Female Endurance Running: Why is it that women don't slow down as much as men do when they go for the long one?

by Owen Anderson for peak performance

If a man and woman cross the finish line of a 10K race at the same time, you can usually be sure of one thing: the woman will beat the man if they run a marathon together, in spite of their similar 10-K times.

The simple truth is that women slow down less than men as race distances increase This trend toward female superiority as races lengthen is especially true when one moves to very long, back-breaking competitions. For example, research has determined that female runners with the same 10-K times as a group of men will beat those men by more than 30 minutes if they are challenged to a 90-K race.

Surprisingly (to those accustomed to thinking about male distance-running superiority), studies carried out in South Africa indicate that women can beat men with similar VO2max and running-economy values - as long as the distance is greater than about 24K. Below that distance, the sexes are evenly matched - or else males tend to win when VO2max and economy are the same. Strangely enough, exercise scientists, who normally can explain even the most unusual aspects of endurance exercise, haven't been exactly sure why this is so.

To learn more about the phenomenon, scientists at the University of Witwatersrand Medical School in Johannesburg, South
Africa, recently compared 10 experienced female runners with 10 proficient males, analysing their times at selected 10-K, half- marathon, marathon, and 90-K races. Each subject was tested for VO2max, running economy, lactate threshold, and percent body fat. Training histories and psychological tests (the Profile of Mood States, or POMS, and Personal Motivation, or PM) were also completed by each runner. The 10-K, half-marathon, and marathon races were all held at an altitude of 5900 feet (males and females competed together in the same races), while the 90-K affair (the Comrades Marathon) was run at sea level.

The men and women were alike in many ways. Prior to the study, the females normally ran the marathon in an average time of 3:36, while the males did it in about 3:39 (this difference wasn't statistically significant). Average age (34 years) and running economy were identical, and both males and females trained about five times a week, had been training for three years, and covered about 12K per workout. Average intensity of training (about five minutes per kilometre) was also equivalent in the two groups.

In spite of that, the males held some advantages. Fat-free mass was 33 per cent greater in the men, percent body fat was 27
per cent lower (16 versus 22 per cent), and VO2max was around 6 per cent higher (54.6 versus 51.5 ml/kg.min). Note that in spite of these edges, the male marathon times were no better than those of the females.


How did they do in races?
Males ran a little faster than females in the 10K, running at an average speed of 233.2 metres per minute, compared with 227.4 for the women (10-K times of 42:53 and 43:59, respectively). And males were still a nip faster in the half-marathon, too, at 213.8 metres per minute against 211.8 (1:38:42 versus 1:39:37).

In contrast, females tended to be a bit faster in the marathon, coursing along at 194.8 metres per minute, compared with 192.6 for males (that's 3:36:38 versus 3:39:06). And in the 90K, it wasn't even close: females sizzled along, relatively speaking, at 171 metres per minute, while males were almost 10-per cent slower at 155.2 metres per minute. The males were almost an hour behind the females in the Comrades race!

The Witwatersrand researchers took a close look at physiological and psychological data in hopes of finding an explanation for the male fade-outs. Basically, they learned that the females worked harder than males at all race distances. For example, female runners moved along at an intensity of 84.4% VO2max in the 10K, while males were content to cruise at 79.9%. In the half-marathon, the difference was 78.7 to 73.5%. In the marathon, it was 73.4 to 66.3%. And in the 90K, the gap widened to 59.8 versus 50.2%. In each case, the women were working at higher percentages of their maximum capacities!
Actual power outputs showed a similar trend. While males and females expended energy at similar rates in the 10K, females burned about 3 per cent more calories per minute in the marathon, and the difference in rates of energy expenditure reached epic proportions in the 90-K effort, as females put out 10.4 Watts of energy per kilogram of body weight while males shuffled along at 9.2.

What's the mechanism for this? Why do males begin to stumble as race distances increase? Differences in VO2max, running economy, and/or training aren't the answer; after all, those variables were nearly identical in males and females in the South African study (in fact, the males had slightly higher aerobic capacities). Clearly, the female-male performance difference is the result of females' abilities to use a higher fraction of VO2max as race distances increase (which can more than offset an inherent VO2max disadvantage), but that still doesn't explain why females are better able to put the pedal to the metal in long races.

Differences in blood glucose are not the answer; blood-sugar levels were the same in males and females. Differing rates of dehydration are also not the reason; males and females dehydrated to the same extent in the longer races.


Is it in the fat - or in the brain?
Variation in rates of fat burning might be a factor: males had much higher blood-fat levels at the end of the 90-K exertion. Although this might seem to give men an advantage (more fat means more fuel), it might actually reflect the lower rate of fat metabolism in male runners (the less fat that is burned, the more is left floating around in the blood, to put it in lay terms). The advantage of fat utilisation is that it can prevent muscle-glycogen wipeouts, but in long races like the marathon and 90K any fat- burning 'edge' for females could be taken away if males judiciously ingested carbohydrates during the race.

It's possible that females generally have a psychologically stronger disposition which allows them to 'work at the edge' of numbing fatigue more effectively than males in multi-hour physical struggles. However, the Witwatersrand researchers found no gender-related differences in psychological fortitude or personality traits. The Profile of Mood States test was administered under normal resting conditions and then immediately after the 90-K race to see if personality changes varied between the sexes in response to extreme exercise; however, this test revealed that males and females showed decreased anger and vigour and increased fatigue and confusion to the same degree during the incredibly difficult 90-K run.

The Personal Motivation test was also not revealing. This exam is actually composed of two parts - goal directedness and personal excellence. Individuals who score high on goal directedness tend to be very intent on achieving personal goals and persevere without hesitation in spite of adversity. People who do very well on the personal excellence part of the test believe that fate is entirely in their hands and are also convinced that goals will be achieved by taking the initiative rather than leaving it to luck. Obviously, all of these personal characteristics could have a profound effect on athletic performances, but the Witwatersrand researchers found no male-female differences in any of the characteristics.


What about oestrogen?
Could the key female sex hormone - oestrogen - somehow be responsible for female resilience in long-distance racing? Could it be true to say that 'When the going gets tough, the tough have oestrogen on their side' - or something like that?
Most people aren't aware of oestrogen's possible role in improving performance, preferring instead to focus on the muscle-building potential of the male chemical counterpart - testosterone. However, interest in oestrogen's potentially ergogenic role dates back quite awhile - and seemed to reached a peak in the former 'Soviet-bloc' countries in the 1970s and 1980s, when Russian and Eastern-European women began to dominate Olympic and World-Championship competitions.

Observers of the Eastern-European athletic scene subsequently claimed that some female athletes participated in the practice of deliberately becoming pregnant at a key stage of training - usually just before a major competitive period. This nightmarish scheme was believed to be effective in enhancing performances, partially because of the hormonally related 20 to 30-per cent increase in blood volume which can occur during the first few months of pregnancy.This plasma growth was thought to boost performances by providing greater blood flow to the skin for cooling and superior movement of fuel and oxygen to the muscles. In the horrendous culmination of this 'training strategy', the females would abort their foetuses after about six to eight weeks - before the increased weight gain associated with foetal growth actually began to slow them down.

Although the expanded blood volume was believed to be ergogenic, another underlying thought was that the hormones associated with early pregnancy, including oestrogen, could enhance muscle growth (just as they would encourage foetal development) and also protect muscles from damage during extremely high-quality training. Although oestrogen is usually viewed as a hormone which merely maintains the health of the female reproductive system, encourages breast growth, stimulates release of an egg cell during menstrual cycling, and protects the linings of blood vessels, it is also a fairly powerful 'anabolic' (tissue-building) hormone.

For instance, oestrogen is known to dramatically stimulate growth of the uterine endometrium, the inner lining of the uterus. While it's true that the endometrium does not play a key role during endurance exercise, oestrogen also increases 'calcium binding' in 'smooth' muscle tissue (a unique kind of muscle found in the walls of blood vessels and internal organs), an effect which should greatly magnify the force of muscle contractions. Oestrogen's effects on skeletal muscle (the type of muscle which moves you around as you run, swim, ski, or cycle) are rather poorly known (in a male-dominated scientific world, one would expect this to be true), but this muscle-stimulating mode of oestrogen action does make one think of the female runners who can work at 60 per cent of maximal during ultramarathons, while males with equal aerobic capacities are stumbling along with miserly power outputs of only 50 percent of max.

Oestrogen and muscles
Actual research into oestrogen's effects on muscles and exertion first came to the forefront in the 1970s, when investigators at various universities began to discover that when oestrogen was added to animal feed, the animals grew larger and had greater muscle mass. This came as a bit of a shock, since it was believed that oestrogen fattened - rather than beefed up - living organisms, but the observation was repeated in literally hundreds of different studies.

Basically, researchers were able to show that the addition of oestrogen to the diets of cattle or sheep could hike weight gain by about 15 per cent and boost 'feed efficiency' (the degree to which ingested food is actually transformed into new tissue) by around 12 per cent. As mentioned, these weight gains were produced in animals which ended up with relatively more muscle and less fat, compared to cattle or sheep who grazed without oestrogen additives.

What was notable about these studies was that oestrogen seemed to produce a decline in blood levels of amino acids and in blood and urinary concentrations of nitrogen, effects which basically meant that oestrogen was either stimulating muscles to synthesise protein at greater rates or else protecting the proteins which they already contained more effectively. Oestrogen-fed animals also did a better job of holding on to calcium and phosphorus, two minerals which are critical for muscle function. Overall, experts claimed that adding oestrogens to cattle feed would provide the United States with 135 million (!) extra kilograms of animal protein per year, without any increase in what the animals actually ate! It was as though oestrogen was behaving just like its male counterpart, testosterone (of course, most people aren't aware that oestrogen is formed from androgens in the ovaries and so is not very chemically dissimilar from its hormonal brother).

And a critical piece of information was that increased oestrogen boosted blood levels of 'growth hormone', an extremely important chemical released by the pituitary which stimulates tissue growth, enhances fat degradation, and protects muscle cells from breakdown. In fact, scientists discovered that one could either inject animals with growth hormone or simply place oestrogen in their feed; the end results were fairly similar.

And as you might guess, the tissue-building effects of oestrogen were usually observed in female cattle, but not in males. In fact, when bulls were given oestrogen they began to get fat and grow breasts, instead of bulking up (that's one of many reasons why American beef herds aren't all charged up on oestrogen right now). However, young, sexually immature bulls did grow like wildfire when given oestrogen supplements.


Muscle protection
That's all very interesting, but the key effect of oestrogen is probably not to enhance muscle growth but rather to protect muscles from damage during strenuous exertions and thereby boost recovery rates during rigorous training. Studies have shown that females regain muscle strength more quickly than males following very hard, muscle-damaging workouts.

How can oestrogen preserve muscle function? Well, since about 1986 scientists have known that oestrogen has unique 'antioxidant potential', which basically means that it can shield cell membranes (including muscle membranes) from 'peroxidation reactions'. Peroxidation is serious; it can destroy membranes and ultimately lead to the destruction of muscle cells themselves. Since tissue-damaging peroxidation reactions are stimulated by endurance exercise, it's easy to see a mechanism by which oestrogen could promote muscle preservation and recovery during tough training. Oestrogen's exact modus operandi in protecting membranes isn't known, although it has been established that muscle membranes do contain receptors for oestrogen.

In fact, some studies have suggested that oestrogen and its related compounds are more potent antioxidants than the highly touted vitamin E. In addition to giving cell membranes a boost, oestrogen is also thought to protect against the peroxidation of LDL-cholesterol (aka bad cholesterol), an effect which may at least partially explain the lower incidence of heart disease in females, compared to males. Studies have shown that therapeutic doses of oestrogen significantly reduce the incidence of and mortality from cardiovascular disease, as well as chest pain and blood-vessel blockages in postmenopausal women.


Oestrogen in the athletic arena
What about oestrogen and athletic activity? When male and female rowers recently embarked on an extremely challenging 30-day training period, males exhibited significant signs of membrane peroxidation (determined by examining blood levels of chemicals produced by peroxidative processes), while females did not. In addition, when male rats become vitamin-E deficient, they respond to training very poorly and suffer from reduced exercise capacities, while female rats low on E tend to get along just fine, as long as oestrogen levels are okay. Similarly, high-intensity exercise depletes muscle vitamin-E levels in sexually immature animals but not in sexually mature females with normal oestrogen levels, another indication that oestrogen operates in muscles as an antioxidant and protects them from damage during strenuous training.

And it's tempting to think that the female advantage in ultra- competitions may operate in this way: during the race, muscle membranes become progressively more damaged, but to a lesser extent in females, compared to males. In addition, mitochondrial membranes and a membranous network inside muscle cells called the sarcoplasmic reticulum begin to break down. As healthy calcium ebbs and flows between the reticulum and the contractile proteins inside muscle cells, the cells alternately relax and contract. If the reticulum becomes torn and leaky, muscle power decreases. Could oestrogen-induced preservation of muscle membranes be a reason why exercise intensity during muscle-damaging ultras plummets from 60% VO2max in women to just 50% in men?. We've put that thought in the form of a question, since the phenomenon hasn't actually been tested yet.

Does oestrogen also have any direct effect on muscle force per se? Well, yes. For example, females generally experience a fairly precipitous loss in muscle strength after they have gone through menopause. This decline is not necessarily the result of muscle atrophy (the actual loss of muscle tissue), because it is also apparent if muscle force production is expressed per unit of muscle cross-sectional area. However, studies carried out at University College in London reveal that this drop-off in force can be prevented when post-menopausal women are given oestrogen therapy, indicating that oestrogen may have a fairly direct effect on force production in muscles. As an aside, males don't experience a 'testopause' which is quite as dramatic as the female menopause. As a result, they aren't hit with a similar decline in muscle strength per unit area until they reach the age of 60 or so.


Preventing long-distance slowdowns
Will male bodybuilders soon begin to worry about being too oestrogen-poor and begin injecting themselves with oestrogen in order to bulk up and enhance their ability to recover from harsh training? Since they're wimps when it comes to injections, will long-distance runners soon be sprinkling oestrogen on their breakfast cereal in hopes of improving their marathon or ultra-marathon times? Well, amazingly enough, scientific studies have shown that - at least in rats - males treated with oestrogen before embarking on two-hour runs do experience less muscle damage. This overall 'oestrogen-stacking' scenario is not too likely, however, bearing in mind the swagger of machismo - and the fact that the experimental bulls got fat instead of muscular after taking oestrogen. But we shouldn't be at all surprised to see the girls winning and placing high in ultra-race competitions and outdistancing those male runners who can beat them rather handily in 10Ks. As the South African research has shown, females can dominate males in such longer races, even though the males have greater aerobic capacities and faster 10-K times.

We don't know whether this is because oestrogen pushes muscle metabolism toward fat oxidation during exercise, an effect which conserves glycogen, or if it happens because oestrogen preserves strength and protects muscles so well during high-mileage training and actual marathon and ultra-marathon racing. The bottom line is that females certainly tend to outwork males in such events, moving energetically along at 73% of VO2max in marathons, versus 66 to 70% for males, and at about 60% of their VO2max in ultramarathons, while males crawl toward the finish line at just 50%. of maximum.

If you're a male - or female - who tends to slow down too much when you run the marathon, what can you do to prevent it? Focusing more heavily on long runs in training is not the answer; in fact, it's one of the key causes of marathon slowdowns. For example, most people who run the 10K in 40 minutes prepare for marathons by doing a lot of running at about eight-minute per mile pace. That's a big mistake!
You see, if you can run a 10K in 40 minutes, you should be able to run a marathon in about 3:07 (we get the 3:07 by multiplying 40 by 4.667, the 10K-to-marathon conversion factor). That's a pace of 7:08 per mile. Going out and running lots of 15- to 20-milers at about eight minutes per mile, the usual gambit, is going to enhance your ability to run your marathon at eight-minute pace, not at 7:08 tempo. Those long runs are fine for general strength, aerobic development, and calorie burning, but your marathoning will get a greater shot in the arm if you focus instead on gradually increasing the distance you can run at your goal speed, which in this case is 7:08 velocity. Simply start with two to three continuous miles and gradually progress until you can cover 12 or 13 miles at your goal pace in one big swallow.

Of course, overall fitness is also more critical than an ability to handle very long runs at slow paces. Intervals at 5-K speed, long intervals at 10-K pace, tempo runs at just off 10-K pace, and hill sessions are going to do far more for your marathoning than just ambling along lethargically at well-off marathon pace. With more specific, higher-quality training and a proper taper, you can cruise through your marathon in your best-possible time, not in a too-well-practised shuffle.

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