Abstract
BackgroundWhile performing a unilateral muscle contraction, electrical muscle activity also arises in the contralateral homologous muscle, muscle group, or limb. When the muscle contraction induces muscle fatigue, females show not only a greater resistance than males but also a reduced contralateral muscle activation. The study aimed at investigating whether, during a high-intensity 30-s unilateral maximal effort isometric leg extension exercise, the contralateral non-exercising limb (NEL) knee extensor muscle activation would differ between females and males.MethodsTwenty participants, 11 females (23.80 ± 2.15 years old) and 9 males (26.50 ± 2.45 years old), performed a unilateral 30-s exercise while surface electromyography (sEMG) was measured from the vastus lateralis (VL), vastus medialis (VM), and rectus femoris (RF) on both limbs. The maximal voluntary contraction (MVC) was measured for both the exercising limb (EL) and the NEL before (MVC PRE) and after (MVC POST) the 30-s exercise to assess muscle fatigue.ResultsWhile both females and males exhibited muscle fatigue in the EL (p = 0.015), females exhibited a lower MVC reduction than males (p = 0.042), suggesting that females were less fatigued than males. Although no muscle fatigue, i.e., no MVC force reduction was found in the NEL for either group before and after the 30-s exercise, the muscle activity of the VL was found to be of greater magnitude during the MVC POST only for females (p = 0.047) while it remained unchanged for males. During the 30-s exercise, the force output of the EL decreased only for males (p = 0.029) while females showed a preservation of the force output (p > 0.05). The sEMG activity of the NEL during the 30-s unilateral exercise increased for both groups in all measured muscles (all p-values < 0.03).ConclusionsLikely, different underlying muscle fatigue mechanisms occurred in the EL between females and males. Yet, our findings suggest that the cross-over effect to the NEL during the 30-s exercise occurred in a similar fashion in both groups. The current study suggests that the contralateral muscle activation seen with a unilateral exercise is independent of the sex of individuals. Therefore, unilateral training or rehabilitation-based protocols would similarly impact females and males.
Highlights
While performing a unilateral muscle contraction, electrical muscle activity arises in the contralateral homologous muscle, muscle group, or limb
Maximal voluntary contractions Overall and as expected, the maximal voluntary contraction (MVC) of the exercising limb (EL) significantly decreased from Pre-30-s exercise test (PRE) to Post-30-s exercise test (POST) tests (main time effect: F(1,18) = 7.227; p = 0.015; η2p = 0.286; observed power = 0.720; Fig. 2)
The associated maximal surface electromyography (sEMG) root mean square (RMS) muscle activity (Table 2) of the EL did not modify from PRE to POST in the vastus lateralis (VL) (F(1,18) = 0.008; p = 0.928; η2p = 0.000; observed power = 0.051), and neither any main effect of gender (F(1,18) = 2.860; p = 0.108; η2p = 0.137; observed power = 0.360) nor any interaction were found (F(1,18) = 2.860; p = 0.108; η2p = 0.137; observed power = 0.360)
Summary
While performing a unilateral muscle contraction, electrical muscle activity arises in the contralateral homologous muscle, muscle group, or limb. The study aimed at investigating whether, during a high-intensity 30-s unilateral maximal effort isometric leg extension exercise, the contralateral non-exercising limb (NEL) knee extensor muscle activation would differ between females and males. Following neurological disease, such as stroke, cerebral palsy, brain injury, or periods of limb immobilization after an accident or an injury, some rehabilitation protocols are performed unilaterally to restore as much as possible the bilateral motor function [1]. While the first refers to the impaired muscle capacity to generate force within the muscle fiber, modifications in the voluntary neural drive from the corticospinal pathway innervating muscles may concurrently occur [9, 10]
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