In the first ever study of its kind, US researchers have found that with training, women can develop the type of muscle fibers needed for heavy weightlifting just like men, and in some cases, may even have more than their male counterparts.
Carried out by researchers at San Francisco State University and California State University, the new small-scale study analyzed muscle fibers from thigh muscle biopsies performed on six world/Olympic-class female athletes, nine national-caliber female athletes, and six national-caliber male athletes during the 2017 World Weightlifting Championships.
Humans have three main types of muscle fibers, each containing a different variety of a protein called myosin heavy chain ("MHC"), which the researchers explained is the "microscopic motor" that makes your muscles move. The three types include MHC I (slow twitch fibers), IIa (fast twitch) and IIx (super-fast twitch).
The amount of each fiber type influences muscle performance, with fast twitch fibers especially suited to fast and powerful movements, such as those in "clean and jerk" weightlifting moves.
However, the researchers pointed out that how the fibers influence performance has not been well explored in elite athletes, particularly those from strength and power sports.
The findings of the new study, published in the journal PLOS ONE, showed that the weightlifters had the most fast twitch fibers ever reported in athletes -- 67 percent on average.
According to the researchers, this abundance of fast-twitch fibers partially explains how elite weightlifters are able to generate high forces in short time-frames.
In addition, they also found that the elite women weightlifters had the same amount of the muscle fibers needed for the sport as men, and in fact, with over 85 percent fast twitch fibers, two of the World/Olympic-class women actually had more than any of the men.
The authors commented that the findings now help disprove a stereotype about female athletes.
"Despite no high-level data, people thought that women had fewer fast twitch fibers and that was seen as a negative thing," said study co-author Jimmy Bagley. "We've shown that that is not true."
"These findings suggest athlete caliber, training experience and body mass determine the percentage of fast twitch fiber more than gender," said Bagley. "It used to be thought that fiber type was what you were born with, but we show that's not the case -- training has a huge influence."
Kaylie Zapanta, who helped perform the muscle fiber analysis in the study, also added that although men and women are different in terms of hormones and body type, the study shows that in terms of muscle, women are pretty much the same as men.
"When you look at muscle tissue, you can't really differentiate between a man's muscle fibers and a woman's," she said.