The 1990s marked the dawn of a new era in professional baseball in which the sport's best players began hitting unprecedented numbers of home runs. Between 1995 and 2003, several players hit between 20 and 50 percent more home runs than the top players of the past century, according to Roger Tobin, a physics professor at Tufts University. Tobin demonstrated how steroids might be the reason for this spike in a packed Friday lecture, "Sox and Drugs: Baseball, Steroids and Physics."
"Babe Ruth's record of 60 [home runs] was set in 1927," Tobin said. "Over 71 years, this record changed by one. And then in 1998, Mark McGwire hit 70."
To prove that steroids which are used to increase strength by building lean muscle mass might explain the spike in home runs, Tobin broke a home run down into its major components.
"First you have to hit the ball, which means you have to bat and you have to not strike out and not walk," Tobin said. "The reason for dividing it up this way is that whether or not you hit the ball has really rather little to do with how strong you are."
Because strength is not correlated to whether or not a person hits the ball, Tobin suggested looking at a player's number of home runs per balls in play. Before 1980, 10 percent of all balls that the top baseball players hit would be home runs, he said. After 1980, however, that statistic increased to near 15 percent.
"But then you look at, say, McGwire his average was 18 percent," Tobin explained. "There were two years when he was close to 20 percent. Think about it: if you actually hit the ball, one out of every five was a home run."
If a player is already good at hitting the ball, the added strength from steroid usage increases the speed of the bat's motion, Tobin said, which would explain the higher number of home runs. A 10 percent increase in muscle mass which is common if someone uses steroids leads to a 3 percent increase in a batted ball's speed, he added. Because of the rarity of home runs, this small increase in speed is enough to raise the proportion of balls that make it over the fence by 30 percent.
"Home runs are particularly sensitive to these small increases in muscle mass," he said.
In an absolute sense, the extra force exerted by steroid use is fairly minimal, Tobin explained. The drug can only account for the spike in home runs because home runs are rare events located on "the tail of a batter's range distribution," he said.
Because the improvement in actual performance is small, steroid use does not make as great an impact in other sports, Tobin said. Professional athletes competing in track and field, swimming and other sports many of whom are known to use steroids do not experience the massive improvements that baseball players have achieved.
"Shot putters have been caught constantly using steroids, but the record there has only gone up by a little over 4 percent," he said. "You don't see 20 or 30 percent effects."
Tobin asserted throughout the lecture, however, that his research has only proven that steroid use is one possible explanation for the spike in home runs in the past two decades.
"The question that I asked was is it plausible," he said. "Clearly it is plausible."
