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Purpose <p>The primary purpose of this study was to develop and validate two novel dynamic strength index (DSI) metrics which feature temporal efficiency and body size normalisation. Secondary objectives were to compare their diagnostic utility against the traditional DSI (DSI<sub>trad</sub>), examine associations among component variables, and assess their effectiveness in identifying performance deficits in healthy and ACL-reconstructed (ACLR) populations.</p> Methods <p>Fifty-eight male participants (16 ACLR, 42 healthy controls) completed isometric mid-thigh pull (IMTP) and countermovement jump (CMJ) tests on force plates. DSI<sub>trad</sub>, normalised-DSI (reactive strength index/normalised IMTP force), and scaled-DSI (modified reactive strength index/scaled IMTP force) metrics were calculated. Statistical analyses included independent <i>t</i>-tests for between-group differences, linear regression for component associations, Pearson correlations, and bivariate logistic regression with ROC curve analyses to determine diagnostic utility [area under the curve (AUC)] and optimal cut-off points.</p> Results <p>The scaled DSI (AUC = 0.81) and modified reactive strength index (AUC = 0.80) demonstrated considerable diagnostic utility in differentiating ACLR from healthy performances, contrasting with DSI<sub>trad</sub> (AUC = 0.59), which showed poor utility. The novel metrics provided a more accurate classification of performance deficits. ACLR patients exhibited significantly lower modified reactive strength index values (0.32 ± 0.06&#xa0;m/s vs. 0.44 ± 0.12&#xa0;m/s in healthy controls, <i>p</i> &lt; 0.001). Divergent associations between IMTP derivatives and dynamic metrics were observed between ACLR and healthy cohorts, highlighting compromised strength transferability in the ACLR group.</p> Conclusion <p>This study supports the modification, rather than replacement, of dynamic strength indexes. The scaled-DSI metric was diagnostically effective in identifying injury status and offered insights into an athlete’s force conversion capabilities, suggesting it as a viable alternative for tailoring training and rehabilitation programs.</p>

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All dynamic strength indexes are relative, but only some are useful: should they be reworked or retired?

  • 期刊论文

  • 发表日期：

    2026年1月5日

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  • M. Kramer

摘要

Purpose

The primary purpose of this study was to develop and validate two novel dynamic strength index (DSI) metrics which feature temporal efficiency and body size normalisation. Secondary objectives were to compare their diagnostic utility against the traditional DSI (DSItrad), examine associations among component variables, and assess their effectiveness in identifying performance deficits in healthy and ACL-reconstructed (ACLR) populations.

Methods

Fifty-eight male participants (16 ACLR, 42 healthy controls) completed isometric mid-thigh pull (IMTP) and countermovement jump (CMJ) tests on force plates. DSItrad, normalised-DSI (reactive strength index/normalised IMTP force), and scaled-DSI (modified reactive strength index/scaled IMTP force) metrics were calculated. Statistical analyses included independent t-tests for between-group differences, linear regression for component associations, Pearson correlations, and bivariate logistic regression with ROC curve analyses to determine diagnostic utility [area under the curve (AUC)] and optimal cut-off points.

Results

The scaled DSI (AUC = 0.81) and modified reactive strength index (AUC = 0.80) demonstrated considerable diagnostic utility in differentiating ACLR from healthy performances, contrasting with DSItrad (AUC = 0.59), which showed poor utility. The novel metrics provided a more accurate classification of performance deficits. ACLR patients exhibited significantly lower modified reactive strength index values (0.32 ± 0.06 m/s vs. 0.44 ± 0.12 m/s in healthy controls, p < 0.001). Divergent associations between IMTP derivatives and dynamic metrics were observed between ACLR and healthy cohorts, highlighting compromised strength transferability in the ACLR group.

Conclusion

This study supports the modification, rather than replacement, of dynamic strength indexes. The scaled-DSI metric was diagnostically effective in identifying injury status and offered insights into an athlete’s force conversion capabilities, suggesting it as a viable alternative for tailoring training and rehabilitation programs.