Single marker method to estimate center-of-mass velocity during vertical jumps.

Problem statement: Center-of-mass (CoM) analysis of takeoff speeds in jumps preceded by run-ups (such as volleyball spike jumps), using a force platform, requires prior information on CoM speed at touchdown. This, however, can only be evaluated through kinematic methods (KIN). To this end, KINs must be evaluated for accuracy and concurrent validity. An example is a double integration of force (DIF) method for jumps in which the initial CoM speed is zero in countermovement jumps with and without arm swing. Aim: To evaluate the reliability and accuracy of three methods for calculating takeoff velocity and their concurrent validity during vertical jumps. Material and methods: Fifteen female volleyball players performed 10 vertical countermovement jumps (CMJ), and 10 countermovement jumps with arm swing (CMJa). Two methods were used to measure CoM takeoff velocity: (1) numerical DIF and (2) full-body 3D model (KIN). The latter was implemented using two minimalist marker setups between the right anterior and posterior iliac spines (RASI) and (RPSI), respectively. Results: KIN and DIF were more reliable in all jumps (ICC: 0.93-0.96) than minimalistic methods (ICC: 0.87-0.93). The standard error of measurement was lower in KIN and DIF (SEM mean= 1.9) than in minimalistic methods (SEM mean= 3.1). KIN was valid regarding DIF in CMJ, with bias equal to zero, no proportional bias (p=0.514), and narrow limits of agreement (LoA) (0.1 m/s). KIN was also valid in CMJa (bias = 0.01 m/s), with no proportional bias (p=0.244), LoA =0.21 m/s. The minimalist RPSI method was valid only in CMJ (bias= -0.12m/s), with no proportional bias (p=0.27), LoA=0.31 m/s. The RASI method showed a bias difference compared to DIF (p=0.001) and was not valid with either jump types. A large displacement of the pelvis may lead to increased errors using a single marker. Conclusions: All procedures were reliable and accurate, but minimalist marker setups decreased the values. The KIN method using a Plug-in-Gait model was valid in both jumps. Minimalist marker setups with a single marker at RPSI may be applied only in CMJ. Minimalist marker setups with a single marker may also lead to controversial results depending on the pelvis's jump type and marker position. These possibilities should be considered to calculate takeoff and touchdown velocities during volleyball spike jumps. [ABSTRACT FROM AUTHOR]