Torque time integral (TTI) is the combination of intensity and duration of a contraction.

Aim of the study : to compare neuromuscular alterations following different isometric sub-maximal contractions of the knee extensor muscles but with similar TTI.

Conclusions : Central and peripheral alterations accounting for muscle fatigue are similar following isometric contractions with similar TTI. TTI should be considered in the exploration of muscle fatigue during sustained isometric contractions.

Rozand et al. (2014)

Aim of the study : to compare the mechanisms of fatigue induced by a unilateral vs a bilateral submaximal isometric knee extension.

Conclusion : The present results demonstrated that time to task failure of a submaximal fatiguing contraction may depend on the number of limbs involved in the task. The greater time to task failure with one leg may have induced greater contractile alterations and a larger MVC loss following the unilateral task.

Matkowski et al. (2011)

Aim of this study : To assess H-reflex plasticity and activation pattern of the plantar flexors during a sustained contraction where voluntary EMG activity was controlled via an EMG biofeedback.

Conclusion : The balance between excitation and inhibition affecting the motoneuron pool remains constant during a sustained contraction where myoelectrical activity is controlled via an EMG biofeedback or let free to vary.

Place et al. (2009)

Aims of the study : To examine (1) endurance time and (2) activation pattern of vastus lateralis (VL), vastus medialis (VM) and rectus femurs (RF) muscles during fatiguing isometric knee extensions performed with different EMG biofeedbacks.

Conclusions : (1) task failure occurs when sustaining a submaximal level
of EMG activity for as long as possible and (2) CNS is not able to differentiate descending drive to the different heads of the quadriceps at the beginning of a sustained contraction, despite a different activation pattern for the bi-articular RF muscle compared to the mono-articular vasti muscles during fatigue.

Place et al. (2006)

Aim of the study : To compare central and peripheral mechanisms of fatigue after an isometric contraction of the knee extensor muscles performed at 20% maximal voluntary contraction (MVC) at two knee angles (35°, short length vs. 75°, long length; 0°
full extension) until exhaustion.

Conclusions : 1) central fatigue at task failure for a sustained isometric contraction was not dependent on the muscle length, and 2) the longer endurance time of a sustained isometric contraction performed at a shortened length is related to potentiation. It is suggested that the greater endurance time of a sustained isometric contraction observed at 35° is related to the occurrence of potentiation at this short length, because central fatigue is similar at task failure for both tasks.

Place et al. (2005)

Aim of the study : To compare the endurance time of a sustained isometric
contraction of the knee extensor muscles at 20% of the maximum voluntary contraction (MVC) torque performed on three separate occasions in a seated posture.

Conclusions : The time to task failure for the knee extensor muscles that have a common tendon insertion did not alter over repeat sessions as had been observed for the elbow flexor muscles (Hunter SK and Enoka RM. J Appl Physiol 94: 108–118, 2003).

Rochette et al. (2003)