Comparison of Different Bio-Mechanical Models to Identify the Phases of the Vertical Jump

The vertical jump analysis has a broad range of applications in sports medicine and exercise science such as performance evaluations, following the training of athletes from various disciplines, and monitoring the recovery process from injuries and/or surgeries. The analysis provides measures of one’s ability to create power in short period of time by the key variables of vertical jump such as rate of force development (RFD) and take-off velocity (TOV). Researchers have established numerous different phase identification methods, most of which requires information about the ground reaction forces (GRF), or velocity/position of the center of mass (COM). Kinetic methods using force platforms are the most commonly used methods for vertical jump analysis in the literature. The GRF recorded by the force platform is used to estimate the velocity/position of COM to be used in kinetic phase identification methods. Motion capture systems utilize kinematic methods of estimating the position/velocity of COM. There are many differences between these methods in terms of price, ease of use, the time required for subject preparation, data collection, data pre-processing/processing, and the ability to deliver accurate results for different jump types (e.g. countermovement jump with or without arm swing). A trade-off between the methods needs to be made to choose the appropriate system and phase identification method for a specific application. Therefore, this research aims to investigate the agreement level between commonly used two kinetic and two kinematic phase identification methodologies of countermovement jump (CMJ). Experimental data collected from 14 healthy young adults (7 female age = 23.2 ± 1.95 yrs, height = 1.66 ± 0.07 m, weight = 60.8 ± 10.10 kg; 7 male age = 22.7 ± 2.98 yrs, height = 1.80 ± 0.08 m, weight = 81.52 ± 11.15 kg). Participants performed ten CMJ; five with arm swing and five without arm swing. Kinetic data was recorded using a force platform, and kinematic data was recorded using a motion capture system. Five performance variables (eccentric phase time (EPT), concentric phase time (CPT), time to peak force (TPF), RFD, and TOV) were extracted using four-phase identification methodologies; two force platform methods and two motion capture models. A comparison was made to identify the differences among the four methodologies for the CMJ with and without arm swing. Comparative results revealed that there were significant differences between the two force platform methods and the two motion capture models. For EPT, TPF, and TOV, the effects of both methodologies and jump type were found significant (p < 0.05). The motion-capture model using a segmental kinematic model appeared to be the most reliable among all phase identification methodologies compared in this study. According to the findings of this study, the force platform methods and the motion-capture model using one landmark fails to identify the phases of the CMJ with and without arm swing. Therefore, caution should be exercised when identifying the phases of CMJ with force platform methods or motion-capture models using one landmark models to detect the motion of the whole-body COM