Effects of a Visual Feedback LED Pacing System in Middle-Distance Pool Freestyle Swimming

ZuLin Chen^1*LiHan Lin^2*Yuqi He^1,3YiKun Zheng¹Weiwei Zhang¹Dingtao Yan¹Shumin Luo¹Huangtao Chen¹Hongmiao Chen^1*

• ¹Huaqiao University, Quanzhou, China
• ²Fujian Normal University, Fuzhou, China
• ³Tokyo Daigaku, Bunkyo, Japan

Objective: This study examined the effects of an intelligent LED pacing system with visual feedback on training performance and physiological responses in middle-distance freestyle swimming. Methods: Twelve high-level swimmers completed two 200 m freestyle trials in a self-controlled design: first a self-paced swim, followed 24 h later by an LED-paced swim. The LED system converted individualized target times from each swimmer’s personal best into underwater light signals, providing real-time feedback. Trials were conducted in a 50 m indoor pool under standardized conditions. Each race was timed by three referees with synchronized stopwatches, heart rate was monitored with a Polar H10 under the swim cap, and fingertip blood lactate was sampled one minute before and after each trial. Recorded outcomes included entire and segmental times, coefficient of variation (CV) of split time, blood lactate change (Δ mmol·L⁻¹), heart rate range, and normalized HR range (HR CV). Normality was tested (Shapiro–Wilk), and paired-sample t-tests with Bonferroni adjustment (adjusted α = 0.01) were applied. Results included t values, P values, 95% confidence intervals, and effect sizes (Cohen’s d). Results: LED pacing showed no significant differences in entire 200 m time or split times compared with self-pacing (entire: 150.21 ± 18.44 vs 153.78 ± 20.26 s, d = 0.185; P = 0.014, not significant after Bonferroni adjustment). Pacing stability, assessed by CV of split times, showed no significant difference between LED pacing (8.49 ± 2.82%) and self-pacing (8.48 ± 2.56%) conditions (P = 0.981, d = 0.004). Physiologically, LED pacing lowered blood lactate accumulation (Δ lactate: 7.18 ± 1.61 vs 8.63 ± 1.19 mmol·L⁻¹, P = 0.028, d = 1.019), smaller heart rate fluctuations (overall range: 45.50 ± 7.40 vs 53.67 ± 7.75 bpm, P < 0.001, d = 1.078), and reduced HR CV across all segments (overall HR CV: 27.18% ± 4.46 vs 32.51% ± 5.07, P < 0.001, d = 1.117). Conclusion: In highly trained swimmers, LED pacing exerted negligible effects on pacing consistency and race time but was associated with reduced post-exercise blood lactate and heart rate fluctuations, indicating potential utility for training load management rather than immediate performance enhancement.