Abstract: |
Introduction: The counter movement jump (CMJ) is often used to assess explosive strength, power, fatigue and physical fitness in sports. The CMJ height can assessed by force plates and by smartphone apps. Although force plates provides high precision data analysis, their high cost make their use in clinical practice limited. On the other hand, smartphone applications are less expensive and consequently more accessible for clinicians. Objective: Evaluate the concurrent validity and intra- and inter-rater reliability of the PysioCode Posture application (PCP app) to assess the CMJ height. Methods: The participants were instructed to perform the CMJ three times for familiarization and three valid CMJ, with intervals of 15 seconds, in a force plate (Bertec a 1000Hz, Bertec Corp, Columbus, OH). The CMJ were also recorded with the PCP app using a smartphone Motorola Motog6 Play® (4:3 13MP, HD 720p - 30fps) vertically positioned at the height of the participant’s knee and at a distance of 1.5 meters. The PCP app is avaiable for Android™ and, in addition to camera integration with the inertial sensor, presents features such as the amplification of the analyzed point by screen touch. For the force plate, the time interval between the ground reaction force disappearance and reappearance was considered for the analysis of the CMJ height. For the PCP app, two trained examiners selected the moment in the video when the feet lost contact with the ground and the moment they touched it again and the time interval between these two events was used for analysis of the CMJ height. We used the following formula to calculate CMJ height: h= t2×1,23, where h is the height in meters and t is the time in seconds. For the intra-rater reliability, the examiners repeated the analysis in the PCP app after seven days without contact with the previous data or the other examiner’s data. Data were tested for normal distribution using the Shapiro-Wilk test and did not present normal distribution. Therefore, Spearman's nonparametric test was used to verify the correlation between data from PCP app and force plate measurements. For reliability measures, the Intraclass Correlation Coefficient (ICC) was used. The significance was set at α=0.05. SPSS 19 software (SPSS Inc., Chicago, IL) was used for all analyses. Results: Thirty-seven healthy individuals (18 women and 19 men) participated in this study. The sample characteristics were: mean age of 23.5 years (standard deviation [SD]: 4.0), mean body mass of 65.2 kg (SD: 10.5), mean height of 170.0 cm (SD: 10.0), mean body mass index of 22.2 kg/m2 (SD: 3.0). The mean (SD) CMJ height for the examiner 1 was 26.48 cm (8.63); for examiner 2 was 26.39 cm (8.46); and in the force plate was 27.83 cm (8.29). The PCP concurrent validity with force plate was excellent, with a Spearman's correlation index of 0.98. The height of the CMJ using the PCP app presented excellent intra-rater reliability (Intraclass Correlation Coefficient [ICC]3,3: 0.99; Confidence Interval [CI95%]: 0.98–0.99; Standard Error of Measurement [SEM]: 0.73 cm) and also excellent inter-rater reliability (ICC3,3: 0.96; CI95%: 0.94–0.98; SEM: 1.54 cm). Conclusion: The use of PCP app to measure the CMJ height was valid and demonstrated excellent intra- and inter-rater reliability levels. This accessible and low-cost method of evaluation is essential for professionals in clinical settings. |