body fat: is it a handicap to racehorses?

Guest Editorial

Body Fat: Is it a Handicap to Racehorses?

The Veterinary Journal 2002, 163, 223±225doi:10.1053/tvjl.2001.0680, available online at http://www.idealibrary.com on

This volume of The Veterinary Journal includes aninteresting paper, which provides new insights intothe relationships between body composition andathletic performance in standardbred racehorses(Kearns et al., 2002). Given the difficulties ofundertaking this type of investigation, the studyinvolves only a limited number of horses and there-fore the inevitable questions relating to the statisticalpower of the results may be raised. However, despitethis, the paper provides some valuable new findingson factors contributing to athletic performance inhorses and, as such, should be considered a worthyaddition to the literature.

Assessments of performance capacity andresponses to exercise and training have been thesubject of considerable scientific endeavour formore than a century. A substantial increase in thenumber of reports of investigations into the changesoccurring in response to exercise and predictors ofperformance in humans has occurred since the late19th century, but it is only since the 1960s that therehas been a rapid expansion in and acceptance ofexercise science as a reputable scientific discipline.Initially, these investigations involved humans,laboratory rodents and some other animal species.Given the global nature of equestrian athleticpursuits, it is not surprising that by the 1970slaboratories designed to investigate determinants ofperformance capacity in athletic animals were dev-eloped in a number of countries. Initially, many ofthe experiments in all the species studied weredescriptive in nature, providing essential baselineinformation as a foundation for the more sophisti-cated hypothesis-driven studies that were to follow.Examples of some of the pivotal findings as theyrelated to athletic performance may be found inTable I.

Most of the variables referred to in Table I areintegral to and reflective of the oxygen deliverypathway. It has been understood that optimal func-tion of this pathway is pivotal to successful athletic

1090-0233/02/$ ± see front matter # 2002 Elsevier Science Ltd. All r

performance, but the sheer magnitude of the res-ponses found in elite equine athletes has been thesubject of much discussion among comparativephysiologists. Despite our improved understandingof the physiology of exercise, it has becomeincreasingly clear that comparable contributionsfrom many other body systems are required ifappropriate athletic performance is to be achieved.Thus, the elite racehorse requires superior cardio-respiratory capacity, but without appropriate con-formation, body morphometry, training, diet andwillingness to perform, performance is likely to beless than is considered optimal.

Doubtless there is a significant genetic contri-bution to successful athletic performance. Whendiscussing the physiological basis for the trainingprocess in humans, Wilmore and Costill (1988)suggested that one of the most effective ways tobecome a champion athlete is `to be selectivewhen choosing one's parents'. This statement issupported by the studies of identical twins, whoseVO2max values are extraordinarily similar (R� 0.92).In addition, the endurance capacity of identicaltwins is much more analogous than that for non-identical twins, whose performance is also more akinto that of brothers (Bouchard et al., 1986, 1992).From this, it has been estimated that the geneticcontribution to VO2max and endurance capacityis approximately 40% and 60%, respectively.

One might ask: Does the same apply to race-horses? Records for thoroughbreds have beenmaintained in the Stud Book since 1791. Referenceto these records indicate that about 50% of allthe genes in the current thoroughbred populationcome from 10 horses with 80% from just 31 horses.These findings prompted Cunningham (1991) toundertake a study investigating possible geneticcontributions to racing performance. The records ofover 30 000 three-year-old thoroughbreds were stu-died and it was concluded that only approximately35% of the variation in performance between horses,

ights reserved.

Table IValues for selected physiological variables in different athletic species

Human (athlete) Thoroughbred/standardbred Greyhound Camel

(racing)

Relative max speed (m/s) 10±11 19±20 16±17 10±11

VO2max (mL/kg/min) 69±85 160±200 > 100 50

Resting HR (beats/min) 40±60 20±30 100 30

Max exercising HR (beats/min) 190 210±240 300 150

Resting cardiac stroke index (mL/kg) 1.1±1.4 1.3±2.3 ± ±

Max cardiac stroke index (mL/kg) 1.5 2.5±4.0 ± ±

Resting PCV (%) 40±50 32±42 54 33

Max PCV (%) 40±50 60±70 64 36

Peak lactate (mmol/L) 15 > 30 20 15

Muscle fiber composition >75% Type II in sprinters >80% Type II in sprinters ± ±

>75% Type I in endurance �30% Type I in endurance

(Adapted from Derman & Noakes, 1994)

224 THE VETERINARY JOURNAL, 163, 3

as assessed by Time Form rating was explained byhereditary factors. Key contributors to the other 65%were considered to be training, nutrition and otherunspecified factors.

Body composition has been shown to be a criticaldeterminant for successful performance in a varietyof human athletic events (Barr et al., 1994). Thepaper by Kearns et al. (p. 00) indicates that the sameis likely to be the case for successful racing perfor-mance in standardbreds. The major finding fromthe study is that a large fat-free mass makes thegreatest contribution to successful performance,especially when sprinting. The authors suggest thatthe most likely explanation for the inverse relation-ship between the fat mass and performance is rela-ted to the relative energy expenditure requiredperforming the same amount of work. Much ofthe fat-free tissue is likely to contribute directly tothe energetics of exercise. In contrast, fat is a non-working tissue in terms of energetic contribution toperformance, with a lower fat-free mass resultingin a decrease in the power-to-weight ratio for thehorse. Alterations in the power-to-weight ratio arethe key to the handicapping system in thoroughbredracing and, as such, a subjective understanding ofeffects have been known for centuries. The moreweight a horse is assigned in terms of handicap themore likely performance is to be reduced ± certainlythat is the concept.

Recently, an indirect study examining the effectsof increasing (reducing body mass via administrationof the diuretic furosemide) the power-to-weight ratiohave demonstrated, albeit indirectly, the beneficialeffects of this improvement in power-to-weight ratio

(Gross et al., 1999). Thus, the findings from the studyof Kearns et al. are likely to be beneficial in severalways. Determination of fat mass, and therefore fat-free mass, using ultrasonographic techniques isapparently simple and the results reproducible.Thus, this technique may have application as anadjunct to the selection of horses and to assess theresponses to specific training and dietary regimens.

DAVID HODGSON

Faculty of Veterinary Science,University Veterinary Centre,

PMB 4, Narellan Delivery Centre,Narellan,

NSW 2567 Australia

REFERENCES

BARR S. I., MCCARGAR L. J. & CRAWFORD S. M. (1994).Practical use of body composition analysis in sport.Sports Medicine 17, 277±82.

BOUCHARD, C., LESAGE, R., LORTIE, G., SIMONEAU, J. A.,HAMEL, P., BOULAY, M. R., PERUSSE L., THERIAULT G. &LEBLANC C. (1986). Aerobic performance in brothers,dizygotic and monozygotic twins. Medicine and Science inSports and Exercise 18, 639±46.

BOUCHARD, C., DIONNE, F. T., SIMONEAU J. A. & BOULAY M. R.(1992). Genetics of aerobic and anaerobic perfor-mances. Exercise and Sports Science Reviews 20, 27±58.

CUNNINGHAM, P. (1991). The genetics of Thoroughbred horses.Scientific American 264, 56.

DERMAN, K. D. & NOAKES, T. D. (1994). Comparativeaspects of exercise physiology. In Principles and Practiceof Equine Sports Medicine: The Athletic Horse edsD. R. Hodgson & R. J. Rose, pp. 13±25. PhiladelphiaPennsylvania: W.B. Saunders Company.

225GUEST EDITORIAL

GROSS, D. K., MORLEY, P. S., HINCHCLIFF, K. W. &WITTUM, T. E. (1999). Effect of furosemide onperformance of thoroughbreds racing in the UnitedStates and Canada. Journal of the American VeterinaryMedical Association 215, 670±5.

KEARNS, C. F., MCKEEVER, K. H., KUMAGAI, K. & ABE, T.(2002). Fat-free mass is related to one mile race

performance in elite standardbred horses. The VeterinaryJournal 163, 260±6.

WILMORE, J. H. & COSTILL, D. L. (1988). Training for Sportand Activity: The physiological Basis of the ConditioningProcess. pp. 37±167. Dubuque Iowa, Wm C BrownPublishers.