Skeletal muscle adaptation to exercise involves various phenotypic changes that enhance the metabolic and contractile functions. One key regulator of these adaptive responses is the activation of AMPK, which is influenced by exercise intensity. However, the mechanistic understanding of AMPK activation during exercise remains incomplete. In this study, we utilized an in vitro model to investigate the effects of mechanical loading on AMPK activation and its interaction with the mTOR signaling pathway. Proteomic analysis of muscle cells subjected to static loading (SL) revealed distinct quantitative protein alterations associated with RNA metabolism, with 10% SL inducing the most pronounced response compared to lower intensities of 5% and 2% as well as the control. Additionally, 10% SL suppressed RNA and protein synthesis while activating AMPK and inhibiting the mTOR pathway. We also found that SRSF2, necessary for pre-mRNA splicing, is regulated by AMPK and mTOR signaling, which, in turn, is regulated in an intensity-dependent manner by SL with the highest expression in 2% SL. Further examination showed that the ADP/ATP ratio was increased after 10% SL compared to the control and that SL induced changes in mitochondrial biogenesis. Furthermore, Seahorse assay results indicate that 10% SL enhances mitochondrial respiration. These findings provide novel insights into the cellular responses to mechanical loading and shed light on the intricate AMPK-mTOR regulatory network in muscle cells.

This study aims to develop an ex vivo organ-on-a-chip model, intervertebral Disc-on-a-ChipMF, to investigate integrated effects of mechanical loading and nutrition on disc health. The system consists of a detachable multilayer microfluidic chip, a Computer-Arduino-based control system, and a mechanical loading unit, which were optimized for accurate axial force measurement and the maintenance of a 21-day ex vivo disc culture. To ensure accuracy of axial force, we optimized the axial mechanical loading regimen, used the Computer-Arduino-based system and low-profile force sensors (LPFS) to control the mechanical loading unit, and modeled the force distribution by using computational simulation. A 21-day ex vivo disc culture was demonstrated using the Disc-on-a-ChipMF system, with optimized mechanical loading (0.02 MPa at 1Hz, 1.5 hr/day) and flow rate (1 μL/min). The structural integrity, collagen breakdown, catabolic enzyme activities, and disc cell and collagen alignment revealed that the on-chip cultured discs exhibited a preferred disc health similar to that of native discs for up to 21 days, while discs in a static culture showed detrimental degenerative changes. The mouse Disc-on-a-ChipMF system mimics in vivo disc microenvironment and provides a valuable platform for studying the effects of various factors on disc health and degeneration and testing new therapies.

It is not clear as to whether weight bearing and ambulation may affect bone growth. Our goal was to study the role of mechanical loading (one of the components of ambulation) on endochondral ossification and longitudinal bone growth. Thus, we applied cyclical, biologically relevant strains for a prolonged time period (4 weeks) to one tibia of juvenile mice, while using the contralateral one as an internal control. By the end of the 4-week loading period, the mean tibial growth of the loaded tibiae was significantly greater than that of the unloaded tibiae. The mean height and the mean area of the loaded tibial growth plates were greater than those of the unloaded tibiae. In addition, in female mice we found a greater expression of PTHrP in the loaded tibial growth plates than in the unloaded ones. Lastly, microCT analysis revealed no difference between loaded and unloaded tibiae with respect to the fraction of bone volume relative to the total volume of the region of interest or the tibial trabecular bone volume. Thus, our findings suggest that intermittent compressive forces applied on tibiae at mild-moderate strain magnitude induce a significant and persistent longitudinal bone growth. PTHrP expressed in the growth plate appears to be one growth factor responsible for stimulating endochondral ossification and bone growth in female mice.

BACKGROUND: Understanding how healthy articular cartilage responds to mechanical loading is critical. Moderate mechanical loading has positive effects on the cartilage, such as maintaining cartilage homeostasis. The degree of mechanical loading is determined by a combination of intensity, frequency, and duration; however, the best combination of these parameters for knee cartilage remains unclear. This study aimed to determine which combination of intensity, frequency, and duration provides the best mechanical loading on healthy knee articular cartilage in vitro and in vivo.
RESULTS: In this study, 33 male mice were used. Chondrocytes isolated from mouse knee joints were subjected to different cyclic tensile strains (CTSs) and assessed by measuring the expression of cartilage matrix-related genes. Furthermore, the histological characteristics of mouse tibial cartilages were quantified using different treadmill exercises. Chondrocytes and mice were divided into the control group and eight intervention groups: high-intensity, high-frequency, and long-duration; high-intensity, high-frequency, and short-duration; high-intensity, low-frequency, and long-duration; high-intensity, low-frequency, and short-duration; low-intensity, high-frequency, and long-duration; low-intensity, high-frequency, and short-duration; low-intensity, low-frequency, and long-duration; low-intensity, low-frequency, and short-duration. In low-intensity CTSs, chondrocytes showed anabolic responses by altering the mRNA expression of COL2A1 in short durations and SOX9 in long durations. Furthermore, low-intensity, low-frequency, and long-duration treadmill exercises minimized chondrocyte hypertrophy and enhanced aggrecan synthesis in tibial cartilages.
CONCLUSIONS: Low-intensity, low-frequency, and long-duration mechanical loading is the best combination for healthy knee cartilage to maintain homeostasis and activate anabolic responses. Our findings provide a significant scientific basis for exercise and lifestyle instructions.

The primary aim of this study was to explore the effects of team sports practice on bone health indices in adults engaged in team sports. The secondary aim was to investigate the osteogenic effects of each type of team sport. This systematic literature search was conducted using common electronic databases from inception in June 2023, using key terms (and synonyms searched for by the MeSH database) that were combined using the operators \"AND\", \"OR\", \"NOT\": (``men\'\' OR ``man\'\' OR ``women\'\' OR ``woman\'\') AND (``bone mineral density\'\' OR ``BMD\'\' OR ``bone mineral content\'\' OR ``BMC\'\' OR ``peak bone mass\'\' OR ``mechanical loading\'\' OR ``osteoporosis\'\' OR ``bone geometry\'\' OR ``bone resistance\'\') AND (``team sport\'\' OR ``sport\'\' OR rugby OR basketball OR volleyball OR handball OR soccer OR football OR ``players\'\'). After screening, 16 studies were included in the final analysis (5 continents, 2740 participants). The training duration lasted 1 to 13 years. Team sport training had a moderate impact on whole body bone mineral density (WB BMD) (1.07 SMD; 95 % [0.77, 1.37], p < 0.00) but a more significant impact on whole body bone mineral content (WB BMC) (1.3 SMD; 95 % [0.81, 1.79], p < 0.00). Subgroup analyses indicated that rugby training had a moderate but non-significant impact on WB BMD (1.19 SMD; 95 % [-0.13, 2.52], p = 0.08) but a greater impact on WB BMC (2.12 SMD; 95 % [0.84, 3.39], p < 0.00); basketball training had a moderate but significant impact on WB BMD (1 SMD; 95 % [0.35, 1.64], p < 0.00) and a trivial non-significant impact on WB BMC (0.18 SMD; 95 % [-1.09, 1.46], p = 0.78); volleyball training had a moderate but non-significant impact on WB BMD (0.63 SMD; 95 % [-0.22, 1.49], p = 0.15) and a significant impact on WB BMC (2.39 SMD; 95 % [1.45, 3.33], p < 0.00). Handball training produced a moderate significant impact on WB BMD (1.02 SMD; 95 % [0.33, 1.71], p < 0.00) and WB BMC (0.97 SMD; 95 % [0.47, 1.48], p < 0.00), and soccer training led to moderate but significant effects on WB BMD (1.16 SMD; 95 % [0.88, 1.44], p < 0.00) and a large effect on WB BMC (1.34 SMD; 95 % [0.92, 1.77], p < 0.00). Rugby training was associated with a higher WB BMC compared to basketball training (p = 0.03). Our systematic review and meta-analysis suggests that team sports, such as rugby, basketball, volleyball, handball and soccer have moderate to large effects on WB BMD and WB BMC. Specifically, our findings indicate that handball and soccer enhance WB BMD and WB BMC, whereas rugby only increases WB BMC. There is currently insufficient evidence indicating the superiority of any type of sport training that improves bone health in adults.

The importance of mechanical loading and its relationship to orthobiologic therapies in the treatment of post-traumatic osteoarthritis (PTOA) is beginning to receive attention. This review explores the current efficacy of orthobiologic interventions, notably platelet-rich plasma (PRP), bone marrow aspirate (BMA), and mesenchymal stem/stromal cells (MSCs), in combating PTOA drawing from a comprehensive review of both preclinical animal models and human clinical studies. This review suggests why mechanical joint loading, such as running, might improve outcomes in PTOA management in conjunction with orthiobiologic administration. Accumulating evidence underscores the influence of mechanical loading on chondrocyte behavior and its pivotal role in PTOA pathogenesis. Dynamic loading has been identified as a key factor for optimal articular cartilage (AC) health and function, offering the potential to slow down or even reverse PTOA progression. We hypothesize that integrating the activation of mechanotransduction pathways with orthobiologic treatment strategies may hold a key to mitigating or even preventing PTOA development. Specific loading patterns incorporating exercise and physical activity for optimal joint health remain to be defined, particularly in the clinical setting following joint trauma.

Traditional tendon engineering using cell-loaded scaffold has limited application potential due to the need of autologous cells. We hypothesize that potent mechanical loading can efficiently induce in situ Achilles tendon regeneration in a rabbit model by using a cell-free porous composite scaffold. In this study, melt-spinning was used to fabricate PGA (polyglycolic acid) and PLA (polylactic acid) filament fibers as well as non-woven PGA fibers. The PLA/PGA (4:2) filament fibers were further braided into a hybrid yarn，which was knitted into a PLA/PGA tubular mesh with potent mechanical property for sustaining natural tendon strain. The results showed that a complete cross-section of Achilles tendon created a model of full mechanical loading on the bridging scaffold, which could efficiently induce in situ tendon regeneration by promoting host cell infiltration, matrix production and tissue remodeling. Histologically, mechanical loading assisted in forming parallel aligned collagen fibers and tenocytes in a fashion similar to those of native tendon. Transmission electron microscope further demonstrated that mechanical strain induced collagen fibril development by increasing fibril diameter and forming bipolar structure, which resulted in enhanced mechanical properties. Interestingly, the synergistic effect between mechanical loading and hyaluronic acid modification was also observed on the induced tenogenic differentiation of infiltrated host fibroblasts. In conclusion, potent mechanical loading is the key inductive microenvironment for in situ tendon regeneration for this polymer-based composite scaffold with proper matrix modification, which may serve as a universal scaffold product for tendon regeneration.

In response to mechanical loading of bone, osteocytes produce nitric oxide (NO•) and decrease sclerostin protein expression, leading to an increase in bone mass. However, it is unclear whether NO• production and sclerostin protein loss are mechanistically linked, and, if so, the nature of their hierarchical relationship within an established mechano-transduction pathway. Prior work showed that following fluid-shear stress (FSS), osteocytes produce NOX2-derived reactive oxygen species, inducing calcium (Ca2+) influx. Increased intracellular Ca2+ results in calcium-calmodulin dependent protein kinase II (CaMKII) activation, which regulates the lysosomal degradation of sclerostin protein. Here, we extend our discoveries, identifying NO• as a regulator of sclerostin degradation downstream of mechano-activated CaMKII. Pharmacological inhibition of nitric oxide synthase (NOS) activity in Ocy454 osteocyte-like cells prevented FSS-induced sclerostin protein loss. Conversely, short-term treatment with a NO• donor in Ocy454 cells or isolated murine long bones was sufficient to induce the rapid decrease in sclerostin protein abundance, independent of changes in Sost gene expression. Ocy454 cells express all three NOS genes, and transfection with siRNAs targeting eNOS/Nos3 was sufficient to prevent FSS-induced loss of sclerostin protein, while siRNAs targeting iNOS/Nos2 mildly blunted the loss of sclerostin but did not reach statistical significance. Similarly, siRNAs targeting both eNOS/Nos3 and iNOS/Nos2 prevented FSS-induced NO• production. Together, these data show iNOS/Nos2 and eNOS/Nos3 are the primary producers of FSS-dependent NO•, and that NO• is necessary and sufficient for sclerostin protein control. Further, selective inhibition of elements within this sclerostin-controlling mechano-transduction pathway indicated that NO• production occurs downstream of CaMKII activation. Targeting Camk2d and Camk2g with siRNA in Ocy454 cells prevented NO• production following FSS, indicating that CaMKII is needed for NO• production. However, NO• donation (1min) resulted in a significant increase in CaMKII activation, suggesting that NO• may have the ability to tune CaMKII response. Together, these data support that CaMKII is necessary for, and may be modulated by NO•, and that the interaction of these two signals is involved in the control of sclerostin protein abundance, consistent with a role in bone anabolic responses.

Many physical and chemical properties of solids, such as strength, plasticity, dispersibility, solubility and dissolution are determined by defects in the crystal structure. The aim of this work is to study in situ dynamic, dispersion, chemical, biological and surface properties of lacosamide powder after a complete cycle of mechanical loading by laser scattering, electron microscopy, FR-IR and biopharmaceutical approaches. The SLS method demonstrated the spontaneous tendency toward surface-energy reduction due to aggregation during micronisation. DLS analysis showed conformational changes of colloidal particles as supramolecular complexes depending on the loading time on the solid. SEM analysis demonstrated the conglomeration of needle-like lacosamide particles after 60 min of milling time and the transition to a glassy state with isotropy of properties by the end of the tribochemistry cycle. The following dynamic properties of lacosamide were established: elastic and plastic deformation boundaries, region of inhomogeneous deformation and fracture point. The ratio of dissolution-rate constants in water of samples before and after a full cycle of loading was 2.4. The lacosamide sample, which underwent a full cycle of mechanical loading, showed improved kinetics of API release via analysis of dissolution profiles in 0.1 M HCl medium. The observed activation-energy values of the cell-death biosensor process in aqueous solutions of the lacosamide samples before and after the complete tribochemical cycle were 207 kJmol-1 and 145 kJmol-1, respectively. The equilibrium time of dissolution and activation of cell-biosensor death corresponding to 20 min of mechanical loading on a solid was determined. The current study may have important practical significance for the transformation and management of the properties of drug substances in solid form and in solutions and for increasing the strength of drug matrices by pre-strain hardening via structural rearrangements during mechanical loading.

Introduction Fixed prosthodontic treatment involves the replacement of missing tooth structures with a variety of materials. Several newer metal-free ceramics have been developed in recent years to meet patients\' aesthetic needs. The long-term performance of all ceramics, however, is unknown, necessitating a continuous evaluation of the materials\' strength. Aim The aim of this study was to compare and evaluate the fracture resistance of IPS E max pressable crowns and graphene crowns, which are luted with Rely X U200 self-adhesive resin cement on the respective dies, as well as thermocycling of IPS E max pressable crowns and thermocycling of graphene crowns. The current review was conducted as an in vitro examination at the Division of Prosthodontics, GSL Dental School, Rajahmundry, Andhra Pradesh, India. Materials and methods On a typodont tooth, a shoulder finish line design was prepared and incisal reduction was performed. The tooth was scanned, designed, and milled to produce 18 metal dies made of cobalt-chrome alloy. These metal dies produced a total of (n=36) all-ceramic crowns, which were divided into two groups based on crown type: 18 IPS E max crowns and 18 graphene crowns. The participants were once again divided into two subgroups within each group, with the purpose of assessing fracture resistance. This evaluation was conducted using a universal testing machine both before and after subjecting the specimens to thermocycling. The obtained data were sent for statistical analysis. Results Fracture resistance values were reduced after thermocycling of both IPS E max and Graphene crowns. Without thermocycling, the fracture resistance values of IPS E max crowns were higher than those of graphene crowns. Conclusions The fracture resistance of IPS E max crowns exhibited a statistically significant increase when compared to graphene crowns. Additionally, it was shown that the fracture resistance of both materials was reduced upon exposure to thermocycling.