Evaluation of various traditional machine learning techniques for predicting the acute effect of different hamstring muscle stretching methods among male soccer players

This study investigated the acute effects of static (SS), dynamic (DS), and ballistic (BS) hamstring stretching on performance in male soccer players and applied machine learning (ML) to predict protocol efficacy. A total of 249 players with and without hamstring shortening completed each protocol across three sessions with 72 h of rest. Hamstring shortening classified via passive knee extension test (> 32.2° knee angle). Flexibility, strength, sprint, power, and agility were measured pre- and post-stretching. Each protocol: 4 sets × 30 s (holds/swings/bounces at 50-60 bpm), 10 s rest. ML models (k-NN, SVM, random forest) were trained on pre-post difference scores, with feature selection applied to identify key predictors and Synthetic Minority Over-sampling Technique used to address class imbalance. Findings indicate SS optimally acutely improves flexibility, whereas DS offers broader immediate performance benefits for a subsequent activity. Combining feature selection and data balancing increased k-NN accuracy to 53% (only ~ 20% points above the chance level of 33.3% for this three-class problem), highlighting methodological challenges in predicting individual responses. Exploratory analysis using ML using synthetic minority over-sampling technique reached a peak accuracy of 53.06% (compared to a baseline of 33.3%), demonstrating the promise of the approach but also highlighting the challenges of applying ML to predict individual responses to stretching interventions, underscoring the need for larger datasets and more advanced models.