Interplay between body stabilisation and quadriceps muscle activation capacity

The study aimed to distinguish the effect of stabilisation and muscle activation on quadriceps maximal isometric voluntary contraction (MVC) torque generation. Nine subjects performed (a) an MVC with restrained leg and pelvis (Typical MVC), (b) a Typical MVC with handgrip (Handgrip MVC), (c) an MVC focusing on contracting the knee extensors only (Isolated knee extension MVC), and (d) an MVC with unrestrained leg and pelvis (Unrestrained MVC). Torque and activation capacity between conditions were compared with repeated measures ANOVA and dependent t-tests. EMG (from eleven remote muscles) was compared using Friedman's and Wilcoxon. Typical MVC (277.2 ± 49.6 Nm) and Handgrip MVC (261.0 ± 55.4 Nm) were higher than Isolated knee extension MVC (210.2 ± 48.3 Nm, p < 0.05) and Unrestrained MVC (195.2 ± 49.7 Nm, p < 0.05) torque. Typical MVC (83.1 ± 15.9%) activation was higher than Isolated knee extension MVC (68.9 ± 24.3%, p < 0.05), and both Typical MVC and Handgrip MVC (81.8 ± 17.4%) were higher than Unrestrained MVC (64.9 ± 16.2%, p < 0.05). Only flexor carpi radialis, biceps brachii, triceps brachii and external oblique muscles showed EMG differences, with Isolated knee extension MVC consistently lower than Typical MVC or Handgrip MVC. Stabilisation of the involved segments is the prime concern allowing fuller activation of the muscle, reinforcing the need for close attention to stabilisation during dynamometry-based knee joint functional assessment.