Nine members of the U.S. Men's Olympic Rowing Team were studied during the in-season (IS) and off-season (OS). Maximum power, VE, VO2, and heart rate were measured during a 6-min rowing ergometer exercise during IS and OS. Per cent body fat and isokinetic quadriceps strength were also determined. Biopsies were removed from the vastus lateralis and analyzed histochemically and morphometrically during OS only. No changes were noted for body composition between IS and OS. VEmax and VO2max increased significantly from OS to IS; absolute VO2max increased from 5.09 to 6.01 l/min and relative values increased from 56.5 to 69.1 ml . kg-1 . min-1. Power increased 14% from OS to IS while heart rate showed no difference. Leg strength increased significantly at 6 different angular velocities from IS to OS especially at the lower speeds. Biopsy data revealed an average ratio of 75% slow twitch Type I fibers and 25% fast twitch Type II fibers. Larger fiber diameters were noted for Type II fibers but this difference was not significant. Although seasonal effects were expected, the unusually large differences in metabolic and strength capacities between IS and OS reflect a high degree of training specificity.