Clark, IE, West, BM, Reynolds, SK, Murray, SR, and Pettitt, RW. Applying the critical velocity model for an off-season interval training program. J Strength Cond Res 27(12): 3335–3341, 2013—The critical velocity (CV) model offers an opportunity to prescribe and to test empirically different velocity-time (V–t) configurations of high-intensity interval training (HIIT); however, such experiments are lacking. We evaluated a group of competitive, female soccer players (age = 19 ± 1 years, height = 168 ± 6 cm, mass = 61 ± 6 kg) completing 1 of 2 different HIIT regimes: a short group (n = 6) completing higher V and shorter t configurations, and a long group (n = 10) completing lower V, longer t configurations. Both groups trained 2 d·wk−1 for 4 weeks. For each workout, both groups ran at velocities exceeding CV and designed to deplete identical fractional percentages of the finite work capacity above CV (D′). The metrics of CV and D′ were evaluated at pretraining and posttraining using the 3-minute all-out exercise test on an indoor track using video digitizing of displacement relative to time. Despite differences in the V–t configurations, both groups increased their CV (+0.22 m·s−1, +6%) and decreased their D′ (−24 m, −13%; p < 0.05). We conclude that 2- to 5-minute HIIT bouts are suitable for increasing CV, in previously trained athletes, but they result in a decline of D′. To increase D′, we suggest examining HIIT of intensities that are <2 minutes and >130% of maximum oxygen uptake.