When fat-free mass is considered, men are 40% heavier (Lassek & Gaulin, 2009; Mayhew & Salm, 1990) and have 60% more total lean muscle mass than women. Men have 80% greater arm muscle mass and 50% more lower body muscle mass (Abe, Kearns, & Fukunaga, 2003). Lassek and Gaulin (2009) note that the sex difference in upper-body muscle mass in humans is similar to the sex difference in fat-free mass in gorillas (Zihlman & MacFarland, 2000), the most sexually dimorphic of all living primates.
These differences in muscularity translate into large differences in strength and speed. Men have about 90% greater upper-body strength, a difference of approximately three standard deviations (Abe et al., 2003; Lassek & Gaulin, 2009). The average man is stronger than 99.9% of women (Lassek & Gaulin, 2009). Men also have about 65% greater lower body strength (Lassek & Gaulin, 2009; Mayhew & Salm, 1990), over 45% higher vertical leap, and over 22% faster sprint times (Mayhew & Salm, 1990).
(Puts, David, A. “Beauty and the Beast: Mechanisms of Sexual Selection in Humans.” Evolution & Human Behavior 31.3 (2010): 157-75.)
So why should women be serving as firefighters and LEOs? Strength-training for women is limited by the material. If you have two LEOs trying to subdue a suspect, do you want two men or one man and one woman?