The purpose of this investigation was to determine how swimming velocity (SV), stroke rate (SR), stroke length (SL) and blood lactate concentration change as adaptations to six months of aerobic swim training. Subjects were trained male college swimmers (n = 8). Measurements were obtained following specially designed 400m freestyle swim tests, pre- and post-intervention. The swim test consisted of 4 x 400 m freestyle over two days. On day 1, subjects performed a maximal effort 400 m freestyle swimming trial; maximal mean velocity (Vmax) for each swimmer was calculated from this effort. On the next day, subjects were instructed to perform three 400 m freestyle swims at constant velocities equal to 85%, 90% and 95% of Vmax, respectively. Subjects rested one hour between swims. During each 400 m trial, lap time and time to complete 10 mid-pool strokes (50 m) were measured to determine SV (m.s-1), SR (stroke.min-1) and SL (m.stroke-1). Mixed arterial blood samples were taken at the end of each 400 m trial to evaluate blood lactate concentration. Results indicated that post-maximal swimming velocity (Vpostmax) increased significantly from pre-intervention measures (p < 0.05). Blood lactate concentration decreased significantly relative to SV and absolute lactate concentration following Vpostmax was significantly lower than that at Vpremax (p < 0.05). Six of seven subjects increased Vmax due to increases in SL. Mean SL during the second test was significantly higher (p < 0.05). Also, during the 400 m maximal test, SL increased significantly after sixth lap (p < 0.05). There was no significant difference between SRs.(ABSTRACT TRUNCATED AT 250 WORDS)