ECSS Paris 2023: OP-BM18
INTRODUCTION: Periods of short-term physical inactivity are experienced by nearly all individuals during their lives and can cause several health issues (1). Recent studies employing unilateral lower limb suspension as a model of muscle disuse (2,3) have shown signs of neural alterations at the level of the neuromuscular junction (NMJ) and motor unit (MU) behavior. In step reduction (SR), a milder model of physical inactivity, the change of neural components of muscle control remains largely unknown. In this study, we aim to characterize neuromuscular alterations induced by SR and investigate whether a subsequent exercise intervention can guarantee an adequate recovery. METHODS: Fifteen healthy young subjects (7 females, age 22 ± 2.3 years) participated in the study. Measurements were taken at baseline, after a 2-week of SR (<1500 steps/day), and following a 3-week exercise training (ET) intervention (3 sessions/week, 1 hour/session). At each time point, we assessed maximal voluntary isometric contraction (MVIC) of knee extensors, and vastus lateralis (VL) muscle activity during trapezoidal isometric contractions at 25% (5s ramp up, 20s steady state, 5s ramp down) and 50% (10s ramp up, 10s steady state, 10s ramp down) of MVIC. Muscle activity was recorded using high-density electromyography (HDEMG, OT Bioelettronica). HDEMG signals were decomposed into individual motor unit (MU) firings, from which we calculated absolute recruitment threshold (RT), derecruitment threshold (DT), and mean discharge rate (DR) at steady state. Statistical analysis included one-way ANOVA for comparing MU properties across time points at the same contraction level, and repeated measures ANOVA for MVIC values, with Bonferroni post-hoc correction (significance at P<0.017). RESULTS: In total, 735 MUs were identified and reconstructed. The MVIC torque did not change among the three sessions (P=0.339). A difference was observed between SR and ET for RT at 25% of MVC (P=0.027), although it was not significant after Bonferroni correction. No significant differences were found for DT. The DR was reduced from baseline to SR at 25% and 50% of MVC (P=0.010 and P<0.001, respectively), and it recovered after ET only at 25% of MVC (P=0.005). CONCLUSION: Knowledge of the pathophysiological mechanisms related to short-term physical inactivity is fundamental to overcome its deleterious effects. Muscle force production greatly depends on MU properties and their discharge rate. This is the first study assessing MU adaptations after a period of SR. Our findings suggest that neural degeneration might precede alterations in functional capacity, and exercise can successfully overcome this negative effect. The study was funded by PRIN project (InactivAge n. 2020EM9A8X) and NextGenerationEU/MUR PRIN 2022 PNRR, (ReActiveAge, Project n. P2022FNCPR). 1 Bowden et al. Ther Adv Endocrinol Metab. 2019 2 Sarto et al. J Physiol, 2022 3 Valli et al. MSSE. 2024
Read CV Mohammadhossein GhasemiECSS Paris 2023: OP-BM18
INTRODUCTION: Muscle atrophy is a debilitating condition that significantly affects quality of life. Recent studies suggest estrogen-related receptor alpha (ERRα) as a potential therapeutic target to counteract muscle decline associated with aging or inactivity, as it is known to regulate mitochondrial function and contribute significantly to skeletal muscle exercise capacity. The purpose of this study was to evaluate the targeting of ERRα, by treatment with an agonist, SLU-PP-332, in myoblasts isolated from inactive elderly women, to mimic the muscle conditions found in active elderly women. METHODS: 20 women with a mean age of 70 years undergoing hip arthroplasty for coxarthrosis were enrolled and divided into two groups based on self-reported physical activity: 10 women who practiced moderate physical activity, such as walking or bicycling, at least 30 minutes a day three times a week, and 10 women who did not practice regular, structured physical activity. A clinical and instrumental assessment was conducted during hospitalization, measuring bone mineral density, visual analogue scale (VAS) values, harris hip score (HHS) and handgrip strength test. During surgery, muscle biopsies were taken for histological and western blotting analysis. In addition, primary cultures of myoblasts were set up from the muscle tissue of inactive women and were treated with SLU-PP-332 for subsequent qualitative and quantitative investigations. RESULTS: The clinical and instrumental evaluation revealed that inactive women were characterized by osteopenic/osteoporotic T-score values, higher VAS values, reduced hip function and significantly lower handgrip strength values. In agreement, the histological and morphometric analysis showed a reduced fiber diameter and increased expression of NADPH oxidase 4 (NOX4), a producer of oxidative stress, in association with reduced expression of sirtuin 1 (SIRT1), peroxisome proliferator-activated receptor gamma coactivator 1-alpha (PGC-1α), ERRα and fibronectin type III domain-containing protein 5 (FNDC5), all mediators of muscle adaptations to exercise. SLU-PP-332-treated myoblasts showed a reduction in cytotoxicity, intracellular reactive oxygen species (ROS) levels, and senescence β-galactosidase activity, as well as an increase in reduced glutathione. In addition, down-regulation of NOX4 and up-regulation of SIRT1, PGC-1α, ERRα and FNDC5 were detected in treated cells. CONCLUSION: Exercise counteracts the onset and/or progression of muscle atrophy, presumably through the positive regulation of ERRs. The future perspective of this study is to investigate the modulation of ERRs as potential biomarkers in response to different training protocols to optimize muscle response to exercise.
Read CV Ida CariatiECSS Paris 2023: OP-BM18
INTRODUCTION: Age-related neuromuscular decline impairs the ability to maintain a steady force during a submaximal voluntary contraction, a measure known as force steadiness (FS). Given its critical role in physical function, reduced FS has been linked to lower functional performance in older adults. This study aimed to investigate the association between FS in the hip abductor, knee extensor, plantar flexor, and performance in functional tests among older adults. METHODS: Twenty physically active older adults (3275.0±1800.3 METS/week) participated in this study. Participants completed the Short Physical Performance Battery (SPPB) and underwent a gait assessment using the OptoGait system. Additionally, strength tests were performed for hip abductor, knee extensor, and plantar flexor, along with steady submaximal isometric activations at 20%, 30% and 20% of maximum effort, respectively, using an isokinetic dynamometer (HUMAC NORM) on the non-dominant limb. Gait speed over 4m and 6m, Sit-to-Stand (STS) muscle power, Time Up and Go (TUG), coefficient of variation (ST_CV%) and Root Mean Square of the Successive Differences (ST_RMSSD) of step time were recorded to assess the association with FS variables, including CV% (FS_CV%) and RMSSD (FS_RMSSD) of the tested limb. Pearson and Spearman correlations were conducted to determine the strength of the these relationship. RESULTS: Ten women (67.2±1.3 years; Fat mass percentage 39.0±3.9%), and ten men (69.1±1.4 years; Fat mass percentage 30.3±6.7%), classified as robust according to the SPPB score participate in the study. A moderate correlation was found between FS_RMSSD of hip adductor and ST_RMSSD in the whole sample (r= - 0.46, p<0.05). Interestingly, sex-specific differences in correlation patterns were observed. In women, a significant positive correlation was found between TUG time and FS_RMSSD of hip adductor (r= 0.65, p< 0.05) and FS_RMSSD of plantar flexor (r= 0.68, p< 0.05). In contrast, these correlations were weaker and non-significant in men (hip adductor, r= -0.29, p > 0.05; plantar flexor: r= -0.48, p > 0.05). Additionally, a strong negative correlation was found between ST_RMSSD and FS_RMSSD of the hip adductor in men (r= - 0.70, p<0.05), whereas this relationship was weaker and non-significant in women (r = 0.38, p > 0.05). A moderate negative correlation was also observed between ST_RMSSD and CV% of the plantar flexor in men (r= -0.70, p < 0.05), while in women, this association was weaker and not significant (r= 0.21, p > 0.05). CONCLUSION: These findings highlight the role of FS in neuromuscular function and its link to functional performance, emphasizing the need for controlled variability in specific muscles to maintain gait stability. Moreover, they stress the importance of considering sex-specific neuromuscular differences when assessing FS and functionality in aging. Future research should explore these compensatory strategies and their impact on tasks challenging medio-lateral stability, such as obstacle stepping.
Read CV Maria Alejandra Camacho Camacho VillaECSS Paris 2023: OP-BM18