(1) RELIABILITY AND PRECISION OF ECCENTRIC RATE OF FORCE DEVELOPMENT DURING COUNTERMOVEMENT VERTICAL JUMPING

During vertical jumping activities, a portion of the countermovement phase incorporates eccentric actions and is the focus of this report.  The rate of force development can be calculated during this phase and may be termed the eccentric rate of force development (ERFD). ERFD may be expressed as a slope and is calculated as the change in force from a designated initial point to a designated final point divided by the change in time over which the change in force occurred.  Operationally, eccentric actions do not occur during the countermovement until the musculature is engaged to slow and eventually reverse the direction of movement.  During this time, elastic energy is stored in the connective and contractile tissues which is then released during the concentric phase.   Different strategies may be used to accomplish this that may affect the amount of stored elastic energy. Some individuals may exert forces early on to oppose the force of gravity while others may wait longer to do so.  The strategy chosen will affect ERFD and may affect jumping proficiency. Also, eccentric strategies may be implemented inconsistently in those not highly trained in jumping. The reliability and precision for specific applications of ERFD may affect its utility.

PURPOSE 

To To determine the stability reliability and precision of ERFD during countermovement vertical jumping.

METHODS

Sixty young adults (31 men, 29 women), 18 to 35 years of age, performed three vertical jumps (CMVJ) on two occasions using a self-selected countermovement depth and constrained arm swing. A nine-camera 3D motion capture system (240 Hz, Qualisys Inc., Sweden) and force platform (1200 Hz, AMTI, Watertown, MA, USA) were used to collect 3D marker position data and vertical ground reaction force (vGRF) data for the right side of the body, respectively. Unilateral ERFD was computed from vGRF data and expressed both as absolutes and normalized for body mass. Stability reliability was determined using an intraclass correlation coefficient (two-way random model), and precision using both the standard error of measurement and the coefficient of variation. Statistical analyses were performed for all subjects, as well as separately for men and women.

RESULTS

See Table 1.

CONCLUSIONS)

< !Stability reliability was attained for absolute and normalized expressions of ERFD for all subjects, men only, and women only.

< !Precision was more problematic for ERFD measurements, regardless of absolute versus normalized expressions or biological sex.

PRACTICAL APPLICATIONS
Due to marginal measurement precision, the average of multiple sessions is recommended to represent ERFD performance during countermovement vertical jumping in populations like the ones used in this study.

Acknowledgements: None