OBJECTIVES: To investigate whether tethered swimming (TS) performed 8 minutes before a 50-m freestyle swimming sprint could be an effective postactivation potentiation method to improve performance in young swimmers. METHODS: Fourteen regional-level male adolescent swimmers (age 13.0 [2.0] y; height 161.1 [12.4] cm; body mass 52.5 [9.5] kg) underwent 2 trial conditions in a randomized and counterbalanced order (1 experimental [TS], 1 control) on different days. During the experimental session, the participants performed a standard warm-up of 1200 m followed by a TS exercise, which consisted of 3 × 10-second maximal efforts of TS with 1-minute rests between bouts. In the control condition, the warm-up phase was immediately followed by 200 m at a moderate pace (same duration as the TS in the experimental session). Performance (time trial); biomechanical (stroke length), physiological (blood lactate concentrations), and psychophysiological (ratings of perceived exertion) variables; and countermovement-jump (CMJ) flight time were collected. RESULTS: TS warm-up had no significant effect on 50-m swimming performance (P =.27), postexercise ratings of perceived exertion, stroke length, or CMJ flight time (P ≥.05). Blood lactate concentrations significantly increased at the end of the warm-up in the TS condition only (interaction effect: F1.91,29.91 = 4.91, P =.01, η2 =.27) and after the 50-m trial in both conditions (F1.57,20.41 = 62.39, P =.001, η2 =.82). CONCLUSIONS: The present study demonstrated that 3 × 10-second TS exercises performed 8 minutes prior to the event did not affect ratings of perceived exertion, stroke length, or CMJ flight time. In addition, tethered swimming did not affect 50-m freestyle sprint performance in young swimmers.