McLean, S.P., & Hinrichs, R.N. (1998). Sex differences in the center of buoyancy location of competitive swimmers. Journal of Sports Science, 16(4), 373-383.

This study identified differences in the center of buoyancy (CB) and center of mass (CM) locations of male and female collegiate swimmers, and assessed the influence that buoyancy had on freestyle kicking performance.

Female collegiate swimmers (N = 16) had significantly more adipose tissue (20.2 +/- 4.4%) than 15 male collegiate swimmers (N = 15; 12.6 +/- 3.8%). The ratio of the sum of abdominal and suprailiac skinfolds to the thigh skinfold was significantly greater for males (2.07 +/- 0.37) than females (1.31 +/- 0.32), implying that females had proportionately more fatty tissue caudally than males. The distance between the centers of buoyancy and mass was significantly larger for males (0.79 +/- 0.43 cm) than females (0.16 +/- 0.34 cm). Both points were more caudal in females (59.9 +/- 0.7% and 59.8 +/- 0.7% of body height respectively) than in males (61.7 +/- 0.8% and 61.2 +/- 0.9% respectively).

The difference in distance between the centers could be attributed to the difference in the location of the center of buoyancy, because the center of mass difference was not significant and was characterized by a smaller effect size. The amount and distribution of adipose tissue accounted for a significant proportion of variance in the distance (R2 = 0.25 and 0.29 respectively). Males had a significantly higher proportional kick time, defined as the ratio of times to complete a 22.9 m sprint when kicking and swimming respectively, than females (1.57 +/- 0.09 and 1.51 +/- 0.13 respectively). This showed that the male swimmers kicked proportionally more slowly than the female swimmers. However, the distance between centers did not account for a significant proportion of variance in the proportional kick time.

These results do not support the assertion that skilled male swimmers are at a performance disadvantage in terms of natural buoyancy characteristics.

Implication. Male swimmers have different buoyancy characteristics to females. However, when kicking was used as a performance measure the buoyancy differences were unrelated to performance. Males generally kicked slower than females probably because their kicks had to travel a greater distance.

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