Monday, February 21, 2011

Closing the Gender Gap: Relative and Absolute Strength Differences between Men and Women.


“Female muscle has the same physiological characteristics as male muscle and, therefore, responds to training in the same fashion […] The belief that women will become excessively hypertrophied, that their resistance training programs must be different from those of men, and that resistance training programs will leave them excessively muscle bound are unfounded (Fleck & Kraemer, 2003).”

“Natural talent only determines the limits of your athletic potential. It is dedication and a willingness to discipline your life that makes you great (Billie Jean King, Founder of the Women’s Sports Foundation).”

The history of sport and women in sport in particular, is a complex area of sociological research. For many contemporary athletes, the idea of women being able to compete, be strong, be fast, and be aggressive on the field are taken as granted. However, conversations many of the female athletes I know and many of the research studies I have read highlight the struggles, preconceptions about, and misconceptions about female athletes that plague sports today. These attitudes, all though certainly not universally expressed or accepted by either gender, suggest that while women can enjoy a new level of freedom and independence in which they can compete against other women; women are simply not as athletically gifted as men. This implicit assumption is accepted even at the highest levels of sport, where in the Olympics, we test the gender of our female athletes, but we do not test the gender of our male athletes. The logic of this asymmetrical testing is clear: any man competing among women is cheating, whereas any woman competing among men is only handicapping herself.

The goal of this blog post is not to resolve the issue of gender differences in athletics beyond a shadow of a doubt or to argue for a massive a re-tooling of competitive sports. Many more qualified researchers have taken greater time and care to explore these issues, and if you are interested I would suggest you read some of these works on the history of women in sport, the policy of separating men and women, and continued growth of women in sport.  What I will try to do in this post is (a) explain some of the often-times bizarre history of the women’s sports movement and (b) explore the science behind athletic differences in men and women. 

Croquet – The Game of Revolution?
Although it is a rather humble place to begin, women in sport in the west begins with women playing croquet in the Victorian Age (Powell, B. R., 1981, "Women and Sport in Victorian America."). Still bound by the extreme social constraints of their time, women were not allowed to engage in strenuous physical activity because (according to the argument of the day) the metabolic demands of a woman’s reproductive system prevented her from engaging in strenuous activity, or else risk damage to the uterus. At the time, many ailments for women were attributed to the uterus ranging from headaches, to back pain, to “hysteria”. Despite these “medical” warnings (which scarily enough persist in folk lore today!) women wanted the freedom to play sports, especially on college campuses. (The co-evolution of increasing numbers of women in higher education and higher numbers of women in sport is a fascinating topic.)  

Croquet was one of the few sports publicly acceptable for women to play, although excessive playing of croquet was discouraged as it might “cause an unpleasant rounding of the shoulders” (Vertinsky, 1994). As women in sport gained momentum, however, progressively more and more doors opened and archery, golf, and cycling became progressively more acceptable for women to participate in. Interestingly, cycling might have had a lot of influence in changes in women's fashion. As demand for less restrictive clothing rose, designers and manufactures had to meet to the demands of their customers; corsets fell out of style, women’s shoes were designed for function rather than form, and knickerbockers became a standard for the active woman. (As a side note, I am sad to say that knickerbockers have apparently left the English vernacular!)
 In the more modern mindset, the history of women’s sports seems to begin with the passage of Title IX (an act which has its conflicts and problems, but I would argue has been overwhelmingly good). And although women do enjoy a new-found liberty to pursue their passions there is still a pervading miasma of sexism in athletics. Any athlete, parent, or coach only has to look around to see and hear the sexism that betrays our implicit beliefs, “She loves sports, she’s a real tomboy;” “You throw like a girl;” “Man up;” “Stop being a pussy.”

Certainly, there are profound biological differences between men and women… mostly between the legs… and it is reasonable and correct to conclude that these biological differences will have an effect on athletic performance. What I think is important is to use the tools of science to recognize what the real differences are between men and women, what differences are genetic, what differences are culturally created, and what really is the impact of these differences? Accepting these differences as universal and immutable is damaging, not only to young girls and women, but to our morality as a culture. However, I think it is also damaging to ignore potential differences and treat everyone as equal. Differences, both between genders and within genders, need to be recognized and above all understood. Differences are not deficiencies. 

Strength Differences between Men and Women – Social and Physiological Factors
Before we explore the physiological differences between men and women in athletics it is important to understand that these differences can never be divorced from their social and cultural context. Starting in infancy, males and females will be exposed to the cultural expectations and preconceptions of their gender. 

The summative of effects of years of being treated “as a girl” or “as a boy” will have tremendous impacts on an athlete’s physiology. Masculine and feminine ideals are entrenched in sports, with those sports requiring more aggression, power, and strength being traditionally regarded as more masculine. In a 1986 survey, 94% of respondents said that participation in sport did not diminish femininity, but 58% simultaneously held the contradictory notion that women are often forced to chose between athletics and being feminine (Miner, 1987). 

From a psychological research, we can see that young boys and girls learn very early on what kind of behavior is socially expected of their gender (O’Brien & Huston, 1985) and there is strong evidence that from infancy on, boys are encouraged to engage in more physically active, rough, and contact based play whereas girls are discouraged from these activities (Thorne, 1993). Disturbingly, girls as young as 2 years old have explicit beliefs about body image that parallel those of adult women (Grogen, 2008; Stafieri, 1967). In the United States, rounder endomorphic physiques are consistently rated as less preferable, long thin ectomorphic bodies are more preferable for women than for men, and broad shouldered, mesomorphic bodies are more preferable for men than for women. Although body-image issues are a growing concern for men, research suggests that women are at greater risk for disordered eating and body-image issues, and especially female athletes in sports that emphasize leanness (Sundgot-Borgen, 1994).

Bearing these sociological concerns in mind, we can turn our attention to the issue of physiological differences between males and females. In terms of absolute strength, power, or speed, research has consistently found that males tend to be stronger than females (see the NSCAs position paper on strength training for female athletes that I will cite heavily here). There are two important scientific facts to remember in interpreting these findings. First, in these studies gender is confounded with other variables such as height, weight, and body composition, and once these factors are controlled for the differences between men and women diminish substantially. Second, these are statistical comparisons of two overlapping populations (see the graphic below). The strongest man is certainly stronger than the strongest woman and perhaps, on average, men are stronger than women. The problem with presenting the data based only on these normative statistics is that group means ignore the large numbers of women who are stronger/faster/more powerful than men (the overlapping part of the curves in the graphic). It is important to recognize the amount of variation within-genders as well as between-genders.

For instance, in terms of absolute strength (not equating for differences in size or body composition) men are found to be 30-40% stronger than women, although this difference is not consistent across all muscle groups. The largest difference would appear to be between the upper body and the lower body. In upper body strength, some studies have shown women to be 43-63% weaker than men, but in lower body strength this difference reduces to about 25%. There are a number of mediating variables that can potentially explain these gender differences however.

For instance, when we equate men and women on lean body mass and body dimensions, these differences disappear almost entirely. When these anthropomorphic differences are controlled for, gender accounts for only 1% of the difference in upper body strength and 2% of the difference in lower body strength (Hosler & Morrow, 1982). We also know that at maturity, males are taller, heavier, and possess greater lean body mass than females, on average. Thus, we can reasonably conclude that much of males’ increased strength is a function of their increased size. Some factors are not attributable to size, for instance broad shoulders confer a biomechanical advantage in tests of upper body strength, and broad shoulders are more characteristic of males than females (…although there are plenty of females with broad shoulders!). Longitudinal studies show that some of this increased strength is also attributable to increased rough and tumble play of boys in childhood; this early and consistent engagement in vigorous play improves performance on tests of heavy lifting. 

It is also important to explain that the biggest determinant of voluntary force is the cross sectional area of the muscle (Kanehisa et al., 1994; Maughan et al., 1983) and the proportional relationship between cross-sectional area and maximum force is the same regardless of gender (Maughan et al., 1983; Miller et al., 1993). Thus, with proper training and muscle development (specifically hypertrophy), females show the same rate of improvement in strength as their male counterparts. 

Often, it is asserted that females’ lower androgen levels do not allow for hypertrophy at the same rate or magnitude as males. Some studies of untrained males and females suggest that females do not show hypertrophy to the same extent, on average, as males. However, this is not always the case and some studies show no differences in hypertrophy between untrained male and female populations (Weiss, Clark, & Howard, 1988). Some of these studies also suffer from methodological flaws. For instance, one study by Fahey et al (1976) found that after a single session of weight lifting, serum testosterone levels rose significantly in males, but not in females. However, the female subjects in this study were described as not being experience with weight training and performed a DIFFERENT exercise program than males, who were experienced weight lifters. (I was amazed that people cited such a hugely confounded study!) In a much better, more controlled study, Weiss and colleagues (1983) found that men did have higher serum testosterone levels following a single session of weight lifting, but that this increase was proportional to resting testosterone level. Thus, the authors concluded, “… men have a greater absolute testosterone response to weightlifting than females, whereas the absolute androstenedione response to weight lifting is similar in males and females.” 

It is important to note that the role of androgens in muscle hypertrophy is not completely understood (even when we limit the discussion to the effects of testosterone; Weiss, Cureton, & Thompson, 1983) which might explain why the effect of sex on muscle hypertrophy is so contestable. Furthermore, few studies have looked at long term hormonal responses to training. Most studies, like those listed above, only look at acute changes in hormones following a single session of exercise.

2 comments:

  1. By "sports in the west" you must mean "Western Europe" or "Western Asia" as America has always had female sports including lacrosse, basketball and handball. Indeed, America has never thought of women as weak, remember, mainly because American women have never been a weak proponent of American society. Weakness just never existed in America, plain and simple.

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