TrainingShould your BMI dictate your ideal swim distance?

We’ve all noticed through watching national or Olympic running competitions that different distances favour different body types. You’ll see the line-up of tall, muscular, powerful athletes at the 100m and 200m races; the lean but still well-toned athletes of various heights racing the middle distances; then we see the thinner, smaller runners dominate the 10k and marathon.

In running there is a big trade-off between weight and power. Faster runners attain faster speeds by hitting the ground more forcefully – up to five times their bodyweight – than other runners do in relation to their body weight. One of the essential characteristics of elite sprinters is their highly developed musculature, and these large muscles add to their overall mass.

The more powerfully built sprinters thus have a higher BMI, while distance runners have a much lower BMI. There is a strong inverse relationship between BMI and race distances.

However it is a different story in the water.

Drag, not weight, is the primary limitation on the speed of swimmers.

New research  that looked at Olympic swimmers competing across a range of events from 50m to the 10k open water race found no statistical difference between the BMI of the swimmers.

Most swimmers had a BMI within a narrow band of 22-24 for men and 20-22 for women. The study also found no differences in height and weight of swimmers across the various distances.

There are a few points to note here.
Firstly, the study only looked at freestyle swimmers, so we cannot say that there may not be ideal body types for different distances in breaststroke, butterfly or backstroke.
Secondly, we can’t make an assumption about a person’s body fat percentage (ie whether muscle or fat) as BMI is the ratio of someone’s weight to the square of their height.
Thirdly, there may be other ‘body type’ characteristics that hold true for swimmers over different distances. For instance there is another study showing that long distance swimmers have a a higher concentration of slow twitch muscle fibres than spent swimmers.

The main takeaway seems to be that swimmers should never get pigeonholed, either by themselves or their coach, into certain freestyle race distances based on body type alone.

© Chris St Cartmail