Sex hormones and the nervous system, do they matter for physical performance?

Abstract

There are well-known oscillations in circulating sex hormones that occur in both men and women on daily and monthly cycles, as well as across the lifespan. The non-reproductive effects of estrogen and progesterone, particularly in women, on physical performance have been an area of intense debate. This presentation will examine the evidence that sex hormones can modulate the nervous system from the cellular-level to a whole-body perspective and impact human physical performance. The cell-level and animal literature clearly indicates sex hormones have the capability to directly modulate the excitability of the nervous system through gamma-Aminobutyric acid (GABA) receptors. Pregnenolone, a first-order metabolite of progesterone, is able to directly activate GABA receptors creating either a neuro-excitatory or inhibitory effect depending on whether pregnenolone is sulfonated. Progesterone is able to enhance the GABA receptor response in the presence of GABA, increasing neural inhibition. Additionally, estrogen creates an excitatory effect on the nervous system by attenuating the release of GABA from neurons. Research from our work group has shown that the discharge of motor neurons are altered across the menstrual cycle 1 Tenan M.S. Peng Y.L. Hackney A.C. Griffin L. MSSE. 2013; 45: 2151-2157 Google Scholar and that quadriceps MVC may decrease by as much as 23% in the mid luteal phase of the menstrual cycle, when both estrogen and progesterone are high. 2 Tenan M.S. Hackney A.C. Griffin L. EJAP. 2016; 116: 153-160 Google Scholar In relative time to exhaustion, the mid luteal menstrual phase also has the least stable force production across the entire isometric task. At the cellular level, sex hormones clearly have the capability to modulate nervous system function. Our research indicates that this translates to measurable effects on human performance; however, this finding is not uniform across all studies. In conclusion, sex hormones have the theoretical ability to modify physical performance but the inconsistent findings at the clinical level may be a result of individual variability in the level of sex hormones both in circulation and uniquely within the central nervous system, making broad generalizations across a population of men or women challenging.