Is there sufficient evidence to explain the cause of sexually dimorphic behaviour in force steadiness?

Abstract

Neuromuscular noise is a determining factor in the control of isometric force steadiness (FS), quantified as coefficient of variation (CV) of force around a preestablished target output. In this paper we examine sex-related differences of neural, muscular, and tendon influences on neuromuscular noise to understand FS in females and males. We use evidence from the literature to identify that CV of force is higher in females compared with males in the upper and lower body, with sex-related differences becoming less apparent with increasing age. Evaluation of sex-related physiology in tandem with results from FS studies indicate that differences in fibre type, contractile properties, and number of motor units (MUs) are unlikely contributors to differences in FS between females and males. MU type, behaviour of the population (inclusive of number of active MUs from the population), agonist-antagonist activity, maximal strength, and tendon mechanics are probable contributors to sexually dimorphic behaviour in FS. To clearly determine underlying causes of sex-related differences in FS, further study and reporting between females and males is required. Females and males are included in many studies; however, rich data on sexually dimorphic behaviour is lost when data are collapsed across sex or identified as nonsignificant without supporting values. This poses a challenge to identifying the underlying cause of females having higher CV of force than males. This review provides evidence of sexually dimorphic behaviour in FS and suggests that physiological differences between females and males effect neuromuscular noise, and in-turn contribute to sex-related differences in FS.

Oscillations in neural drive and age-related reductions in force steadiness with a cognitive challenge

“…Women were observed to have greater CV of force during low-force isometric tasks for both the upper and lower limb muscles compared with men (31). Furthermore, the increase in the CV of force with either imposition of a cognitive challenge during a motor task or after a stressful event is larger for women than for men for the upper limb muscles (8,54,58).…”

Force Control and Motor Unit Firing Behavior Following Mental Fatigue in Young Female and Male Adults

“…Additionally, during isometric contractions, the CV of force is higher in females than males in both upper and lower limbs (Jakobi et al, 2018). Relevant factors likely contributing to this sex-specific response include muscle strength and agonistantagonist activity (Jakobi et al, 2018).…”

“…Additionally, during isometric contractions, the CV of force is higher in females than males in both upper and lower limbs (Jakobi et al, 2018). Relevant factors likely contributing to this sex-specific response include muscle strength and agonistantagonist activity (Jakobi et al, 2018). When a cognitive task is performed concurrently during an elbow flexion isometric contraction, females have a greater increase in the CV of force and demonstrate greater co-activation than males (Pereira et al, 2015), though this finding is less consistent in the ankle dorsiflexors (Vanden Noven et al, 2014).…”

Dynamic Wrist Flexion and Extension Fatigue Induced via Submaximal Contractions Similarly Impairs Hand Tracking Accuracy in Young Adult Males and Females

“…While a majority of literature focuses on fatigue at the muscle fiber level, far less focus is on the effects of muscular fatigue at the tendon. There has been a growing emphasis on the tendon and its role in force steadiness (Johannsson et al, 2015;Jakobi et al, 2018;Smart et al, 2018). In the presence of muscular fatigue, after an acute bout of submaximal dynamic exercise, the Achilles tendon has been shown to exhibit sex-dependent behaviors, in which females exhibit greater tendon elongation and reduced tendon stiffness (Joseph et al, 2014).…”

“…This was not observed in our previous study on an isometric fatiguing task, which may have been due to the previous isometric fatiguing protocol being matched with a dynamic task, whereas the present study matches a dynamic fatigue protocol with a dynamic task . We also hypothesized that males would be more proficient at tracking than females due to the reported sex differences for force steadiness (Brown et al, 2010;Jakobi et al, 2018).…”