Greater distal activation of the biceps femoris long head during knee flexion and hip extension tasks reflects differences in peripheral, not central, motor unit properties.

Albarello, J. C. d. S.; Cabral, H. V.; Negro, F.; de Oliveira, L. F.

doi:10.1101/2024.10.14.618251

Home/Archive/bioRxiv

bioRxiv · 10.1101/2024.10.14.618251

Greater distal activation of the biceps femoris long head during knee flexion and hip extension tasks reflects differences in peripheral, not central, motor unit properties.

Albarello, J. C. d. S.·Cabral, H. V.·Negro, F.·de Oliveira, L. F.

View original source ↗Export metadata ↓

Abstract

PurposeRecent research has explored region-specific responses within the biceps femoris long head. However, evidence on regional muscle activation remains controversial, primarily because information derived solely from surface electromyograms (sEMG) amplitude does not necessarily provide an accurate estimate of neural drive to the muscle. To address this limitation, this study investigated whether there are proximodistal differences in motor unit properties of the biceps femoris long head during isometric hip extension and knee flexion tasks. MethodsSeventeen resistance-trained males performed isometric knee flexion and hip extension tasks at 20% and 40% of maximal voluntary contraction. High-density sEMG were recorded from proximal and distal regions of the biceps femoris long head and decomposed into individual motor units. Central motor unit properties (mean discharge rate, discharge rate variability, recruitment and de-recruitment thresholds) and action potential properties (amplitude and conduction velocity) were analyzed. Bipolar sEMG amplitude was also calculated for each region to simulate traditional sEMG measurements. ResultsBipolar sEMG amplitude, motor unit action potential amplitude and conduction velocity were significantly greater in the distal region during both tasks. In contrast, no proximodistal differences were observed in central motor unit properties. ConclusionThese findings suggest that increased bipolar sEMG amplitude in the distal region of the biceps femoris long head is driven by motor unit action potential properties rather than differences in central modulation, likely influenced by intra-muscular variations in muscle mechanics and geometry. This emphasizes limitations of relying solely on sEMG amplitude to infer neural control strategies in the biceps femoris long head.

Explore related subjects

physiology Preprint

Keep this discovery

Explore connections, maps & timelines

BibTeX RIS

Albarello, J. C. d. S., Cabral, H. V., Negro, F., de Oliveira, L. F.. 2024-10-16. Greater distal activation of the biceps femoris long head during knee flexion and hip extension tasks reflects differences in peripheral, not central, motor unit properties.. https://doi.org/10.1101/2024.10.14.618251

Cite the original work for its findings. Save a collection to share your selection of sources.

KEEP EXPLORING

Related preprints

bioRxiv2026

DEPP1 connects nutrient and oxygen availability to maintenance of muscle mass

Nutrients and oxygen are sensed within the muscle to control growth and disruption of either signal is sufficient to lead to muscle atrophy. While nutrient limitation is sensed via a conserved transcriptional atrophy program (commonly referred to as atrogenes) dictated via the Forkhead box O (FoxO) transcription factors, how low oxygen promotes muscle loss remains unknown. Accordingly, the downstream mechanisms that initiate muscle loss when oxygen and nutrients are limiting are only partly understood. Here, we find Hypoxia Inducible Factor (HIF), the master regulator of our adaptation to low oxygen, is necessary and sufficient to mediate muscle loss under hypoxia in mice. RNA sequencing in skeletal muscle isolated from starved or hypoxic mice identifies Decidual Protein Induced by Progesterone 1 (Depp1), which is induced in skeletal muscle when nutrients or oxygen is limiting via FoxO1 and HIF activation, respectively. Whole body Depp1 loss in mice reduces muscle loss under fasting and hypoxia and skeletal muscle Depp1 overexpression is sufficient to mediate muscle atrophy. Mechanistically, Depp1 localizes to the mitochondria and is necessary to control autophagy activation and mitochondrial degradation in skeletal muscle. Taken together, our studies nominate Depp1 as a new atrogene necessary for muscle loss under multiple atrophy scenarios involving FoxO and HIF.

physiology↗

bioRxiv2026

The CREB-regulated co-activators 2/3, have a role, in vivo, in osteoblastic gene expression.

Many hormones and substances acting through G-protein coupled receptors and protein kinase A (PKA) activation inhibit the salt-inducible kinases (SIKs) by phosphorylation. SIKs tonically phosphorylate CREB-regulated transcriptional coactivators (CRTC1, 2 and 3), sequestering them in the cytoplasm and, thus, preventing their translocation into the nucleus. Once in the nucleus, CRTCs bind CREB family member transcription factors and enhance their activity. We and others have shown that parathyroid hormone (PTH) activation of PKA and resultant SIK2/3 inhibition allows CRTC2/3 nuclear translocation. One of the major actions of CRTC2/3 in the osteoblast lineage is the regulation of transcription of Rankl, as well as other PTH-controlled genes. However, little is known about the role of these co-activators in the osteoblast lineage in vivo. Here, we have investigated whether there are basal effects in vivo on bone examined at 2 different ages of conditional deletion of these two co-activators in the osteoblast lineage using Col2.3-Cre. We found significant increases in body weight, length, bone mineral density, bone volume/total volume, trabecular thickness and number with decreased trabecular separation in young (2 months old) male mice, all of which dissipated by 6 months of age. Female mice showed minimal changes in the bone phenotype at either age. Nevertheless, there were gene expression changes in bones of both sexes at both ages, and in particular decreases in Rankl, Runx2 and Sost, and accompanying changes in Wnt pathway genes. These effects may explain the changes in the bone phenotype in the young male mice, but it is notable that there is a sexual dimorphism in the action of CRTC2 and CRTC3. Overall, the work supports the data from research in vitro and forms a basis for investigation of the role of these co-activators in PTH action in vivo.

physiology↗

bioRxiv2026

Cholinergic impairment in the dorsal motor nucleus of the vagus during experimental Alzheimer's disease

Cholinergic neurons in the dorsal motor nucleus of the vagus (DMN) in the brainstem are a key source of efferent vagus nerve fibers that regulate vital functions, including heart rate and inflammation. Whether the integrity of DMN cholinergic neurons is affected during Alzheimer's disease (AD) remains unknown. Here, in female and male mice with experimental AD (5xFAD), which exhibit age-dependent memory impairment, basal forebrain cholinergic neurodegeneration, and microglial alterations, we observe a reduction in cholinergic neuron density in the DMN at 6 and 10 months of age. Furthermore, while an important physiological function of DMN cholinergic signaling, such as suppression of heart rate, is preserved in control mice upon electrical DMN stimulation, the extent of suppression diminishes with age in both female and male 5xFAD mice. In addition, while electrical DMN stimulation lowers pro-inflammatory cytokine levels in control mice subjected to endotoxemia, this anti-inflammatory effect is diminished with age in 5xFAD mice, with females showing earlier dysfunction at 6 months. These results reveal previously unrecognized age-dependent cholinergic deficits in the DMN and disrupted brain - to - periphery vagus nerve circuits in experimental AD. These findings advance our understanding of AD mechanisms and are of interest for the development of conceptually novel therapies.

physiology↗