Development and Internal Validation of a Field-Based Equation for Predicting Half-Squat One-Repetition Maximum in Youth Soccer Players Using Standing Long Jump Performance and Body Mass

Purpose: This study aimed to examine the validity of field-based tests, specifically the 5-Jump Test (5JT) and Standing Long Jump (SLJ), combined with anthropometric measures for predicting one-repetition maximum (1RM) half-squat performance in U-13 male soccer players. Methods: Forty-one male youth soccer players (age: 12.77 +/-.25 years; body-mass (BM): 46.54 +/- 7.86 kg; body-height: 157.70 +/- 9.58 cm) participated in this investigation. Following a one-week familiarization session that included practice trials of all testing procedures and movement pattern instruction, participants completed three testing sessions comprising anthropometric measurements, 1RM half-squat assessment, and field tests (5JT and SLJ). Multiple linear regression analysis was employed to develop prediction equations, with model validation including assessments of normality, homoscedasticity, and multicollinearity. Results: The final prediction model incorporating only BM and SLJ explained 70% of the variance in 1RM half-squat performance (R-2=.696, P<.001). The resulting equation (1RM=-114.503+ 1.953xBM+71.468xSLJ) demonstrated robust statistical properties, with both predictors showing significant contributions (BM: beta=1.953, 95% CI [1.3-2.5], P<.001; SLJ: beta=71.468, 95% CI [45.3-97.6], P<.001). The model satisfied assumptions of normality (Shapiro-Wilk: P=.06) and homoscedasticity (Breusch-Pagan: P=.521), with acceptable multicollinearity indices (VIF<4.0). While initially considered, age, standing height, and 5JT did not significantly improve prediction accuracy. Conclusions: This study validates a practical equation for estimating maximal half-squat strength in youth soccer players using readily available field measures. The combination of SLJ performance and BM provides coaches with a time-efficient, low-risk method for strength assessment in young athletes. This approach provides coaches with an accessible, time-efficient tool for strength monitoring that requires minimal equipment while maintaining scientific validity.