EQUINE VETERINARY JOURNAL
75
Equine w. .I(1992) . 24 (2) 75-76
Editorials
Sodium bicarbonate: more than iust a 'miIkshake'? OVER THE PAST five years, racing authorities world wide have become aware of so called 'milkshake' being administered to horses via a stomach tube 4 to 6 h prior to racing. The milkshake is usually a mixture of substances, the principal ingredient being sodium bicarbonate. However, vitamins, glucose and P-agonists such as clenbuterol and salbutamol may be included. A company in the United States is now marketing a commercial paste formulation trade marked 'milkshake', which contains vitamins B, C and E, methyl sulphonyl methane, selenium, sodium sesquicarbonate and sodium bicarbonate (Jones 1990). Recently, venous acid base measurements were performed prior to racing and revealed that more than 50% of Standardbreds had blood bicarbonate concentrations that were higher than normal, with values as high as 50 mrnolflitre. In contrast, the incidence of elevated blood bicarbonate concentrations in Thoroughbreds was less than 5% (Lloyd and Rose 1991, unpublished data). Already authorities in the Standardbred industry in New Zealand have moved to regulate the administration of sodium bicarbonate by implementing a pre-race testing programme using venous blood gas and acid base analysis. Many trainers feel 'milkshakes' are beneficial to a horse's racing performance. What could the benefit be and why is the 'milkshake' used more commonly in Standardbreds than Thoroughbreds? Early studies by Hill and Lupton (1923) showed that in stimulated frog muscle, there was a relationship between the onset of fatigue and the accumulation of lactic acid. They suggested that if hydrogen ions were buffered, exercise duration could be prolonged. Later studies by Snow, Harris and Gash (1985) showed that, during repeated exercise bouts in horses, there was a progressive decline in muscle pH and a decrease in the ATP concentration in skeletal muscle. Other studies in man showed that administration of ammonium chloride, which produces a metabolic acidosis, could decrease high intensity exercise capacity (Dennig, Talbot, Edwards and Dill 1931).These studies and a variety of others indicated that the capacity for short term high intensity exercise was adversely affected by increased concentrations of H+ in skeletal muscle. Therefore, alkalinising agents, such as sodium bicarbonate, may exert a beneficial effect on performance by buffering the increased concentration of H+ that occurs during exercise and so delay the onset of fatigue. The earliest studies of bicarbonate administration to man (Dennig et a1 1931; Margaria, Edwards and Dill 1933) used only one subject but an increase in running duration was found. A later study by Sutton, Jones and Towes (1976)
showed that during cycle ergometry at 90% of maximal oxygen uptake, sodium bicarbonate administration at 0.3 mg/kg bodyweight [bwt] resulted in an almost 50% increase in exercise time to exhaustion. The beneficial effects on athletic performance were demonstrated by Wilkes, Gledhill and Smyth (1 983) who showed that, in university athletes, sodium bicarbonate at a dose of 0.3 mgJg bwt resulted in an average improvement of approximately 3 sec in an 800 m run time. In studies in which the total exercise time was only 30 sec at a high work intensity: sodium bicarbonate had no effect on total work output (McCartney, Heigenhauser and Jones 1983). Other studies with lower dose rates of sodium bicarbonate demonstrated no effects on high intensity performance capacity Kindermann, Keul and Huber 1977; Katz et a1 1984). These studies and many others indicate that sodium bicarbonate at dose rates of 0.3 mg/kg bwt or greater have a beneficial effect on exercise performance in human athletes where the exercise duration is 2 to 3 mins and the intensity is close to that producing maximal oxygen uptake. The relationship between performance enhancement and exercise duration could be the reason why there is a high incidence of sodium bicarbonate use in Standardbred racehorses. Standardbred horse races normally last between 2 and 3 mins over distances of 1,600 to 2,400 m, whereas most Thoroughbred races are over distances of 1,OOO to 1,600 rn, which are completed in about 1.5 mins or less. It is possible that bicarbonate administration is of more benefit to those horses for which races are 2 to 3 mins rather than 1 to 2 min in duration. Therefore, if sodium bicarbonate does have beneficial effects on performance, Standardbreds may obtain more benefit than Thoroughbreds. However, the evidence for a beneficial effect on performance in horses is not very convincing. Studies by Kelso et a1 (1987), Lawrence et a1 (1987a. b), Lawrence et a1 (1990) and Greenhaff et a1 (1991) found no significant difference in exercise capacity. The study in this issue of the Equine Veterinary Journal (p 94) by Harkins and Kamerling also reports no statistical difference in exercise times of 16 horses during simulated races. An interesting part of the study by Harkins and Kamerling was that they made an attempt to compensate for variations in track conditions by including an analysis of covariance to account for differences in track moisture content, ambient temperature, humidity and wind velocity. The difficulty in demonstrating a performance enhancing effect is illustrated by the study of Wilkes et a1 (1983) in human athletes, in which an improvement of 3 secs in a mean exercise
EQUINE VETERINARY JOURNAL
76
duration of 2:05 mins was found-an improvement of less than 3%. Variations in racetrack conditions, riding by the jockey, environmental temperature and other variables make the reproducibility of such studies difficult to achieve in the horse. Even using standardised treadmill conditions, the run time to fatigue, using repeated runs at high speed was found by Plummer, Knight, Ray and Rose (1991) to have a mean coefficient of variation of 9.6%. The treadmill test (Plummer et al 1991), and track tests such as that described by Harkins and Kamerling (1992) would not have demonstrated the 3% improvement found by Wilkes et a/ (1983) in human athletes. However, even a 1 sec improvement in equine performance represents approximately 6 lengths when translated into racetrack performance. Unless a drug alters a horse's exercise capacity by more than 10%. it may be difficult to prove, statistically, its beneficial or detrimental effects. The other variables in horse studies have been the dose rate and timing. Greenhaff, Snow, Hams and Roberts (1990) showed that sodium bicarbonate administered by stomach tube gave peak blood bicarbonate concentrations between 3 and 6 h after administration of a dose of 0.6 &g bwt. They also demonstrated that a dose of 0.3 m&g bwt, which has been used frequently in equine studies, was probably too low. Therefore, to optimise the potential for sodium bicarbonate to affect performance, a large enough dose should be administered approximately 4 to 6 h prior to exercise. If there are similar trends in horses as there are in man, it may be that doses of sodium bicarbonate higher than those used to date would produce significant effects on performance. As well as the change in acid base status, there is also a large sodium load being administered at dose rates around 0.4 to 0.5 m&g bwt. For a 500 kg horse, this represents 3,000 mmol of sodium, or more than 20% of the body's total exchangeable sodium. This will have an effect on plasma volume and will result in substantial renal sodium and water excretion. Changes in plasma volume per se may be responsible for significant alterations in performance. Some controversy now exists over whether or not sodium bicarbonate use should be regulated. Many opposed to a ban claim that it does not affect performance; and until such a time that a positive effect is demonstrated its use should be allowed. At present there is enough evidence, based on human studies, to suggest that bicarbonate administration may be of benefit to racehorses, except possibly in Quarterhorse racing in which the duration of exercise is only a little over 20 secs. Another factor that needs to be considered is that by administering large doses of bicarbonate the urinary pH becomes more alkaline. This can influence the rate of elimination of certain drugs from the body. Acidic drugs, such as phenobarbitone and frusemide, are excreted more rapidly in urine with higher urinary pH. the practical implication is that urinary alkalinisation results in a reduced time of the drug being held in the body. Alternatively basic drugs such as procaine and amphetamine, are excreted in the urine more slowly in alkaline urine. In both these cases the drug is more difficult to detect in urine samples collected for drug analysis. Although it is important to try to show a positive effect of bicarbonate administration of a horse's performance, this should not necessarily be a prerequisite for implementation of a testing programme. After all, how many other drugs presently on the prohibited substance lists have been shown
to alter a horse's running time? In the meantime only the horse knows whether sodium bicarbonate drenches are more than just a milkshake.
R. J. ROSE and D. R. LLOYD Department of Veterinary Clinical Sciences University of Sydney, NSW 2006 Australia References Dennig, H., Talbot, J. H.. Edwards, H. T. and Dill. D. B. (1931) Influence of acidosis and alkalosis upon capacity for work. J. d i n . Inivst. 9,601-613. Greenhaff. P. L., Hanak. J., Harris, R. C.. Dobias. P., Jahn, P., Skdlicky, J. and Snow, D. H. (1991) Metabolic alkalosis and exercise performance in the Thoroughbred horse. In: Equine E-vercise Physiology 3. Eds: S. G. B., Persson, A. Lindholm and 1. Jeffcott. ICEEP Publications. Stockholm. pp 353-360. Greenhaff, P. L., Snow, D. H., Harris, R. C. and Roberts, C. A. (1990) Bicarbonate loading in the Thoroughbred: dose. method of administration and acid-base changes. Equine vet. J. Suppl. 9,8345. Harkins, J. K. and Kamerling, S . G. (1992) Effects of induced alkalosis on performance in Thoroughbreds during a I .600-m race. Equine iw. J . 24, 94-98. Hill, A. V. and Lupton. H. (1923) Muscular exercise, lacti supply and utilisation of oxygen. Quart. 1.Mrd 16, 135- I7 I . Jones, W. E. (1990) Milkshakes. Equine vet. Dum 11, 17 I . Katz, A,, Costill. D. L., King, D. S.. Hargreaves, M. and Fink, W. J. (1984) Maximal exercise tolerance after induces alkalosis. Int. J . Sports Med. 5. 107-110. Kelso, T.B.. Hodgson. D. R.. Witt, E. H., Bayly, W. M., Grant, B. D. and Gollnick. P. D. (1987) Bicarbonate administration and Muscle metabolism during high-intensity exercise. In: Equine E.rercise Physiolo,qj~2. Eds: J. R. Gillespie and N. E. Robinson. ICEEP Publications, Davis. CA. USA. pp 448-455.. KindemdM, W., Keul, J. and Huber, G. (1977) Physical exercise after induced alkalosis (bicarbonate or tris-buffer). EUJ:J . uppl. Phy.siol. 37. 197-204. Lawrence. L. M., Miller, P. A,, Bechtel, P. J.. Kane, R. A,, Kurez. R. A,, Kurez, E. V. and Smith, J. S. ( I 987a) The effect of sodium bicarbonate ingestion on blood parameters on exercising horses. In: Equine E.rercise Pliysiology 2, Eds: J. R. Gillespie and N. E. Robinson. KEEP Publications, Davis CA. pp 448-455. Lawrence, L., Kline. K., Miller, P.. Smith, J., Siegel. A,. Kurez, E., Kane, R.. Fisher, M. and Bump, K. (1987b) Effect of sodium bicarbonate on racing Standardbreds. In: P mceediwgs .f the tet7rh Equi/re Nutritiutr und Php.~iok~.~y Syniposiuni,Ft. Collins, Colorado. USA. pp 499-503. Lawrence, L., Kline, K., Miller-Graber. P.. Siegel, A,. Kurez. E.. Fisher. M.. and Bump. K. (1990) The effect of sodium bicarbonate on racing Standardbreds.J. Anin~.Sci. 68,673-677. Margaria. R.. Edwards, H. T. and Dill, D. B. (1933) The possible mechanisms of contracting and paying the oxygen debt and the role of lactic acid in muscular contraction.Am. J. Phyiol. 106.689-7 15. McCartney, N.. Heigenhauser. G. J. F. and Jones, N. L. ( 1983) Effects of pH on maximal power output and fatigue during short-term dynamic exercise. J . uppl. Physiol. 60, 1164- 1169. Plummer. C.. Knight, P. K.. Ray. S. P. and Rose, R. J. (1991) Cardiorespiratory and metabolic effects of propranolol during maximal exercise. In: Equine Exercise Physiology 3 Eds: S. G. B., Persson. A. Lindholm, and L. Jeffcott. ICEEP Publications. Davis, CA, USA. pp 465-474. Snow, D. H.. Harris, R. C. and Gash, S . P. (1985) Metabolic response of equine muscle to intermittent maximal exercise. J . uppl. Physiol. 58, 1689-1697. Sutton. J. R.. Jones, N. L. and Toews. C. J. (1976) Growth hormone secretion in acid-base alterations at rest and during exercise. C h i . Sci. 50.24 1-247. Wilkes, D., Gledhill. N. and Smyth, R. (1983) Effect of acute induced metabolic acidosis on 800-m racing time. Med. Sci. S ~ J J YE.verc. S 15. 277-280.
75
Equine w. .I(1992) . 24 (2) 75-76
Editorials
Sodium bicarbonate: more than iust a 'miIkshake'? OVER THE PAST five years, racing authorities world wide have become aware of so called 'milkshake' being administered to horses via a stomach tube 4 to 6 h prior to racing. The milkshake is usually a mixture of substances, the principal ingredient being sodium bicarbonate. However, vitamins, glucose and P-agonists such as clenbuterol and salbutamol may be included. A company in the United States is now marketing a commercial paste formulation trade marked 'milkshake', which contains vitamins B, C and E, methyl sulphonyl methane, selenium, sodium sesquicarbonate and sodium bicarbonate (Jones 1990). Recently, venous acid base measurements were performed prior to racing and revealed that more than 50% of Standardbreds had blood bicarbonate concentrations that were higher than normal, with values as high as 50 mrnolflitre. In contrast, the incidence of elevated blood bicarbonate concentrations in Thoroughbreds was less than 5% (Lloyd and Rose 1991, unpublished data). Already authorities in the Standardbred industry in New Zealand have moved to regulate the administration of sodium bicarbonate by implementing a pre-race testing programme using venous blood gas and acid base analysis. Many trainers feel 'milkshakes' are beneficial to a horse's racing performance. What could the benefit be and why is the 'milkshake' used more commonly in Standardbreds than Thoroughbreds? Early studies by Hill and Lupton (1923) showed that in stimulated frog muscle, there was a relationship between the onset of fatigue and the accumulation of lactic acid. They suggested that if hydrogen ions were buffered, exercise duration could be prolonged. Later studies by Snow, Harris and Gash (1985) showed that, during repeated exercise bouts in horses, there was a progressive decline in muscle pH and a decrease in the ATP concentration in skeletal muscle. Other studies in man showed that administration of ammonium chloride, which produces a metabolic acidosis, could decrease high intensity exercise capacity (Dennig, Talbot, Edwards and Dill 1931).These studies and a variety of others indicated that the capacity for short term high intensity exercise was adversely affected by increased concentrations of H+ in skeletal muscle. Therefore, alkalinising agents, such as sodium bicarbonate, may exert a beneficial effect on performance by buffering the increased concentration of H+ that occurs during exercise and so delay the onset of fatigue. The earliest studies of bicarbonate administration to man (Dennig et a1 1931; Margaria, Edwards and Dill 1933) used only one subject but an increase in running duration was found. A later study by Sutton, Jones and Towes (1976)
showed that during cycle ergometry at 90% of maximal oxygen uptake, sodium bicarbonate administration at 0.3 mg/kg bodyweight [bwt] resulted in an almost 50% increase in exercise time to exhaustion. The beneficial effects on athletic performance were demonstrated by Wilkes, Gledhill and Smyth (1 983) who showed that, in university athletes, sodium bicarbonate at a dose of 0.3 mgJg bwt resulted in an average improvement of approximately 3 sec in an 800 m run time. In studies in which the total exercise time was only 30 sec at a high work intensity: sodium bicarbonate had no effect on total work output (McCartney, Heigenhauser and Jones 1983). Other studies with lower dose rates of sodium bicarbonate demonstrated no effects on high intensity performance capacity Kindermann, Keul and Huber 1977; Katz et a1 1984). These studies and many others indicate that sodium bicarbonate at dose rates of 0.3 mg/kg bwt or greater have a beneficial effect on exercise performance in human athletes where the exercise duration is 2 to 3 mins and the intensity is close to that producing maximal oxygen uptake. The relationship between performance enhancement and exercise duration could be the reason why there is a high incidence of sodium bicarbonate use in Standardbred racehorses. Standardbred horse races normally last between 2 and 3 mins over distances of 1,600 to 2,400 m, whereas most Thoroughbred races are over distances of 1,OOO to 1,600 rn, which are completed in about 1.5 mins or less. It is possible that bicarbonate administration is of more benefit to those horses for which races are 2 to 3 mins rather than 1 to 2 min in duration. Therefore, if sodium bicarbonate does have beneficial effects on performance, Standardbreds may obtain more benefit than Thoroughbreds. However, the evidence for a beneficial effect on performance in horses is not very convincing. Studies by Kelso et a1 (1987), Lawrence et a1 (1987a. b), Lawrence et a1 (1990) and Greenhaff et a1 (1991) found no significant difference in exercise capacity. The study in this issue of the Equine Veterinary Journal (p 94) by Harkins and Kamerling also reports no statistical difference in exercise times of 16 horses during simulated races. An interesting part of the study by Harkins and Kamerling was that they made an attempt to compensate for variations in track conditions by including an analysis of covariance to account for differences in track moisture content, ambient temperature, humidity and wind velocity. The difficulty in demonstrating a performance enhancing effect is illustrated by the study of Wilkes et a1 (1983) in human athletes, in which an improvement of 3 secs in a mean exercise
EQUINE VETERINARY JOURNAL
76
duration of 2:05 mins was found-an improvement of less than 3%. Variations in racetrack conditions, riding by the jockey, environmental temperature and other variables make the reproducibility of such studies difficult to achieve in the horse. Even using standardised treadmill conditions, the run time to fatigue, using repeated runs at high speed was found by Plummer, Knight, Ray and Rose (1991) to have a mean coefficient of variation of 9.6%. The treadmill test (Plummer et al 1991), and track tests such as that described by Harkins and Kamerling (1992) would not have demonstrated the 3% improvement found by Wilkes et a/ (1983) in human athletes. However, even a 1 sec improvement in equine performance represents approximately 6 lengths when translated into racetrack performance. Unless a drug alters a horse's exercise capacity by more than 10%. it may be difficult to prove, statistically, its beneficial or detrimental effects. The other variables in horse studies have been the dose rate and timing. Greenhaff, Snow, Hams and Roberts (1990) showed that sodium bicarbonate administered by stomach tube gave peak blood bicarbonate concentrations between 3 and 6 h after administration of a dose of 0.6 &g bwt. They also demonstrated that a dose of 0.3 m&g bwt, which has been used frequently in equine studies, was probably too low. Therefore, to optimise the potential for sodium bicarbonate to affect performance, a large enough dose should be administered approximately 4 to 6 h prior to exercise. If there are similar trends in horses as there are in man, it may be that doses of sodium bicarbonate higher than those used to date would produce significant effects on performance. As well as the change in acid base status, there is also a large sodium load being administered at dose rates around 0.4 to 0.5 m&g bwt. For a 500 kg horse, this represents 3,000 mmol of sodium, or more than 20% of the body's total exchangeable sodium. This will have an effect on plasma volume and will result in substantial renal sodium and water excretion. Changes in plasma volume per se may be responsible for significant alterations in performance. Some controversy now exists over whether or not sodium bicarbonate use should be regulated. Many opposed to a ban claim that it does not affect performance; and until such a time that a positive effect is demonstrated its use should be allowed. At present there is enough evidence, based on human studies, to suggest that bicarbonate administration may be of benefit to racehorses, except possibly in Quarterhorse racing in which the duration of exercise is only a little over 20 secs. Another factor that needs to be considered is that by administering large doses of bicarbonate the urinary pH becomes more alkaline. This can influence the rate of elimination of certain drugs from the body. Acidic drugs, such as phenobarbitone and frusemide, are excreted more rapidly in urine with higher urinary pH. the practical implication is that urinary alkalinisation results in a reduced time of the drug being held in the body. Alternatively basic drugs such as procaine and amphetamine, are excreted in the urine more slowly in alkaline urine. In both these cases the drug is more difficult to detect in urine samples collected for drug analysis. Although it is important to try to show a positive effect of bicarbonate administration of a horse's performance, this should not necessarily be a prerequisite for implementation of a testing programme. After all, how many other drugs presently on the prohibited substance lists have been shown
to alter a horse's running time? In the meantime only the horse knows whether sodium bicarbonate drenches are more than just a milkshake.
R. J. ROSE and D. R. LLOYD Department of Veterinary Clinical Sciences University of Sydney, NSW 2006 Australia References Dennig, H., Talbot, J. H.. Edwards, H. T. and Dill. D. B. (1931) Influence of acidosis and alkalosis upon capacity for work. J. d i n . Inivst. 9,601-613. Greenhaff. P. L., Hanak. J., Harris, R. C.. Dobias. P., Jahn, P., Skdlicky, J. and Snow, D. H. (1991) Metabolic alkalosis and exercise performance in the Thoroughbred horse. In: Equine E-vercise Physiology 3. Eds: S. G. B., Persson, A. Lindholm and 1. Jeffcott. ICEEP Publications. Stockholm. pp 353-360. Greenhaff, P. L., Snow, D. H., Harris, R. C. and Roberts, C. A. (1990) Bicarbonate loading in the Thoroughbred: dose. method of administration and acid-base changes. Equine vet. J. Suppl. 9,8345. Harkins, J. K. and Kamerling, S . G. (1992) Effects of induced alkalosis on performance in Thoroughbreds during a I .600-m race. Equine iw. J . 24, 94-98. Hill, A. V. and Lupton. H. (1923) Muscular exercise, lacti supply and utilisation of oxygen. Quart. 1.Mrd 16, 135- I7 I . Jones, W. E. (1990) Milkshakes. Equine vet. Dum 11, 17 I . Katz, A,, Costill. D. L., King, D. S.. Hargreaves, M. and Fink, W. J. (1984) Maximal exercise tolerance after induces alkalosis. Int. J . Sports Med. 5. 107-110. Kelso, T.B.. Hodgson. D. R.. Witt, E. H., Bayly, W. M., Grant, B. D. and Gollnick. P. D. (1987) Bicarbonate administration and Muscle metabolism during high-intensity exercise. In: Equine E.rercise Physiolo,qj~2. Eds: J. R. Gillespie and N. E. Robinson. ICEEP Publications, Davis. CA. USA. pp 448-455.. KindemdM, W., Keul, J. and Huber, G. (1977) Physical exercise after induced alkalosis (bicarbonate or tris-buffer). EUJ:J . uppl. Phy.siol. 37. 197-204. Lawrence. L. M., Miller, P. A,, Bechtel, P. J.. Kane, R. A,, Kurez. R. A,, Kurez, E. V. and Smith, J. S. ( I 987a) The effect of sodium bicarbonate ingestion on blood parameters on exercising horses. In: Equine E.rercise Pliysiology 2, Eds: J. R. Gillespie and N. E. Robinson. KEEP Publications, Davis CA. pp 448-455. Lawrence, L., Kline. K., Miller, P.. Smith, J., Siegel. A,. Kurez, E., Kane, R.. Fisher, M. and Bump, K. (1987b) Effect of sodium bicarbonate on racing Standardbreds. In: P mceediwgs .f the tet7rh Equi/re Nutritiutr und Php.~iok~.~y Syniposiuni,Ft. Collins, Colorado. USA. pp 499-503. Lawrence, L., Kline, K., Miller-Graber. P.. Siegel, A,. Kurez. E.. Fisher. M.. and Bump. K. (1990) The effect of sodium bicarbonate on racing Standardbreds.J. Anin~.Sci. 68,673-677. Margaria. R.. Edwards, H. T. and Dill, D. B. (1933) The possible mechanisms of contracting and paying the oxygen debt and the role of lactic acid in muscular contraction.Am. J. Phyiol. 106.689-7 15. McCartney, N.. Heigenhauser. G. J. F. and Jones, N. L. ( 1983) Effects of pH on maximal power output and fatigue during short-term dynamic exercise. J . uppl. Physiol. 60, 1164- 1169. Plummer. C.. Knight, P. K.. Ray. S. P. and Rose, R. J. (1991) Cardiorespiratory and metabolic effects of propranolol during maximal exercise. In: Equine Exercise Physiology 3 Eds: S. G. B., Persson. A. Lindholm, and L. Jeffcott. ICEEP Publications. Davis, CA, USA. pp 465-474. Snow, D. H.. Harris, R. C. and Gash, S . P. (1985) Metabolic response of equine muscle to intermittent maximal exercise. J . uppl. Physiol. 58, 1689-1697. Sutton. J. R.. Jones, N. L. and Toews. C. J. (1976) Growth hormone secretion in acid-base alterations at rest and during exercise. C h i . Sci. 50.24 1-247. Wilkes, D., Gledhill. N. and Smyth, R. (1983) Effect of acute induced metabolic acidosis on 800-m racing time. Med. Sci. S ~ J J YE.verc. S 15. 277-280.
