The relationship between whole-body muscle mass and the isokinetic knee extensor strength of the non-operated side following anterior cruciate ligament reconstruction

BACKGROUND: Recovery of the isokinetic knee extensor strength on the operated side following anterior cruciate ligament (ACL) reconstruction is commonly calculated as a ratio with the value from the non-operated side serving as the denominator. However, the validity of the values of the non-operated side remains unclear. OBJECTIVE: This study aimed to determine the relationship between whole-body muscle mass and non-operated knee extensor strength after ACL reconstruction. METHODS: In 27 patients who underwent ACL reconstruction, muscle mass was measured using bioelectrical impedance analysis, and bilateral concentric knee extensor strength was measured using an isokinetic dynamometer at angular velocities of 60 ∘ /s and 180 ∘ /s. Correlation and single regression analyses were performed to examine the relationship between whole-body muscle mass and knee extensor strength. RESULTS: There was a strong to very strong positive association between whole-body muscle mass and non-operated knee extensor strength (60 ∘ /s: <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" alttext="r=" display="inline" overflow="scroll"> <mml:mrow> <mml:mi>r</mml:mi> <mml:mo>=</mml:mo> <mml:mi/> </mml:mrow> </mml:math> 0.85, 180 ∘ /s: <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" alttext="r=" display="inline" overflow="scroll"> <mml:mrow> <mml:mi>r</mml:mi> <mml:mo>=</mml:mo> <mml:mi/> </mml:mrow> </mml:math> 0.90, <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" alttext="P&lt;" display="inline" overflow="scroll"> <mml:mrow> <mml:mi>P</mml:mi> <mml:mo>&lt;</mml:mo> <mml:mi/> </mml:mrow> </mml:math> 0.01). Univariate regression analysis showed that whole-body muscle mass was a strong predictor of non-operated knee extensor strength (R 2 = 0.71-0.81). CONCLUSIONS: Assessing both whole-body muscle mass and knee extensor strength may be used to determine whether muscle strength on the non-operated side is appropriate for the individual’s body composition.