Economy and efficiency of swimming at the surface with fins of different size and stiffness

Abstract

The aim of this study was to investigate how fins with varying physical characteristics affect the energy cost and the efficiency of aquatic locomotion. Experiments were performed on ten college swimmers who were asked to swim the dolphin kick while using a monofin (MF) and to swim the front crawl kick with a small-flexible fin (SF), a large-stiff fin (LS) and without fins (BF, barefoot). The energy expended to cover one unit distance (C) was highest for BF (C=10.6+/-1.8 kJ m(-1) kg(-1) at 0.8 m s(-1)) and decreased by about 50% with LS, 55% with SF and 60% with MF, allowing for an increase in speed (for a given metabolic power) of about 0.4 m s(-1) for MF and of about 0.2 m s(-1) for SF and LS (compared with BF). At any given speed, the fins for which C was lower were those with the lowest kick frequency (KF): KF=1.6+/-0.22 Hz at 0.8 m s(-1) (for BF) and decreased by about 40% for SF, 50% for LS and 60% for MF. The decrease in KF from BF to SF-LS and MF was essentially due to the increasing surface area of the fin which, in turn, was associated with a higher Froude efficiency (eta(F)). eta(F) was calculated by computing the speed of the bending waves moving along the body in a caudal direction (as proposed for the undulating movements of slender fish): it increased from 0.62+/-0.01 in BF to 0.66+/-0.03 in SF and 0.67+/-0.04 in LS reaching the highest values (0.76+/-0.05) with MF. No single fin characteristic can predict a swimmer's performance, rather the better fin (i.e. MF) is the one that is able to reduce most KF at any given speed and hence to produce the greatest distance per kick (d=v/KF). The latter indeed increased from 0.50+/-0.01 m in BF to about 0.90+/-0.05 m in SF and LS and reached values of 1.22+/-0.01 m in MF.

The underwater environment: cardiopulmonary, thermal, and energetic demands

“…Estimating the efficiency of underwater work is complicated, compared with terrestrial work, using a traditional approach (only considering external work) and yields a very low efficiency (about 5-8%) (80); during swimming the swimmer has to accelerate water when moving through it and also perform internal work moving body parts around the body center of gravity. Once these factors are accounted for, the efficiency is similar (i.e., ϳ25%) during fin swimming (at the surface, and underwater) as when exercising on land (107). The implication of this is that the energy cost of movement in water increases exponentially as a function of velocity and is independent of body weight, as opposed to walking or running where it increases linearly and is weight dependent.…”

“…Thus both external and internal work are increased (79,80,107). Drag in water is velocity dependent (80) and increases as a function of kV n , where k is a constant, V is velocity, and n is the exponent of V, with n ϭ 1 for friction between the body and water, n ϭ 2 for the pressure to separate the water as the body moves through it (pressure drag), and n ϭ 4 for wave generation (67).…”

Defining and Monitoring Power Measurement in Elite Swimmers

“…It has been reported that at lower speeds the contribution of arm stroke internal work to speed is low Zamparo et al [5], However this changes in sprint and maximal swims where power output should be maximized.…”

“…This may have led to why it is not often monitored in swimming. Zamparo et al [5] described that the total work was made up of the work needed to accelerate and decelerate limbs with respect to the centre of mass (internal work or power American Journal of Sports Science and Medicine 58 input) and the work needed to overcome external forces. The latter was also broken down into that force which overcomes drag and contributes to thrust and the kinetic work that does not add to thrust but does add energy to the water.…”

“…Total power outputs were described to average 2720 w for 100 freestyle swims and 1940watts for 200m freestyle swims. We are assuming that these values relate to what Zamparo et al [5] described as internal power, that is, the power that is generated within the body before it is applied. As such, these values are higher than those suggested by a standard calculation of watts (where watts = 1000 x E(kj)/time), and appear high in relation to time lines when compared to swimming and other sports ( Table 1).…”