly lower in HiWU than in LoWU and MoWU. There were no significant differences in stroke volume, run time or arterial-mixed venous O2 concentration.

Conclusions: These results suggest HiWU accelerates inline image kinetics and reduces reliance on net anaerobic power compared with LoWU at the onset of the subsequent sprint.


Abbreviations
Cao2

Arterial oxygen concentration

inline image

Arterio-mixed venous oxygen concentration difference

Co2

Blood oxygen concentration

inline image

Mixed venous oxygen concentration

HiWU

High-intensity warm-up (120 s at 100% inline image)

HR

Heart rate

[La]

Blood lactate concentration

LoWU

Low-intensity warm-up (400 s at 30% inline image)

inline image

Blood lactate accumulation rate

MoWU

Moderate-intensity warm-up (200 s at 60% inline image)

Paco2

Arterial carbon dioxide partial pressure

Pao2

Arterial oxygen partial pressure

PCV

Packed cell volume

pHa

Arterial pH

inline image

Mixed-venous carbon dioxide partial pressure

inline image

Mixed-venous oxygen partial pressure

inline image

Specific cardiac output

RER

Respiratory exchange ratio

SV/kg

Specific stroke volume

STPD

Standard temperature and pressure, dry

TPA

Pulmonary arterial temperature

inline image

Carbon dioxide production rate

inline image

Oxygen consumption rate

inline image

Maximal oxygen consumption rate

Introduction

  1. Top of page
  2. Summary
  3. Introduction
  4. Materials and methods
  5. Results
  6. Discussion
  7. Acknowledgement
  8. Manufacturers' addresses
  9. References

Although equine oxygen consumption rate (inline image) kinetics are extremely rapid in comparison with those found in man (Rose et al. 1990), during exercise at intensities above the onset of blood lactate accumulation the rapid inline image kinetics are markedly slowed (Langsetmo et al. 1997). As a result, racehorses need to warm-up adequately ahead of time to accelerate inline image maximally during a race.

There are several variables by which warm-up protocols can be structured, including its intensity, duration, mode and recovery time, and these combinations may influence the performance of subsequent main exercise (Bishop 2003). High-intensity warm-up (HiWU) before races and games in human athletes is typical and many reports indicate that low-intensity warm-up (LoWU) does not effectively change aerobic capacity and race and/or game performance (Gerbino et al. 1996; Bishop 2003; Bailey et al. 2009). On the other hand, some researchers have indicated that in horses, even LoWU can accelerate inline image kinetics and HiWU provides no additional benefit during a subsequent sprint compared with LoWU (McCutcheon et al. 1999; Geor et al. 2000). However, warm-up routines usually performed in conjunction with Thoroughbred races in Japan, which increase heart rates (HR) of racehorses over 90% of their maxima (Mukai et al. 2007), are typically more intense than those described in previous studies of warm-up effects (McCutcheon et al. 1999; Geor et al. 2000).

We have previously reported that high-intensity warm-up, 115% inline image for 1 min, accelerates inline image kinetics and O2 delivery in working muscles more than moderate-intensity warm-up, 70% inline image for 1 min or no warm-up (Mukai et al. 2008). In our previous study, we used a warm-up protocol with the same warm-up duration, thus the running distance and total energy expenditure during each warm-up bout was different. In constructing warm-up programmes, various combinations of factors can alter performance or aerobic metabolic power. Knowledge of warm-up effects that directly affect subsequent race performance is essential for trainers; however, there are few scientific analyses of detailed warm-up protocols in Thoroughbred horses. Therefore, the purpose of this study was to examine the effects of 3 warm-up protocols with equivalent running distance (and total energy expenditure) on aerobic metabolism in Thoroughbred horses. We hypothesised that high-intensity warm-up with equivalent running distance would still accelerate the kinetics of aerobic power onset and increase the contribution of aerobic power to total metabolic power in subsequent supramaximal exercise compared with lower-intensity warm-up.

Materials and methods

  1. Top of page
  2. Summary
  3. Introduction
  4. Materials and methods
  5. Results
  6. Discussion
  7. Acknowledgement
  8. Manufacturers' addresses
  9. References

Protocols for the study were reviewed and approved by the Animal Welfare and Ethics Committee of the Japan Racing Association (JRA) Equine Research Institute.

Horses

Nine Thoroughbreds (4 males, one gelding, 4 females; mean ± s.d. age 3.4 ± 1.0 years) were studied. The horses underwent surgery to reposition the left carotid artery from the carotid sheath to a subcutaneous position to facilitate arterial catheterisation. After recovery from surgery, the horses were trained to run on a motorised treadmill (Mustang 2200)1 while wearing an open-flow mask (Pascoe et al. 1999). At least one year passed between the surgery and treadmill experiments. Horses were exercised 5 days/week on a treadmill inclined at a 10% grade and were pastured in 2 hectare pastures for approximately 6 h/day on the other 2 days for 14 weeks before the onset of the study. The training programme consisted of a warm-up (1.7 m/s for 1 min and 3.5 m/s for 3 min), cantering for 5 min, and a cool-down (1.7 m/s for 3 min). The speed of cantering increased as the training progressed: Weeks 1–7, 6 m/s for 5 min; Week 8, 80% inline image of each horse for 5 min; Weeks 9–10, 80% inline image for 3 min and 100% inline image for 2 min; Weeks 11–14, 80% inline image for 3 min and 100% inline image for 2 min for 2 day/week, and 60% inline image for 1 min, 80% inline image for 1 min and 100% inline image for 1 min for 3 day/week.

Treadmill measurements

Following the carotid loop surgery and familiarisation with the treadmill, horses performed an incremental step protocol (described below) to identify each horse's inline image and speed required to attain it (speed at 100% inline image). During this procedure, the horses wore an open-flow mask for measurement of inline image and inline image and a jugular catheter was used to sample venous blood for determination of [La] and inline image.

Approximately one week following the step protocol, warm-up exercise studies were performed at weekly intervals to quantify O2 transport variables at speeds calculated to elicit approximately 115% inline image for each horse. During these studies, blood samples were drawn and inline image and inline image measured before the run began and at 30 s intervals during the run, allowing the O2 transport system to come to steady-state by the end of the first minute both during the warm-up run and during the sustained sprint. After catheters and transducers were connected and tested, the horse began its exercise. The horse would exercise at its warm-up speed or its sprint speed on the treadmill while inline image was measured and arterial and mixed venous blood samples were drawn simultaneously for the measurement of blood gases and blood oxygen concentration (Co2), from which cardiac output (inline image) and stroke volume (SV) were calculated with the Fick Principle. Heart rate was determined from ECG recordings from bipolar electrodes across the long axis of the heart that were amplified (SM-29)2 and recorded on a personal computer with commercial hardware and software (Windaq/Pro+)3 sampling at 200 Hz. Following a run, the R-R intervals were counted over 15 s to calculate the mean HR at that sampling time.

Experimental design

The effects of warm-up on O2 uptake and transport during exercise were examined in a 3-way semi-randomised crossover study. Nine horses participated in a preliminary step protocol measurement and each of 3 experimental treatments with protocols as follows.

For the preliminary incremental (step) measurement run, the horse warmed-up by walking at 1.7 m/s for 2 min and trotting at 3.5 m/s for 5 min, then cantered or galloped up a 10% incline for 1 min each at 6, 8, 9, 10, 11 and 12 m/s until it could not maintain its position at the front of the treadmill. For the next 3 runs, horses warmed-up according to one of the following 3 protocols 10 min prior to the sprint. Then, for the sprint measurements, the horse was galloped up a 10% incline at a speed calculated to elicit 115% inline image (based on the preliminary incremental measurement) until the horse could not maintain its position at the front of the treadmill. The 3 warm-up protocols consisted of:

  • 1) 
    LoWU trial in which the horse walked on the treadmill for 1 min at 1.7 m/s then cantered for 400 s at a speed equivalent to 30% inline image (based on the preliminary incremental measurement)
  • 2) 
    MoWU trial in which the horse walked on the treadmill for 1 min at 1.7 m/s then cantered for 200 s at a speed equivalent to 60% inline image (based on the preliminary incremental measurement)
  • 3) 
    HiWU trial in which the horse walked on the treadmill for 1 min at 1.7 m/s then galloped for 120 s at a speed equivalent to 100% inline image (based on the preliminary incremental measurement)

After performing the initial incremental performance measurement, each horse completed each of the experimental protocols once in semi-random order with ≥6 days between trials for individual horses.

Oxygen consumption

Horses wore a 25 cm diameter open-flow mask on the treadmill through which a rheostat-controlled 3.8 kW blower drew air. Air flowed through 20 cm diameter tubing and across a 25 cm diameter pneumotachograph (LF-150B)4 connected to a differential pressure transducer (TF-5)4; this ensured that the bias flows during measurements were identical to those used during calibrations. Bias flow was set to keep changes in [O2] and [CO2] <1%. Oxygen consumption and CO2 production were measured by use of O2 and CO2 analysers (MG-360)5 and gas calibration was carried out by use of the N2-dilution/CO2-addition mass-balance technique (Fedak et al. 1981). Gas analyser and mass flowmeter outputs were recorded on personal computers.

Blood sampling

Before leading a horse onto the treadmill, an 18 gauge x 6.4 cm catheter (Surflow)6 was placed in the horse's carotid artery, and an 8.5 French x 9 cm introducer (MO95H-8.5)7 in the jugular vein. A Swan-Ganz catheter (SP5107U)8 was passed via the introducer so that its tip was positioned in the pulmonary artery, confirmed by measuring pressure at its tip with a pressure transducer (Statham P23d)9. Mixed venous blood samples were drawn from the tip of the Swan-Ganz catheter and arterial samples from the carotid catheter at timed intervals into heparinised syringes and stored on ice until measurements were made following the experiment. Blood samples were analysed for blood gases with a blood gas analyser (ABL-555)10 and for Co2 with a haemoximeter (OSM3)10. Accuracy of the blood gas analyser was verified with blood samples tonometered with precision gas mixtures, and accuracy of the haemoximeter set to its equine blood algorithm was verified by comparing tonometered samples with direct measurements of Co2 made with a galvanic cell (Lex-O2-Con K)11. Following measurement of blood gases and oximetry, the blood was sampled for PCV by microcentrifugation and for [La] with a lactate analyser (YSI 2300 STAT Plus)12. The inline image was calculated as the change in blood lactate concentration per min of sprint exercise.

Temperature measurements

The Swan-Ganz catheter in the pulmonary artery was connected to a cardiac output computer (COM-2)8 so that its thermistor registered TPA, which was recorded at each blood sampling and used to correct the blood gas measurements. Blood temperatures detected by the thermistor were corrected for systematic bias by calibrating the catheter thermistor immediately following each run in a water bath using a Hg thermometer with calibration traceable to the Japan Bureau of Standards.

Statistical analysis

Data are presented as mean ± s.d. Data were analysed for differences between warm-up regimens and time within a regimen by use of one-way repeated measures ANOVA, and pairwise comparisons were made with Tukey's test. Values reported as fatigue were the last sample taken before a horse stopped running for a given protocol. Statistical analyses were made with commercial software (JMP 6.0.3)13 and significance defined as P≤0.05.

Results

  1. Top of page
  2. Summary
  3. Introduction
  4. Materials and methods
  5. Results
  6. Discussion
  7. Acknowledgement
  8. Manufacturers' addresses
  9. References

Preliminary exercise (step) test

All horses completed the initial incremental step procedure without difficulty. Mean specific inline image and speed to achieve 100% inline image of the horses were 3.23 ± 0.16 ml (STPD)/(s kg) and 10.6 ± 0.8 m/s (up a 10% incline), respectively.

Exercise tests

Work intensity (speed) during the sprint runs was 12.0 ± 0.5 m/s, which was equivalent to 113.1 ± 5.4% inline image. All horses completed 120 s of exercise on the treadmill during these warm-up exercise tests.

Exercise time

The mean run time to fatigue was not different among the 3 groups (LoWU, 146.0 ± 29.7 s; MoWU, 134.6 ± 26.3 s; HiWU, 135.2 ± 21.5 s) (Table 1).

Table 1. Bodyweight, run time to fatigue, blood lactate accumulation rate (inline image), packed cell volume (PCV), arterial pH (pHa), arterial (a) and mixed venous (inline image) blood O2 concentration difference (inline image), specific cardiac output (inline image), heart rate (HR) and specific stroke volume (SV/kg) of 9 Thoroughbred horses during warm-up and supramaximal sprint exercise following low-, moderate- or high-intensity warm-up (LoWU, MoWU, HiWU, respectively). Values are mean ± s.d. Different letter superscripts show significant differences between warm-up protocols at a given time (P≤0.05)
 UnitsLoWUMoWUHiWU
Run times146.0 ± 29.7a134.6 ± 26.3a135.2 ± 21.5a
Bodyweightkg464.7 ± 24.4a464.8 ± 26.0a468.8 ± 25.5a
PCV    
 0 s%52.9 ± 4.5a53.7 ± 3.3a55.4 ± 2.7a
 60 s%57.5 ± 3.2a58.0 ± 3.4a57.8 ± 2.2a
 Fatigue%60.2 ± 2.7a60.3 ± 2.1a59.6 ± 2.2a
pHa    
 Pre warm-up 7.442 ± 0.013a7.444 ± 0.027a7.445 ± 0.018a
 Post warm-up 7.443 ± 0.018a7.419 ± 0.024a7.269 ± 0.051b
 0 s 7.458 ± 0.013a7.462 ± 0.018a7.406 ± 0.049b
 60 s 7.306 ± 0.019a7.307 ± 0.026a7.289 ± 0.040a
 Fatigue 7.127 ± 0.046a7.150 ± 0.047a7.122 ± 0.037a
inline image (0–60 s)mmol/(l min)6.66 ± 0.73a6.31 ± 1.02a3.53 ± 1.54b
inline image (60–120 s)mmol/(l min)5.66 ± 0.76a5.95 ± 1.09a4.92 ± 0.81a
inline image    
 Pre warm-upml O2 (STPD)/l31 ± 13a32 ± 14a32 ± 7.0a
 Post warm-upml O2 (STPD)/l139 ± 24a195 ± 10b246 ± 8.0c
 0 sml O2 (STPD)/l90 ± 13a97 ± 14a87 ± 10a
 60 sml O2 (STPD)/l192 ± 13198 ± 14a201 ± 18a
 Fatigueml O2 (STPD)/l240 ± 4.0a240 ± 10a237 ± 10a
HR    
 0 sBeat/min102.6 ± 9.0a106.9 ± 14.6a120.0 ± 8.1b
 60 sBeat/min203.5 ± 5.6a206.3 ± 5.9b209.8 ± 5.1c
 FatigueBeat/min209.6 ± 5.9a211.0 ± 6.5ab212.8 ± 7.7b
inline image    
 0 sml blood/(s kg)6.52 ± 1.54a6.70 ± 1.63ab8.34 ± 1.79b
 60 sml blood/(s kg)15.8 ± 1.6a16.1 ± 1.6a16.5 ± 1.6a
 Fatigueml blood/(s kg)13.5 ± 1.1a14.2 ± 1.3a14.1 ± 1.1a
SV/kg    
 0 sml blood/kg3.79 ± 0.77a3.76 ± 0.78a4.19 ± 0.82a
 60 sml blood/kg4.66 ± 0.39a4.69 ± 0.48a4.73 ± 0.49a
 Fatigueml blood/kg3.89 ± 0.31a4.07 ± 0.40a3.99 ± 0.37a

Blood temperature

All warm-up exercises significantly increased pulmonary arterial temperature (TPA), which was significantly higher in HiWU than in LoWU and MoWU throughout the sprint exercise. At 30 and 60 s, TPA in MoWU was significantly higher than in LoWU (Fig 1a).

image

Figure 1. Mean ± s.d. a) blood temperature ( TPA) in the pulmonary artery and b) blood lactate concentration [LA] of horses before (pre) and after (post) warm-up protocols and during a sprint at a speed eliciting 115% inline image. Horses received LoWU (triangles), MoWU (squares) or HiWU (circles). a: Significant (P≤0.05) difference between LoWU and MoWU. b: Significant (P≤0.05) difference between LoWU and HiWU. c: Significant (P≤0.05) difference between MoWU and HiWU.

Download figure to PowerPoint

Blood lactate concentration

Immediately after the warm-up exercise and at the onset of sprint exercise, blood lactate concentration was significantly higher in HiWU than in MoWU and LoWU; however, blood lactate concentration was not different among the 3 treatments after 60 s of the sprint exercise (Fig 1b). The inline image (0–60 s) was significantly lower in HiWU than in LoWU and MoWU, and inline image (30–90 s) in HiWU was also significantly lower than in MoWU. There were no differences among the 3 groups in inline image (60–120 s).

Gas exchange measurements

The inline image was significantly higher in HiWU than in LoWU during the initial 60 s of the sprint and was also higher in HiWU than in MoWU at 30 s (Fig 2a). The inline image was significantly lower in HiWU than in LoWU and MoWU at 60 s and 90 s (Fig 2b). The respiratory exchange ratio (RER) was significantly higher in LoWU and MoWU than in HiWU during the initial 60 s of the sprint and was also higher in LoWU than in HiWU after 90 s (Fig 2c). The HR was significantly higher in HiWU than in LoWU throughout the sprint exercise and was also higher in HiWU than in MoWU after 0, 60 and 90 s of sprinting (Table 1).

image

Figure 2. Mean ± s.d. cardiorespiratory gas exchange variables: a) specific O2 consumption (inline image); b) specific CO2 production (inline image); and c) respiratory exchange ratio (RER) measured during warm-up and sprint exercise in the same horses as in Figure 1. See Figure 1 for key.

Download figure to PowerPoint

Blood gas measurements

The Cao2, inline image, inline image and pHa of HiWU were significantly different from other trials only at the onset of the sprint, and inline image and SV/kg were not different among trials (Fig 3 and Table 1). The Paco2 and inline image of HiWU were significantly lower than LoWU and MoWU until 90 and 60 s of the sprint exercise, respectively (Figs 3c, d).

image

Figure 3. Mean ± s.d. arterial (a) and mixed venous (inline image) blood gas measurements (a, Pao2; b, inline image; c, Paco2; d, inline image; e, Cao2; f, inline image) during warm-up and sprint exercise in the same horses as in Fig 1. Open symbols are arterial, closed symbols mixed venous. See Fig 1 for key.

Download figure to PowerPoint

Discussion

  1. Top of page
  2. Summary
  3. Introduction
  4. Materials and methods
  5. Results
  6. Discussion
  7. Acknowledgement
  8. Manufacturers' addresses
  9. References

Higher inline image during the first 60 s of the sprint exercise at HiWU in this study demonstrates that higher warm-up intensity accelerates inline image kinetics. This contrasts with previous reports that low-intensity warm-up enhances the aerobic contribution to total energy expenditure (Tyler et al. 1996) and that there are no additional benefits to performing intense prior exercise in horses (McCutcheon et al. 1999). Because the metabolic changes induced by prior high-intensity exercise increased inline image kinetics, our results suggest that several different mechanisms may contribute to determining inline image kinetics according to work intensity. Several factors likely to accelerate inline image kinetics in the sprint bout are: 1) vasodilatation and elevated blood flow at the onset of the sprint; 2) the acidaemia-induced Bohr shift of the oxyhaemoglobin equilibrium curve improving the diffusional gradient for O2 between the capillary blood and the mitochondria of the working muscles and 3) increased TPA after warm-up exercise (Boning et al. 1991; Clifford and Hellsten 2004).

The improvement in inline image kinetics associated with higher HR and inline image at the onset of sprint exercise in this study is consistent with the concept that blood flow limitation can slow inline image kinetics at the onset of exercise (Hughson et al. 1993). Hughson et al. (1996) investigated forearm blood flow and muscle O2 consumption (inline image) in 10 human subjects during rhythmic handgrip exercises with the arm either above or below heart level and found that inline image increased in proportion to increased blood flow. The flow and the inline image kinetics at the onset of exercise were significantly faster when the arm was below rather than above heart level. These observations suggest that blood flow can play an important role in determining the inline image kinetics at the onset of exercise. Indeed, not only does hyperaemia deliver more O2 to the working muscle convectively, the associated shorter transit time of erythrocytes through the muscle capillaries inevitably creates a higher time-integrated pressure head for diffusion of O2 into the myocytes, as shown by the Bohr equation (Karas et al. 1987).

Oxygen delivery to working muscles may be affected by a number of metabolic changes that occur in response to active warm-up. Increases in proton concentration, Pco2 and temperature in response to warm-up may enhance O2 delivery to muscles by decreasing oxyhaemoglobin affinity (Boning et al. 1991). In our previous study (Mukai et al. 2008), the faster inline image kinetics with a high-intensity warm-up exercise (60 s at 115% inline image) compared with the trial without a warm-up was accompanied by higher inline image resulting from enhanced extraction of O2 by working muscles. In that study, pHa was significantly lower and Paco2 higher after HiWU than with the other 2 protocols, which would also contribute to higher inline image during warm-up exercise. However, the difference in pHa between HiWU and the other protocols at the onset of the sprint bout in this study was smaller than during the warm-up, thus the acidosis induced by intense prior exercise may not have contributed as much to the change in inline image during the sprint exercise. On the contrary, these results indicate that even low-intensity warm-up in which running distance is equivalent to a higher-intensity warm-up exercise can increase O2 extraction in the working muscles in horses.

Increased metabolic activity within working muscles during exercise increases muscle temperature. The increase in body temperature contributes to increasing O2 consumption due to the Q10 effect (Schmidt-Nielsen 1997). The measured differences in TPA between the treatments that were maintained throughout the sprint exercise would be predicted to increase HiWU metabolic rates above LoWU by approximately 5% and from MoWU by approximately 3%, assuming a Q10 of 2.3 (Geor et al. 2000). These increased metabolic rates are similar to the measured inline image and could explain most of the elevated inline image throughout the exercise, although they do not specifically explain the accelerated inline image at the onset of the sprint.

The RER of HiWU at 30–90 s of the sprint bouts was significantly lower than with LoWU and MoWU due to both increased inline image and reduced inline image. The reduction in inline image, pHa, Pco2 and inline image at the onset of the sprint exercise is consistent with the human study (Gerbino et al. 1996), suggesting that improved perfusion of the working muscle consequent to the vasodilating effects of the acidosis after HiWU reduces lactate accumulation and less CO2 evolves from bicarbonate buffering. These findings are similar to our previous study (Mukai et al. 2008) but not to other studies (Tyler et al. 1996; Geor et al. 2000), which showed that inline image kinetics increased following warm-up exercise. Those authors suggest that prior exercise increases in CO2 storage in the muscle and the subsequent output of CO2 from working muscle. However, it is unclear whether differences in experimental protocols between our studies and those of other investigators may have contributed to these different findings.

The run time to fatigue in the 3 trials in this study was not different despite HiWU having faster inline image kinetics and lower Pco2 and inline image compared with LoWU and MoWU. Fatigue during sprint exercise seems to be associated with several factors, including accumulation of blood lactate and hydrogen ions (Kronfeld et al. 1999), high body temperature (Reilly et al. 2006) and decreased i.m. phosphocreatine (Glaister 2005). At the onset of the sprint, HiWU [La] was higher and pHa lower than with LoWU and MoWU. However, the differences in both factors gradually decreased and no differences were observed at exhaustion. On the other hand, TPA was higher with HiWU throughout the sprint and this may have affected the performance in a variety of ways following HiWU, possibly contributing to onset of fatigue despite increased inline image kinetics and availability of aerobic power. These results suggest that it may be desirable to balance the warm-up regimen to accelerate inline image kinetics and improve performance without excessively generating heat, lactacidosis and associated metabolic changes that cause fatigue.

In conclusion, the current study indicates that HiWU with equivalent running distance (total energy expenditure) in horses accelerates inline image kinetics and reduces reliance on net anaerobic power compared with LoWU. Multiple factors, including hyperaemia, hyperthermia and metabolic acidemia-induced Bohr shift, may contribute to produce the warm-up effects observed during subsequent sprint exercise.

Acknowledgement

  1. Top of page
  2. Summary
  3. Introduction
  4. Materials and methods
  5. Results
  6. Discussion
  7. Acknowledgement
  8. Manufacturers' addresses
  9. References

We thank the technical staff of the JRA Equine Research Institute for expert technical assistance, training and husbandry throughout the study.

Manufacturers' addresses

  1. Top of page
  2. Summary
  3. Introduction
  4. Materials and methods
  5. Results
  6. Discussion
  7. Acknowledgement
  8. Manufacturers' addresses
  9. References

1 Kagra, Fahrwangen, Switzerland.

2 Fukuda Denshi, Tokyo, Japan.

3 DATAQ, Akron, Ohio, USA.

4 G. N. Sensor, Chiba, Japan.

5 VISE Medical, Chiba, Japan.

6 Telmo, Tokyo, Japan.

7 Baxter International, Deerfield, Illinois, USA.

8 Becton, Dickinson and Company, Franklin Lakes, New Jersey, USA.

9 Gould Instruments, Valley View, Ohio, USA.

10 Radiometer, Copenhagen, Denmark.

11 Lexington Instruments, Waltham, Massachusetts, USA.

12 Yellow Springs Instruments, Yellow Springs, Ohio, USA.

13 SAS Institute Inc., Cary, North Carolina, USA.

References

  1. Top of page
  2. Summary
  3. Introduction
  4. Materials and methods
  5. Results
  6. Discussion
  7. Acknowledgement
  8. Manufacturers' addresses
  9. References
  • Bailey, S.J., Vanhatalo, A., Wilkerson, D.P., Dimenna, F.J. and Jones, A.M. (2009) Optimizing the ‘priming’ effect: influence of prior exercise and recovery duration on O2 uptake kinetics and severe-intensity exercise tolerance. J. appl. Physiol. 107, 1743-1756.
  • Bishop, D. (2003) Warm up II: Performance changes following active warm up and how to structure the warm up. Sports Med. 33, 483-498.
  • Boning, D., Hollnagel, C., Boecker, A. and Goke, S. (1991) Bohr shift by lactic acid and the supply of O2 to skeletal muscle. Respir. Physiol. 85, 231-243.
  • Clifford, P.S. and Hellsten, Y. (2004) Vasodilatory mechanisms in contracting skeletal muscle. J. appl. Physiol. 97, 393-403.
  • Fedak, M.A., Rome, L. and Seeherman, H.J. (1981) One-step N2-dilution technique for calibrating open-circuit inline image measuring systems. J. appl. Physiol. 51, 772-776.
  • Geor, R.J., McCutcheon, L.J. and Hinchcliff, K.W. (2000) Effects of warm-up intensity on kinetics of oxygen consumption and carbon dioxide production during high-intensity exercise in horses. Am. J. vet. Res. 61, 638-645.
  • Gerbino, A., Ward, S.A. and Whipp, B.J. (1996) Effects of prior exercise on pulmonary gas-exchange kinetics during high-intensity exercise in humans. J. appl. Physiol. 80, 99-107.
  • Glaister, M. (2005) Multiple sprint work: Physiological responses, mechanisms of fatigue and the influence of aerobic fitness. Sports Med. 35, 757-777.
  • Hughson, R.L., Cochrane, J.E. and Butler, G.C. (1993) Faster O2 uptake kinetics at onset of supine exercise with than without lower body negative pressure. J. appl. Physiol. 75, 1962-1967.
  • Hughson, R.L., Shoemaker, J.K., Tschakovsky, M.E. and Kowalchuk, J.M. (1996) Dependence of muscle inline image on blood flow dynamics at onset of forearm exercise. J. appl. Physiol. 81, 1619-1626.
  • Karas, R.H., Taylor, C.R., Jones, J.H., Lindstedt, S.L., Reeves, R.B. and Weibel, E.R. (1987) Adaptive variation in the mammalian respiratory system in relation to energetic demand: VII. Flow of oxygen across the pulmonary gas exchanger. Respir. Physiol. 69, 101-115.
  • Kronfeld, D.S., Ferrante, P.L., Taylor, L.E. and Tiegs, W. (1999) Partition of plasma hydrogen ion concentration changes during repeated sprints. Equine vet. J., Suppl. 30, 380-383.
  • Langsetmo, I., Weigle, G.E., Fedde, M.R., Erickson, H.H., Barstow, T.J. and Poole, D.C. (1997) inline image kinetics in the horse during moderate and heavy exercise. J. appl. Physiol. 83, 1235-1241.
  • McCutcheon, L.J., Geor, R.J. and Hinchcliff, K.W. (1999) Effects of prior exercise on muscle metabolism during sprint exercise in horses. J. appl. Physiol. 87, 1914-1922.
  • Mukai, K., Hiraga, A., Eto, D., Takahashi, T., Hada, T., Tsubone, H. and Jones, J.H. (2008) Effects of warm-up intensity on oxygen transport during supramaximal exercise in horses. Am. J. vet. Res. 69, 690-696.
  • Mukai, K., Takahashi, T., Eto, D., Ohmura, H., Tsubone, H. and Hiraga, A. (2007) Heart rates and blood lactate response in Thoroughbred horses during a race. J. equine Sci. 18, 153-160.
  • Pascoe, J.R., Hiraga, A., Hobo, S., Birks, E.K., Yarbrough, T.B., Takahashi, T., Hada, T., Aida, H., Steffey, E.P. and Jones, J.H. (1999) Cardiac output measurements using sonomicrometer crystals on the left ventricle at rest and exercise. Equine vet. J., Suppl. 30, 148-152.
  • Reilly, T., Drust, B. and Gregson, W. (2006) Thermoregulation in elite athletes. Curr. Opin. Clin. Nutr. Metab. Care 9, 666-671.
  • Rose, R.J., Hodgson, D.R., Bayly, W.M. and Gollnick, P.D. (1990) Kinetics of inline image and Vco2 in the horse and comparison of five methods for determination of maximum oxygen uptake. Equine vet. J., Suppl. 9, 39-42.
  • Schmidt-Nielsen, K. (1997) Temperature effects. In: Animal Physiology: Adaptation and Environment, 5th edn., Cambridge University Press, New York. pp 218-221.
  • Tyler, C.M., Hodgson, D.R. and Rose, R.J. (1996) Effect of a warm-up on energy supply during high intensity exercise in horses. Equine vet. J. 28, 117-120.