SummaryScientific research in swimming over the past 10 to 15 years has been oriented toward multiple aspects that relate to applied and basic physiology, metabolism, biochemistry, and endocrinology. This review considers recent findings on: 1) specific physical characteristics of swimmers; 2) the energetics of swimming; 3) the evaluation of aerobic fitness in swimming; and 4) some metabolic and hormonal aspects related to swimmers.Firstly, the age of finalists in Olympic swimming is not much different from that of the participants from other sports. They are taller and heavier than a reference population of the same age. The height bias in swimming may be the reason for lack of success from some Asian and African countries. Experimental data point toward greater leanness, particularly in female swimmers, than was seen 10 years ago. Overall, female swimmers present a range of 14 to 19% body fat whereas males are much lower (5 to 10%).Secondly, the relationship between O2uptake and crawl swimming velocity (at training and competitive speeds) is thought to be linear. The energy cost varies between strokes with a dichotomy between the 2 symmetrical and the 2 asymmetrical strokes. Energy expenditure in swimming is represented by the sum of the cost of translational motion (drag) and maintenance of horizontal motion (gravity). The cost of the latter decreases as speed increases. Examination of the question of size-associated effects on the cost of swimming using Huxley’s allometric equation (Ŷ = axb) shows an almost direct relationship with passive drag. Expressing energy cost in litres of O2/m/kg is proposed as a better index of technical swimming ability than the traditional expression of V̇O2/distance in L/km.Thirdly, maximal direct conventional techniques used to evaluate maximal oxygen consumption (V̇V̇O2 max) in swimming include free swimming, tethered swimming, and flume swimming. Despite the individual pecularities of each method, with similar experimental conditions similar results for V̇O2 maxwill be found. Free swimming (unimpeded) using the backward extrapolation method will, however, lead to reliable and valid results obtained in a condition that is closer to the competitive situation than with a direct test. A maximal indirect field-test has been recently made available. This test can predict V̇O2 maxwith an acceptable accuracy (r = 0.877), and provides a mean to evaluate the functional maximal aerobic power in swimming which corresponds to the maximal aerobic swimming velocity.Finally, although general principles of metabolic and endocrine aspects of exercise also apply to swimming, researchers have given a new but growing attention to specific aspects of metabolic and hormonal responses in swimmers. Metabolic studies in swimming point to a certain degree of disparity between swim training and the competitive events as far as substrate utilisation is concerned. Lactate response during swimming has also been used extensively to estimate the kinetics of energy production at submaximal and maximal exercise levels. Reports on endocrine responses specifically related to swimmers have mainly been directed toward the study of the menstrual cycle. Contrary to female gymnasts, the age ofmenarche of girl swimmers has been shown to be somewhat delayed or not delayed at all, although a later age at menarche has been recently observed for the more competitive swimmers. The incidence of athletic amenorrhoea also appears to be higher in runners and ballet dancers than in swimmers.