Limited difference in time to failure between sustained force and position control contractions with the knee extensors

Different types of contractile fatiguing tasks (force/position tasks) have shown that the rate of neuromuscular impairment is task dependent. Whether fatigue resistance is uniform across different types of limb joints is poorly understood because the force-position paradigm has mainly been applied to upper extremity joints under unstable conditions. Therefore, the purpose of the present study was to investigate task dependency in the more stable knee joint. Fourteen subjects performed two sustained isometric knee extensor contractions to failure. In the force task, 20% of maximal voluntary contraction force was maintained for as long as possible with visual feedback of the force, while in the position task, the load was similar, but subjects received visual joint angle feedback. No significant difference was observed in time to failure (force task: 423 +/- 61 s, position task: 379 +/- 48 s), increase in electromyographic amplitude or perceived exertion between tasks. The force-position paradigm has not been applied previously to the quadriceps, and the difference between the present and the previous results may partly be attributed to joint stability and the volume of co-contracting muscles, such that in addition to the previously noted mechanisms of muscle fatigue, the mechanical design of the relevant joint and muscle actuators may influence task dependency during sustained submaximal contractions.