Effect of the underwater torque on the energy cost, drag and efficiency of front crawl swimming

5nonenoneZAMPARO P.; CAPELLI C.; TERMIN B.; PENDERGAST D.R.; DI PRAMPERO PZamparo, P.; Capelli, C.; Termin, B.; Pendergast, D. R.; DI PRAMPERO, Pietro Enric

An energy balance of front crawl

With the aim of computing a complete energy balance of front crawl, the energy cost per unit distance (C = Ev(-1), where E is the metabolic power and v is the speed) and the overall efficiency (eta(o) = W(tot)/C, where W(tot) is the mechanical work per unit distance) were calculated for subjects swimming with and without fins. In aquatic locomotion W(tot) is given by the sum of: (1) W(int), the internal work, which was calculated from video analysis, (2) W(d), the work to overcome hydrodynamic resistance, which was calculated from measures of active drag, and (3) W(k), calculated from measures of Froude efficiency (eta(F)). In turn, eta(F) = W(d)/(W(d) + W(k)) and was calculated by modelling the arm movement as that of a paddle wheel. When swimming at speeds from 1.0 to 1.4 m s(-1), eta(F) is about 0.5, power to overcome water resistance (active body drag x v) and power to give water kinetic energy increase from 50 to 100 W, and internal mechanical power from 10 to 30 W. In the same range of speeds E increases from 600 to 1,200 W and C from 600 to 800 J m(-1). The use of fins decreases total mechanical power and C by the same amount (10-15%) so that eta(o) (overall efficiency) is the same when swimming with or without fins [0.20 (0.03)]. The values of eta(o) are higher than previously reported for the front crawl, essentially because of the larger values of W(tot) calculated in this study. This is so because the contribution of W(int) to W(tot )was taken into account, and because eta(F) was computed by also taking into account the contribution of the legs to forward propulsion

An energy balance of front crawl

With the aim of computing a complete energy balance of front crawl, the energy cost per unit distance (C = Ė-v -1, where Ė is the metabolic power and v is the speed) and the overall efficiency (ηo = Wtot/C, where Wtot is the mechanical work per unit distance) were calculated for subjects swimming with and without fins. In aquatic locomotion Wtot is given by the sum of: (1) Wint, the internal work, which was calculated from video analysis, (2) Wd, the work to overcome hydrodynamic resistance, which was calculated from measures of active drag, and (3) Wk, calculated from measures of Froude efficiency (ηF). In turn, ηF Wd/(Wd + Wk) and was calculated by modelling the arm movement as that of a paddle wheel. When swimming at speeds from 1.0 to 1.4 m s-1, ηF is about 0.5, power to overcome water resistance (active body drag × v) and power to give water kinetic energy increase from 50 to 100 W, and internal mechanical power from 10 to 30 W. In the same range of speeds Ė increases from 600 to 1,200 W and C from 600 to 800 J m-1. The use of fins decreases total mechanical power and C by the same amount (10-15%) so that ηo (overall efficiency) is the same when swimming with or without fins [0.20 (0.03)]. The values of ηo are higher than previously reported for the front crawl, essentially because of the larger values of Wtot calculated in this study. This is so because the contribution of Wint to Wtot was taken into account, and because ηF was computed by also taking into account the contribution of the legs to forward propulsion

Bioenergetics and biomechanics of front crawl swimming

''Underwater torque'' (T') is one of the main factors determining the energy cost of front crawl swimming per unit distance (C-s). In turn, T' is defined as the product of the force with which the swimmer's feet tend to sink times the distance between the feet and the center of volume of the lungs. The dependency of C-s on T' was further investigated by determining C-s in a group of 10 recreational swimmers (G1: 4 women and 6 men) and in a group of 8 male elite swimmers (G2) after T' was experimentally modified. This was achieved by securing around the swimmers' waist a plastic tube filled, on different occasions, with air, water, or 1 or 2 kg of lead. Thus, T' was either decreased, unchanged, or increased compared with the natural condition (tube filled with water). C-s was determined, for each T' configuration, at 0.7 mis for G1 and at 1.0 and 1.2 m/s for G2. For T' equal to the natural value, C-s (in kJ.m(-1) m body surface area(-2)) was 0.36 +/- 0.09 and 0.53 +/- 0.13 for G1 in women and men, respectively, and 0.45 +/- 0.05 and 0.53 +/- 0.06 for G2 at 1.0 and 1.2 m/s, respectively. In a given subject at a given speed, C-s and T' were linearly correlated. To compare different subjects and different speeds, the single values of C-s and T' were normalized by dividing them by the corresponding individual averages. These were calculated from all single values (of C-s or T') obtained from that subject at that speed. The normalized C-s was found to be a linear function of the normalized T' (r = 0.84, P < 0.001; n = 86) regardless of sex, speed, or swimming skill. We concluded that, in the speed range of 0.7-1.23 m/s, T' is indeed the main determinant of C-s regardless of sex or swimming skill