Depth-specific responses to 8-week additional aquatic plyometric training on explosive performance and start-turn metrics in collegiate male swimmers.

Background: Aquatic plyometric training (APT) may improve explosive performance while reducing impact loading; however, the extent to which immersion depth influences transfer to swimming-specific start and turn performance remains unclear. This exploratory randomized study compared depth-specific responses to 8 weeks of additional aquatic plyometric-style training performed at different immersion depths in collegiate male swimmers who maintained regular swim training. Methods: Thirty collegiate male swimmers were randomized to shallow (knee/patella), mid-depth (waist/umbilicus), or deep (xiphoid/chest) APT groups. Participants completed two APT sessions per week for 8 weeks while maintaining regular swim training. Countermovement jump, squat jump, 15-m start time, turn 5-m in time, wall contact time, and turn 5-m out time were assessed before and after the intervention using high-speed video. Three trials were averaged for each outcome. Linear mixed-effects models were used to test group-by-time interactions, and within-rater reliability was assessed in a subsample of 10 participants. Results: Significant group-by-time interactions were observed for countermovement jump (p = 0.033), squat jump (p = 0.009), 15-m start time (p <0.001), and wall contact time (p = 0.016), indicating depth-dependent patterns of change. All groups showed favorable within-group changes in countermovement jump, squat jump, and 15-m start time, with the largest mean changes generally observed in the mid-depth group. Turn 5-m out time improved within groups, but the group-by-time interaction did not reach statistical significance (p = 0.095). No significant interaction was observed for turn 5-m in time (p = 0.457). Video-derived outcomes showed excellent within-rater reliability (ICC = 0.991-0.997; CV = 0.19%-1.40%). Conclusion: In collegiate male swimmers who maintained regular swim training, 8 weeks of additional APT was associated with favorable changes in lower-limb explosive performance and selected race-section metrics. Immersion depth appeared to influence the magnitude of adaptation, with the mid-depth condition showing larger mean changes in several outcomes, particularly compared with deep immersion, whereas differences between mid-depth and shallow immersion were less consistent. These findings should be interpreted as depth-specific responses to additional aquatic plyometric-style training performed alongside regular swim training, rather than as definitive evidence that APT alone caused the observed changes or is superior to other training approaches.