Surgical instrument

A tool comprises a distal portion and a proximal portion spaced apart by a shaft along a longitudinal axis. The distal portion includes a distal link and the proximal portion including a proximal link. The distal link and proximal link form a pair of links. The tool also comprises a set of tension load bearing members connecting the proximal link and the distal link and terminating at the links of the pair to transfer movement therebetween. The tool also comprises an articulation lock positioned between the distal portion and the proximal portion and configured to allow through passage of the set of tension load bearing members. The articulation lock is adjustable between an unlocked configuration in which the proximal and distal links are moveable and a locked configuration in which an effective length of the shaft is increased, creating a force to impede movement of the proximal and distal links.