Mechanisms of Fatigue and Task Failure Induced By Sustained Submaximal Contractions

Abstract

It follows that task failure from a sustained isometric contraction is mainly affected by central/motivational factors, whereas MVC force loss is largely explained by the extent of contractile failure of the muscle.

Comparison of neuromuscular adjustments associated with sustained isometric contractions of four different muscle groups

“…This contention is corroborated by the slight force decline below 50% MVC, observed just before task failure, and the maximal RPE when task failure was reached. These results are in agreement with our previous study in which the subjects' muscles were still capable of developing briefly a force equal to about 50% of prefatigue MVC force, despite being unable to voluntarily sustain anymore the mere 20% MVC force level requested in that study (53). Burnley et al (17) reported that, after repeated sustained submaximal contractions below a "critical torque" threshold (corresponding to the intensity below which the contraction could theoretically be sustained indefinitely), a greater force than that requested could still be produced immediately after the exercise.…”

“…RPE was analyzed at 25, 50, 75, and 100% of the endurance time (53), and the rate of increase was calculated using the linear mixed effect model.…”

“…A high-voltage (400 V maximum) constantcurrent stimulator (DS7AH; Digitimer, Hertfordshire, UK) was used to deliver single and paired electrical stimuli. For KE, the cathode (5-cm diameter, Dermatrode; American Imex, Irvine, CA) and the anode (5 ϫ 10 cm; Compex, Ecublens, Switzerland) were placed over the femoral nerve at the femoral triangle level beneath the inguinal ligament and on the lower part of the gluteal fold opposite to the cathode, respectively (53). For the PF, the cathode (1-cm diameter, Meditrace 100 Kendall; Tyco, Markham, Ontario, Canada) was placed in the popliteal fossa (over the tibial nerve), and the anode (5 ϫ 10 cm, Compex) was located on the anterior surface of the knee (57).…”

“…This intensity was then increased by 10% and kept constant throughout the experiment. Such supramaximal stimulation intensity, as used in previous studies (46,53,56), limits the discomfort associated with the stimulation compared with higher supramaximal levels. Pulse width was set at 0.1 ms for the upper limbs (68) and at 1 ms for the lower limbs (53,57).…”

Impact of High-Intensity Interval Duration on Perceived Exertion

“…This effect was observed even though the overall workload was the same, and this finding could be explained through at least two mechanisms. First, prior research indicates that recovery from effortful work is more than just recovery from peripheral muscle fatigue and suggests that cognitive mechanisms are as important in dealing with the discomfort associated with ex ertion (31). A potential influence on discomfort is that the anticipation of a long sustained interval effort can be per ceived as more aversive.…”