title: Individuals with intellectual disability have lower voluntary muscle activation level.
abstract: The aim of this study was to explore the voluntary activation level during maximal voluntary contraction (MVC) in individuals with intellectual disability (ID) versus individuals without ID using the twitch interpolation technique. Ten individuals with mild ID (ID group) and 10 sedentary men without ID (control group) participated in this study. The evaluation of neuromuscular function consisted in three brief MVCs (3s) of the knee extension superimposed with electrical nerve stimulation (NES) to measure voluntary activation. Muscle activity levels were also measured with surface EMG. The root mean square (RMS) was extracted from the EMG signal. The RMS/Mmax ratio and the neuromuscular efficiency (NME) were calculated. Our results reported that individuals with ID present lower muscle strength (p < 0.001), lower voluntary activation level (p < 0.001), lower RMS values of vastus lateralis (p < 0.05), vastus medialis (p < 0.05), and rectus femoris (p < 0.001) muscles. In addition, our results showed lower RMS/Mmax values in the ID group than in the control group for the VM (0.05 ± 0.01 mV vs. 0.04 ± 0.01 mV; p < 0.05) and the RF (0.06 ± 0.02 mV vs. 0.05 ± 0.02 mV; p < 0.05) muscles. However, no significant difference was reported for the VL muscle (0.05 ± 0.02 mV vs. 0.05 ± 0.02 mV; p=0.463). Moreover, Individuals with ID present smaller potentiated twitch (p < 0.001). However, no significant difference was reported in the NME ratio. These results suggest that the lower muscle strength known in individuals with ID is related to a central nervous system failure to activate motor units and to some abnormal intrinsic muscle properties. It seems that the inactive lifestyle adopted by individuals with ID is one of the most important factors of their lower voluntary activation levels. Therefore, physical activities should be introduced in life style of individuals with ID to improve their neuromuscular function.
authors.affiliation: Unité de Recherche Education, Motricité, Sports et santé, Institut Supérieur du Sport et de l'Education Physique de Sfax, Université de Sfax, Tunisia. Electronic address: borji-rihab1@hotmail.fr.
authors.forename: Rihab
authors.initials: R
authors.lastname: Borji
authors.affiliation: Laboratoire Adaptations Métaboliques à l'Exercice en Conditions Physiologiques et Pathologiques (AME2P, EA 3533), Université Blaise Pascal, Clermont-Ferrand, France. Electronic address: zghal.firas2012@yahoo.fr.
authors.forename: Firas
authors.initials: F
authors.lastname: Zghal
authors.affiliation: Laboratoire des techniques d'imagerie médicale (LR 12ES06, LTIM), Faculté de Médicine de Monastir, Université de Monastir, Tunisia. Electronic address: nidhal.zarrouk@yahoo.com.
authors.forename: Nidhal
authors.initials: N
authors.lastname: Zarrouk
authors.affiliation: Unité de Recherche Education, Motricité, Sports et santé, Institut Supérieur du Sport et de l'Education Physique de Sfax, Université de Sfax, Tunisia. Electronic address: sonia.sahli@yahoo.fr.
authors.forename: Sonia
authors.initials: S
authors.lastname: Sahli
authors.affiliation: Unité de Recherche Education, Motricité, Sports et santé, Institut Supérieur du Sport et de l'Education Physique de Sfax, Université de Sfax, Tunisia. Electronic address: haithem.rebai@yahoo.fr.
authors.forename: Haithem
authors.initials: H
authors.lastname: Rebai
mesh_terms: D000328:Adult; D016022:Case-Control Studies; D004558:Electric Stimulation; D004576:Electromyography; D006801:Humans; D008607:Intellectual Disability / Q000503:physiopathology*; D008297:Male; D009119:Muscle Contraction / Q000502:physiology*; D053580:Muscle Strength / Q000502:physiology*; D018482:Muscle, Skeletal / Q000503:physiopathology; D052097:Quadriceps Muscle / Q000503:physiopathology*; D055815:Young Adult
keywords: Electrical stimulation; Intellectual disability; Knee extensor muscles; Twitch interpolation technique; Voluntary activation level