Energy balance of human locomotion in water

Abstract

In this paper a complete energy balance for water locomotion is attempted with the aim of comparing different modes of transport in the aquatic environment (swimming underwater with SCUBA diving equipment, swimming at the surface: leg kicking and front crawl, kayaking and rowing). On the basis of the values of metabolic power (E), of the power needed to overcome water resistance (Wd) and of propelling efficiency (etaP=Wd/Wtot, where Wtot is the total mechanical power) as reported in the literature for each of these forms of locomotion, the energy cost per unit distance (C=E/v, where v is the velocity), the drag (performance) efficiency (etad=Wd/E) and the overall efficiency (etao=Wtot/E=etad/etaP) were calculated. As previously found for human locomotion on land, for a given metabolic power (e.g. 0.5 kW=1.43 l.min(-1) VO2) the decrease in C (from 0.88 kJ.m(-1) in SCUBA diving to 0.22 kJ.m(-1) in rowing) is associated with an increase in the speed of locomotion (from 0.6 m.s(-1) in SCUBA diving to 2.4 m.s(-1) in rowing). At variance with locomotion on land, however, the decrease in C is associated with an increase, rather than a decrease, of the total mechanical work per unit distance (Wtot, kJ.m(-1)). This is made possible by the increase of the overall efficiency of locomotion (etao=Wtot/E=Wtot/C) from the slow speeds (and loads) of swimming to the high speeds (and loads) attainable with hulls and boats (from 0.10 in SCUBA diving to 0.29 in rowing).

The underwater environment: cardiopulmonary, thermal, and energetic demands

“…As previously reported for nude immersed subjects, divers' initial drop in core temperature was associated with their subcutaneous fat thickness (2). Other studies in submersed fin-swimming divers have shown that the energy cost of locomotion was 20% higher and V O 2max 25% lower in cold water than in thermoneutral water and that this was due to a reduced net mechanical efficiency and not drag (75,79).…”

“…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).…”

“…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). 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.…”

“…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. The exponent of the rise in energy cost and drag with velocity is determined by the type of drag, which is velocity dependent, and the exponent(in kV n ) typically ranges from ϳ1.5 to 1.8 for surface fin swimming and from 1.2 to 1.5 for underwater fin swimming (80). Another interesting observation is that the energy cost of locomotion in water, being more technique dependent, is highly variable among individuals (i.e., ϳ25%), which is not the case for walking or running.…”

Swimming bodysuit in all-out and constant-pace trials

“…In the 50 m crawl trial; the most of the difference in speed was gained during the diving and gliding phase (most notably during start and turn, ) and no difference was observed while swimming Moreover, in the second half of 400 m trial, when we usually expect higher front resistance (caused by fatigue and sinking legs) [4], the subjects swimming in bodysuit sustained the same stroke frequency as in the first 200m with lower lactate values, which was not observed while wearing regular suit.…”