Analysis of the correlation between knee extension torque and patellar tendon elastic property

Purpose: Quadriceps strength and patellar tendon (PT) are directly linked and intimately related to daily activities and lower limb function. However, the correlation between knee extension torque (KT) and PT Young's modulus (E) measured directly is still unknown. Method: We used supersonic shearwave imaging (SSI) to evaluate the elastic property of PT in healthy young men and analysed its correlation with KT. Twenty-two healthy young males were included and both knees were examined. The E of the PT in the dominant and non-dominant legs was assessed by SSI elastography. KT in maximal voluntary isometric contraction was measured with an isokinetic dynamometer. Result: No correlations between KT and PT E were observed in dominant or non-dominant side (P=0458 and 0126, respectively). No significant differences in KT or PT E were observed between both legs (P=0096 and 0722, respectively). Intra-day ICC was rated good (D1 - 0886, P<0001 and 088, P<0001) and excellent (D2 - 0928, P<0001 and 0900, P<0001) for both legs. Inter-day ICC was rated moderate for both legs (0651, P=0016 and 0630, P=0018, respectively). Conclusion: No significant correlations were found between KT and PT E, suggesting that quadriceps strength is not an accurate predictor for PT mechanical properties in subjects with no specific training engagement. Habitual loading pattern can play a determinant role in PT mechanical properties, regardless of quadriceps strength. Further investigation on SSI acquisition protocols should be conducted to guarantee higher inter-day ICC values.