It's not just about how far and how fast. It's also about how a horse depletes its glycogen stores. And a rider can make a difference.
28 July 2012
For today’s technical look at Monday’s eventing cross-country effort, we turn to Dr David Marlin, Britain’s sport horse science specialist who played such key roles in helping horses at the Atlanta and Beijing Olympics. He offers his insight into the Greenwich Park course, saying that its hills and twists may use a horse’s energy store in ways that are very different from a “big gallop” cross-country course.
From Dr Marlin:
During the eventing cross country on Monday at Greenwich Park, 90 percent of the energy the horse will use, whether for galloping between the jumps or the jumping efforts themselves, will come from their muscles’ storage of glycogen. By the end of the course, the horses are likely to use around half of their muscles’ glycogen store.
So why should the rider be looking to conserve the horse’s muscle glycogen?
The bad news about glycogen is that it will take 24 to 48 hours to fully restore the muscles’ supply. As a general rule, the more glycogen a horse uses on cross country, the longer the recovery, the lower the level for show-jumping and the lower the force generated at the show-jumps.
In simple terms: the more you use your horse up on the cross-country, the worse they are likely to show-jump.
As far as recovery time, the later your cross-country run and the earlier you show-jump, the greater the disadvantage to your horse, as it will have had less time to recover. So the ideal scenario would be to have an early cross-country start and a late show-jumping time.
So what factors increase how much muscle glycogen is used on the cross-country? It’s a pretty long list. The faster the horse is ridden, the more jumping efforts and the more changes of pace a horse makes will mean they use more glycogen. Other factors include the going (soft going uses more glycogen), and the weather (the warmer it is, the more glycogen is used).
The terrain (hills!) also has a big impact. Going up hills may double the amount of glycogen used compared with the same speed on the flat. And cantering/galloping through water is also very hard work and increases glycogen use. Failure to warm-up adequately and warming up for too long will also mean more glycogen is “wasted”.
So what will riders have to contend with on Monday and what would be the ideal strategy?
As far as the weather, Monday should be ideal with respect to temperature and humidity: partly cloudy, 20°C (68°F), light wind and no rain.
Greenwich Park has some significant hills that feature in the cross-country course. The aim in dealing with the terrain should be to ride for constant effort not constant speed. Event riders work on minute markers: i.e., knowing where they should be on the course after 1, 2, 3 minutes etc. This works fine for flat or nearly flat courses when riding at a constant pace.
However, if a horse is travelling at a steady pace on the flat and then the rider asks the horses to maintain that pace as they come to a hill, the effort goes up considerably. This will have several implications. Firstly, there may be a serious implication for the horse’s ability to jump the next obstacle half way up or at the top of a hill due to the increased effort and fatigue.
Secondly, the rate of glycogen use will have increased dramatically.
Finally, the horse may not recover from this sudden increase in effort and will fatigue earlier, being more likely to make jumping errors and struggling to make the time.
Riding for constant effort and not constant speed means actually galloping faster on the flat or slightly downhill sections of the course and easing off going uphill, i.e., reducing speed.
It is not likely that the course designers and FEI will have adjusted the time to take into account the terrain. They work on a distance and a time irrespective of the terrain. The problem is the effort required for a 10-minute cross country track over a course with some hills could mean 20-30 percent more energy required than the same track on flat terrain.
The implication is that if you ride on minute markers, you are likely to tire your horse early on in the course. If you ride to make the time, your horse may be very tired. If you ride by feel, then you are unlikely to make the time.
The bottom line is that this course will take more out of the horses than a normal Olympic cross-country course.
Another factor in the Greenwich course that will have an impact on how much glycogen is used is the turning. The twisty course will require riders to slow down and speed up to take the turns safely. The problem is that just as in a car, deceleration and acceleration use up considerable amounts of energy (i.e. glycogen).
This cost also applies to the jumps themselves. In order to make up time lost in slowing down into a jump, riders often push their horses quite hard on the way out, wasting energy.
So the ideal strategy for Greenwich park? Warm-up for 20-30 minutes. The warm up should start with 10 minutes walking, 5-10 minutes trotting and then a few minutes of cantering, followed by some jumps and a short burst of gallop around 5 minutes before the start.
The pace out of the start box should not be slow but should not be flat out. The ideal pacing will appear smooth–with no obvious sudden increases or decreases in pace–to conserve energy. The pace should be faster on the flat and straight parts of the course, reducing through turns and up hills. The brave riders may even want to push on downhill as the least energy used is on a slight downhill slope.
Through jump complexes the changes in pace should also be as smooth as possible.
I predict that those inside the optimal time will either have tired out their horses with potential negative implications for the show jumping or will have ridden a brilliant round based on feel.
There may even be the odd rider or team who is aware of how going, turns, jumping efforts and terrain all interact and throw away their minute markers!David Marlin PhD is co-author of the textbook Equine Exercise Physiology. An internationally-recognised expert in the field of equine and sport science, he has pblished over 200 scientific papers and conducted research within the sport of eventing to improve safety and welfare of horses during competition. He is a well-known speaker and is advisor to the British firm,Science Supplements.