Sex Differences in Knee Flexor Strength and Limb Symmetry Across Different Strength Testing Conditions in Healthy Recreational Athletes

Urban, Natalia; Andrzejczak, Klara; Witkowski, Wiktor; Daszkiewicz, Maciej; Reichert, Paweł; Prill, Robert; Kentel, Maciej; Królikowska, Aleksandra

doi:10.3390/jcm15135219

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Sex Differences in Knee Flexor Strength and Limb Symmetry Across Different Strength Testing Conditions in Healthy Recreational Athletes

by

Natalia Urban

^1,†,

Klara Andrzejczak

^1,†

,

Wiktor Witkowski

¹,

Maciej Daszkiewicz

²

,

Paweł Reichert

³

,

Robert Prill

^4,5

,

Maciej Kentel

⁶

and

Aleksandra Królikowska

^2,*

¹

Student Research Group of Evidence-Based Healthcare, University Centre of Physiotherapy and Rehabilitation, Faculty of Physiotherapy, Wroclaw Medical University, 50-372 Wroclaw, Poland

²

Physiotherapy Research Laboratory, University Centre of Physiotherapy and Rehabilitation, Faculty of Physiotherapy, Wroclaw Medical University, 50-372 Wroclaw, Poland

³

Clinical Department and Department of Orthopedics, Traumatology and Hand Surgery, Faculty of Medicine, Wroclaw Medical University, 50-556 Wroclaw, Poland

⁴

Center of Orthopaedics and Traumatology, University Hospital Brandenburg/Havel, Brandenburg Medical School Theodor Fontane, 14770 Brandenburg, Germany

⁵

Faculty of Health Sciences Brandenburg, Brandenburg Medical School Theodor Fontane, 14770 Brandenburg, Germany

⁶

eMKa MED Medical Center, 53-110 Wroclaw, Poland

^*

Author to whom correspondence should be addressed.

^†

These authors contributed equally to this work.

J. Clin. Med. 2026, 15(13), 5219; https://doi.org/10.3390/jcm15135219

Submission received: 17 May 2026 / Revised: 21 June 2026 / Accepted: 1 July 2026 / Published: 3 July 2026

(This article belongs to the Special Issue Current Measures for Diagnosis, Monitoring, and Outcome Assessment in Orthopedics, Traumatology, and Hand Surgery, 2nd Edition)

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Abstract

Background: Normalized strength outcomes and limb symmetry indices (LSIs) are widely used but poorly characterized across testing conditions, and it is unclear if these vary by sex. This study aimed, first, to investigate sex-related differences in normalized knee flexor strength and LSI values across multiple strength-testing conditions in healthy recreational athletes, and, second, to descriptively examine associations among strength outcomes obtained under different testing conditions within female and male participants. Methods: In this cross-sectional study, 52 healthy, recreationally active adults (26 females and 26 males) underwent bilateral knee flexor strength testing using three force plate-based isometric assessments, one static dynamometer-based isometric assessment, and three isokinetic dynamometer-based assessments. Differences were analyzed with a mixed analysis of variance (ANOVA), and associations were assessed using Pearson correlations. Results: Males showed higher normalized knee flexor strength than females across all testing conditions (main effect of sex: p < 0.001; partial η² = 0.334–0.371), with the magnitude of these sex-related differences varying across testing conditions (sex-by-testing condition interaction: p < 0.001; partial η² = 0.215–0.230). LSI values did not differ by sex (p = 0.896) and remained consistent across testing conditions (p = 0.385). Correlations were generally stronger within force plate-based and isokinetic dynamometer-based assessments (r = 0.528–0.922) than between different testing conditions. Conclusions: Sex-related differences were observed for normalized knee flexor strength but not for LSI values. Strength outcomes obtained under different testing conditions should not be considered directly interchangeable.

Keywords: injury prevention; injury risk reduction; isokinetics; isometrics; muscle strength assessment; limb symmetry index; physiotherapy; rehabilitation; sex differences; sports medicine

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MDPI and ACS Style

Urban, N.; Andrzejczak, K.; Witkowski, W.; Daszkiewicz, M.; Reichert, P.; Prill, R.; Kentel, M.; Królikowska, A. Sex Differences in Knee Flexor Strength and Limb Symmetry Across Different Strength Testing Conditions in Healthy Recreational Athletes. J. Clin. Med. 2026, 15, 5219. https://doi.org/10.3390/jcm15135219

AMA Style

Urban N, Andrzejczak K, Witkowski W, Daszkiewicz M, Reichert P, Prill R, Kentel M, Królikowska A. Sex Differences in Knee Flexor Strength and Limb Symmetry Across Different Strength Testing Conditions in Healthy Recreational Athletes. Journal of Clinical Medicine. 2026; 15(13):5219. https://doi.org/10.3390/jcm15135219

Chicago/Turabian Style

Urban, Natalia, Klara Andrzejczak, Wiktor Witkowski, Maciej Daszkiewicz, Paweł Reichert, Robert Prill, Maciej Kentel, and Aleksandra Królikowska. 2026. "Sex Differences in Knee Flexor Strength and Limb Symmetry Across Different Strength Testing Conditions in Healthy Recreational Athletes" Journal of Clinical Medicine 15, no. 13: 5219. https://doi.org/10.3390/jcm15135219

APA Style

Urban, N., Andrzejczak, K., Witkowski, W., Daszkiewicz, M., Reichert, P., Prill, R., Kentel, M., & Królikowska, A. (2026). Sex Differences in Knee Flexor Strength and Limb Symmetry Across Different Strength Testing Conditions in Healthy Recreational Athletes. Journal of Clinical Medicine, 15(13), 5219. https://doi.org/10.3390/jcm15135219

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Sex Differences in Knee Flexor Strength and Limb Symmetry Across Different Strength Testing Conditions in Healthy Recreational Athletes

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