Preseason Deceleration Index Is Lower in Collegiate Football Athletes Who Sustain Time-Loss Lower-Quarter Injuries: A Three-Season Prospective Cohort Study

Background Deceleration capacity is a fundamental yet underappreciated component of multidirectional sport performance. Non-contact lower-quarter injuries frequently occur during rapid deceleration and change-of-direction tasks, yet braking capacity remains under-evaluated relative to acceleration and speed. The Deceleration Index (DI) has been proposed as a ratio-based metric of peak deceleration to peak acceleration. Hypothesis/Purpose: The purpose of this study was to compare preseason Deceleration Index values between collegiate football athletes who sustained a time-loss lower-quarter injury and position-matched uninjured athletes across three competitive seasons. It was hypothesized that football athletes who sustain a non-contact time-loss lower-quarter injury would demonstrate lower preseason DI values than position-matched uninjured athletes. Study Design Prospective cohort study. Methods Division I male collegiate football athletes completed preseason change-of-direction testing (5-10-5 test) during summer training camp at the beginning of each season. Following a warmup, data were captured using a Global Navigation Satellite System (GNSS) integrated with an Inertial Measurement Unit (IMU). The DI was calculated as peak deceleration value divided by peak acceleration value. Athletes were prospectively followed three consecutive seasons for time-loss lower-quarter injuries. Injured athletes (n = 57) were matched 1:1 by playing position to uninjured controls (n = 57). Independent-samples t-tests compared group means, with Cohen’s d for effect size. Receiver operating characteristic (ROC) analysis assessed within-sample discriminatory ability. Results Injured and uninjured athletes were similar at baseline in age (mean 22 years in each group), height, body mass, and BMI (all p ≥ 0.09). Injured athletes demonstrated significantly lower preseason DI than uninjured athletes (0.90 ± 0.07 vs 1.10 ± 0.10; p < 0.001; Cohen’s d = 2.30). ROC analysis showed excellent within-sample discrimination (AUC = 0.96, 95% CI 0.89–0.99); a DI ≤ 1.00 yielded a sensitivity of 93% and a specificity of 91%. Conclusion Lower preseason DI values were associated with subsequent non-contact time-loss lower-quarter injury in collegiate football athletes. DI may serve as a practical field-based risk indicator reflecting braking capacity relative to acceleration; causal inference and the proposed threshold require independent validation. Level of Evidence 2b (individual prospective cohort study).