Comparison of methods of calculating dynamic strength index

Comfort, P; Thomas, C; Dos'Santos, T; Jones, PA; Suchomel, T; McMahon, JJ

Abstract

Purpose: To determine the reliability and variability of dynamic strength index (DSI) calculated from squat jump (SJ) (DSI-SJ) versus countermovement jump (CMJ) (DSI-CMJ) peak force (PF) and to compare DSI values between methods. Methods: Male youth soccer and rugby league players (n = 27; age = 17.2 ± 0.7 years; height = 173.9 ± 5.7 cm; body mass = 71.1 ± 7.2 kg) performed 3 trials of the SJ, CMJ and isometric mid-thigh pull (IMTP), on two separate days. DSI was calculated by dividing the PF during each jump by the IMTP PF. Results: DSI-SJ exhibited moderate (intraclass correlation coefficient (ICC) = 0.419) within-session reliability and high variability (percentage coefficient of variation (%CV) = 15.91) during session one; however, this improved noticeably during session two (ICC = 0.948; %CV = 4.03). Contrastingly, DSI-CMJ showed nearly perfect within-session reliability (ICC = 0.920-0.952) and low variability (%CV = 3.80-4.57) for both sessions. Moreover, DSI-SJ values demonstrated a small yet significant increase between sessions (P = 0.01, d = 0.37), whereas only a trivial and non-significant increase was observed for DSI-CMJ between sessions (P = 0.796 d = 0.07). Between-session reliability was very high for the DSI-SJ (ICC = 0.741) and nearly perfect for the DSI-CMJ (ICC = 0.924). There was no significant or meaningful difference (P = 0.261; d = 0.12) between DSI-SJ (0.82 ± 0.18) and DSI-CMJ (0.84 ± 0.15). Conclusions: Practitioners should use DSI-CMJ as it is a more reliable measure than DSI-SJ, although it produces similar ratios.

Citation

Comfort, P., Thomas, C., Dos'Santos, T., Jones, P., Suchomel, T., & McMahon, J. (2017). Comparison of methods of calculating dynamic strength index. International Journal of Sports Physiology and Performance, 13(3), 320-325. https://doi.org/10.1123/ijspp.2017-0255

• Journal Article Type: Article
• Acceptance Date: Jun 21, 2017
• Online Publication Date: Jul 17, 2017
• Publication Date: Jul 17, 2017
• Deposit Date: Aug 1, 2017
• Publicly Available Date: Aug 1, 2017
• Journal: International Journal of Sports Physiology and Performance
• Print ISSN: 1555-0265
• Electronic ISSN: 1555-0273
• Publisher: Human Kinetics
• Volume: 13
• Issue: 3
• Pages: 320-325
• DOI: https://doi.org/10.1123/ijspp.2017-0255
• Publisher URL: http://dx.doi.org/10.1123/ijspp.2017-0255
• Related Public URLs: http://journals.humankinetics.com/journal/ijspp
• Additional Information: Additional Information : Accepted author manuscript version reprinted, by permission, from International Journal of Sports Physiology and Performance, 2017, https://doi.org/10.1123/ijspp.2017-0255. © Human Kinetics, Inc.