Why Men Have Nipples

• Every human fetus is female for the first six weeks. At that time the SRY gene in boys cues the formation of testicles, which make testosterone. Boys develop longer forearms in the womb. This gives them greater throwing power than their advantage in height would indicate. The world record female baseball pitch is 65 mph, which is routinely matched by decent high school boys. In running events the world record gaps are more like 11%, while distance swimming gaps are the lowest at 6%. These figures are complicated by the fact that nearly all women’s’ running and throwing records are from the era between the mid 1970s and 1990 when top athletes commonly used performance enhancing drugs.
• Larger skeletons allow men to have about 80% more muscle mass above the waist and 50% more below. Mens’ narrower hips make running more efficient and decreases the chance of ACL tears that women are much more likely to suffer from. Men are also twice as likely to be left-handed, which is an athletic advantage in sports like baseball and tennis. This chapter also discusses complications caused by women with Y chromosomes.

The Talent of Trainability

• The response to training features a wide variability and it’s clear that there is a significant component. One study that gave the same exercise to all participants showed a variation from 0% to 50% increase in the amount of oxygen their bodies could use. The fact that such variations are smaller between brothers proves the genetic factor. Roughly half of one’s ability to improve with training is due to one’s birth parents. It seems that certain genes present in all people are more active in those more susceptible to the training effect. The ultimate combination would be a person who starts with a highly elevated aerobic capacity and also has a rapid training response. (Doug: In school, students vary when it comes to learning ability in subjects like math and reading. Like athletics, this is a mix of nature and nurture.)

The Trainability of Muscle

• Another major variability in our human population is the percentage of fast-twitch and slow-twitch muscle fibers that are mostly a function of one’s genetic composition. Fast-twitch fibers contract at least twice as fast and are good for explosive movements. They also tire quickly and grow twice as fast when exposed to weight training. Sprinters typically have 75% fast-twitch fibers. Top marathoners, on the other hand, can have up to 80% slow-twitch fibers. Due to the explosive nature of fast-twitch fibers, athletes like sprinters are more injury prone as far as their muscles are concerned. Marathoner’s injuries are more likely to be orthopedic in nature due to over use. The reason the best soccer players are not the fastest athletes is that they would be too injury prone to last in a 90 minute game.

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