Energetics of swimming at maximal speeds in humans

The energy cost per unit of distance (C-s, kilojoules per metre) of the front-crawl, back, breast and butterfly strokes was assessed in 20 elite swimmers. At sub-maximal speeds (nu), C-s was measured dividing steady-state oxygen consumption ((V) over dot O-2) by the speed (nu, metres per second). At supra-maximal nu, C-s was calculated by dividing the total metabolic energy (E, kilojoules) spent in covering 45.7, 91.4 and 182.9 m by the distance. E was obtained as: E = E-an + alpha(V) over dot O(2max)t(p) - alpha(V) over dot O(2max)tau(1 - e(-(tp/tau))), where E-an was the amount of energy (kilojoules) derived from anaerobic sources, (V) over dot O-2max litres per second was the maximal oxygen uptake, alpha (= 20.9 kJ . 1 O-2(-1)) was the energy equivalent of O-2, tau (24 s) was the time constant assumed for the attainment of (V) O-2max at muscle level at the onset of exercise, and t(p) (seconds) was the performance time. The lactic acid component was assumed to increase exponentially with t(p) to an asymptotic value of 0.418 kJ . kg(-1) of body mass for t(p) greater than or equal to 120 s. The lactic acid component of E-an was obtained from the net increase of lactate concentration after exercise (Delta[La](b)) assuming that, when Delta[La](b) = 1 mmol . 1(-1) the net amount of metabolic energy released by lactate formation was 0.069 kJ . kg(-1). Over the entire range of nu, front crawl was the least costly stroke. For example at 1 m . s(-1), C-s amounted, on average, to 0.70, 0.54, 0.82 and 0.124 kJ . m(-1) in front crawl, backstroke, butterfly and breaststroke, respectively; at 1.5 m . s(-1), C-s was 1.23, 1.47, 1.55 and 1.87 kJ . m(-1) in the four strokes, respectively. The C-s was a continuous function of the speed in all of the four strokes. It increased exponentially in crawl and backstroke, whereas in butterfly C-s attained a minimum at the two lowest nu to increase exponentially at higher nu. The C-s in breaststroke was a linear function of the nu, probably because of the considerable amount of energy spent in this stroke for accelerating the body during the pushing phase so as to compensate for the loss of nu occurring in the non-propulsive phase

How fins affect the economy and efficiency of human swimming

The aim of the present study was to quantify the improvements in the economy and efficiency of surface swimming brought about by the use of fins over a range of speeds (v) that could be sustained aerobically. At comparable speeds, the energy cost (C) when swimming with fins was about 40 % lower than when swimming without them; when compared at the same metabolic power, the decrease in C allowed an increase in v of about 0.2 ms-1. Fins only slightly decrease the amplitude of the kick (by about 10 %) but cause a large reduction (about 40 %) in the kick frequency. The decrease in kick frequency leads to a parallel decrease of the internal work rate (int, about 75 % at comparable speeds) and of the power wasted to impart kinetic energy to the water (k, about 40 %). These two components of total power expenditure were calculated from video analysis (int) and from measurements of Froude efficiency (k). Froude efficiency (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); F was found to be 0.70 when swimming with fins and 0.61 when swimming without them. No difference in the power to overcome frictional forces (d) was observed between the two conditions at comparable speeds. Mechanical efficiency [tot/(Cv), where tot=k+int+d] was found to be about 10 % larger when swimming with fins, i.e. 0.13±0.02 with and 0.11±0.02 without fins (average for all subjects at comparable speeds)

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

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