Women's Physiology

Women’s physiology is totally different that of men. This is a topic that is sometimes dangerous to discuss as, to many in the modern world, it smacks of inherent sexism to even consider that there are any differences between women and men. Certainly in the past, the idea that there were gender differences got co-opted into the idea that one gender was superior or inferior to the other.

Since it was usually men who were writing about this, and since they tended to assume that they were the default setting, the idea that women were different from men came to mean that women were inferior to men.

Many seem to feel that to discuss or even suggest gender differences are to tie into what some see as inherent male-dominant sexism.

I think this confuses issues. In my mind, the concept of a difference is no way implies an inherent inferiority or superiority even if many interpret it that way. Even in the case where women and men are different, there are clear places where women show a greater response than men and others where they show a lesser response. In most sports, at the elite level, women's performance is about 8-10% below men.

However, in ultra-endurance running and cold water swimming, women's performance is generally superior. Women also show better endurance and tolerate heat better than men. While they often lose fat more slowly, they also lose less muscle than men. Regardless of whether the response is better or worse, I will simply consider them to be differences going forwards into these articles and nothing more.

Honestly, the only reason to address them as differences (rather than simply focusing on women's physiology) is that so much of the information is based on men with the flawed idea that it automatically applies to women. But even this raises the question of why it took so long to even recognize that there were differences between the two.

What the research is saying:

For quite some time, it was basically assumed that research on men, and this cut across most disciplines including general physiology, exercise, fat loss, etc. would apply directly to women. It just wasn't really questioned on any level. In the realm of sports performance, it wasn't until about the mid 80's that any amount of comparative studies on women and men started to be done. But even from the earliest research, it became clear that there were significant differences.

A singular example will hopefully make the point. Endurance athletes such as runners or cyclists will often use a dietary strategy referred to as carbohydrate loading where they combine intense exercise with a drastically increased amount of carbohydrate in their diet. The goal of this is to increase the store of carbohydrate in the body (muscle and liver) to improve performance. Early studies showed that this worked well for men. They increased the storage of carbohydrate in their bodies and their performance improved. But in women it didn't seem to have the same effect. In one comparative study, while men increased their muscle carbohydrate stores when fed a 70% carbohydrate diet, women did not. For fairly logical reasons, biological differences were assumed to be the case since, as often as not, it does explain the differences that are seen. But this was at least partially wrong.

It turned out that part of the reason the female subjects didn't carb-load as well as the men was due to the fact that the same 70% carbohydrate diet provided much smaller amounts of total carbohydrate due to the women being smaller and having a lower energy expenditure. That is, a woman burning 2000 calories per day and eating 70% carbohydrate is getting 350 grams of carbohydrate while a man burning 3000 calories per day and eating 70% carbohydrate is getting 525 grams. The percentage is identical but the total amounts aren't.

When women were fed equivalent amounts as the men, most of the differences went away .

When both women and men were given even larger amounts, there was no gender difference in carbohydrate loading. It had purely to do with the total amount of carbohydrate. But this raised another problem, it created an impossible diet for the women. To get enough total carbohydrate meant eating too many total calories. Their smaller size and energy expenditure basically made it impossible to achieve what men could without eating too much food.

There was another issue.

Many females are restricting their food intake to one degree or another for various reasons. If they need or want to lose fat, they have to eat less than they burn and that may not leave enough total food to support their training. There are solutions to this, what some call nutritional periodization (alternating time periods of restricting food intake with increasing it) and I'll talk about this in articles to come.

But even this singular example brings up one of the key problems that often shows up which is that dietary approaches that work for men don't work or prove impossible for women to implement.

So why did it take so long to include women in research, especially in sports science and exercise research? Some it probably represented pure chauvinism: the majority of scientists were male and they tend to bring a male-oriented mentality to things. But perhaps a bigger part of it was that for the first half of the 20th century, and even into the 70's, women simply weren't as involved in sport as men.

In certain sports, it was long thought that women were incapable of performing them or that they would do physical damage to themselves. Up through the 70's, for example, women were barred from even competing in marathons (there is a famous picture of referees trying to pull a woman off of the course). Some of this mentality persists today as many sports still maintain shorter distances or slightly different events for women versus men.

There wasn't much reason to study women since they didn't make up a large proportion of athletes. Even when research was done either on women or to compare women to men, early research was poorly done and the results were questionable at best.

The reason for that has to do with the incredible complexity of women compared to men which due to the menstrual cycle. This is the roughly 28 day cycle a woman goes through monthly during which her hormonal status and physiology can change in subtle or not so subtle ways.

The cycle is typically divided evenly into two phases called the follicular (from menstruation to ovulation) and the luteal phase (from ovulation through PMS) and each is distinct from another. There are even shifts that occur in the early- and late- phases of each and some even divide each phase into an early-, mid- and late- phase. During this cycle, a woman's primary reproductive hormones (estrogen and progesterone) show complex overlap.

This makes studying women incredibly difficult. Researchers have to control for the phase of the cycle itself and even this can be difficult as determining where in her a cycle a woman is isn't always easy (recent studies will use ultrasound and blood work to determine this but this is not easy or cheap). Add to that no two women have an identical menstrual cycle and even an individual female's cycle may vary from month-to-month.

A woman who starts menstruating a day early might have to wait a month to be retested. To begin to compare women to men, you must control for the phase of the cycle. But when you study her you may change what conclusion you reach. In one phase a woman's response may be identical to a man's; in the other it may be different or even the complete opposite.

As a singular example, women's metabolism of caffeine is similar to men's during the first half of her cycle but different in the second half. If you don't study all of those conditions, you can draw incorrect conclusions and early studies didn't even pay attention to where in her cycle a woman was. She'd come to the lab to be measured and that was it. The results were meaningless. In contrast men have one primary reproductive hormone which changes very little day-to-day. So long as you control a few simple variables like time of day and whether or not the eaten, you can test them any day of the month. Ultimately, it's just simpler to study men.

Coach HB


The above information is taken from the The Woman's Book by Lyle Mcdonald with Eric Elms

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