By Dr Catherine Dunnett
No doubt we are all aware of the plethora of dietary supplements that are now available and that are promoted as offering clear and profound benefits to our horses’ health, general well being and performance. In the latter category are the so-called ergogenic aids. So what are they, and do they work? These are the questions that this article aims to address.
Ergogenic is defined as ‘work producing’. An ergogenic aid is therefore some system, process, device or substance than can boost athletic performance in some fashion, such as speed, strength or stamina. Broadly speaking there are five categories of ergogenic aids: biomechanical, physiological, pharmaceutical, psychological, and nutritional.
From an athletic perspective ergogenic aids may - enhance the biochemical and therefore physiological capacity of a particular body system leading to improved performance, alleviate the psychological constraints that can limit performance accelerate recovery from training and competition.
This article will focus upon the use of nutritional supplements that are marketed or currently being researched for their efficacy in improving athletic performance in horses.
HOW DO THEY WORK?
In principle nutritional ergogenic aids can enhance exercise performance in horses in a variety ways, depending on the nature of the particular supplement. For example an ergogenic aid might -
Enhance the lean mass of a horse by reducing body fat content whilst maintaining muscle mass, leading to an improved power to weight ratio
Improve the ability to counter lactic acid production or accumulation – producing a slower fatigue process in muscle
Increase muscle mass – resulting in increased power or strength
Increase the transport of oxygen around the body
Improve the efficiency of utilisation of body fuels such as fat, glucose and glycogen
Increase the storage of fuels within the body
Enhance the storage and utilisation of high-energy phosphates used in the early stages of fast exercise
WHAT’S ON THE MARKET?
A vast array of supplements are promoted as being effective ergogenic aids to the training and racing of horses. The table below offers an overview of the global ergogenic aids ‘catalogue’ but is by no means intended to be an exhaustive list.
Ergogenic effects in horses and humans for dietary supplements marketed for use in performance horses
Proven* beneficial effect in horses Proven* beneficial effect in humans but not horses
No unequivocal ergogenic effect in either species
ß-hydroxy-ß-methylbutyrate (HMB) Creatine Gamma-oryzanol
Carnitine Dimethylglycine (DMG)
Ubiquinone (Co-enzyme Q10)
Branched chain amino acids (BCAA)
* Based on data produced from scientific trials, rather than anecdotal evidence.
Many of us will have heard of creatine in the context of nutrition and sport. It has been the great success story, efficaciously and financially, within the sports nutrition sector from the 1990s to the present. In 2004, for example, gross revenue from creatine supplement sales to sports people within North America alone was estimated at $400 million.
This success largely stems from the fact that, unusually, it is a supplement that works! Admittedly, its effectiveness varies across different sporting disciplines. It has proven especially beneficial in sporting activities of comparatively short duration, such as the athletic disciplines of sprinting and jumping, but also in sports that require very high levels of power production as in rowing, swimming and track-based cycling.
Creatine accomplishes this performance enhancement, firstly by elevating the levels of high-energy phosphates, ATP (adenosine triphosphate) and PCr (phosphocreatine), stored in muscles. Secondly, creatine can enhance the effect of training; i.e. it boosts the responsiveness of the muscles to stimuli generated by training. This is often observed as increased muscle mass that arises from elevated production of the major muscle protein myosin and from enhanced levels of localised growth factors.
The benefits of creatine supplementation in training and competition have not passed the equine world by, and a number of products are marketed specifically for horses. Unfortunately however, despite the positive claims made for these equine products they are not supported by scientific evidence. Indeed the opposite is the case. Sewell and co-workers in the UK and Essen-Gustavssen’s group in Sweden have conducted three rigorous placebo-controlled studies in horses.
No positive effects of creatine supplementation on performance were found when parameters including time-to-fatigue, high-energy phosphate depletion and lactic acid production were measured. The underlying cause for lack of efficacy in horses is due to poor absorption of creatine from the equine gut, leading to inadequate levels being attained in the muscles.
Even if a strategy could be devised to deliver creatine effectively to the muscle, some researchers are of the opinion that there would still be no effect. They form this view on the basis that in comparison with humans the horses is an elite athlete wherein the level of creatine in equine muscle is at or very near to the physiological upper limit.
Carnitine is another well-known dietary supplement widely marketed as an ergogenic aid in human sports nutrition and within the equine industry. The role of carnitine in exercise in humans and horses has been researched for almost 20 years. The biological actions of carnitine that make it central to exercise include:
Directly: transport of fats into muscle mitochondria where they can be used aerobically (oxidised) to generate ATP
Indirectly: increase aerobic utilisation of glucose to produce ATP
Indirectly: reduce lactic acid production (acidosis)
Some research does indicate a positive effect of carnitine supplementation on exercise performance in human athletes, however there are other studies that seem to indicate the opposite.
Conflicting research results have also been found for horses. Studies carried out by Foster and Harris in Newmarket during the 1990s showed that dietary supplementation could increase carnitine levels circulating in the blood, but did not appear to affect the levels in the muscles.
In 2002 Rivero and his fellow researchers at the University of Cordoba conducted a placebo-controlled study into the effect of carnitine supplementation in 2-year-old horses when used in conjunction with an intensive 5 week long training programme. Improved muscle characteristics were seen in the carnitine-supplemented group of horses, including a 35% increase in the proportion of fast-contracting (type IIA) muscle fibres, a 40% increase in the number of capillaries supplying blood to the muscle and an 11% increase in the level of glycogen stored in the muscle. After a let down period of 10 weeks most of these improvements were reversed. It was concluded that carnitine supplementation enhanced the training effect on muscles and that this could improve performance.
Despite the large number of studies conducted over the years the balance of evidence does not yet allow a consensus to be reached on whether carnitine improves performance in horses (and humans) or not. Of course this does not rule out a beneficial effect, and Rivero’s study would seem to be encouraging.
Gamma-oryzanol is not as the name implies a single substance, but is a mixture of chemicals, mainly ferulic acid esters, derived from rice bran. It has been popularised as a potent anabolic agent, i.e. a substance that promotes muscle growth leading to increased strength and speed. Gamma-oryzanol has been employed in equine and human athletes in the belief that it elicits increased testosterone production and stimulation of growth hormone. To date there is no published research describing the effects of gamma-oryzanol on exercise performance in horses, so in an effort to judge its potential efficacy we have to draw upon comparative studies in humans and other animals.
Efficacy for gamma-oryzanol is debatable, as it is poorly absorbed from the digestive tract. What is more when given to rats, contrary to popular belief, it is reported to actually suppress endogenous growth hormone and testosterone production. Research carried out in humans fed 0.5g per day of gamma-oryzanol showed no improvement in performance, nor indeed any change in the levels of testosterone, growth hormone, or other anabolic hormones even after 9 weeks of supplementation. Thus in summary, no scientific evidence exists to support the anabolic effects ascribed to gamma-oryzanol.
Dimethylglycine (DMG) and trimethylglycine (TMG)
Both DMG and its precursor TMG cannot be regarded as new supplements having been researched briefly in the late 1980s with a single research report being published.
Rose and colleagues at the University of Sydney’s veterinary department looked into the potential benefit of DMG on heart and lung function, and lactic acid production in Thoroughbreds during exercise. In this placebo-controlled trial DMG was fed twice daily to a group of thoroughbred horses that underwent a standardised exercise test at varying intensities before and after supplementation with DMG or the placebo. On completion of the trial it was concluded that DMG produced no measurable improvement in any of the parameters, and that it exerts no beneficial effects on heart and lung function or lactic acid production during exercise. Warren and co-workers following experimental evaluation of TMG as an ergogenic aid came to a similarly negative conclusion.
HMB is one of the few ergogenic aids available for use in performance horses that is supported by at least some credible science. Significantly, research developing and validating the use of HMG in horses (and farm animals) was instigated and carried forward over a number of years at Iowa State University, USA, and the concept and methodology are protected by US patents. HMB is a metabolite of leucine, one of the so-called branched-chain amino acids (BCAAs), that are themselves often touted as ergogenic aids, although there is no convincing evidence to support such a claim.
Research seems to indicate that HMB supplementation when employed in conjunction with an effective training regime can benefit equine performance in a number of ways:
Enhance muscle development and increase lean muscle mass and strength by reducing the proportion of energy needed for exercise that is derived from protein and increasing the proportion derived from fat. Reduce muscle damage (catabolism) during and after exercise and accelerate muscle repair. Some research suggests that HMB is a structural constituent of muscle cells that is destroyed under the physiological stress of exercise. Increase aerobic capacity (oxygen utilisation) in performance horses by increasing both haemoglobin and the proportion of red blood cells in the blood (haematocrit).
When HMB use was evaluated in practice under real racing and training conditions it appeared to reduce muscle damage, and to improve oxygen use by the muscles and overall performance.
Ribose is a potential new dietary ergogenic aid that began to be studied in 2002. It is a sugar that is the central component of ATP. As ATP stores are depleted during intense exercise in horses, it was thought that supplementing the horses’ diet with ribose might lessen the loss of ATP during exercise and enhance its regeneration during recovery. Kavazis and his colleagues at the University of Florida conducted two placebo-controlled studies in Thoroughbreds. In these studies ribose was fed twice daily as a top dressing for two weeks to a group of trained horses. The data from these two studies was contradictory and thus no conclusions can be easily drawn. However, two studies in humans have shown no positive effect of ribose supplementation on exercise performance. The balance of available evidence therefore suggests that ribose provides no ergogenic benefit in performance horses.
Bioavailable stabilised oxygen
An unusual ergogenic product has recently appeared that purports to be a bioavailable supplementary source of oxygen. In simple terms, it is water that is apparently treated by a sophisticated electrical process so that it becomes a super-saturated solution of oxygen. It’s described as containing about 20,000 times more oxygen than that found in average tap water. As yet, there appears to be no convincing scientific evidence for this type of product, and what is more the explanation of its action does not seem to be physiologically credible.
It is suggested that this bioavailable oxygen is absorbed from the stomach and intestine into the blood stream, however these tissues have not evolved for this purpose unlike the lungs. Even if we assume that all the oxygen from e.g. (100 mL) was taken up into the blood, the added benefit would be very small; 100 mL is roughly equivalent to 20 litres of oxygen. In comparison, an average horse exercising at racing speeds breathes in more than 2000 litres of air (420 litres of oxygen) every minute and the muscles use 75 litres of oxygen over the same period. We should also remember that for a normal healthy horse the blood is 98% saturated with oxygen.
The future direction for nutritional ergogenic aids is extremely difficult to predict as any new developments are likely to mirror advances in our detailed understanding of the basic biochemical and physiological processes that underpin exercise performance. In the past, much of the impetus for equine research in this area developed from human sports nutrition and this is likely to continue in the future. A closing comment to put all of this information into context would be that whilst one should always seek a feasible mechanism of action and proof of efficacy for new products, small numbers of horses used in trials and difficulties in measuring ‘performance’ means that science will not always come up with the absolute answer.