The Reliability and Validity of the Fitjump Photoelectric Cell System for Determining Vertical Jump Height

The aim of this investigation was to assess the reliability and validity of the Fitjump system. Fifty-seven participants (age = 22.62 ? 5.24 years, height = 180.69 ? 12.53 cm, body mass = 75.61 ? 9.56 kg) performed three countermovement jump (CMJ) and squat jump (SJ) with a 1-week interval for test and retest reliability. For validity, the participants performed the same jump protocol on the force platform while being simultaneously measured with the Fitjump system. There was excellent test?retest reliability of the Fitjump system for CMJ and SJ with high intraclass correlation coefficient (ICCs) (0.97 and 0.97, respectively), low coefficient variation (CVs) (2.3% and 2.4%, respectively), and low typical error of estimate [(TEE (%)] (4.0% and 4.4%, respectively). For validity, ICCs were extremely high for CMJ and SJ (0.93 and 0.94, respectively), with low TEE (%) (2.9% and 2.0%, respectively). However, Fitjump overestimated jump height for CMJ and SJ (3.54 and 3.37 cm, respectively; p < 0.001) when compared with the force platform. As a conclusion, the Fitjump system demonstrated excellent test?retest reliability and high relationship with a systematic bias for validity. Therefore, the Fitjump system can be used as a portable tool for monitoring vertical jump changes over time, but it should not be used interchangeably with a force platform.