Introduction:
In sports education, Lyndon’s "old way/new way" method (1989) corrects motor skills by comparing existing movements with new ones. However, this method has limitations with unstable or unfamiliar skills. To address these challenges, we proposed "Comparative Practice". This method aims to distinguish between two similar movements, understand the correct movement, and alternate similar movements while comparing them, to improve the ability to learn more effectively. By alternating between movements that are similar but not yet mastered, individuals gradually come to understand the differences in the movements and the required amount of force. This approach may lead to potential advancements in sports education.

Objective:
This study aimed to examine the effectiveness of Comparative Practice for learning the short serve in volleyball through a case study approach from both biomechanical and psychological perspectives.

Methods:
The participant was a 19-year-old female university volleyball player, 154 cm tall, weighing 52 kg, with 11 years of experience, specializing in the jump floater serve. The focus was on mastering the short serve, targeting a 3m x 3m area on the left front side of the net. The participant watched her own videos and tried to master the movement by reducing trunk extension (arch). Comparative Practice involved alternating between short and long serves, with 15 repetitions of each serve type per sessions, conducted four times over a week. The participant was asked to freely record her observations during the exercises, and measurements were taken after one week. For the following three weeks, she continued with her regular practice, and no recordings were required. Evaluations included serve performance, error analysis, biomechanical assessment using markerless motion capture (Theia3D), and psychological evaluation using a sport-specific Self-Regulated Learning Scale. A follow-up interview explored the rationale for the chosen correction task, the movement acquisition process, and differences from previous practices.

Results:
The participant demonstrated significant improvement in performance, with the number of successful serves increasing from 2 out of 10 before the experiment to 5 out of 10 after one week and stabilizing at 4 out of 10 after three weeks. Serving errors decreased and got closer to the target in both post-experiment evaluations. Biomechanical analysis revealed a reduction in peak truncal extension angles from 31.77±1.08° (Mean±SD) before the experiment to 23.87±0.43° (Mean±SD) after one week, and 23.27±0.66° (Mean±SD) after three weeks, with significant differences noted between measurements (p<.01). The problematic arch was notably reduced, and psychological indicators, such as the “evaluation and reflection” factor of the Self-Regulated Learning Scale, also improved. Introspective comments showed that Comparative Practice improved the identification of ball position and force adjustment. Additionally, the interviews revealed that the participant was practicing with the intention of simulating real competitions.

Conclusion:
These findings suggest that the Comparative Practice approach is effective in promoting motor skill acquisition. It offers a valuable method for sports education by enhancing an individual’s ability to introspectively analyze their own behavior, ultimately fostering the development of independent learners.

Keywords: movement correction, Comparative Practice, discrimination, markerless motion capture, self-regulated learning.