ECSS Paris 2023: OP-BM22
INTRODUCTION: Motor imagery (MI) and neuromuscular electrical stimulation (NMES), that induce a partial activation of the neuromuscular system (SNM), are known as effective methods to limit the decrease of muscle strength during the early stages of limb immobilization (1,2). Recently, it has been suggested that combining both modalities (MI+NMES) may be more efficient as compared to one or the other modality alone (3). Here, the aim was to evaluate the effect of MI+NMES during a 48-hour dominant arm immobilization on corticospinal excitability and muscle strength. We hypothesized that MI+NMES would limit the decrease of muscle strength induced by immobilization associated with alterations of corticospinal excitability. METHODS: In this study, eight healthy participants (age: 23 ± 3 years) took part in three experimental conditions performed in a random order: control (CON), immobilization (IMMO) and immobilization with intervention (INTER). All conditions lasted 48 hours and were separated from each other by a minimum of two weeks. During IMMO and INTER, participants had their dominant arm immobilized with an arm and a wrist splints. Additionally, during INTER, participants performed one session of MI+NMES every two hours consisting in 4 series of 10 imagined maximal contractions of palmar flexion, performed simultaneously with evoked contractions of wrist flexors. NMES intensity was set at 20% of actual maximal voluntary contraction (MVC). For each experimental condition, maximal grip force and corticospinal excitability of flexor carpi radialis (FCR) were measured before and immediately after each condition. Corticospinal excitability was assessed at rest by evoking motor evoked potential (MEP) using transcranial magnetic stimulation. The MEPs were normalized by maximal M-wave (Mmax) evoked by nerve stimulation of the median nerve. RESULTS: The preliminary results showed no significant difference on maximal grip force after CON (-0.8 ± 5.5%), IMMO (-9.7 ± 20.2%) and INTER (-5.1 ± 17.5%) (all P>0.1). Regarding MEP/Mmax of FCR, we found no significant difference after CON (+1.4%), IMMO (-8.5%) and INTER (+15.6%) (all P>0.05). CONCLUSION: These preliminary results did not show that a training of MI+NMES during a 48-hour arm immobilization may limit the decrease of muscle strength and corticospinal excitability. However, we observed a high interindividual variability, which may explain we did not find any significant differences. In addition, these outcomes are still favourable as the loss of force and corticospinal excitability after immobilization were lower than after immobilization with MI+NMES. More participants are needed to examine the impact of MI+NMES on SNM during the early stages of immobilization.
Read CV Pauline EonECSS Paris 2023: OP-BM22
INTRODUCTION: High-density surface EMG (HDsEMG) offers valuable non-invasive insights into individual motor unit (MU) activity and properties. However, large intersubject variability in the number of identified MU is often observed due to specific neural aspects and anatomical factors (e.g. volume conductor properties)1,2. A recent study3 on young males revealed that greater muscle electrode distance (MED), which includes skin, subcutaneous fat and superficial muscle aponeurosis, adversely affects HDsEMG signal decomposition in biceps brachii, especially at low force levels. Here, we investigated the influence of body composition and anatomical features on the number of identified MU in the human vastus lateralis (VL) muscle. METHODS: To date, 48 healthy participants (17% female) representing two age categories (young adults (YG): 19-30 yr., elderly: 66-82 yr.) were enrolled in this study. They performed submaximal isometric knee extensions at 15%, 35%, 50%, and 70% of maximal voluntary contraction (MVC), while HDsEMG recorded the activity of the VL of the right leg (RL). HDsEMG signals were decomposed into individual MU for each force level. Multiple body composition features were evaluated using BIA and DXA, while ultrasonography (US) was used to measure MED precisely below the HDsEMG electrodes. Correlations and regression analyses were used to assess the relationships between the number of detected MU and body composition features according to force levels. RESULTS: A total of 1476 unique MU were detected from the VL. Significantly negative correlations (Spearman’s, p<.05 in all cases) were observed between MU number and fat mass (FM) estimated by BIA (15%: r=-.33; 50%: r=-.32; 70%: r=-.35) and DXA (15%: r=-.36; 35%: r=-.36; 50%: r=-.32; 70%: r=-.39), as well as FM RL estimated by DXA (15%: r=-.50; 35%: r=-.58; 50%: r=-.59; 70%: r=-.59), and MED (15%: r=-.69; 35%: r=-.72; 50%: r=-.72; 70%: r=-.72). Conversely, no associations were found between any other anthropometrical variable and the number of detected MU. When stratified by age group, simple linear regression analysis revealed that MED alone explained 79%, 66%, 61%, and 64% of the variance in the number of detected MU at 15%, 35%, 50%, and 70% MVC, respectively, in elderly, whereas 38%, 37%, 30%, and 32% at the same force levels in YG. CONCLUSION: Our findings further confirm the influence of FM, and particularly MED (mainly composed of subcutaneous fat), on the quality of HDsEMG signal decomposition among healthy individuals with diverse characteristics. Specifically, greater body FM assessed by BIA and DXA were associated with decreased detectable MU. Notably, a more localized analysis of the anatomical area underlying HDsEMG electrodes enhanced the accuracy of MU number prediction. Our results highlight the importance of assessing MED using the US prior to HDsEMG recordings, as it emerges as the primary predictive parameter for MU number identification. 1Del Vecchio et al 2020 2Farina and Holobar 2016 3Souza de Oliveira et al 2022
Read CV alessandro sampieriECSS Paris 2023: OP-BM22
INTRODUCTION: Effort perception is a major regulator of physical activity engagement and pacing strategies for endurance races [1,2]. In this framework, reducing effort perception during physical activity could be beneficial to both performance and physical activity engagement. A study has demonstrated that muscle spindles desensitization induced by a 10-min tendon vibration protocol reduces effort perception during subsequent isometric contractions of elbow flexors [3]. However, the effects of tendon vibration on effort perception during ecological tasks such as cycling remains to be explored. Therefore, the present study aims to assess the effects of tendon vibration on effort perception during cycling. We hypothesized that, for a same perceived effort, power output and vastus lateralis electrical activity would be higher after a tendon vibration protocol. METHODS: Fifteen participants attended the laboratory for 2 experimental visits, involving Vibration and Sham Vibration conditions. In each visit, participants completed two 3-minute cycling bouts on an ergometer before (PRE) and two 3-minute bouts after (POST) a 10-minute tendon vibration protocol administered bilaterally to the patellar and Achilles tendons (100Hz frequency 1mm amplitude for Vibration; 15 Hz frequency 0.5mm amplitude for Sham Vibration). For each individual bout, participants were instructed to maintain a constant perceived effort level. Specifically, they pedaled at either a moderate (23) or a strong perceived effort level (50), as determined by the CR100 scale. Relative changes in power output and vastus lateralis electromyography (EMG) between PRE and POST were analyzed with a 2-Condition × 2-Intensity repeated analysis of variances (ANOVAs). Effect sizes were expressed as partial eta-squared and when ANOVAs were significant, Bonferroni post hoc tests were performed. Significance was set at p < 0.05. RESULTS: For mean power output, the ANOVA revealed a significant main effect of the condition (F = 20.8 ; p < 0.001 ; η2p = 0.598). Relative power output changes in the Vibration condition were positive (+18% at 23 and in +2% at 50) but were negative in the Sham vibration Condition (~-7% for both intensities). The ANOVA revealed similar outcomes for vastus lateralis EMG. CONCLUSION: In line with our hypothesis, we found that power output and VL electrical activity increased after the ten-minute vibration protocol at controlled perceived effort intensities. This suggests that the desensitization of muscle spindles actually leads to a reduction in the perception of effort during submaximal cycling exercises. REFERENCES: Behrens M. et al., (2023). Fatigue and Human Performance: An Updated Framework. Sports medicine, 53, 7–31. Cheval B., & Boisgontier, M. P. (2021). The Theory of Effort Minimization in Physical Activity. Exercise and sport sciences reviews, 49, 168–178. Monjo F. et al., (2018). The sensory origin of the sense of effort is context-dependent. Experimental brain research, 236, 1997–2008.
Read CV Florian MarchandECSS Paris 2023: OP-BM22