Investigating the validity and test-retest reliability of the optojump device in comparison to force plates during jump tests within female football players

Background: The Optojump is a practical and cost-effective alternative for assessing lower bodypower and RSI through jump tests like the CMJ and DJ. While it demonstrates excellent validity andreliability for CMJ metrics compared to force plates, its performance in assessing DJ metrics hasshown conflicting results. Additionally, studies often lack diversity in participant pools, with limitedfemale representation and an absence of female football players. Moreover, not all metricsmeasured by the Optojump have been thoroughly analysed compared to the force plates. Objective:The purpose of this research was to investigate the validity and test-retest reliability of the Optojumpat assessing all CMJ and DJ metrics provided by the Optojump in comparison to force plates withinfemale football players. Methods: Twenty-Six female football players (age: 23.8 ± 6.2, height (cm):164.8 ± 3.7, mass (kg): 65.1 ± 6.3) playing in the first team or academy of a club competing in the topleague of woman’s football in Scotland were recruited to participate in the study. Participantsperformed three trials of both CMJ and DJ on two separate testing sessions separated by one week.The best trial from each jump on both testing sessions was used for analysis. Results: Smallsystematic bias was found between the Optojump and force plates within all CMJ and DJ metricsrecorded by the Optojump, indicating marginal overestimations in jump metrics by the Optojump.However, the presence of proportional bias was not found. The Optojump device exhibited moderatetest-retest reliability for DJH, DJ CT and DJ RSI (ICC=0.50-0.74) and good test-retest reliability for DJ FT(ICC=0.75-0.90). The CV% values for DJ CT and DJ RSI did not meet the criteria for excellent reliability(CV < 10%) although DJH and DJ FT fulfilled the classification criteria for excellent reliability (6.7% and3.4%, respectively). The Optojump device provided good test-retest reliability for CMJH (ICC=0.89(0.77-0.95)) and CMJ FT (ICC=0.89 (0.77-0.95)) with CV% values being defined as excellent (2.8% and1.4%). Conclusion: The findings from the current study indicate that the Optojump may serve as aviable alternative to the force plates for measuring CMJH, CMJ FT, DJH and DJ FT but not DJ CT or DJRSI. However, caution must be taken when interpretating these results as despite excellent ICC (ICC >0.9) and very small CV values (CV < 2%) between devices, there was a presence of systematic biasreported in all CMJ and DJ metrics.