Reliability of a marker-less camera system during a deceleration test and relationships between deceleration variables and countermovement jump, drop jump and Nordic hamstring test results in full-time soccer

Marker-less camera systems may provide a viable alternative for measuring maximal horizontal deceleration ability than other technologies used to date. This study aimed to determine the intra-day and inter-day reliability of kinematic variables derived from a maximal horizontal deceleration test using a marker-less camera system. The study also aimed to correlate deceleration variables to common neuromuscular tests, including Countermovement Jump (CMJ), Drop Jump (DJ) and Nordic Hamstring Exercise (NHE) tests. The study consisted of 14 male participants from a full-time soccer club in Scotland, all of which completed two separate trials of a maximal horizontal deceleration test as well as CMJ, DJ and NHE tests. Reliability of kinematic deceleration variables was assessed using a combination of intraclass correlation coefficient (ICC) and coefficient of variation (CV%). Strength and significance of correlations between kinematic variables and CMJ, DJ and NHE test variables were determined using Pearson’s Correlation Coefficient (r), with statistical significance set to p<0.05. A total of five kinematic variables had moderate intra-day reliability (MaxVel, AvgDec, MaxDec, AvgEDec & TT50%MaxVel), with four kinematic variables displaying moderate levels of inter-day reliability (MaxVel, AvgDec, MaxDec, AvgEDec, TT50%MaxVel & DTS) (ICC<0.75, CV%<10). The study found that of all CMJ, DJ and NHE variables, eight variables from the CMJ and five variables from the DJ had large and significant correlations with deceleration kinematics (r=.50-.69 & p<.05). Using a marker-less camera system can provide moderately reliable results for kinematic variables of a maximal horizontal deceleration test and correlate with both concentric and eccentric variables of a CMJ and DJ test. Future research should consider further assessment of the reliability of kinematic variables using this methodology and explore whether training interventions that improve specific CMJ and DJ variables also improves maximal deceleration performance.