The aim of this study was to examine the influence of several explanatory factors: anthropometry, buoyancy, passive underwater torque, drag and swimming technique on the energy cost of swimming front crawl in children and adults. Submaximal V(.)O(2) was measured in ten children (age 12) and 13 adults (age 21), as well as body length (BL), body mass, arm length, propelling size, active drag, hydrostatic lift, passive torque, intracyclic velocity fluctuation, hand slip, stroke length and body angle. The results show that body length ( r=0.74), body mass ( r=0.86) propelling size ( r=0.61), arm length ( r=0.66), distance between the center of mass and the center of volume (Delta d, r=0.74) and body angle during swimming ( r=-0.56) all showed significant linear relationships with the cost of swimming at 1.0 m x s(-1) (CS(1.0)). When normalizing the cost of swimming to body size (CS(1.0) x BL(-1)) there were no differences between the two groups. The conclusions of this study are that the combination of BL, body mass, active drag factor, passive torque, drag efficiency and hydrostatic lift were able to explain 97% of the variation in the cost of swimming for the whole group of swimmers. The size-independent factors of torque and floating abilities (density and Delta d in % of BL), together with swimming technique and active drag were found to explain 75% of the variations in CS(1.0) x BL(-1). The identical values for CS(1.0) x BL(-1) for children and adults are explained through the opposing effects of a better swimming technique in the adults, and a better passive torque in the children.