I've always guesstimated that swimming was about one-quarter the speed of running. I was a bit bored, so I compared the world records of the long course meter freestyle records to that of the outdoor track records. (The conditions used for Olympic Games.)
Here are the men:
| SWIMMING | TRACK | |||
|---|---|---|---|---|
| Distance (LCM) | Time | Distance (Outdoor) | Time | Factor |
| 100 | 00:47.50 | 100 | 00:09.72 | 4.89 |
| 200 | 01:43.86 | 200 | 00:19.32 | 5.38 |
| 400 | 03:40.08 | 400 | 00:43.18 | 5.1 |
| 800 | 07:38.65 | 800 | 01:41.11 | 4.54 |
| 1500 | 14:34.56 | 1500 | 03:26.00 | 4.25 |
And the Women:
| SWIMMING | TRACK | |||
|---|---|---|---|---|
| Distance (LCM) | Time | Distance (Outdoor) | Time | Factor |
| 100 | 00:52.88 | 100 | 00:10.49 | 5.04 |
| 200 | 01:55.52 | 200 | 00:21.34 | 5.41 |
| 400 | 04:01.53 | 400 | 00:47.60 | 5.07 |
| 800 | 08:16.22 | 800 | 01:53.28 | 4.38 |
| 1500 | 15:42.54 | 1500 | 03:50.46 | 4.09 |
It's interesting that the women are faster runners in the shorter distances (100, 200,) than the men, but men are faster in the longer distances (800, 1500). The 400 is just about a dead heat. The first reason that comes to mind for the difference is the upper body strength of women. Sprinting in swimming requires significant arm and shoulder strength. Perhaps men are more evenly built between the upper and lower parts of their body?