Page 15 - The Game October 2006

Your Thoroughbred Racing Community Newspaper The Game, October 2006 15
MILKSHAKES AND RED HERRINGS
Equine Health
by Karen Briggs
Dave Landry Photo
Health & Nutrition 2006
Special Advertorial Feature
Right about now I’m feeling like I missed a memo.
In another life, I worked as an equine nutritionist for a large Ontario feed company. I was responsible for making feed recom- mendations for all manner of equine athletes, from Percherons to ponies, so I had to have an understanding of basic exercise physiology and what feeds supply the raw ingredients to fuel a horse’s muscles to do work.
Conventional wisdom, when it came to energy pathways, was that there are two main ways to fuel muscles: aerobically and anaerobically. Aerobic metabolism was considered a ‘clean burning system’, which used oxygen to burn the energy substrate, ATP (adenosine triphosphate, as you no doubt recall from your high school biology classes), which is in turn derived from carbohydrates and/or fatty acids supplied by the horse’s diet. The byproducts of this energy pathway were water and carbon dioxide, harmlessly expelled from the body via the lungs and the excretory systems. It was to a horse’s advantage to work aerobically as long as possible · but eventually (so sayeth the gospel), the readily available ATP would run out. Then, if the horse had to continue to exert himself, he would have to draw on the anaerobic lactic energy pathway, a sort of metabolic ‘super- charger’, to augment or replace the aerobic fuel-burning.
The anaerobic lactic system, as I was taught, and as I told my customers, was far less efficient a system than aerobic metabolism and depleted glycogen (an ATP source) rapidly. It also had a toxic byproduct called lactic acid, or lactate, which was thought to be the trade-off for that second wind the pathway provides. Lactic acid (again, according to conventional wisdom) was usually swept away from the muscles by the bloodstream, but if a horse is exercising at high intensity, the rate of production might exceed the rate of removal, resulting in lactic acid buildup in the muscles. The point at which lactic acid began to build up was called the anaerobic threshold (usually occurring at a heart-rate of about 150 beats per minute), and until recently it was considered a major contributor to fatigue and subsequent performance reduction.
Lactic acid was an equine athlete’s arch enemy. Or that’s what everyone believed for decades.
So it’s quite a shock to discover that we who feed and train horses have been a little slow on the uptake, and that in the world of human exercise physiology, it’s been accepted for more than a decade now that lactic acid is actually an ally rather than an enemy. That it’s an energy SUBSTRATE rather than a spanner in the works. That it is, in fact, a favoured fuel of the mitochondria in muscle fibres, and that progressive conditioning programs can as much as double the mass of those mitochondria so they can use lactic acid more efficiently. That a muscle awash in lactic acid is, in fact, one with a plentiful fuel supply.
Whoa.
The belief that lactic acid was responsible for muscle fatigue is now being called ‘one of science’s classic mistakes’. Its origins lie in a study by a Nobel laureate, Otto Meyerhof, who in the early years of the 20th century cut a frog in half and put its hind legs, no longer privy to blood circulation or oxygen, in a jar.
Then he applied electric shocks to the legs, but after a few twitches, the muscles stopped contracting. When Meyerhof examined the muscles, he discovered they were bathed in lactic acid and concluded, erroneously as it turns out, that lack of oxygen supply to muscles leads to lactic acid buildup, which leads to fatigue of the muscles.
It took George A. Brooks, a professor in the department of integrative biology at the University of California/Berkeley, to shoot holes in Meyerhof’s logic, decades later. But when Brooks first conducted studies which showed rats burned lactic acid as an energy source, in the late 1970s, he was ridiculed. It took decades of persistence, and repeatable lab results, before the gospel of lactate began to be seriously questioned. Eventually, however, his evidence was acknowledged as over- whelmingly convincing. Not only is lactic acid an energy substrate, it’s the preferred energy source for nerve endings, cardiac and skeletal muscle, and even the brain.
Mike Lindinger, Ph.D., an associate profes- sor in the department of Human Health and Nutritional Sciences, and an instructor in the Equine Science Certificate program at the University of Guelph, calls lactate a red herring. “It irks me,” he says, “that we still have elite athletes talking about pushing back their anaerobic thresholds, when that’s really been proven to tell us very little about what’s happening in the contracting muscles. And the word still hasn’t gotten out in the horse industry.”
As for the idea that lactic acid causes muscle soreness, that doesn’t make much sense either. Studies have demonstrated that lactic acid is swept from the muscles within an hour of exercise - and muscle soreness generally appears a day or more later. The timeframe doesn’t compute.
So what DOES cause fatigue in equine (or human) muscles? Mostly, Lindinger says, it’s cytokines, small proteins that act as chemical messengers between cells. They react to nerve endings in the muscle, causing pain. Imbalances in the levels of sodium and potassium ions across cell membranes also have something to do with it. And damage from free radicals can contribute in horses exercising over the long term. But there’s no single super-villain to slay.
This information likely won’t have a lot of impact on the way we condition or feed race- horses because although the reasoning behind it might have been faulty, trainers have already figured out what works in terms of improving performance. But it SHOULD, by all rights, put an end to a practice which has been based on dubious logic all along: milkshaking. The idea that dosing a horse with large amounts of an alkalytic substance such as sodium bicarbonate will ‘buffer’ a system suffering from too much lactic acid buildup · and thus, delay the onset of fatigue, is pretty much rendered ridiculous once we accept that lactic acid is our friend.
Cal Stiller DVM notes that high levels of sodium bicarbonate in the horse’s system might still have a performance-enhancing effect, by virtue of the chemical’s ability to help haemoglobin ‘donate’ its oxygen molecules to firing muscles. But Salix (aka Lasix), which is legal, provides the same effect, making milkshaking a red herring, indeed.
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