ECSS Paris 2023: CP-BM01
INTRODUCTION: The elbow flexors consist of the biceps brachii (BB), brachialis (BRC), and brachioradialis (BRR). Among them, BB is a biarticular muscle crossing not only the elbow but also the shoulder joint, and lengthened more in a shoulder-extended than shoulder-flexed position. Previous studies have found greater muscle hypertrophy after training at long than short muscle lengths (e.g. seated > prone leg curl for the hamstrings [Maeo et al., 2021] and standing > seated calf raise for the triceps surae [Kinoshita et al., 2023]). Based on these findings, this study examined the effects of incline (shoulder-extended, BB lengthened) versus preacher (shoulder-flexed, BB shortened) arm curl training on elbow flexor hypertrophy. METHODS: Twenty-one untrained healthy young adults participated in this study. Using a dumbbell, they performed incline arm curls with one arm and preacher arm curls with the other arm (shoulder 50-deg extended and flexed, respectively) at 70% of one repetition maximum of the corresponding task. Each arm performed 5 sets of 10 repetitions per session (2 s for each of the concentric/eccentric phases), 2 sessions per week for 12 weeks. Before and after the intervention, T1-weighted axial 3-T MR images (field of view: 200 × 200 mm, slice thickness & gap: 2.5 mm) were obtained to assess muscle volume of BB, BRC, BRR, and the whole elbow flexors. In addition to muscle volume, anatomical cross-sectional area (ACSA) was calculated/interpolated at 10% intervals of muscle length (i.e. 10–90%, proximal–distal) for each muscle to examine whether regional hypertrophy occurred after each training. RESULTS: Muscle volume significantly increased in all three muscles and the whole elbow flexors for both arms. The changes in whole elbow flexor volume did not significantly differ between the incline and preacher conditions (+16.5% vs +17.6%, P = 0.167, Cohen’s d = 0.18). However, the changes in BB muscle volume were significantly greater for the incline than preacher condition (+18.0% vs +14.9%, P = 0.026, Cohen’s d = 0.41), with significant between-condition differences in ACSA changes found in proximal muscle regions (at 20–40%, P = 0.015–0.045, d = 0.48–0.80). On the other hand, BRC (+17.0% vs +21.0% P = 0.022, d = 0.52) and BRR (+10.0% vs +13.0%, P = 0.018, d = 0.49) had significantly greater muscle volume changes after the preacher condition. Significant between-condition differences in ACSA changes were found in distal muscle regions (at 70–80%, P = 0.005–0.014, d = 0.76–0.81) for BRC and in a middle muscle region (at 60% P = 0.001, d = 0.72) for BRR. CONCLUSION: While incline and preacher arm curls resulted in similar whole elbow flexor hypertrophy, the former appears more effective for BB and the latter for BRC/BRR hypertrophy, especially their proximal and distal/middle regions, respectively. REFERENCES: Maeo et al. (2021) Med Sci Sports Exerc, 53(4), 825-37. Kinoshita et al. (2023) Front Physiol, 14, 1272106.
Read CV Yuto KobayashiECSS Paris 2023: CP-BM01
INTRODUCTION: Recent findings have demonstrated that low-frequency repetitive magnetic stimulations (rTMS) over the primary motor cortex (M1) impaired short-term consolidation of a balance task, underscoring the causal connection between M1 and the consolidation of balancing skills (Egger et al., 2023). However, the underlying neural mechanisms induced by rTMS and whether these adaptations endure over an extended period, encompassing multiple acquisition sessions, remain insufficiently elucidated. So far, its is widely acknowledged that GABAergic processes play an important role for consolidation (Sanes & Donoghue, 2000), at the same time, balance learning can enhance GABA-mediated inhibition (Taube et al., 2020). Therefore, the present study aimed to investigate the impact of rTMS on GABA-mediated short-interval intracortical inhibition (SICI) and to explore the role of M1 in the long-term consolidation of a balance task (i.e., across multiple acquisition sessions). METHODS: Thirty-one volunteers underwent six balance acquisition sessions on a rocker-board, each followed by either rTMS or sham rTMS based on group affiliation. During the first and last training session, SICI was measured twice; before the balance acquisition and after the application of rTMS or sham-rTMS to investigate potential short- and long-term adaptations in intracortical inhibition. Adaptations were assessed during the execution of the learned balance task and in a non-learning postural control task (i.e., stable upright stance). RESULTS: Regardless of group affiliation, all participants achieved comparable improvements within the balance acquisition sessions. However, consolidation varied between groups. In particular, between the third and the fourth acquisition session, as Tukey corrected post-hoc tests showed a significant decline in performance for the rTMS group (p = 0.006). Both short- (p = 0.014) and long-term (p = 0.038) adaptations in SICI were affected by rTMS: while the sham rTMS group upregulated SICI, rTMS led to reduced levels of inhibition. No neurophysiological effects were observed in the non-learning control task (upright stance). CONCLUSION: The task-specific interference effect of rTMS on balance consolidation and on upregulation of SICI indicates that increased intracortical inhibition is an important mechanism to protect and consolidate newly acquired motor memories. REFERENCES: Egger, S., Wälchli, M., Rüeger, E., & Taube, W. (2023). Short-term balance consolidation relies on the primary motor cortex: a rTMS study. Scientific reports, 13(1), 5169. https://doi.org/10.1038/s41598-023-32065-x Sanes, J. N., & Donoghue, J. P. (2000). Plasticity and primary motor cortex. Annual review of neuroscience, 23, 393-415. https://doi.org/10.1146/annurev.neuro.23.1.393 Taube, W., Gollhofer, A., & Lauber, B. (2020). Training-, muscle- and task-specific up- and downregulation of cortical inhibitory processes. The European journal of neuroscience, 51(6), 1428-1440. https://doi.org/10.1111/ejn.14538
Read CV Sven EggerECSS Paris 2023: CP-BM01
INTRODUCTION: Assessment of neural control of skeletal muscles is achieved by analyzing motor unit (MU) discharge properties. Typical testing scenarios involve force modulation in non-weight bearing tasks, e.g. isolated knee extension in a seated position. However, humans evolved to stand and move in an upright posture where the leg extending muscles generate force against gravity (1). To address this gap, we devised a setup to measure MU activity during force modulation in different knee angles in an upright weight-bearing scenario. METHODS: Five participants underwent measurements while standing with both feet on a force plate, with a loaded barbell fixed above their necks, providing immovable resistance. Shin position was standardized to ensure identical ankle angle for all trials. Measurements involved isometric maximal voluntary contractions (MVC) and biofeedback-controlled submaximal force modulation (15 seconds at body weight (BW) followed by 15 seconds at BW+20%MVC) against the immovable barbell in three knee angles (30°, 60°, 90° adjusted by barbell height). High-density EMG signals from vastus lateralis (VL) and vastus medialis (VM) were recorded and decomposed (2,3) into MU discharge rates (DR). Mean DR was calculated for low-threshold (LT, already firing at BW) and high-threshold MUs (HT, start firing above BW). Two-way ANOVA for factors muscle and angle and RM ANOVA for force modulation of LT was performed. Linear regression for relative MVC vs. LT modulation (from BW to BW+20%MVC) was calculated. RESULTS: While the MVCs increased with a more upright position (90°: 164±51N/kg; 60°: 238±67N/kg; 30°: 341±106N/kg; p<0.001), there was no difference in DR between angles or muscles for LT. At BW+20%MVC, LT showed higher discharge rate than HT (11.90±2.25 and 10.71±2.08pps; p>0.001). During force modulation from BW to BW+20%MVC, LT increased firing rate from 10.06±2.42 to 11.90±2.25pps (p<0.001). There was a significant correlation between relative MVC (averaged across angles) and the difference of DR in LT from low- to high-force (R=0.8630; p=0.0225). CONCLUSION: As the first study to introduce force modulation in a weight-bearing task, we observed that LT are already firing when bearing own bodyweight, which reveals a functional importance not reflected by isolated non-weight bearing setups. Despite the force differences between angles, the firing rate of MUs at submaximal force did not change indicating that the neural control of VL and VM is regulated independently of muscle length. However, we observed that stronger individuals have a higher ability to increase LT firing rate during force modulation, indicating an association between submaximal neural modulation ability and maximal force generation capacity. REFERENCES: 1) Winter, Gait Posture, 1995 2) Holobar & Zazula, IEEE Trans signal Process, 2007 3) Holobar et al., J Neur Eng, 2014
Read CV Rafael KrätschmerECSS Paris 2023: CP-BM01