The dynamic control ratio masks bilateral asymmetries – A gender-specific analysis of 264 healthy and ACL-injured athletes

ABSTRACT

Isokinetic strength tests are frequently applied to assess anterior cruciate ligament (ACL) rehabilitation processes. However, diverging methodologies cause misleading conclusions. This cross-sectional study evaluated the effects of gender (male vs. female), group (healthy vs. ACL-injured) and limb (dominant/healthy vs. non-dominant/ACL-injured) on thigh muscle balance of 138 female and 126 male athletes (50% ACL-injured, averagely 12.8 months after surgery). Balance was analysed between legs (bilateral asymmetry) and between concentric knee extensor (Qcon) and eccentric knee flexor strength (Hecc) (DCR = dynamic control ratio, DCRe = DCR at the equilibrium point). Females were generally 17–27% weaker than males. Independent of gender and time after surgery, ACL-injured athletes demonstrated bilateral asymmetries (7–20%) in peak (PM_Qcon, PM_Hecc) and DCRe moments (p ≤0.030; 0.018≤η_p²≤0.215). ACL-injured athletes’ affected (24–28%) and unaffected (12–24%) hamstrings and quadriceps peak moments were significantly weaker compared to healthy athletes (p<0.001; 0.061≤η_p²≤0.362). The bilateral asymmetries of PM_Qcon significantly decreased from early to late self-reported rehabilitation phases (p<0.001; η_p²=0.158). Peak and DCRe moments detected bilateral asymmetries, whereas DCR revealed ~50% false negative attributions. This knowledge provides guidance for future design and interpretation of isokinetic tests.

KEYWORDS:

• Screening tool
• isokinetic dynamometry
• joint moments
• thigh muscle balance
• rehabilitation
• return to sport
• injury prevention

Abbreviation list

ACL anterior cruciate ligament

H hamstrings

ecc eccentric

Q quadriceps

con concentric

DCR dynamic control ratio

DCRe dynamic control ratio at the equilibrium point

PM peak moment

SEM standard error of measurement

ICC intra-class correlation coefficient

SD standard deviation

ROM range of motion

p probability value

η_p² partial eta squared

ROC Receiver operating characteristic curves

AUC area under the curve

Acknowledgments

The authors would like to thank all subjects who volunteered to participate in this study and demonstrated great motivation and commitment.

Disclosure of intreset statement

No potential conflict of interest was reported by the authors.

Additional information

Funding

This work was not funded.