Neuromuscular fatigue and recovery profiles in individuals with intellectual disability

Abstract

Purpose: This study aimed to explore neuromuscular fatigue and recovery profiles in individuals with intellectual disability (ID) after exhausting submaximal contraction.

Methods: Ten men with ID were compared to 10 men without ID. The evaluation of neuromuscular function consisted in brief (3 s) isometric maximal voluntary contraction (IMVC) of the knee extension superimposed with electrical nerve stimulation before, immediately after, and during 33 min after an exhausting submaximal isometric task at 15% of the IMVC. Force, voluntary activation level (VAL), potentiated twitch (Ptw), and electromyography (EMG) signals were measured during IMVC and then analyzed.

Results: Individuals with ID developed lower baseline IMVC, VAL, Ptw, and RMS/M_max ratio (root-mean-square value normalized to the maximal peak-to-peak amplitude of the M-wave) than controls (p < 0.05). Nevertheless, the time to task failure was significantly longer in ID vs. controls (p < 0.05). The 2 groups presented similar IMVC decline and recovery kinetics after the fatiguing exercise. However, individuals with ID presented higher VAL and RMS/M_max ratio declines but lower Ptw decline compared to those without ID. Moreover, individuals with ID demonstrated a persistent central fatigue but faster recovery from peripheral fatigue.

Conclusion: These differences in neuromuscular fatigue profiles and recovery kinetics should be acknowledged when prescribing training programs for individuals with ID.

Keywords: Central fatigue; Intellectual disability; Neuromuscular fatigue; Peripheral fatigue; Sustained sub-maximal exercise; Twitch interpolation technique.

Fig. 1

Schematic representation of the experimental protocol. To evaluate exercise-induced fatigue and recovery, 3 and then 12 repeated isometric maximal voluntary contractions (IMVC) superimposed and followed by peripheral nerve electrical stimulation (PNS) were performed before (pre-EX) and after fatiguing exercise (post-EX), respectively.

Fig. 2

Evolution of the (A) IMVC (%max), (B) VAL (%max), and (C) Ptw (%max) before (pre-EX), immediately after the fatiguing isometric task (post-EX), and during the recovery period (post-EX 3–9, post-EX 12–21, post-EX 24–33) in individuals. *p < 0.05, compared with baseline; ^†p < 0.05, compared with ID group; ^‡p < 0.05, compared with post-Ex; ^§p < 0.05, compared with post-EX 3–9. ID = intellectual disability; IMVC = isometric maximal voluntary contraction; post-Ex = post-exercise; post-Ex 3–9 = 3 sets performed in the recovery period 3 to 9 min after exercise; post-Ex 12–21 = 4 sets performed from 12 to 21 min after exercise; post-Ex 24–33 = 4 sets performed from 24 to 33 min after exercise; pre-Ex = pre-exercise; Ptw = potentiated twitch; VAL = voluntary activation level.