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.

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.

[Avoiding cognitive bias : example of quantified assessment of muscle strength]. / Éviter les biais cognitifs : exemple lors de l'évaluation quantifiée de la force musculaire.

Optimizing treatments requires the prevention of diagnostic errors. The use of shortcuts, cognitive biases, may lead to errors of judgement that can impair clinical reasoning and distort decision-making. Objective, quantifiable and comparable assessment is a safeguard against this, and for instance force quantification is used for this purpose. We will present here the use of hand-held dynamometers with recommendations for best practice as well as simple but essential tools for interpreting the results. Indeed, the use of these easy-to-use dynamometers requires rigour to ensure the quality of measurements and data analysis by/for the clinician. The use of this equipment should be widely promoted and democratized in informed clinical practice.

L'optimisation des traitements passe par la prévention des erreurs de diagnostic. L'utilisation de raccourcis et les biais cognitifs peuvent engendrer des erreurs de jugement nuisant au raisonnement clinique et risquant de pervertir les prises de décision. L'évaluation objective, quantifiable et comparable en est un rempart et la quantification de la force est, par exemple, utilisée à cette fin. Nous présentons ici l'utilisation des dynamomètres à main avec des recommandations de bonne pratique ainsi que des outils d'interprétation des résultats simples mais indispensables. En effet, l'emploi de ces dynamomètres d'utilisation aisée nécessite de la rigueur pour assurer la qualité des mesures et l'analyse des données par/pour le clinicien. Le recours à ce matériel doit être largement promu et démocratisé en pratique clinique éclairée.

Supraspinal Control of Recurrent Inhibition during Anisometric Contractions.

PURPOSE: Increase in recurrent inhibition was observed during eccentric compared with isometric and concentric maximal voluntary contractions but the neural mechanisms involved in this specific control of the Renshaw cell activity are unknown. This study was designed to investigate the supraspinal control of the recurrent inhibition during anisometric contractions of the plantar flexor muscles. METHODS: To that purpose, the paired Hoffmann-reflex (H-reflex) technique permitted to assess changes in homonymous recurrent pathway by comparing the modulations of test and conditioning H-reflexes (H' and H1, respectively) in the soleus (SOL) muscle during maximal and submaximal isometric, concentric and eccentric contractions. Submaximal contraction intensity was set at 50% of the SOL electromyographic activity recorded during maximal isometric contraction. Fourteen volunteer subjects participated in an experimental session designed to assess the activity of the recurrent inhibition pathway. RESULTS: The results indicate that the amplitude of H1 normalized to the maximal M-wave were similar (P > 0.05) regardless of the muscle contraction type and intensity. Whatever the contraction intensity, the ratio between H' and H1 amplitudes was significantly decreased (P < 0.05) during eccentric compared with isometric and concentric contractions. Furthermore, this ratio was significantly smaller (P < 0.05) during submaximal compared with maximal contractions whatever the muscle contraction type. CONCLUSION: Together, the current results confirm the supraspinal control of the Renshaw cell activity when muscle contraction intensity is modulated and show that this control remains similar for isometric, concentric and eccentric contractions. Data further suggest that recurrent inhibition pathway may serve as variable gain regulator at motoneuronal level to improve resolution in the control of motor output for the SOL during eccentric contractions.

Neural adaptations to submaximal isokinetic eccentric strength training.

PURPOSE: This study investigated the neural adaptations following submaximal isokinetic eccentric strength training of the plantar flexors. The modulation of electromyographic (EMG) activity and spinal excitability were compared in the soleus muscle (SOL) during isometric, concentric and eccentric maximal voluntary contractions (MVC) before and after submaximal isokinetic eccentric training. METHODS: Eighteen healthy subjects were divided into a training group (n = 8) and a control group (n = 10). The training protocol consisted of sixteen sessions of isokinetic eccentric strength training during 8 weeks. Normalized EMG was used to assess the activity of SOL and medial gastrocnemius muscle (MG). For SOL, maximal Hoffmann reflex (H-reflex) and compound motor potential were evoked during isometric, concentric and eccentric actions at rest (Hmax and Mmax, respectively) and during MVC (Hsup and Msup, respectively). RESULTS: The results showed that the torque and normalized EMG of SOL significantly increased after training during eccentric (+20.5 and +28.8 %, respectively) and isometric (+18.2 and +23.0 %, respectively) MVC (p < 0.05). Hmax/Mmax and Hsup/Msup ratios were not significantly modified after training for SOL (p > 0.05), and remained significantly depressed during eccentric compared to isometric and concentric actions (p < 0.05). In contrast, no significant difference was observed on normalized EMG of MG (p > 0.05). CONCLUSIONS: These results suggested that the increase in voluntary torque after submaximal isokinetic eccentric training can be at least partly ascribed to enhanced neural drive for SOL that does not affect the H-reflex pathway.