Interrelationships between countermovement jump, assisted acceleration–deceleration, and isometric belt squat metrics in American football players - exploratory study

Background Practitioners increasingly seek proxy metrics that allow key neuromuscular qualities to be monitored using field-based tests. However, the extent to which countermovement jump (CMJ), sprint-based deceleration tasks, and isometric strength tests share underlying constructs remains unclear. Purpose To examine relationships between metrics derived from CMJ, assisted 30 m acceleration-deceleration (ADA30), and isometric belt squat (IBS) tests, and to identify candidate proxy metrics for acceleration, peak sprint velocity, and braking. Methods Twenty-four American football players completed CMJ no-arms-swing, ADA30 in assisted mode, and IBS at ∼120° knee flexion. From exports, 30 CMJ, 8 ADA30 phase 1a, and 9 IBS variables were retained. Spearman rank correlations were computed between CMJ–ADA30, CMJ–IBS, and ADA30–IBS pairs. False discovery rate was controlled using the Benjamini-Hochberg procedure (q = 0.10). Results Phase 1a peak assisted sprint velocity was associated with CMJ propulsive metrics (ρ = 0.61–0.81). CMJ braking phase variables were associated with IBS relative peak force, including relative braking force metrics (ρ = 0.63–0.66) and braking phase duration (ρ = −0.61). Braking phase duration and stiffness were associated with phase 1a peak deceleration (ρ = −0.58 and −0.57). Peak IBS rate of force development was counterintuitively associated with early assisted acceleration metrics, comprising phase 1a 0–5 m time (ρ = 0.58) and phase 1a peak acceleration (ρ = −0.57). Conclusions CMJ propulsive metrics appear to be robust proxy candidates for assisted peak sprint velocity, whereas CMJ braking phase variables and IBS force outputs may reflect indirectly neuromuscular capacities related to horizontal deceleration. Further work, including unassisted sprint and deceleration tasks, is required.