Kinematics of the typical beach flags start for young adult sprinters

This study profiled beach flags start kinematics for experienced young adult sprinters. Five males and three females (age = 20.8 ± 2.1 years; height = 1.70 ± 0.06 meters [m]; mass = 63.9 ± 6.0 kilograms) completed four sprints using their competition start technique. A high-speed camera, positioned laterally, filmed the start. Data included: start time; hand clearance time; posterior movement from the start line; feet spacing during the start; elbow, hip, knee, trunk lean, and trajectory angles at take-off; and first step length. Timing gates recorded 0-2, 0-5, and 0-20 m time. Spearman's correlations identified variables relating (p ≤ 0.05) to faster start and sprint times. The beach flags start involved sprinters moving 0.18 ± 0.05 m posterior to the start line by flexing both legs underneath the body before turning. Following the turn, the feet were positioned 0.47 ± 0.07 apart. This distance negatively correlated with start (ρ = -0.647), 0-2 (ρ = - 0.683), and 0-5 m (ρ = -0.766) time. Beach flags start kinematics at take-off resembled research analyzing track starts and acceleration. The elbow extension angle (137.62 ± 13.45°) of the opposite arm to the drive leg correlated with 0-2 (ρ = - 0.762), 0-5 (ρ = -0.810), and 0-20 m (ρ = -0.810) time. Greater arm extension likely assisted with stability during the start, leading to enhanced sprint performance. The drive leg knee extension angle (146.36 ± 2.26°) correlated with start time (ρ = - 0.677), indicating a contribution to a faster start completion. A longer first step following the start related to faster 0-5 m time (ρ = -0.690). Sprinters quicker over 0-2 and 0-5 m were also quicker over 20 m (ρ = 0.881-0.952). Beach flags sprinters must ensure their start is completed quickly, such that they can attain a high speed throughout the race. © Journal of Sports Science and Medicine (2012).