Do platform recommendation logics shape public engagement with sports health content? 400-video evidence from Douyin and Bilibili

Background Digital video platforms are not neutral conduits; their ranking signals and interfaces shape what becomes visible and valuable. Badminton—balancing spectacle and instruction—offers leverage to compare Douyin's engagement-optimized short video with Bilibili's community- and knowledge-oriented ecology. Objective To examine whether engagement patterns differ across platform-native discovery environments and to interpret these differences through an algorithmic cultural filtering lens. Methods We analyzed 400 videos sampled in June 2025 (200 per platform) using each platform's native discovery orders; coders recorded content type, creator identity, duration, and public counters (likes, comments, shares, and bookmarks), with excellent inter-coder reliability (κ = 0.94). Because engagement metrics were highly right-skewed, cross-platform differences were first examined using two-tailed Mann–Whitney U -tests with effec