Wrist Flexors are Steadier than Extensors

Abstract

To examine torque variability in 2 antagonistic muscles 20 individuals performed maximal and submaximal (5, 10, 20, 50 and 75% of Maximal Voluntary Contraction, MVC) isometric wrist flexions and extensions (5 s) at 5 different angles (230, 210, 180, 150 and 130°). The EMG activity of Flexor Carpi Ulnaris (FCU) and Extensor Digitorum (ED) was recorded and quantified as the integral of EMG. Participants showed higher maximal isometric torque (32.43±11.17 vs. 17.41±3.84 Nm) and lower coefficient of variability during wrist flexion compared to extension. The normalized agonist EMG increased across higher levels of torque for both wrist muscles. Interestingly, the coactivation of ED during wrist flexion was greater compared to the coactivation of FCU during wrist extension at 50 and 75% of MVC, regardless of wrist angle (f.e.: at 180° and 75% of MVC the normalised EMG of ED as antagonist was 14.84±5.18% vs. 9.33±6.94 of the FCU). It is concluded that a stronger isometric wrist flexion is more steadily produced, with greater coactivation compared to a weaker wrist extension, independently from muscle length and torque level. Even if the relative contribution of antagonists to the resultant torque is to be considered, altered activation patterns responsible for differences in force fluctuations could be suggested.

Responses of finger flexor and extensor muscles to transcranial magnetic stimulation during isometric force production tasks

“…The mean MVC force was 119 6 38 N for finger flexors and 55 6 19 N for finger extensors. Finger force increased with the force level during both flexion and extension tasks, and flexion forces were greater than extension forces at all force levels [F (1,9) 5 56.80, P < 0.001] (Fig. 3A).…”

“…4B). A 2way ANOVA, with factors of TASK and FL, showed a main effect of TASK [F (1,9) 5 6.65, P 5 0.03], but no interactions.…”

“…During finger extension, the TMS-induced force was continuously decreased with force level (R 2 5 0.96). A 2-way ANOVA, with factors of TASK and FL, showed a main effect of TASK [F (1,9) 5 24.79, P < 0.001], but no interactions.…”

“…5,6 In the comparison of different muscles, F COV is higher for a weaker and smaller muscle than for a bigger and stronger muscle. 4,[7][8][9] Thus, we expect that F COV would be lower in the stronger FDS compared with the weaker EDC.…”

“…The magnitude of fluctuation, expressed as standard deviation (SD), increases linearly with force levels, whereas the coefficient of variation of force (F COV , defined by SD / background force) is usually constant . In the comparison of different muscles, F COV is higher for a weaker and smaller muscle than for a bigger and stronger muscle . Thus, we expect that F COV would be lower in the stronger FDS compared with the weaker EDC.…”