Sex differences in human fatigability: mechanisms and insight to physiological responses

Abstract

Sex-related differences in physiology and anatomy are responsible for profound differences in neuromuscular performance and fatigability between men and women. Women are usually less fatigable than men for similar intensity isometric fatiguing contractions. This sex difference in fatigability, however, is task specific because different neuromuscular sites will be stressed when the requirements of the task are altered, and the stress on these sites can differ for men and women. Task variables that can alter the sex difference in fatigue include the type, intensity and speed of contraction, the muscle group assessed, and the environmental conditions. Physiological mechanisms that are responsible for sex-based differences in fatigability may include activation of the motor neuron pool from cortical and subcortical regions, synaptic inputs to the motor neuron pool via activation of metabolically-sensitive small afferent fibres in the muscle, muscle perfusion, and skeletal muscle metabolism and fibre type properties. Non-physiological factors such as the sex bias of studying more males than females in human and animal experiments can also mask a true understanding of the magnitude and mechanisms of sex-based differences in physiology and fatigability. Despite recent developments, there is a tremendous lack of understanding of sex differences in neuromuscular function and fatigability, the prevailing mechanisms and the functional consequences. This review emphasises the need to understand sex-based differences in fatigability in order to shed light on the benefits and limitations that fatigability can exert for men and women during daily tasks, exercise performance, training and rehabilitation in both health and disease.

Age-related decline in muscle mass and muscle function in Flemish Caucasians: a 10-year follow-up

“…There is some evidence that the proportional area of type I fibers is significantly greater in women compared to men and that men have larger fibers across most of the fiber types (Simoneau and Bouchard 1989;Staron et al 2000;Hunter 2014). Moreover, a decline in fiber size, of type Data are beta-coefficients.…”

Sex Differences in Arm Muscle Fatigability With Cognitive Demand in Older Adults

“…Fatigability is quantified as a reduction in maximal strength or the time to failure of a submaximal fatiguing contraction [6,10]. There are sex differences in fatigability because women are frequently less fatigable than men, although the specific demands of a task may change this difference [10].…”

“…There are sex differences in fatigability because women are frequently less fatigable than men, although the specific demands of a task may change this difference [10]. For example, when a high-cognitive demand task, which increased stress, was performed while sustaining a contraction with the elbow flexor muscles, young women (18-30 years) had greater reductions in the time-to-task failure than young men [38], suggesting increased fatigability.…”

ge and Gender Differences of Fatigue during Sustained Maximal Isometric Contractions in Adults

“…Dauguma mokslininkų, nagrinėjusių nuovargio mechanizmus, tvirtina, kad moterys gali ilgiau nei vyrai palaikyti nenutrūkstamus arba kartotinius žemo arba vidutinio intensyvumo raumens susitraukimus (Fulco et Hunter, 2014). Be to, keturgalvio šlaunies raumens nuovargio po maksimalių izometrinių susitraukimų (MVJ) tyrimų duomenys yra kontraversiški (Allman, Rice, 2002;Avin, Frey Law, 2011).…”

“…Iš pradinių matavimų duomenų matyti, kad vyrai pasiekia didesnę valingą jėgą nei moterys, taip pat senyvo amžiaus tiriamųjų prastesni valingos ir nevalingos jėgos rodikliai nei jaunų tiriamųjų. Alkūnės lenkiamųjų raumenų tyrimai rodo, kad raumenų silpnumas yra glaudžiai susijęs su senėjimo metu atsiradusiu nervinės sistemos negebėjimu iki galo aktyvinti motorinius neuronus (Yoon et al, 2007;Hunter, 2014), daugiau dėmesio kreipėme į tyrimus, atliktus su šlaunies tiesiamaisiais raumenimis. Nors daugumoje jų nustatyti skirtumai tarp jauno ir senyvo amžiaus tiriamųjų, tačiau poroje studijų aprašytas valingos aktyvacijos trūkumas analizuojant senyvo amžiaus tiriamuosius (Stevens et al, 2003).…”