Marathon training: race pacing for endurance athletes

Owen Anderson provides an insight into how Kenyan runners pace themselves during distance running events

Most endurance athletes can achieve their best times by 'negative-splitting' their races (i. e., by competing the second halves of their competitions faster than their first halves). For runners, this appears to be true at all distances ranging from the mile up to the marathon, and the optimal timing strategy seems to be about 50.5-49.5 to 51-49, which simply means that the first half of the race should take about 50.5 to 51 percent of total time and the second portion 49 to 49.5 percent.

So why do the Kenyans go out so fast? Although the race tactics of Kenyan runners vary from competition to competition and from runner to runner, the elite Kenyans are known for starting their races incredibly fast and daring other runners to stay with them. This seems to be particularly true in cross country, a sport in which the Kenyans go out so fast that the possible winners and also-rans are separated from each other within the first 800 metres or so of the race, even in a 12-K competition. If you're a non-Kenyan cross-country runner, you must stay at least somewhat close to the lead pack if you have any hope of finishing among the top 10 competitors. In other words, you must go out very fast and stray away from the optimal strategy of negative-splitting.

I have been fortunate enough to witness many great races over the years, but one of my most vivid racing memories is from the first World Cross-Country Championship I ever attended - the 1991 event in Antwerp, Belgium. In the first race of the day, the junior women's 4.435K, two young Kenyan women - Lydia Cheromei and Jane Ekimat - swept out of the starting area so fast and left their competitors so far behind that I thought they were doing some unaccompanied pre-race strides, instead of actually beginning the competition.

After 400 metres, they had opened a 50-metre gap between themselves and their closest competitors; I conservatively estimated that their first 400 took 63 to 65 seconds. After 800 metres, the incredible Kenyan duo appeared to be over 100 metres clear, and they held this margin for much of the rest of the race. A late charge by American phenomenon-at-the-time Melody Fairchild closed the margin dramatically on Ekimat, but Cheromei, in spite of her outrageously positive-split race, managed to continue to build her lead until the very last portions of the competition and finished 29 seconds ahead of Fairchild and 21 seconds in advance of Ekimat. Both Kenyans had shunned scientific wisdom and had run great 'positive-split' races, with their first halves much faster than their seconds. Fairchild was more prudent and scientifically in-vogue, and that kept her from winning or placing.

So why do they do it?

The Kenyans' rapid starts defy our golden negative-splitting principle, so we must ask what is going on. Is negative-splitting not as great as it's cracked up to be, or are the Kenyans doing something which allows them to evade the immutable laws of exercise physiology?

To answer these questions, a good starting point would be to examine the mechanism underlying the negative-split principle. Basically, exercise scientists like to argue that positive-splitting - starting out fast - often leads to sub-optimal finishing times because the fatigue which accrues from beginning quickly takes a serious toll in the second half of the race, slowing an endurance athlete rather significantly. On the other hand, negative-splitting leaves one fresher for the second half of the race, and although fatigue can build to nearly insurmountable levels as the finish line nears, a competitor who knows that the finish line is close-at-hand can cope with the fatigue more readily.

Basically, if an endurance athlete negative- rather than positive-splits a race, the total time spent dealing with deadly fatigue - usually the last one-eighth to one-quarter of a race (with negative-splitting) instead of the last five-eighths to three-quarters of the competition (with positive splitting) - is much less; therefore, there is a less dramatic slowing effect when one negative-splits. To put it another way, the cautious start, with its 'lost' time associated with the lukewarm pace, is more than made up for by the resulting ability to finish the race very strongly. In contrast, the fast start, with its time gained, is negated by the numbing fatigue which holds sway through much of the race.

Those pesky little hydrogen ions

Physiologically, exercise researchers like to point to hydrogen ions as being the key source of the extra fatigue associated with going out too fast, and that makes good sense. During the early stage of a race, heart rate has not yet reached its highest point, blood flow to the leg muscles has not yet peaked, and thus oxygen-dependent energy creation within the leg muscles has not yet reached its top plateau. As a result, oxygen-independent energy-creating processes are fairly important, and a fair amount of lactic acid is produced.

Lactic acid can dissociate into lactate and hydrogen ions; the lactate itself is a wonderful compound, a tremendous source of energy for muscle cells. The hydrogen ions are also a natural constituent of muscle cells which are engaged in the intense work of racing, but the potential problem associated with the hydrogens is that if enough of them build up within the muscles, intramuscular pH drops (the muscle-cells' interiors become more acidic), and it becomes more difficult for the cells to contract forcefully (i.e., fatigue ensues). Acidification of muscles lowers muscular power production and produces fatigue.

Bear in mind that there are several different ways that this fatigue-inducing acidification process can be resisted. One technique, of course, is to start races somewhat slowly. As race beginnings become more moderate, oxygen-independent energy creation becomes less important, hydrogen-ion production is lowered, and the extent of acidification is diminished. Of course, the only problem with this strategy is that the sensible racer may see Kenyans (or key competitors) disappearing far off into the distance as he/she keeps hydrogen ions under control. The race always goes to the swiftest, not to the best hydrogen-ion minimizer. If someone else can start very fast and then hang on, you may be in a heap of trouble from a competitive standpoint, even though you are prudently negative-splitting and perhaps setting a nice PB for yourself in the process.

Fortunately, there are other ways to deal with the troubling hydrogens when you compete, in addition to being a milk-toast race starter. For one thing, as lactate and hydrogen ions build up in your cells as you move along briskly, a 'co-transporter' system pushes both of them out of your muscle cells, thus preserving relative pH peace by preventing hydrogen ions from accruing too extravagantly. Endurance training improves the capacity of this co-transport system, but research has yet to tell us whether intense or high-volume training is the superior way to optimize co-transport function (the appropriate investigations simply haven't been completed yet in humans). Interestingly enough, hypoxia (exposure to altitude) has little effect on the system. This is a bit surprising, since you might expect altitude residence or altitude training to increase oxygen-independent energy creation and hydrogen-ion concentrations and thus force muscle cells to adapt by boosting their lactate-hydrogen co-transport capability.

However, the lactate-hydrogen transportation system is not the only way that muscle cells can prevent acid build-ups during exercise. There is also something called the Na+/H+ exchange system, which basically pumps hydrogen ions out of muscle cells and brings sodium ions in to replace them (lactate does not participate in this process). Like the hydrogen-lactate transportation system, this exchange consumes energy, and the Na+/H+ exchange appears to be critically important during exercise.

In one study, subjects carried out moderate-intensity knee-extension exercise which caused a net outflow of lactate and hydrogen ions from their leg muscles. After about 10 minutes of leg work, they added high-intensity arm exercise to their leg exertions, a combination which caused hydrogen ions to continue to flow out of the leg muscles even though lactate dynamics in the legs changed from a net release to a net lactate uptake. In effect, the leg muscles were taking up the lactate given off by the arms at a higher rate than they were releasing lactate, and the net hydrogen-ion release from the leg-muscle cells (and control of acidity) was produced not via lactate-hydrogen co-transport but by the Na+/H+ exchange system ('Dissociation between Lactate and Proton Exchange in Muscle During Intense Exercise in Man,' Journal of Physiology, vol. 504, pp. 489-499, 1997). As it turns out, research indicates that this crucial Na+/H+ exchange system is unaffected by endurance training at moderate to low intensities but is dramatically enhanced by highly intense training. That certainly is what one would expect, since intense running (or cycling, swimming, rowing, or cross-country skiing) produces high hydrogen-ion concentrations and forces muscle cells to develop some way of dealing with the hydrogens if fatigue is to be thwarted. In contrast, moderate to low intensities of exercise induce small changes in hydrogen-ion levels and pH and apparently don't force muscle cells to upgrade their Na+/H+ exchangers.

Interestingly enough, research also reveals that 'hypoxic treatments', i. e., exposure to reduced oxygen concentrations, as would be the case at moderate to high altitude, also tend to spike the Na+/H+ processing capacity. This is also logical, since reduced oxygen would produce an uptick in oxygen-independent energy creation and thus magnify hydrogen-ion concentrations and lower pH.

Come back, little Kenyans

Re-enter the Kenyans, who train more intensely than anyone else in the world and are also - by and large - born and bred at altitude. Their scalding training no doubt optimizes their Na+/H+ exchange systems, forcing their muscle cells to learn to pump out hydrogen ions at high rates and bring the sodium on in. Their altitude birth and breeding produces the same effect, and thus the Kenyan who starts a race with alarming speed is in a far different situation than the athlete who trains less intensely and/or does not reside at altitude.

With their powerhouse Na+/H+ systems, the Kenyans can amplify hydrogen-ion levels within their muscles by roaring away from the starting line - and yet suffer little because their Na+/H+ pumps clear up the mess quite quickly. The high-mileage (moderate-intensity) and/or sea-level runner who tries the same strategy does quite well for the first third of the race - but then bogs down in a quagmire of fatigue resulting from those lingering hydrogens. Positive-splitting is truly a Kenyan thing, but it can work for any endurance athlete who develops an enormous Na+/H+ exchange potential, either through high-intensity training or altitude residency (or preferably both).

To make this article complete, we should mention briefly that there is yet another mechanism which helps control intramuscular acidity. This is the buffering capacity of the muscles, i. e., the ability of muscle cells to 'sop up' hydrogen ions by forcing them to combine with chemicals within the muscles. These chemicals then cling rather avidly to the hydrogens, preventing them from jumping back into the intramuscular 'bath' and lowering pH.

Bicarbonate is a wonderful natural buffer, both within muscles and in the blood (its fine action explains why exercise scientists have long been interested in sodium bicarbonate as a potential performance aid). There are also proteins within muscle cells which help resist drops in pH; one of the most notable of these proteins is carnosine (there'll be more on this compound and the potential merits of carnosine supplementation in a future edition of PP). Research indicates that the buffering capability of muscles can be increased by as much as 38 per cent in as little as eight weeks, and that very high-intensity training induces more positive change in buffering ability than does moderate- to low-intensity work (surprise, surprise!).

Summing up

So what's the bottom line? Truthfully, the research favouring negative-splitting has been carried out with 'normal' endurance athletes, not Kenyans. These normal individuals have probably trained in routine ways, with an emphasis on volume rather than quality of training. In addition, most of them have not resided at altitude. As a result, they have had mediocre Na+/H+ exchange systems, and it is not surprising that they did best by negative-splitting.

In contrast, the Kenyans are probably the best Na+/H+ exchangers in the world, and as a result they are the world's best positive-splitters, too. We can't say for sure that positive-splitting is the best strategy for the Kenyans (i. e., that it helps them produce their best-possible times) but can simply state that the hard-training, altitude-dwelling Kenyans can carry out positive-splitting more effectively than anyone else in the world - and often use the strategy to devastate their opponents.

We also can't go so far as to recommend that you change your basic race strategy from negative- to positive-splitting, but it certainly does make sense to progressively expand the intensity of your training. By doing so, you'll develop a more Kenyan-like Na+/H+ exchange system, and you'll be much better at handling very fast race starts, in case you accidentally go out too fast or just want to 'lose' or intimidate an opponent early in a race. It makes sense, too, that a superior Na+/H+ exchange will enable you to more effectively carry out within-race surges, whether they occur in the early, middle, or late stages of a race, and will also improve your ability to handle hilly race courses with aplomb (blasting up a hill during a race can turn the insides of your leg muscles into hydrogen-ion 'baths', but if your Na+/H+ exchange is working well you can dispose of those hydrogens quickly).

An upgraded Na+/H+ system will also help you resist interval-workout 'fades' (i.e., interval sessions in which your last few work intervals are of significantly lower quality than your initial ones). This resistance to fading will certainly amplify your fitness over time. The bottom line is that if you can handle your hydrogens more efficiently, you will be better able to resist fatigue - and you'll be able to start and finish your races more quickly.

Owen Anderson