n International SportMed Journal - The reliability of force-time variables recorded during vertical jump performance and their relationship with jump height in power trained athletes : original research article

Volume 15, Issue 2
  • ISSN : 1528-3356



Vertical jump tests have been put forward as a measure of explosive strength, yet the importance of rate of force development (RFD) to vertical jump performance remains unclear.

To determine the reliability of force-time variables recorded during countermovement jumps (CMJ) and to investigate the relationships between force-time variables and jump height (JH).
A cross-sectional experimental design.
Thirty-five male resistance-trained subjects (mean ± SD: age 24.7±1.3 years; mass 71.3 ± 56.4 kg; height 1.76 ± 0.06 m) involved in distinct power sports participated in the present study. Each subject performed three maximal CMJ trials in a Smith Machine with three minutes of rest between jumps. A linear position transducer was fixed to the barbell which provided instantaneous vertical position data from which the mechanical variables of high jump, peak vertical force (PF), time to peak vertical force (PF), maximum rate of force development (RFD), time to maximum rate of force development (RFD) and percentage of PF at RFD (RFD). The reliability of the force-time variables was assessed by calculating the change in the mean, the coefficient of variation (CV), and the intraclass correlation coefficients (ICC). The relationship between the force-time variables and JH were assessed using correlation coefficients.
All force-time variables demonstrated acceptable reliability (CV range: 3.3-12.4%; ICC range: 0.80-0.92). RFD, PF and RFD demonstrated very large correlations with jump height ( > 0.80), while both PF and RFD demonstrated high correlations with CMJ performance ( > 0.50).
The force-time variables calculated during CMJ using a linear position transducer are reliable. Furthermore, the rapid development of force is an important determinant of JH during CMJ performed with a low external load in well-trained athletes, and so JH represents a valid measure of explosive strength.

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