  Grip strength loss in extended and flexed wrist postures has been explained
by reduced force-generating capacities of extrinsic finger flexor resulting
from non-optimal length, owing to the force-length relationship. Recent works
suggested that other muscles, especially wrist extensors, participate in this
grip strength loss. The objective of this study was to clarify the role of the
force-length relationship in finger force production. 18 participants performed
maximal isometric finger force production during pinch grip (Pinch) and
four-finger pressing (Press) tasks in four different wrist postures (extended,
flexed, neutral, spontaneous). The maximum finger force (MFF), finger and wrist
joint angles, as well as activation of four muscles were determined using
dynamometry, motion capture, and electromyography. The force and length of the
four muscles were estimated from joint angles and muscle activation using a
musculoskeletal model. MFF decreased for flexed wrist during Pinch but remained
stable across wrist postures during Press. The results suggested that the loss
of pinch grip force in deviated wrist posture is partially related to
force-length relationship of finger extensors. In opposition, MFF during Press
was not influenced by the modulation of muscle capacities but was probably
first limited by mechanical and neural factors related to finger
interdependence
