Changes in constraint of proximal segments effects time to task failure and activity of proximal muscles in knee position-control tasks

Highlights ► When maintaining the position of a segment against an external load, the time until the position cannot be maintained (time to task failure; TTF) is greater if potential for movement of the more proximal limb segments is restricted with supports. ► Shorter TTF in tasks with less proximal segment constraint is associated with greater activity of the prime mover muscle as well as antagonist muscles, and muscles of more proximal segments. ► Manipulations of the amount of imposed limb constraint may partly explain the differences in TTF that have been reported in studies of muscle contractions, which differ in load type (muscle contractions to a target force vs. muscle contractions to control a limb position).