Timing light height affects sprint times.

Timing light systems are commonly used to measure sprint times of athletes. In this study, the reliability and effect of timing light height on sprint times was investigated. Two sets of timing lights set at hip and shoulder height, simultaneously timed subjects over 10 and 20 meters. The within-trial variation of both timing light heights were equally consistent; all coefficients of variation (CV) less than 1.2% with less variability associated with the longer (20 m) distances (CV < 0.85%). The typical error between the two timing light heights for both distances was small (< or = 1.3%). The mean difference between the two heights was significantly different (0.7 second, 95% CL = 0.05-0.10 second) at both the 10 and 20 m distances. Faster times were recorded at hip height as opposed to shoulder due to the legs breaking the beam before the upper body. It is suggested that standardized procedures are necessary for speed assessment using timing lights in order for comparisons to be made between athletic populations.