ISSN:
1600-0838
Source:
Blackwell Publishing Journal Backfiles 1879-2005
Topics:
Medicine
,
Sports Science
Notes:
Two forces act on a human body motionless in water: weight (W) and buoyancy (B). They are applied to the center of mass (CM) and to the center of volume (CV) of the subject, respectively. CM and CV do not coincide; this generates a torque that is a measure of the tendency of the upper part of the body to rise, rotating around its center of mass. To quantify this tendency, Pendergast & Craig defined ‘underwater torque’ (T1) as the product of the net force with which the feet of a subject lying horizontally in water tend to sink, times the distance between the feet and the center of volume of the lungs. In this paper we have investigated: (a) the relationships between T1 and body weight (BW), height (H), body surface area (BS), body density (BD) and leg density (LD) in a group of 30 subjects (group A, 14 females and 16 males, age range 16-50 years); and (b) the effect of gender and growth on T1 in a group of 110 subjects (group B, 67 girls and 43 boys, age range 12-17 years). In group A, T1 was found to be linearly related with BW (r= 0.833, P 〈 0.001), H (r= 0.803, P 〈 0.001), BS (r= 0.866, P 〈 0.001), BD (r= 0.617, P 〈 0.001) and LD (r= 0.549, P 〈 0.005). A multiple linear regression analysis showed that BS and BD explained about 85% of the variability of T1 (r2= 0.85). In group B, T1 was found to increase linearly with age (r= 0.47, P 〈 0.01), the increasing rate being three times higher in boys compared with girls. As a consequence, the T1 ratio between boys and girls increased with age, from 1.69 at 13 years to 2.04 at 16 years.
Type of Medium:
Electronic Resource
URL:
http://dx.doi.org/10.1111/j.1600-0838.1996.tb00470.x
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