Introduction: Performance in swimming is primarily governed by two factors, energy output and technical skill. Practice and training during the season should focus on producing systematic adaptations that will bring swimmers to their peak physiological and biomechanical performance. There is evidence to suggest that both biomechanical and physiological components improve during early season training (Wakayoshi K. et al. 1993) however there have been no previous attempts to interrelate the time course or magnitude of physiological and biomechanical adaptations to early season training. Methods: After providing informed consent, 26 male college swimmers (19 ± 2yr) were tested prior to the start of a 12-week training program and subsequently at the end of weeks 4, 8, and 12. Each subject completed 3 pairs of 200 yd (183 m) freestyle swims at a self-perceived 75%, 85%, and 95% of maximum effort, respectively. One-minute rest was provided after each swim. Blood samples, obtained by using a finger-stick technique were collected after each pair of swims, analyzed for blood lactic acid. Swimming velocity at 4 mM blood lactate V4 (m/sec) was calculated for each individual at each testing period based on individual linear regressions of log (lactate) vs. swimming velocity. The test swims were filmed for analyzing stroke length-SL (m/stroke), stroke rate-SR (strokes/sec), breakout distance-BD (m), and stroke efficiency index-SEI (m/sec/cycle). V4 was compared to SR, SL, BD, and SEI using multiple correlation. Mean differences in these variables across speed and time were analyzed using a 3 × 4 (speed × time) repeated measures ANOVA. Results: This study showed that there was a significant difference in V4 from test 1(1.34 ± 0.01) to test 3 (1.37 ± 0.01), in SEI from test 1 (96.8 ± 1.5) to test 4 (99.7 ± 1.2), and in SR from test 1 (0.54 ± 0.02) to test 3 (0.57 ± 0.02). However, there was no significant change in SL and BD from test 1 to test 4 for the 18 subjects who had complete data. On the other hand, there was a high correlation for the peak value of the dependent variable V4 and the independent variables SEI (p < 0.01), SL (p < 0.05), and BD (p < 0.05) (R = 0.87, SEE = 0.04). In addition, the change in V4 (peak value minus test1) was not correlated with changes in SEI, SL, SR, and BD. Discussion: These findings support recent studies (1,2) showing that six months of training improved technical proficiency and, therefore, resulted in a reduction in the metabolic cost of swimming at the same velocity as before training. However, our study found that there was an interrelationship between a V4 and SEI, SL, and BD with a multiple correlation 0.87. This finding indicates that there is improvement in both physiological and biomechanical adaptation in early season training. Whether the improvement in V4 is dependent on the improvement in biomechanical performance remains to be determined. Acknowledgments: This research was supported by a grant from The Egyptian Cultural and Educational Bureau 1303 New Hampshire Ave NW, Washington, DC 20036.