Reliability of the Dynamic Strength Index in College Athletes

in International Journal of Sports Physiology and Performance
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Purpose:

To determine the reliability of the Dynamic Strength Index (DSI) in college athletes.

Method:

Nineteen male college athletes performed the squat jump (SJ) and isometric midthigh pull (IMTP) to determine peak force, on 2 separate days. Reliability was assessed by intraclass correlation coefficient (ICC), typical error (TE), percentage change in the mean, smallest worthwhile change (SWC), and coefficient of variation (%CV).

Results:

Peak force for the SJ was 2137 ± 499 N and 2781 ± 435 N for the IMTP, resulting in a mean DSI of 0.78 ± 0.19. Peak forces in the SJ (ICC = .99, TE = 57.22 N, change in mean = 0.2%, SWC = 4.7%, CV = 2.6%) and IMTP (ICC = .95, TE = 104.22 N, change in mean = 0.5%, SWC = 3.1%, CV = 3.8%) were considered highly reliable between sessions. However, IMTP peak force was the only variable with an overall TE < SWC. The DSI was also highly reliable (ICC = .97, TE = 0.03, change in mean = −0.3%, SWC = 5.1%, CV = 4.6%) between sessions.

Conclusion:

This study demonstrates that peak force in the SJ and IMTP are reliable, resulting in a reliable assessment of dynamic-force-production capabilities via the DSI. The DSI may be used to guide individualized training interventions and monitor specific adaptations to training. Changes in SJ peak force, IMTP peak force, and DSI were >4.67%, 3.13%, and 5.13%, respectively, identifying meaningful changes in response to training or competition.

The authors are with the Directorate of Sport, Exercise and Physiotherapy, University of Salford, Salford, UK.

Address author correspondence to Christopher Thomas at C.Thomas2@edu.salford.ac.uk.