Tissue Accumulation of Neutrophil Extracellular Traps Mediates Muscle Hyperalgesia in a Mouse Model

Accumulation of uric acid (UA) during muscular trauma is a causative factor involved in the development of muscle hyperalgesia. Neutrophil extracellular traps (NETs), DNA-based reticular structures to capture UA, play a central role in the pain onset of gout attacks; however, the involvement of NETs via the elevation of local UA level in muscle hyperalgesia due to overuse injuries remains unknown. The triceps surae muscles (TSMs) in the unilateral hindlimb of mice were electrically stimulated to induce excessive muscle contraction. Mechanical withdrawal thresholds, tissue UA levels, neutrophil recruitment, protein amount of citrullinated histone 3 (citH3), a major marker of NETs, were investigated. Furthermore, whether neutrophil depletion, extracellular DNA cleavage, and administration of the urate-lowering agent febuxostat could improve muscle hyperalgesia due to NET formation was examined. CitH3 expression upon neutrophil recruitment significantly increased in the stimulated TSMs with an increase in tissue UA levels, whereas febuxostat administration improved muscle hyperalgesia with decreases in citH3 and tissue UA levels, as observed in neutrophil depletion and extracellular DNA digestion. The underlying mechanism of muscle hyperalgesia associated with locally recruited neutrophils forming NETs due to the increased tissue UA levels potentially plays a significant role in creating a vicious circle of muscle pain.

3D Models Reveal the Influence of Achilles Subtendon Twist on Strain and Energy Storage

The Achilles tendon (AT) has complex function in walking, exchanging energy due to loading by the triceps surae muscles. AT structure comprises three subtendons which exhibit variable twist among themselves and between individuals. Our goal was to create 3D finite element (FE) models to explore AT structure-function relationships. By simulating subtendon loading in FE models with different twisted geometries, we investigated how anatomical variation in twisted tendon geometry impacts fascicle lengths, strains, and energy storage. Three tendon FE models, built with elliptical cross sections based on average cadaver measurements, were divided into subtendons with varied geometric twist (low, medium, and high) and equal proportions. Tendon was modeled as transversely isotropic with fascicle directions defined using Laplacian flow simulations, producing fascicle twist. Prescribed forces, representing AT loading during walking, were applied to proximal subtendon ends, with distal ends fixed, and tuned to produce equal tendon elongation in each case, consistent with ultrasound measurements. Subtendon fascicle lengths were greater than free tendon lengths in all models by 1–3.2 mm, and were longer with greater subtendon twist with differences of 1.2–1.9 mm from low to high twist. Subtendon along-fiber strains were lower with greater twist with differences of 1.4–2.6%, and all were less than free tendon longitudinal strain by 2–5.5%. Energy stored in the AT was also lower with greater twist with differences of 1.8–2.4 J. With greater subtendon twist, similar elongation of the AT results in lower tissue strains and forces, so that longitudinal stiffness of the AT is effectively decreased, demonstrating how tendon structure influences mechanical behavior.

Multi- and Single-Joint Resistance Exercises Promote Similar Plantar Flexor Activation in Resistance Trained Men

The present study aimed to compare soleus, lateral, and medial gastrocnemius muscles activation during leg press and calf raise exercises in trained men. The study involved 22 trained men (27.1 ± 3.6 years, 82.7 ± 6.6 kg, 177.5 ± 5.2 cm, 3.6 ± 1.4 experience years) who performed one set of each exercise using a 10-repetition maximum (10RM) load in a counterbalanced randomized order and separated by 10 min of rest. The electromyographic signal was measured for the three major plantar flexors: soleus, medial, and lateral gastrocnemius. A comparison between exercises showed that the mean adjusted by peak values during the leg press were 49.20% for the gastrocnemius lateralis, 51.31% for the gastrocnemius medialis, and 50.76% for the soleus. Values for calf raise were 50.70%, 52.19%, and 51.34% for the lateral, medial gastrocnemius, and soleus, respectively. There were no significant differences between exercises for any muscle (lateral gastrocnemius (p = 0.230), medial gastrocnemius (p = 0.668), and soleus (p = 0.535)). The present findings suggest that both leg press and calf raises can be used with the purpose to recruit triceps surae muscles. This bring the suggestion that one can chose between exercises based on personal preferences and practical aspects, without any negative impact on muscle activation.

In Vivo Human Gastrocnemius Architecture With Changing Joint Angle at Rest and During Graded Isometric Contraction of Normal and Weak Muscle

Architectural properties of the triceps surae muscles complex were determined In Vivo for thirty subjects. These subjects were assigned to two groups. The first group of subjects consisted of 8 healthy men and the second group of subjects was composed of 22 patients with motor disorders. The ankle was positioned at -15 ° (dorsiflexion), and 0 ° (neutral anatomical position), and 15 °, and 30 ° (plantarflexion), with the knee set at 120 °and with an angle in the ankle joint of 90 °. At each position, longitudinal ultrasonic images of the Medial (MG) and Lateral (LG) Gastrocnemius and Soleus (SOL) muscles were obtained while the subject was relaxed (passive) and performed 50 % maximal voluntary isometric plantar flexion (active), from which fascicle Lengths (L) and angles (Θ) with respect to the aponeuroses were determined. From the ultrasonic image, it was observed that and Θ changed during an isometric contraction of the triceps surae muscle. Changes in L and were expressed as a function of relative torque. The Θ change was not identical for the three muscles. The fascicle Θ of MG demonstrated the greatest variation in three muscles. The effects of activation and relaxation positions were significant in all three muscles. The differences in MG fascicle Θ because of changes in ankle positions were significant among control and patients both in the passive and active conditions. Fascicle Θ of LG and SOL not differed among control and patient in the relaxation condition but not in the activation condition. For LG, and SOL ol fascicle Θ were changes were larger in control with the patients. The mean values fascicle Θ of MG, LG, and SOL an isometric contraction (50 % MVC) in the control groups increased by 60 %, 41 %, and 41 %, respectively; in the patient groups were a smaller increase, by 28 %, 26 %, and 36 %, respectively. Different lengths and angles of fascicles, and their changes bу contraction by patients and normal subjects, might bе related to differences in force-producing capabilities of the muscles and elastic characteristics of tendons and aponeuroses.

Relationship between running economy and mechanical characteristics of triceps surae assessed with tensiomyography

Tensiomyography (TMG) is a non-invasive technique commonly used for evaluating muscle properties in highly trained athletes. The aim of our study was to evaluate the mechanical characteristics of m. triceps surae in competitive runners through TMG measurement and analyze if there was a relationship with running economy (RE). Nine male runners completed the study (mean±SD: age 40.4±9.0 years, body height 176.2±4.9 cm, body mass 70.7±9.4 kg, 10-km time 39.8±5.9 min, VO2peak 56.9 ± 6.5 mL kg- 1 min-1 ). Each subject visited the lab on two occasions with 72h of rest between the trials. On the first day, an incremental test was performed to determine their ventilatory thresholds and peak oxygen consumption. On the second day, RE was evaluated on a treadmill at the velocity of their first ventilatory threshold (VT1), and mechanical characteristics of the soleus and gastrocnemius muscles were analyzed with TMG. Significant differences were found between the economic and non-economic runners in m. soleus in delayed time (Td), contraction time (Tc), and maximal radial displacement of the muscle belly (Dm). Also, significant differences were found in contraction time (Tc) in medium calf (MC) and in half relaxation time (Tr) in lateral twin (LT). The main finding of our study was that the runners with better RE showed greater stiffness in the triceps surae muscles, an aspect that seems to be associated with better performance in athlete runners.

ASIC1a plays a key role in evoking the metabolic component of the exercise pressor reflex in rats

The role of the acid-sensing ion channel 1a (ASIC1a) in evoking the exercise pressor reflex is unknown, despite the fact that ASIC1a is opened by decreases in pH in the physiological range. This fact prompted us to test the hypothesis that ASIC1a plays an important role in evoking the exercise pressor reflex in decerebrated rats with freely perfused hindlimb muscles. To test this hypothesis, we measured the effect of injecting two ASIC1a blockers into the arterial supply of the triceps surae muscles on the reflex pressor responses to four maneuvers, namely 1) static contraction of the triceps surae muscles (i.e., the exercise pressor reflex), 2) calcaneal tendon stretch, 3) intra-arterial injection of lactic acid, and 4) intra-arterial injection of diprotonated phosphate. We found that the 2 ASIC1a blockers, psalmotoxin-1 (200 ng/kg) and mambalgin-1 (6.5 μg/kg), decreased the pressor responses to static contraction as well as the peak pressor responses to injection of lactic acid and diprotonated phosphate. In contrast, neither ASIC1a blocker had any effect on the pressor responses to tendon stretch. Importantly, we found that ASIC1a blockade significantly decreased the pressor response to static contraction after a latency of at least 8 s. Our results support the hypothesis that ASIC1a plays a key role in evoking the metabolic component of the exercise pressor reflex. NEW & NOTEWORTHY The role played by acid-sensing ion channel 1a (ASIC1a) in evoking the exercise pressor reflex remains unknown. In decerebrated rats with freely perfused femoral arteries, blocking ASIC1a with psalmotoxin-1 or mambalgin-1 significantly attenuated the pressor response to static contraction, lactic acid, and diprotonated phosphate injection but had no effect on the pressor response to stretch. We conclude that ASIC1a plays a key role in evoking the exercise pressor reflex by responding to contraction-induced metabolites, such as protons.

Architecture of the Triceps Surae Muscles Complex in Patients with Spastic Hemiplegia: Implication for the Limited Utility of the Silfverskiöld Test

The Silfverskiöld test has long been used as an important tool for determining the affected muscles of the triceps surae in patients with equinus deformity. However, the test may not reflect the altered interactions between the muscles of the triceps which are affected by spasticity. The purpose of this study was to compare the architectural properties of the triceps surae muscles complex using ultrasonography, between hemiplegic patients and typically-developing children. Specifically, we wished to examine any differences in the architecture of the three muscles with various angle configurations of the knee and ankle joints. Ultrasound images of the medial gastrocnemius, lateral gastrocnemius, and soleus were acquired from paretic (group I) and non-paretic (group II) legs of ten patients and the legs (group III) of 10 age-matched normal children. A mixed model was used to evaluate the differences in the measurements of muscle architecture among the groups and the effects of various joint configurations on the measurements within the muscles. Compared to the results of measurements in groups II and III, the fascicle length was not different in the medial gastrocnemius of a paretic leg but it was longer in the lateral gastrocnemius and shorter in the soleus; the pennation angle was smaller in both medial and lateral gastrocnemii and was not different in the soleus; and the muscle thickness was found to be reduced in the three muscles of the paretic leg. Contrary to the observations in both the medial and lateral gastrocnemii, the fascicle length was increased and the pennation angle was decreased in the soleus with an increase of knee flexion. Through the current simulation study of the Silfverskiöld test using ultrasonography, we found that the changes detected in the architectural properties of the three muscles induced by systematic variations of the position at the ankle and the knee joints were variable. We believe that the limited utility of the Silfverskiöld test should be considered in determining an appropriate operative procedure to correct the equinus deformity in patients with altered architecture of the muscles in conditions such as cerebral palsy, as the differing muscle architectures of the triceps surae complex may affect the behavior of the muscles during the Silfverskiöld test.