Absolute and Normalized Normative Torque Values of Knee Extensors and Flexors in Healthy Trained Subjects: Asymmetry Questions the Classical Use of Uninjured Limb as Reference

Abstract

Purpose: To provide normative values of maximal isometric torque of knee extensors and flexors measured at 80° of knee flexion and to characterize the results in healthy subjects practicing activities at risk of anterior cruciate ligament rupture.

Methods: Seventy-four trained volunteers (35 male and 39 female) aged 18 to 41 years were recruited. They alternately performed 3 maximal voluntary isometric contractions of knee extension and flexion. The maximal voluntary isometric contraction net torque was computed as the mean value of the peak torques recorded over the 3 trials.

Results: For women, the absolute torque for extensors was 143.5 ± 34.4 N⋅m (range, 87.7-253.1 N⋅m) and 66.8 ± 13.8 N⋅m (range, 37.5-93.1) for flexors. For men, the absolute torque for extensors was 199.8 ± 47.3 N⋅m (range, 99.3-311.5 N⋅m) and 89.8 ± 21.0 N⋅m (range, 51.8-137.2 N⋅m) for flexors. For women, the body mass normalized torque for extensors was 2.20 ± 0.51 N⋅m.kg^-1 (range, 1.22-3.74 N⋅m.kg^-1) and 1.04 ± 0.26 N⋅m.kg^-1 (range, 0.41-1.50 N⋅m.kg^-1) for flexors. For men, the normalized torque for extensors was 2.74 ± 0.58 N⋅m.kg^-1 (range, 1.51-4.08 N⋅m.kg^-1) and 1.24 ± 0.30 N⋅m.kg^-1 (range, 0.64-2.05 N⋅m.kg^-1) for flexors.

Conclusions: This study provides absolute and normalized normative values of maximal isometric torque measured at 80° of knee flexion for extensors and flexors in a series of healthy trained subjects practicing activities at risk of anterior cruciate ligament rupture. The considerable level of interlimb asymmetry and the weak association between dominance and strength observed in uninjured subjects call into question the classical use of contralateral side as reference for injured patients.

Clinical relevance: Patients with anterior cruciate ligament (ACL) injuries are the most represented subjects using isokinetic dynamometers in many sport medicine and rehabilitation departments. Clinicians need reference values to compare patients with ACL injuries with comparable healthy subjects. This study may provide this information.

Fig 1

Distribution of absolute extensors and flexors torque values for men and women.

Fig 2

Distribution of body weight-normalized extensors and flexors torque values for men and women.

Fig 3

Representation of stronger side depending on subjects’ dominance. (SEm, standard error of measurement.)

Fig 4

Distribution of extensors and flexors asymmetry indexes for men and women.

Appendix Fig 1

Normative values and levels of maximal normalized extensors torque.

Appendix Fig 2

Normative values and levels of maximal normalized flexors torque.