The 100m Freestyle provides another example of a race where women tend to split the race more evenly when compared to men (See also 100m Backstroke vs. 100m Butterfly). Although both men and women tend to have a similar race strategy over a 100m sprint, the different body physique and the different dynamics of the stroke likely leads to different drop-off splits.
As was noted by Mark in the comments of my last post, one reason for the more even splitting of the 100 Backstroke has to do with the start of the race. A Backstroke start gives less speed when compared to a dive start off the blocks. So there is less of an advantage in the first 50m of the race due to the start. As a result, the average drop-off times will be smaller. However, the start does not explain why men tend to have a larger drop-off than women in the 100m Backstroke, yet a smaller comparative drop-off in the 100m butterfly.
In the 100m Freestyle, we return to the same trend that we saw in the 100m Backstroke. Men tend to have a slower second 50 in the 100m Freestyle than do women at the elite level. It is also worth noting that the average drop-off time for both men and women in the Freestyle is higher than Backstroke and significantly lower than Butterfly.
I believe that Freestyle has a larger average drop-off time when compared to Backstroke because of the dive start. The dive allows the athlete to have more speed on the first 50 when compared to a slower Backstroke start.
I think that Freestyle has a smaller average drop-off time compared to Butterfly because of the overall efficiency of the Freestyle stroke. These elite level athletes are maintaining better technique, power, and energy in their Freestyle stroke, allowing them to more evenly split the 100m Freestyle race when compared to the 100m Butterfly.
Still to be explained: Why do women split the long-axis strokes (Freestyle and Backstroke) more evenly than men, but men split the short-axis strokes (or at least the 100m butterfly) more evenly than women?