Influence of Menstrual Cycle Phases on Neural Excitability in the Primary Somatosensory Cortex and Ankle Joint Position Sense

Disruptive compensatory mechanisms in fibromyalgia syndrome and their association with pharmacological agents

Fibromyalgia syndrome (FMS) is a chronic disorder characterized commonly by widespread musculoskeletal pain and fatigue, predominantly affecting women, with its complexity often leading to underdiagnosis and complicating treatment effectiveness. Transcranial magnetic stimulation (TMS) metrics are potential markers to optimize FMS treatments; however, evidence is limited. Our study aimed to explore the relationship between cortical excitability and inhibition, assessed through TMS markers, and clinical characteristics in patients with FMS. This presented cross-sectional study employed baseline data from a clinical trial with 108 FMS patients, mostly female (88.8%), and mean age of 47.3 years old (SD = 12.06). Our analysis showed that decreased short-intracortical inhibition (SICI) was associated with gabapentinoids use, nicotine history, and increased fatigue levels, suggesting its connection with compensatory mechanisms for non-painful FMS features. Increased motor intracortical facilitation (ICF) was linked with greater pain severity and shorter FMS duration, implying its relationship with a reorganization of sensorimotor pathways due to chronic pain. Additionally, higher resting motor threshold (rMT) was associated with less effective pain modulation (lower conditioned pain modulation [CPM]), indicating a disruption of pain compensatory mechanism. Given the role of SICI in indexing homeostatic brain mechanisms and its association with fatigue, a hallmark characteristic of FMS-induced behavioral changes, these results suggest that FMS likely has a deleterious effect on brain inhibitory function, thus providing a potential novel insight for FMS mechanisms. In addition, it seems that this compensatory mechanism's disruption is enhanced by pharmacological agents such as gabapentioids and nicotine.

Alterations of postural control across the menstrual cycle - A systematic review

BACKGROUND

Postural control is a vital component of injury prevention and prediction and plays a critical role in sports performance. Its relationship with the phases of the menstrual cycle (MC) is not yet fully understood and requires further investigation.

RESEARCH QUESTION

Does postural control alter between high hormone and low hormone phases of the MC?

METHODS

Five electronic databases were searched by two reviewers between 30th November and 2nd December 2022. Included were studies that investigated the effects of the MC on static and dynamic postural control in naturally cycling (NC) women by comparing the early follicular phase (EFP) with at least one high hormone phase of the MC. Two reviewers conducted the literature search, selection of eligible studies, data extraction, methodological quality assessment utilizing a modified Downs and Black Checklist, GRADE guidelines and SIGN grading, and synthesis of results.

RESULTS

Nine studies examined the effects of the MC on static (n = 7), dynamic (n = 1), or both forms of postural control (n = 1) in 148 NC women. Included studies were of very low to moderate quality. Level of evidence was either 2 + (n = 1) or 2- (n = 8). Limited evidence of five very low-quality studies indicated decreased static postural control during the ovulatory phase of the MC, compared to the EFP. The decrements were present in balance tasks that altered sensory input of at least two sensory systems of postural control.

SIGNIFICANCE

This systematic review is the first compiling evidence on the effect of the MC on postural control. Evidence that the MC influences postural control is unclear. However, a trend towards decrements in postural control form EFP to OP was observed in balance tasks that eliminated or altered sensory input. Hence, compensatory strategies might be less effective during the OP.

The impact of the menstrual cycle on orthopaedic sports injuries in female athletes

There is a disparity in sport-related injuries between sexes, with females sustaining non-contact musculoskeletal injuries at a higher rate. Anterior cruciate ligament ruptures are between two and eight times more common than in males, and females also have a higher incidence of ankle sprains, patellofemoral pain, and bone stress injuries. The sequelae of such injuries can be devastating to an athlete, resulting in time out of sport, surgery, and the early onset of osteoarthritis. It is important to identify the causes of this disparity and introduce prevention programmes to reduce the incidence of these injuries. A natural difference reflects the effect of reproductive hormones in females, which have receptors in certain musculoskeletal tissues. Relaxin increases ligamentous laxity. Oestrogen decreases the synthesis of collagen and progesterone does the opposite. Insufficient diet and intensive training can lead to menstrual irregularities, which are common in female athletes and result in injury, whereas oral contraception may have a protective effect against certain injuries. It is important for coaches, physiotherapists, nutritionists, doctors, and athletes to be aware of these issues and to implement preventive measures. This annotation explores the relationship between the menstrual cycle and orthopaedic sports injuries in pre-menopausal females, and proposes recommendations to mitigate the risk of sustaining these injuries.

Biomarkers for rapid H-reflex operant conditioning among females

Operant conditioning of a spinal monosynaptic pathway using the Hoffman reflex (H-reflex) is well established in animal and human studies. There is a subset within the human population (∼20% nonresponders) who are unable to up train this pathway suggesting some distinct or unique identifying characteristics. Importantly, females, who have a nine times higher rate of injury during human performance activities than men, have been understudied in areas of CNS neuroplasticity. Our long-term goal is to understand if innate ability to rapidly up train the H-reflex is predictive of future performance-based injury among females. In this study, we primarily determined whether healthy, young females could rapidly increase the H-reflex within a single session of operant conditioning and secondarily determined if electro-physiological, humoral, cognitive, anthropometric, or anxiety biomarkers distinguished the responders from nonresponders. Eighteen females (mean age: 24) participated in the study. Overall, females showed a group main effect for up training the H-reflex (P < 0.05). Of the cohort, 10 of 18 females met the criteria for up training the H-reflex (responders). The responders showed lower levels of estradiol (P < 0.05). A multivariate stepwise regression model supported that extracellular to intracellular water ratio (ECW/ICW) and H-max/M-max ratio explained 60% of the variation in up training among females. These findings support that females can acutely upregulate the H-reflex with training and that electro-physiological and hormonal factors may be associated with the up training.NEW & NOTEWORTHY Young females who acutely increase their H-reflexes with operant conditioning had lower levels of estradiol. However, the best predictors of those who could up-train the H-reflex were baseline H-reflex excitability (H-max/M-max) and extracellular to intracellular water ratio (ECW/ICW). Future studies are warranted to understand the complex relationship between operant conditioning, human performance, and injury among active young females.

Motor Control and Regularity of Menstrual Cycle in Ankle and Knee Injuries of Female Basketball Players: A Cohort Study

Inadequate motor control facilitates ankle and knee injuries in female basketball. Although biomechanical analysis could help to detect it, aspects such as irregular menstruation make these associations controversial. We aimed to evaluate associations between 2D biomechanics during landing and proprioception with ankle and knee injuries of female basketball players, considering their menstruation regularity. Seventy-one players participated in this study. In the preseason, participants performed a drop-jump to obtain biomechanics during landing and a weight-bearing proprioception test. During the competitive season, all the non-contact ankle and knee injuries were registered. Data showed that 16% of players sustained an ankle or knee injury, being more frequent in players with irregular menstruation compared to regulars (22% vs. 13%, χ² = 6.009, p = 0.050, d = 0.6). Players who sustained a left-side injury displayed higher left-side dynamic valgus during landing than uninjured players (χ² = 25.88, p = 0.006, d = 1.5). The rest of the variables did not show any significant difference (p > 0.05). Monitoring 2D dynamic valgus from a drop-jump could help to detect inadequate motor control that may facilitate ankle or knee injuries of female basketball players, mainly for those with irregular menstruation. Proprioception seems not to be related to injuries.

Transcranial direct current stimulation over the posterior parietal cortex improves visuomotor performance and proprioception in the lower extremities

The purpose of this study was to examine whether anodal transcranial direct current stimulation (a-tDCS) over the posterior parietal cortex (PPC) could affect visuomotor performance and proprioception in the lower extremities. We evaluated visuomotor performance in 15 healthy volunteers using a visuomotor control task by plantar dorsiflexion of the ankle joint, and calculated the absolute difference between the target and measured angle. In addition, we evaluated proprioception using a joint position matching task. During the task, the subject reproduced the ankle joint plantar dorsiflexion angle presented by the examiner. We calculated the absolute difference between the presented and measured angles (absolute error) and the variation of measured angles (variable error). Simultaneously, a-tDCS (1.5 mA, 15 min) or sham stimulation was applied to the right PPC. We observed that the absolute error of the visuomotor control task and the variable error of the joint position matching task significantly decreased after a-tDCS. However, the absolute error of the joint position matching task was not affected. This study suggests that a-tDCS over the PPC improves visuomotor performance and reduces the variable error in the joint position matching task.

Biological sex differences in afferent-mediated inhibition of motor responses evoked by TMS

Sensorimotor integration can be assessed by pairing electrical peripheral nerve stimulation with transcranial magnetic stimulation (TMS). The resulting afferent inhibition is observed when TMS precedes nerve stimulation by ∼ 20-25 ms, termed short-latency afferent inhibition (SAI), or by 200 ms, termed long-latency afferent inhibition (LAI). The purpose of this study was to determine whether biological sex influences the magnitude of SAI or LAI. SAI and LAI were assessed in fifteen males (21.5 ± 2.7 years) and fifteen females (20.2 ± 2.3 years). TMS was delivered to the primary motor cortex (M1) following stimulation of the contralateral median nerve at the wrist or digital nerve of the index finger, and motor-evoked potentials (MEPs) were obtained from the right first dorsal interosseous (FDI) muscle. SAI evoked by median and digital nerve stimulation, and LAI evoked by median nerve stimulation, were not different between males and females. LAI evoked by digital nerve stimulation was increased in females compared to males, but this difference between sexes was no longer present following the removal of datapoints where inhibition was not observed. This study is the first to investigate biological sex differences in afferent inhibition.