Energy cost of front-crawl swimming at supra-maximal speeds and underwatertorque in young swimmers

The energy cost of front-crawl swimming (C-s, kJ(.)m(-1)) at maximal volunt ary speeds over distances of 50, 100, 200 and 400 m, and the underwater tor que (T') were assessed in nine young swimmers (three males and six females; 12-17 years old). C-s was calculated from the ratio of the total metabolic energy (E-s, kJ) spent to the distance covered. E-s was estimated as the s um of the energy derived from alactic (AnAl), lactic (AnL) and aerobic (Aer ) processes. In turn, Ant was obtained from the net increase of lactate con centration after exercise, AnAl was assumed to amount to 0.393 kJ(.)kg(-1) of body mass, and Aer was estimated from the maximal aerobic power of the s ubject. Maximal oxygen consumption was calculated by means of the back-extr apolation technique from the oxygen consumption kinetics recorded during re covery after a 400-m maximal trial. Underwater torque (T', N(.)m), defined as the product of the force with which the feet of a subject lying horizont ally in water tends to sink times the distance from the feet to the center of volume of the lungs, was determined by means of an underwater balance. C -s (kJ(.)m(-1)) turned out to be a continuous function of the speed (v, m(. )s(-1)) in both males (C-s = 0.603(.)10(0.228v), r(2) = 0.991, n = 12) and females (C-s = 0.360(.)10(0.339v), r(2) = 0.919; n = 24). A significant rel ationship was found between T' and C-s at 1.2 m(.)s(-1); C-s = 0.042T' + 0. 594, r = 0.839, n = 10, P < 0.05. On the contrary, no significant relations hips were found between C-s and T' at faster speeds (1.4 and 1.6 m(.)s(-1)) . This suggests that T' is a determinant of C-s only at speeds comparable t o that maintained by the subjects over the longest, 400-m distance [mean (S D) 1.20 (0.07) m(.)s(-1)].