Gjc. Ettema et al., THE MOMENT ARMS OF 23 MUSCLE SEGMENTS OF THE UPPER-LIMB WITH VARYING ELBOW AND FOREARM POSITIONS - IMPLICATIONS FOR MOTOR CONTROL, Human movement science, 17(2), 1998, pp. 201-220
In this study we examined moment arms of the complete muscle system of
the elbow, including the wrist flexors that have their proximal attac
hment point on the humerus. This study was performed with the aim to i
dentify the synergistic mover functions of the muscles as an anatomica
l basis for the study of motor control of the elbow. The upper limbs o
f three cadaver specimens were dissected. Muscles were replaced by ela
stic strings. The relationship between muscle length and joint angles
(elbow flexion-extension (F-E) and forearm pronation-supination (P-S))
were determined. The first derivation of the relationship revealed th
e moment arms. The results confirmed the literature with respect to th
e major elbow flexors, extensors, pronators and supinators. Two wrist
muscles had a substantial moment arm at the elbow: The flexor carpi ra
dialis appears to be a pronator of the forearm, and the extensor carpi
radialis longus is an elbow flexor. The ratios of moment arm between
muscles and between the two orthogonal actions were relatively constan
t among the specimens. A mechanical explanation for the existence of s
ubpopulations of motor units (i.e. differences in moment arm for the s
ubpopulations) is viable for supinator, brachialis, and brachioradiali
s, whereas it is less viable for biceps brachii. (C) 1998 Elsevier Sci
ence B.V. All rights reserved.