It is pretty obvious to most people that a muscle's strength has a strong relationship to its cross sectional area (size) in both men and women. Muscle enlargement and the corresponding increase in strength was first measured and discussed at least as early as 1897. The relationship between muscle cross-sectional area and strength is shown for the forearm flexors in the graph below. This graph also shows that while men, on average, have more muscle than females, there is no "difference" between male and female muscle (all points pretty much lie on the same straight line). What is far less obvious is that we become strong in more ways than by simply gaining more muscle mass. Weight training elicits a strong neuromuscular effect and all individuals will in fact gain strength in part by using existing muscle fibres more efficiently. Strength Training increases neuromuscular efficiency in three ways. Increased number of motor units are recruited (a motor unit is the nerve and all the muscle fibres it activates) Increased firing rate of each motor unit Increased synchronization of motor unit firing Put rather more simply you use more of what you already had and you coordinate the force production better. This is one of the reasons CrossFit teaches technical lifts. How much you can lift is a function of skill (coordinated firing of muscle units) as well as muscle strength and power. So even though your lifts might be going up by 40 or 50% or more it doesn't mean your muscles get 40-50% bigger. This fact is often viewed as good news by females and bad news :( by males! The graph below (Narici, et.al. 1989) will take a little explaining but it clearly shows this effect. MVC stands for maximal voluntary contraction, which simply means the maximum force you can generate. CSA is the cross-sectional area of the muscle which is effectively the size of the muscle EMG stands for electromyography, which is a recording of the electrical activity of the muscle. A higher EMG signal means more muscle fibres are being recruited. The graph shows 60 days of training and 40 days of detraining (rest) for the quadriceps. You can see that despite a 22% increase in force output after 60 days the increase in muscle cross-sectional area was only 8%. In another study (Staron et.al. 1994) the amount subjects could lift increased by 100% to 200% but there were no changes to the cross-sectional area of muscle fibres. The amount of improvement in neuromuscular efficiency versus gain in muscle size will vary between individuals. Typically young males, who have higher levels of testosterone, will tend to increase strength by building bigger muscles, whereas females and older males will tend to rely more on improvements in neuromuscular efficiency. We all use both physiologic adaptations (efficiency and size) to become strong but the above discussion does explain why females tend not to bulk up with lots of muscle mass whereas males (particularly young males) often do. Tony Leyland is Senior Lecturer at the School of Kinesiology, Simon Fraser University, Vancouver, British Columbia. He has taught at the university level for 25 years and has been heavily involved in competitive sports such as soccer, tennis, squash, and rugby as both an athlete and a coach for over 40 years. He is a professional member of the National Strength and Conditioning Association, a Canadian National B-licensed soccer coach, a level-1 CrossFit trainer and a muscle up stud. Tony Can be reached at email@example.com.