Reliability And Precision Of Different Iterations Of Concentric Rate Of Force Development

RELIABILITY AND PRECISION OF DIFFERENT ITERATIONS OF CONCENTRIC RATE OF FORCE DEVELOPMENT Weiss, L.W., Powell, D.W., Senatore, S., Paquette, M.R., Massey, L.A., and Daugherty, H.In 1995, Vladimir Zatsiorsky described different indices of the rate of force development (RFD) including 1) starting gradient (S-gradient: 50% of peak force / elapsed time reach it), 2) acceleration gradient (A-gradient: 50% peak force / elapsed time from that point to peak force), 3) index of explosive strength (peak force / time to peak force, and 4) reactivity coefficient (peak force / (time to peak force x body mass). We propose to use slopes from the force-time curve to represent full concentric RFD (CRFD), early-stage CRFD, and late-stage CRFD with the point of demarcation between early and late stages being either 50% of the time to reach peak force or 50% of peak force. PURPOSE: To determine the stability reliability and precision of Zatsiorsky’s four indices of the RFD as well as five slope-based iterations of CRFD during countermovement vertical jumps. METHODS: Sixty young adults (31 men, 29 women) performed three vertical jumps (CMVJ) on two occasions. 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. Full-, early- and late-stage CRFD, as well as Zatsiorsky’s indices of RFD were computed from vGRF data. Reliability was determined using an intraclass correlation coefficient (two-way random model), and precision using the standard error of measurement and coefficient of variation (CV%). RESULTS: Although reliability was generally adequate, precision was poor. Table 1. CONCLUSION: Repeated measures of each of these RFD variables should be employed due to their imprecise nature. Table 1. - Summary information for multiple representations ofconcentric rate of force development. Variables SampleSize Mean Std. Dev. ICC (95% CI) SEM (CV%) 1 Zatsiorsky’s Start Gradient (N . s -1 ) 56 1502.51 944.41 0.72(0.59-0.81) 508.3(46.4) 2 Zatsiorsky’s Start Gradient (N . s -1 ) 59 1595.06 949.28 1 Zatsiorsky’s Acceleration Gradient (N . s -1 ) 56 2061.43 1580.71 0.82(0.73-0.88) 648.32(45.9) 2 Zatsiorsky’s Acceleration Gradient (N . s -1 ) 59 1932.74 1419.59 1 Zatsiorsky’s Index Explosive Strength (N . s -1 ) 56 2386.26 2062.86 0.14(-0.10-0.36) 1495.52(93.3) 2 Zatsiorsky’s Index Explosive Strength (N . s -1 ) 59 2151.98 1016.04 1 Zatsiorsky’s Reactivity Coefficient (N . s -1. kg) 56 32.71 28.81 0.02(-0.21-0.25) 21.78(98.8) 2 Zatsiorsky’s Reactivity Coefficient (N . s -1. kg) 59 29.71 12.54 1 Slope Full CRFD (to Pk Force) Absolute (N . s -1 ) 56 1779.32 1090.15 0.80(0.70-0.86) 467.10(37.3) 2 Slope Full CRFD (to Pk Force) Absolute (N . s -1 ) 59 1763.79 948.98 1 Early-stage (50% Time to Pk Force) CRFD Absolute (N . s -1 ) 56 906.76 633.79 0.80(0.71-0.87) 287.99(43.6) 2 Early-stage (50% Time to Pk Force) CRFD Absolute (N . s -1 ) 59 960.28 652.79 1 Late-stage (50% Time to Pk Force) CRFD Absolute (N . s -1 ) 56 1199.55 864.92 0.64(0.49-0.76) 478.77 (58.5) 2 Late-stage (50% Time to Pk Force) CRFD Absolute (N . s -1 ) 59 1117.07 725.79 1 Early-stage (50% Pk Force) CRFD Absolute (N . s -1 ) 56 1540.93 955.27 0.72(0.57-0.81) 507.85 (45.3) 2 Early-stage (50% Pk Force) CRFD Absolute (N . s -1 ) 59 1628.42 946.33 1 Late-stage (50% Pk Force) CRFD Absolute (N . s -1 ) 56 2042.79 1591.56 0.82(0.73-0.88) 647.35(46.4) 2 Late-stage (50% Pk Force) CRFD Absolute (N . s -1 ) 59 1905.68 1439.29