ECSS Paris 2023: OP-BM23
INTRODUCTION: Motor control occurs at spinal and supraspinal levels, which can be assessed using H-reflex and V-wave/TMS techniques, respectively. Sex related differences in motor control are contradictory and have previously been studied mainly at rest or in isometric conditions (e.g. 1, 2). In terms of daily activity, it is important to investigate the possible differences in dynamic conditions. The objective of this study was to determine potential sex differences in spinal and/or supraspinal motor control during dynamic balance perturbation. In addition, the relationship between neural and balance control responses was evaluated. METHODS: A total of 16 participants (8 male, 8 female) between 30 and 45 years of age, were recruited. The measurement protocol included familiarization on dynamic balance exercises, maximal isometric plantar flexion (MVC) and rate of force development (RFD) measurements, and a dynamic balance perturbation test. For the balance perturbations, eight forward and eight backward perturbations were randomly generated in each set (a total of 9 sets) using a balance perturbation device (3). H-reflex and V-wave responses (normalized with maximal M-wave) were measured from soleus muscle at four different delays (30, 70, 100, 130 ms) from the onset of the perturbation. Additionally, center of pressure (COP) displacement and velocity were measured during the plate movement. RESULTS: Men exhibited higher values in MVC (p<0.001) and RFD (p<0.001), whereas women demonstrated higher values in COP displacement (p<0.001) and COP velocity (p=0.002) during the perturbations. No sex differences were observed in V-wave responses during MVC. A significant correlation was observed between MVC and COP displacement (r=-0.811, n=12, p< 0.001) and between RFD and COP velocity (r=-0.783, n=12, p=0.003). In neural responses, V-wave at 130 ms post-onset, correlated negatively with both COP displacement (r=-0.678, n=12, p=0.015) and COP velocity (r=-0.657, n=12, p=0.02). In addition, 130 ms post-onset V-wave/H-reflex-ratio correlated negatively with COP displacement (r=-0.685, n=12, p=0.014) and COP velocity (r=-0.608, n=12, p=0.036). CONCLUSION: Men demonstrated enhanced supraspinal (voluntary) control during the perturbation which was correlated with more efficient balance control. This may be more related to different control strategies since no sex differences were observed in V-wave responses during MVC. In addition, no difference was observed in spinal control, and there was also no correlation found between spinal control and balance control. However, we did not control the phase of the menstrual cycle which might affect the women´s neural responses and should be studied in future. REFERENCES: 1) Hoffman et al., Neuroreport, 2018 2) Mendonca et al., Exp Physiol, 2020 3) Nevanperä et al., Exp Brain Res, 2023
Read CV Jarmo PiirainenECSS Paris 2023: OP-BM23
INTRODUCTION: Aging is a physiological and morphological process characterized by a progressive loss of muscle mass, strength, and power accompanied by a decline in neuromuscular function [1]. Age-related adaptations affect the muscles structural characteristics and neural control [2, 3]. Regarding neural changes, lower motor unit (MU) discharge rates, and increased variability of MU discharges were previously reported in old with respect to young adults [4]. Furthermore, it was observed that the firing rate of early-recruited MUs increases to a lesser extent in old people during increasing force contractions [4]. It is worth noting that current knowledge on MU firing properties in aging is mainly based on studies performed on male populations [5]. Considering the evidence of sex differences in MU behavior [5] and the aging process [6], differentiating the analysis between the two sexes may provide additional insights to understand age-related adaptations better. In this study, we analyzed sex differences in MU recruitment and firing properties in young, middle-aged, and old adults. METHODS: Thirty middle-aged (MA) adults (15 females, 59±9 years), twenty-eight old (OLD) adults (12 females, 76±4 years), and ten young (YG) as control group (5 females, 26±2 years) were recruited. High-density electromyographic (HDEMG) signals were recorded from the VL muscle using a grid of 64 channels during isometric ramp contractions from 0 to 30% and 50% of the maximum voluntary contraction (MVC) with slow force increase (2% MVC/s). The MUs obtained from HDEMG decomposition were grouped according to their recruitment thresholds in steps of 10% MVC (0-10%, 10-20%, etc.). Changes in MU firing properties were compared between age groups and sexes. RESULTS: An average of 10±3, 8±3, and 9±3 MUs were analyzed for each subject of YG, MA, and OLD groups, respectively. The mean firing rates of all the MUs recruited were significantly lower (p<0.001) in OLD (9.3±1.5 pps at 30% MVC and 10.1±1.8 pps at 50% MVC) with respect to YG (10.3±1.6 pps at 30% MVC and 11.4±1.5 pps at 50% MVC), and MA (10.2±1.9 pps at 30% MVC and 11.2±2.3 pps at 50% MVC). When compared to males of the same age group, females showed higher firing rates in YG (+11.7%, p<0.001) and MA (+8.9%, p<0.001) but not OLD (+2.9%, p=0.60). In comparison to YG and MA, the MU firing rates of the OLD group increased to a lesser extent with the force increase. Interestingly, this behavior was significantly more pronounced in the female subgroup (i.e. lower firing rate modulation with force increase). CONCLUSION: Although preliminary, the observed differences in the firing behavior between sexes and age groups indicate that the trajectory of neuromuscular aging could differentiate between males and females, emphasizing the significance of accounting for sex in aging studies. References 1. Tieland M. et al. (2018) 2. Narici M. V et al. (2003) 3. Roos M. R. et al. (1997) 4. Watanabe K. et al. (2016) 5. Lulic-Kuryllo T. et al.(2022) 6. Hägg S. et al. (20
Read CV Marco CarbonaroECSS Paris 2023: OP-BM23
INTRODUCTION: Concentrations of ovarian hormones fluctuate across the eumenorrheic menstrual cycle, which contribute to modulations in cortical excitability (1) and inhibition (2). Oestrogens have an excitatory effect, whilst progesterone has an inhibitory effect within the motor pathway (3). However, it is unknown how such changes affect nervous system adaptation (neuroplasticity), which has the potential to improve functional capacity in health and disease (4). The aim of this study was to determine the effect of the menstrual cycle on motor cortical excitability and plasticity. METHODS: Data is presented for four of the seventeen female participants who have completed testing so far (age 25 ± 3 years). Participants reported a regular menstrual cycle (≥21 & ≤35 days) and no hormonal contraceptive use over the previous 6 months. After familiarisation, participants visited the lab in three phases of the menstrual cycle: early follicular (EF), late follicular (LF), and mid luteal (ML). One menstrual cycle was tracked with calendar counting and urine ovulation testing prior to data collection, which was repeated with additional blood samples to confirm hormone concentrations during the tested cycle(s). During each visit, participants received transcranial magnetic stimulation (TMS) and percutaneous nerve stimulation at baseline to quantify corticospinal excitability (MEP), short-intracortical inhibition (SICI), intracortical facilitation (ICF), and sarcolemmal excitability (Mmax). This was followed by a paired associative stimulation (PAS) protocol of median nerve (300% perceptual threshold) and TMS (120% resting motor threshold [rMT], 25 ms interstimulus interval, 200 pairs at 0.25 Hz) to assess neuroplasticity. Baseline assessments were repeated immediately, 15, and 30 minutes after the PAS protocol. RESULTS: rMT (50 ± 10, 50 ± 11, 51 ± 10 %MSO) and MEP amplitude (7.8 ± 4.8, 8.7 ± 6.5, 9.1 ± 3.3 %Mmax) remained consistent across phases, for EF, LF and ML, respectively. SICI induced inhibition (46.5 ± 31.0, 46.1 ± 12.5, 54.9 ± 35.8 %unconditioned MEP) and ICF induced facilitation in all phases (172.9 ± 47.86, 178.9 ± 45.8, 158.2 ± 10.5 %unconditioned MEP). PAS elicited an increase in excitability in all phases with a ΔMEP of 164 ± 95, 147 ± 27, 106 ± 42 %baseline. Given the low sample size at present, phase effects were not detected for any variables (p >0.454). CONCLUSION: While caution should be taken interpreting this incomplete sample, baseline measures suggest a possible influence of the menstrual cycle on cortical neurotransmission. PAS elicited neuroplasticity in all phases but was lowest during the ML phase, suggestive of an inhibitory effect of progesterone, which has implications for functional capacity in health and disease. 1) Smith et al., Ann Neurol, 2002 2) Ansdell et al., J Appl Physiol, 2019 3) Piasecki et al., Exerc Sport Sci Rev, 2024 4) Suppa et al, Clin Neurophysiol, 2017
Read CV Padraig SpillaneECSS Paris 2023: OP-BM23