Gender Differences in Endurance Performance and Training

This article is long overdue and I apologize to those who were interested in the topic. To bring up the issue of gender differences in physical performance may suggest sexism, but that is not my intention. Historically, there is no doubt that sport has been a center of faulty assumptions and sexism where female athletes are concerned. Social issues, and misunderstanding about female physical and medical limitations (or the presumption of limitations) conspired to slow the development of female performance for many years (the marathon for women was only added to the Olympic schedule in 1984! ), but those times are gone, at least among young athletes. Among master's athletes, we still see greatly reduced participation by the older female age groups. This participation difference will no doubt diminish over the next couple of decades. As a result, performances by the oldest females will probably improve more rapidly than those of the oldest males, as this new generation of well trained young female athletes moves into age-group competition, and are joined by more and more talented "late bloomers."

"Old" Social norms and habits are still having negative consequences on participation and performance by older (50 +) females. Modern female athletes have repeatedly demonstrated these norms ("women are not built to run long distances" blah- blah-blah) are totally bogus. Currently, teenage daughters are encouraging their formally sedentary mothers and even grandmothers to take up exercise. This transfer of knowledge and norms UPSTREAM is the reverse of what we traditionally see in males (Dad teaching his boy all he knows). However, this is a transitional period for women in sport, so the knowledge transfer across generations is helping to speed the development of women's masters sport.

Having said all that, there ARE some physiological differences between the sexes that impact performance in females independent of age. Some years ago, when the marathon was first becoming a competitive event for women, the rapid improvement in female times led some to predict that female performances would soon equal those of men in the marathon. This has not happened, and it won't. The current world record for women is 2:21, compared to 2:06:50 for the men, a difference in speed of about 10%. This same 10% gap is present across the distance running performance spectrum The reason for the performance gap is not that women don't train as hard as men. There are some important physiological differences between the sexes that can't be overlooked or overcome. I want to point out the most important. Where relevant, I will try to do so in terms of the BIG THREE Performance adaptations that I have discussed on the MAPP.

The Maximal Oxygen Consumption

The "typical" young untrained male will have an absolute VO₂ max of 3.5 liters/min, while the typical same-age female will be about 2 liters/min. This is a 43% difference! Where does it come from? Well first, much of the difference is due to the fact that males are bigger, on average, than females. Us humans are all (sort of) geometrically similar, so heart size scales in proportion to lean body size . If we divide VO₂ by bodyweight, the difference is diminished (45 ml/min/kg vs 38 ml/min/kg) to 15 to 20%, but not eliminated. What is the source of this remaining difference?

If we compare average bodyfat in males and females, we find part of the answer. Young untrained women average about 25% bodyfat compared to 15% in young men. So, if we factor out body composition differences by dividing VO₂ by lean body mass (Bodyweight minus estimated fat weight)) the difference in maximal O₂ consumption decreases to perhaps 7-10%. Keep in mind though that this is only a meaningful exercise on paper. A female athlete cannot expect to improve her performance by reducing her bodyfat down to the sub 7% levels that are often observed in elite males. The health consequences for the female are too severe!

To find an explanation for the remaining 10% difference we must go back to the key limitation on VO2 max, oxygen delivery. On average females have a lower blood hemoglobin content than males, up to 10% lower. Finally, there is some evidence, that the female heart is slightly smaller relative to body size than the male heart. Recent ECG and echocardiographic studies also suggest that the young female heart exhibits less enlargement in response to either endurance or resistance training than the male heart (George et al, 1995) This may be due to differences in androgen receptor density in the female heart. A smaller heart would be expected to be a less effective pump.

Slightly lower oxygen carrying capacity of the blood (lower hemoglobin levels) plus a somewhat smaller or less adaptive heart are sufficient to account for the gender differences in maximal oxygen consumption that are independent of body size and fat percentage.

It is worth noting here the results of a 1993 study by Spina et al. Their data suggested that in previously sedentary older men and women (60 to 65 years old) who trained for 9 months to a year, both men and women increased their VO₂ max by the same amount (an average of 20%). However, the mechanism of improvement was different. The men improved primarily by increasing maximal cardiac output due to higher stroke volume. This is just the pattern of response I have previously described. However, the older women did not demonstrate any increase in cardiac performance, but rather increased oxygen consumption by improving oxygen extraction by the working muscles, due to greater capillarization and more mitochondria. This data supports previous studies in 60+ year old women that show no cardiac hypertrophy in response to endurance training.

To summarize, their is a growing body of data suggesting that females demonstrate a somewhat different pattern of cardiac adaptation to exercise, which may become more dissimilar with age. They also generally have a lower hemoglobin level by several percent. The net effect is a small but significant difference in maximal oxygen consumption, even among similarly trained males and females, and after scaling for differences in size and body composition.

It is important to make note of the fact that these differences are "on average". In reality, there are many women with significantly higher VO₂max values than average men. However, if we look at the "best of the best", the differences persist. Using XC skiing as an example from here in Norway, the highest reliable values for VO2 max recorded in national team XC skiers are about 90 ml/min/kg. The very best Norwegian woman has been measured at 77 ml/min/kg, a 17% difference. So, while this woman will outperform 99.9% of all men, she will not out-perform the national team level males.

The Lactate Threshold

Now we come to the second component of endurance performance, the lactate threshold. As a review, this is the exercise intensity at which lactic acid begins to accumulate in the blood stream at levels significantly above "baseline" values. This intensity sets a (slightly fuzzy) boundary between that exercise intensity which can be sustained for long periods (over one hour) versus those which lead to fatigue in minutes. We have already discussed the fact that changes in the lactate threshold are due to adaptations that occur in the exercising muscle. We call these peripheral adaptations (Changes in cardiovascular performance are called central adaptations).

The question here is, do women demonstrate a different pattern or capacity for peripheral adaptations then men? As best as I can tell, the answer is NO.

First, Female skeletal muscle is not distinguishable from male skeletal muscle. Second, within some margin of error, the fiber type distribution (percentage of slow versus fast fibers) is not different in the male and female population. Third, male and female skeletal muscle responds similarly to endurance exercise. Finally, elite female endurance athletes have similar lactate threshold values compared to men when expressed as a percentage of their VO₂ max. Elite women perform at the same high percentage of their maximal oxygen consumption as their male counterparts.

Some years ago it was proposed by some that women would actually perform better at ultra-endurance type activities. This theory has been disproved both in the laboratory and in practice as a performance difference persists in the ultramarathon events. Some of you may balk and recall a recent Running Times article that suggested women had an edge in the really long events. They discussed a study in which a group of male and female runners who were matched for marathon time were raced head to head in the Comrades marathon, a 90k race. The women won by 54 minutes, suggesting a female edge in longer events. The problem with this study is that when you match men and women for performance, the women are relatively better runners and probably have a higher slow twitch fiber percentage. This advantage becomes bigger in an ultradistance event.

The fact remains that the performance gap between male and female record holders in the really long running races 50k to 6 days is actually more on the order of 15 to 20%, instead of the 10% difference for the standard distances. Part of this larger gap may be to lower participation, and the fact that the most talented females have not yet tested themselves over the ultradistances. But at elite level, I don't think the gap will disappear.

Efficiency

The third component of endurance performance is efficiency which of course has different constraints, depending on the sport. The research information comparing the efficiency of female and male athletes is both sparse and inconclusive. In running, for example females have been found to be more, less, and equally efficient compared to males men depending on the specific study. Some of this confusion comes down to how the differences in bodyweight and bodyfat were accounted for.

After looking over some of the research comparing running economy between genders, I started to go into a couple of studies, but it all starts to become a scaling and factoring game, which I like, but you probably can do without it. So, I decided to just summarize things this way. Currently, I would argue that any inherent economy differences in male and female runners are smaller than the individual variation in running economy that is observed among runners, independent of gender. I would support that argument by suggesting that the differences in VO₂ max observed between elite males and females are sufficient to explain the "10% gap" without other factors being involved. If more data comes to my attention to dispute this, I will share it.

Now, if we look at efficiency/economy differences in other sports, things mostly boil down to body shape/anthropometric differences. In situations like running or cycling, these may actually favor females in general, due to narrower upper bodies for a given total body mass, and potentially less wind or water drag. As I have shown for rowing , differences in VO2 max alone are sufficient to explain the gender performance gap in rowing. I am not aware of any research studies to support or dispute this, but it seems that there are no differences in rowing efficiency among male and female rowers of similar relative ability.

Fat metabolism differences?

Back in the 70s, a theory got started that said "Since women have more fat stores, they will be better at utilizing fat during endurance performance when glycogen stores are depleted." One of the supporting pillars of the theory was that it had been noticed by one female runner/author how "fresh" many female runners looked as they crossed the finish line! Well, this shaky theory was crushed under the harsh light of science. Back in 1979, Costill and colleagues compared males and females who were equally trained during a 60 minute treadmill run. There were no differences in any measures of fat metabolism. These guys even took some muscle out of the runners' legs and tested it in a test tube. Still no difference! This is an often repeated finding among similarly trained males and females. There is no gender difference in the ability of men and women to burn fat!

Are Men Sweatier than Women?

On an absolute basis, and per kg bodyweight, women have lower sweat rates than men. However, because of their higher body surface area to volume ratio, they dissipate heat equally well. Men have an advantage in evaporative cooling, but women have an advantage in radiant cooling, so they come out even.

Summary So Far

Of the three critical components of endurance performance, the only one that is clearly and consistently depressed in females is the maximal oxygen consumption. Even after accounting for differences in bodyweight and body fat percentage, a gap of roughly 10- 15% remains. Now I want to talk about some other comparisons that don't fit so cleanly into the Performance Model for endurance performance.

Muscle Strength and Power

Although maximal muscular strength and anaerobic power has little to do with pure endurance performance, there are many events which can be classified as "power-endurance" events. These events ranging from 2 to about 8 minutes require some combination of aerobic and anaerobic capacity. For this reason, I think it is important to also consider this "anaerobic" component of the performance package. When we talk about anaerobic capacity, the critical determinant is muscle mass. Females, on average, have less total muscle mass than males. As a result, maximal strength measures as well as maximal power measures (power = force/time) are reduced. Gross measures of upper body strength suggest an average 40-50% difference between the sexes, compared to a 30% difference in lower body strength. What about power? Maud and Schultz compared 52 men and 50 women, all about 21 years old using a maximal power test on a bicycle ergometer. Peak power was about 60% lower for the females when comparing absolute values. But, the men were heavier. Peak power per kg bodyweight was more similar, 9.3 watts/kg vs 7.9 watts/kg for the women, an 18% difference. Finally, when power outputs were adjusted for fat-free mass, the values were 10.4 watts/kg and 9.9 respectively. This 5% difference was not statistically different. Numerous other studies using different techniques have demonstrated that when you just look at muscle quality, male and female muscle is not different. Within the accuracy of current comparative techniques, it appears that the strength and power differences between the sexes are a function of muscle quantity only. Biomechanical differences probably play a role in some situations, but this will be very sport specific.

Should Men and Women Train Together?

OK, now we move onto something a little different. I think there are two reasons for making this gender comparison. First, I think it is useful to understand that at the elite levels, male and female performance differences are physiological in origin, not a function of differences in training, desire etc. (The one caveat to this is among the oldest athletes. Here, I think the gender performance gap is probably still wider than it will ultimately be, due to differences in participation and training intensity among the oldest age groups.) The second reason is a very practical one. Men and women live together, work together, and often train together, either as husband and wife, as friends, or as part of a training group. So, if we are going to train together, I think it is pretty important that we understand each other as athletes. Athletes are not just bodies. They have brains too! No, really, they do.

Psychological Differences?

I have examined briefly some physiological gender differences. Now I want to move into the psychological realm. Oh boy, now I am really treading on thin ice, but I'm safely and happily married, and living pretty far away from most everyone I know here in Norway, so I am going to proceed. As a broad generalization, here are a few things I have noticed, read, experienced etc. that I think are important regarding males and females training together. Again, let me repeat. THESE ARE GENERALIZATIONS. For every point I will make here, I myself have seen just the opposite behavior on occasion.

The Numbers Game

If you walk into a fitness center, teeming with men and women huffing and puffing on all manner of computerized exercise machines, take a look at the men first. As a rule, they will be staring directly at the computer screen, calculating, extrapolating, comparing the numbers with their previous efforts, or with measured glances, to the guy on the next machine. Males are number guys.

Now take a look at the women. In my experience, most are using one of several dissociation strategies. They are either listening to music, reading a book or magazine, or simply covering the entire computer screen with a towel. Some use all three methods in combination. The bottom line, is they are NOT paying attention to all the blinking lights! In fact, when I have had the nerve to inquire about this, most tell me that they hate all the numbers, clocks, bells, and whistles.

Now, most of these folk aren't athletes, but I think the tendency remains among the competitive set. On the sports lists that I lurk on via email, and the messages I get from you guys, it is mostly the men that are getting caught up with heart rate, time, power output etc. Men seem to need to quantify their training in as much detail as possible. Have you noticed how men are more likely to keep training logs then the women? Meanwhile, I would argue that women are more sensitive to qualitative, internal, measures of training effectiveness. Which method is better? Neither. We can definitely learn from each other. Sometimes the numbers are helpful for getting us over specific hurdles. They also help us to see small changes in performance and evaluate the effectiveness of our training. On the flip side, a more qualitative approach helps to take some of the internal pressure off sometimes. If the odometer, speedometer, or HR monitor rules our heads, then we men often find ourselves "competing" every workout. This is a sure-fire prescription for become stale and overtrained.

The Sociology of the Training Group

I have not read "Men are from Mars, Women are from Venus", but I have read some similar stuff. Basically, I have to go along with the idea that men and women communicate differently. Men tend to be more hierarchical, while the women develop better horizontal lines of communication. What the heck does this have to do with performance? This is my slant. Men who were active in sports as youth are very familiar with the pecking order mentality. In sports, some get picked first, others get picked last. You have first team and second team etc. "It's not personal. He is just a little faster than you Charlie." Watch a bunch of guys in competitive practice situation. My most recent personal experience is in rowing. On the water, we would do daily battle against each other in our singles. Sweating, grimacing, taunting, yelling, winning, losing. Then we get to the dock, get out of the boat and say "Great workout. See ya tomorrow." On the water each day a hierarchy was established and defended, then dissolved as soon as practice was over. Another example came to me from a coxwain for the men's lightweight national team who was now coaching collegiate rowers. He made the point that the national team athletes had the ability to turn everything on in practice. Then, as soon as practice was over, they forgot about it. No internalization, no dwelling on successes or failures during times when nothing can be done about them!

In my experience, this separation of competition within and outside of the training environment CAN be more difficult among female athletes. The same qualities that often make them more effective communicators and empathizers, also can lead to personalizing the physical battles of daily training. In the extreme it can splinter a team. I have observed it (from a safe distance) in rowing among masters women. Most of those women were not competitive athletes in their youth. Perhaps this made a difference. Battles for seats in the boat waged on the water and coaching decisions that resulted were not forgotten or accepted when practice was over. The women didn't seem to know how to communicate under these new conditions. Disaster!

Competitive training situations are generally good, I think. It helps to train with others who share your goals. However, everyone has their own optimal amount of competitive stimulation. Even among world class athletes, some thrive in an aggressive team environment, and others don't. Here in Norway, I know the coach of last years top female XC skier in Norway, Marit Mickelsplass. She rose to new levels on the international circuit (Top 3 in the world) this year after leaving the national team, and training on her own. The problem was that the stress of daily training in the aggressive team atmosphere was too much for her. Psychological stress led to physical stress and overtraining. Thanks to a good coach who understood the link between psychology and physiology, the problem was solved. I guess my view is that there are often going to be subtle differences in the approach that a coach is going to need to take with female athletes versus male athletes. Failure to understand these differences can impact performance.

Can Women and Men handle the same training Volume?

Here, we return to some physiology. Talking with elite level coaches leads me to believe that there are small but important differences in the recovery capacity of male and females, at least when pushed to the extremes of elite level training. Again I will go to evidence from world class XC skiers here in Norway. It appears that the best women perform optimally at a training volume that is perhaps 10-15% lower than that observed in the best men. Increasing the volume in the women does not improve results, and often leads to overtraining. The general consensus is that the difference lies in the higher average testosterone levels of males. Remember, testosterone is an anabolic hormone. This means it is critical for tissue growth and repair. Anecdotally, I have been told that only one of the Norwegian female national team skiers has been able to maintain the average yearly training volume (measured in hours) that is maintained by the entire Russian female team. The difference appears to be steroid use, but of course this is only a rumor. At any rate, I think we should be aware that there is probably a small gender difference in recovery capacity from hard or high volume training, in addition to the individual variation that is observed.

You and your Significant Other as training partners

I married a woman who loves exercise. Heck, that is one of the reasons I was so attracted to her! We focus on different sports, but sometimes we workout together, either running, cycling or XC skiing, depending on the season here in Norway. What we learned pretty quick was that we couldn't do the same type of workout together effectively. If we run at the same speed, I can be comfortable just under my lactate threshold. Meanwhile she is teetering on the edge of disaster as she runs at or above hers. I have a good run, she is miserable. The same thing happens on a bicycle. What is the solution? Well one is we can just not ever train together. Neither one of us like that idea. So we compromise. Sometimes I train alone. These workouts are usually hard interval sessions or lactate threshold workouts. Then, when we train together, I am running or cycling at a good steady state aerobic pace, and she is doing a tempo run or lactate threshold session on the bike. The bottom line is that we had to understand where we were both at physiologically and make the adjustments necessary to allow us both to profit from our joint training sessions, and not become frustrated with each other.

Even small differences in the performance capacity of you and your partner can be problematic if they are not recognized. The slower partner who always works a little harder to keep up can be at risk of overtraining, or just not achieving the goals of the workout. This may be the man, or the woman. Either way, it can be avoided by taking the time to evaluate the performance difference and make adjustments in the training schedule. One thing is likely. You probably should not train together all the time. Find time for common workouts, but make sure that there remain training sessions were there are no compromises being made. If this means training alone, then do it. It doesn't mean I don't enjoy your company, dear!

Final Words

OK, I think that pretty well hits the main points, from my current vantage point. The bottom line is that there IS a physiological explanation for the gender performance gap observed in endurance (and power)sports. Keep in mind that the best women can still beat 99%+ of the men. However, if you ask me "When will women run as fast as men." I will answer, "just as soon as they have the same VO₂ max as men. Grete Waitz probably said it better, "As long as women are women, I don't think they will surpass men."

I have read at least one very good and quite popular running book, "The Lore of Running" that has tried to explain the gender performance differences in terms of some unmeasured but imagined difference in muscle quality. He has been forced to assume this angle, despite absolutely contrary data, becasue of his even more unsupported theory that VO₂ max is actually not limited at all by cardiac performance. To be honest, this view takes about as much denial of the available data as that of the tobacco industry denying that smoking is bad for you! Enjoy this otherwise wonderful book, but don't read the physiology chapters.

I realize I have skipped over a tremendous area of difference related to the impact of the menstrual cycle and pregnancy on training on performance in females. However, I think there are a lot of excellent resources by much more qualified people available for women athletes with questions on this topic.

As for the presumed psychological differences, I think they are real, but I realize that there are many exceptions. So, please don't flood my mailbox with white hot flame-mail! At least my wife still loves me.