Submaximal fatiguing eccentric contractions of knee flexors alter leg extrapersonal representation

Abstract

This study assessed the immediate and prolonged effects of eccentric-induced fatigue on position sense, utilizing position-pointing tasks, which had not been previously implemented for this purpose. Fifteen healthy adults underwent a fatiguing eccentric protocol that entailed sets of unilateral submaximal contractions of knee flexor muscles until reaching a 20% decrease in maximal isometric torque production. Evaluations of knee flexor neuromuscular function as well as position-pointing tasks at 40° and 70° of knee flexion were conducted prior to the fatiguing eccentric protocol, immediately after (POST), and 24 h after (POST24) exercise termination. To assess neuromuscular fatigue etiology, electrical myostimulations were administered during and after maximal voluntary isometric contractions. At POST, the voluntary activation level and evoked potentiated doublet amplitude at 100 Hz were significantly reduced. In addition, position-pointing errors exhibited a significant increase at POST regardless of the tested angle, with participants positioning the pointer in a more extended position compared to their hidden exercised limb. At POST24, neuromuscular function and position sense parameters had reverted to their baseline levels. The findings of this experiment demonstrate that position-pointing accuracy was impaired immediately after the fatiguing eccentric protocol, manifesting in the presence of both central and peripheral fatigue. As position-pointing accuracy relies heavily on extrapersonal representation of the body at the brain level, acute changes in exercised limb's extrapersonal representation might have resulted from central fatigue-related mechanisms altering the cognitive processes responsible for converting kinesthetic signals into extrapersonal coordinates.

Keywords: Exercise; Hamstrings; Kinesthesia; Neuromuscular fatigue; Position sense.

Fig. 1

Outline of the study design encompassing measurements conducted prior to the fatiguing eccentric protocol, immediately after, and 24 h after exercise termination. The measurements involved the evaluations of knee flexor (KF) neuromuscular function during maximal voluntary isometric contractions (MVICs), as well as during eccentric unilateral 1 repetition maximum tests (1RM ECCs). For more details, please refer to the text.

Fig. 2

Illustration of the custom-made pointing box used to assess knee position sense of the right exercised lower limb at 40° and 70° of knee flexion. For more details, please refer to the text.

Fig. 3

Individual data (left) and means ± standard deviation (right) of A) torque production during maximal voluntary isometric contraction (MVIC), B) voluntary activation level (VA), C) ratings of perceived fatigue (RPF), and D) pointing errors obtained at three measurement times: prior to the fatiguing eccentric protocol (PRE), immediately after (POST), and 24 h after exercise termination (POST24). Statistical analyses indicated that POST values exhibited significant differences in comparison to PRE measurements, with significance levels denoted as *, **, *** for p < .05, p < .01 and p < .001, respectively.

Fig. 4

The individual data (left) and means ± standard deviation (right) of electrically evoked torques [A) potentiated doublet amplitude at 100 Hz (Dt_100Hz), B) potentiated doublet amplitude at 10 Hz (Dt_10Hz), and C) potentiated single twitch (Tw_pot)] as well as D) perceived muscle soreness (PMS) scores are presented. These measurements were performed at three time points: before, immediately after, and 24 h following the fatiguing eccentric protocol (i.e., at PRE, POST, and POST24, respectively). Significant differences were detected between PRE and POST values (with *, **, *** corresponding to p < .05, p < .01 and p < .001, respectively).