VO2 kinetics in the horse during moderate and heavy exercise.
Abstract: The horse is a superb athlete, achieving a maximal O2 uptake (approximately 160 ml . min-1 . kg-1) approaching twice that of the fittest humans. Although equine O2 uptake (VO2) kinetics are reportedly fast, they have not been precisely characterized, nor has their exercise intensity dependence been elucidated. To address these issues, adult male horses underwent incremental treadmill testing to determine their lactate threshold (Tlac) and peak VO2 (VO2 peak), and kinetic features of their VO2 response to "square-wave" work forcings were resolved using exercise transitions from 3 m/s to a below-Tlac speed of 7 m/s or an above-Tlac speed of 12.3 +/- 0.7 m/s (i.e., between Tlac and VO2 peak) sustained for 6 min. VO2 and CO2 output were measured using an open-flow system: pulmonary artery temperature was monitored, and mixed venous blood was sampled for plasma lactate. VO2 kinetics at work levels below Tlac were well fit by a two-phase exponential model, with a phase 2 time constant (tau1 = 10.0 +/- 0.9 s) that followed a time delay (TD1 = 18.9 +/- 1.9 s). TD1 was similar to that found in humans performing leg cycling exercise, but the time constant was substantially faster. For speeds above Tlac, TD1 was unchanged (20.3 +/- 1.2 s); however, the phase 2 time constant was significantly slower (tau1 = 20.7 +/- 3.4 s, P < 0.05) than for exercise below Tlac. Furthermore, in four of five horses, a secondary, delayed increase in VO2 became evident 135.7 +/- 28.5 s after the exercise transition. This "slow component" accounted for approximately 12% (5.8 +/- 2.7 l/min) of the net increase in exercise VO2. We conclude that, at exercise intensities below and above Tlac, qualitative features of VO2 kinetics in the horse are similar to those in humans. However, at speeds below Tlac the fast component of the response is more rapid than that reported for humans, likely reflecting different energetics of O2 utilization within equine muscle fibers.
Publication Date: 1997-10-24 PubMed ID: 9338433DOI: 10.1152/jappl.1997.83.4.1235Google Scholar: Lookup
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- Journal Article
- Research Support
- Non-U.S. Gov't
- Research Support
- U.S. Gov't
- P.H.S.
Summary
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This study examines how the rate of oxygen uptake (VO2) varies in horses during different levels of exercise intensity. The researchers found that despite some similarities, there are notable differences between horses and humans in terms of their VO2 uptake rate and the influence of exercise intensity on it.
Research Methodology
- The study participants consisted of adult male horses who underwent a series of tests on a treadmill at increasing intensity levels. These tests aimed to determine the horses’ lactate threshold (Tlac) and peak VO2 (VO2 peak).
- The kinetic features of VO2 responses to work forcings were studied using exercise transitions from a slow speed (3 m/s) to a moderately intense speed (7 m/s, below Tlac), and to a high intensity speed (12.3 ± 0.7 m/s, between Tlac and VO2 peak).
- Measurements were made during exercise intervals lasting 6 minutes, and an open-flow system was used to measure VO2 and CO2 output.
- The researchers also monitored the pulmonary artery temperature and analysed the mixed venous blood for plasma lactate concentrations.
Key Findings
- VO2 kinetics at speeds below the Tlac were found to fit a two-phase exponential model, with a delay time and a phase 2 time constant that were similar to those found in humans performing leg cycling exercise.
- However, the time constant was much faster than in humans, indicating a more rapid response
- When speeds exceeded the Tlac, the delay time remained almost unchanged, however, the phase 2 time constant was found to be slower.
- A slow secondary increase in VO2 was observed in four out of five horses approximately 136 seconds after the exercise transition. This slow component accounted for approximately 12% of the net increase in exercise VO2.
Conclusion
- The researchers concluded that the VO2 kinetics’ qualitative features in horses are comparable to those in humans, both below and above the lactate threshold.
- However, at exercise speeds below Tlac, the fast component of the response is more rapid in horses than in humans. This difference may reflect varying energetics of oxygen utilization within the equine muscle.
Cite This Article
APA
Langsetmo I, Weigle GE, Fedde MR, Erickson HH, Barstow TJ, Poole DC.
(1997).
VO2 kinetics in the horse during moderate and heavy exercise.
J Appl Physiol (1985), 83(4), 1235-1241.
https://doi.org/10.1152/jappl.1997.83.4.1235 Publication
Researcher Affiliations
- Departments of Anatomy and Physiology and Kinesiology, Kansas State University, Manhattan, Kansas 66506-5602, USA.
MeSH Terms
- Animals
- Body Temperature / physiology
- Carbon Dioxide / metabolism
- Horses
- Kinetics
- Lactic Acid / metabolism
- Male
- Models, Biological
- Muscle Fibers, Fast-Twitch / physiology
- Muscle, Skeletal / metabolism
- Muscle, Skeletal / physiology
- Oxygen Consumption / physiology
- Physical Exertion / physiology
- Running
Grant Funding
- HL-17731 / NHLBI NIH HHS
- HL-50306 / NHLBI NIH HHS
Citations
This article has been cited 7 times.- Poole DC, Copp SW, Colburn TD, Craig JC, Allen DL, Sturek M, O'Leary DS, Zucker IH, Musch TI. Guidelines for animal exercise and training protocols for cardiovascular studies. Am J Physiol Heart Circ Physiol 2020 May 1;318(5):H1100-H1138.
- Poole DC. Edward F. Adolph Distinguished Lecture. Contemporary model of muscle microcirculation: gateway to function and dysfunction. J Appl Physiol (1985) 2019 Oct 1;127(4):1012-1033.
- Buck AK, Elder CP, Donahue MJ, Damon BM. Matching of postcontraction perfusion to oxygen consumption across submaximal contraction intensities in exercising humans. J Appl Physiol (1985) 2015 Aug 1;119(3):280-9.
- Crook TC, Cruickshank SE, McGowan CM, Stubbs N, Wakeling JM, Wilson AM, Payne RC. Comparative anatomy and muscle architecture of selected hind limb muscles in the Quarter Horse and Arab. J Anat 2008 Feb;212(2):144-52.
- Wilkerson DP, Campbell IT, Jones AM. Influence of nitric oxide synthase inhibition on pulmonary O2 uptake kinetics during supra-maximal exercise in humans. J Physiol 2004 Dec 1;561(Pt 2):623-35.
- Ozyener F, Rossiter HB, Ward SA, Whipp BJ. Negative accumulated oxygen deficit during heavy and very heavy intensity cycle ergometry in humans. Eur J Appl Physiol 2003 Sep;90(1-2):185-90.
- Behnke BJ, McDonough P, Padilla DJ, Musch TI, Poole DC. Oxygen exchange profile in rat muscles of contrasting fibre types. J Physiol 2003 Jun 1;549(Pt 2):597-605.
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