Author(s): ZHONG, J., WANG, D., Institution: SHANGHAI UNIVERSITY OF SPORT, Country: CHINA, Abstract-ID: 1093

INTRODUCTION:
Trunk muscles are critical for effective freestyle turn performance because they facilitate dual rotational movements—rolling and twisting. Enhanced trunk strength not only stabilizes the spine and overall body but also improves underwater performance (e.g., gliding and undulatory underwater swimming) by reducing disturbances and drag while increasing body amplitude [1-2]. Previous studies have shown that incorporating trunk strength training (TST) into day-land programs can improve 50 m freestyle performance and turn efficiency (measured as the 5 m segment following wall contact) [3-4]. However, due to differences in performance parameters between sprint- and middle-distance events, the effects of TST on 400 m freestyle remain unclear. Thus, thus study aimed to examine the impact of TST on turn time performance during 400 m freestyle among national-level swimmers.
METHODS:
Fourteen national-level swimmers (8 males, 6 females) specializing in middle-distance freestyle were divided into an experimental group (EG: 18.3 ± 3.3 y, 177.3 ± 9.5 cm, 65.7 ± 9.5 kg) and a control group (CG: 20.3 ± 4.2 y, 179.5 ± 7.3 cm, 69.4 ± 11.7 kg). In addition to their regular day-land training (focusing on upper and lower limb strength), the EG completed an 8 weeks TST program (three sessions per week) divided into two phases: a basic stage (4 weeks) focusing on trunk bilateral rotation stability and dynamic strength, followed by advanced stage (4 weeks) emphasizing explosive power and specific turn exercise. Pre- and post-intervention assessments included trunk isokinetic peak force (PT) using an IsoMed 2000 dynamometer for flexion-extension (60°/s) bilateral rotation (150°/s), and turn time parameters during 400 m freestyle test. Turn performance was evaluated by overall turn time (OTT: the cumulative time for 7 turns, measured from the last 5 m before the rolling rotation to the 10 m mark after wall contact) and the average 5 m round turn time (5 m-RTT). A two-way repeated measures ANOVA was used to analyze intervention effects.
RESULTS:
Significant interactions between time (pre vs. post) and group (EG vs. CG) were found for trunk flexion PT (F = 5.600, p = 0.036, η2p = 0.318), extension PT (F = 5.534, p = 0.037, η2p = 0.316), left rotation PT (F = 19.496, p = 0.001, η2p = 0.619) and right rotation PT (F = 10.626, p = 0.007, η2p = 0.470), OTT (F = 15.061, p = 0.002, η2p = 0.557), 5 m-RTT (F = 21.396, p = 0.001, η2p = 0.641), and overall 400 m freestyle performance (F = 9.526, p = 0.009, η2p = 0.443). Compared to the CG, the EG showed significantly greater improvements in trunk strength and turn performance.
CONCLUSION:
Combined TST can enhance trunk flexion, extension, and bilateral rotation strength, leading to improved turn efficiency and overall performance in 400 m freestyle among national-level swimmers.
Reference:
[1] Kwok et al., 2021; [2] Ikeda et al., 2021; [3] Weston et al., 2015; [4] Karpiński et al., 2020