Impact Of Mechanical Loading Research Articles

Osteocyte-mediated mechanical response controls osteoblast differentiation and function.

Low bone mass is a pervasive global health concern, with implications for osteoporosis, frailty, disability, and mortality. Lifestyle factors, including sedentary habits, metabolic dysfunction, and an aging population, contribute to the escalating prevalence of osteopenia and osteoporosis. The application of mechanical load to bone through physical activity and exercise prevents bone loss, while sufficient mechanical load stimulates new bone mass acquisition. Osteocytes, cells embedded within the bone, receive mechanical signals and translate these mechanical cues into biological signals, termed mechano-transduction. Mechano-transduction signals regulate other bone resident cells, such as osteoblasts and osteoclasts, to orchestrate changes in bone mass. This review explores the mechanisms through which osteocyte-mediated response to mechanical loading regulates osteoblast differentiation and bone formation. An overview of bone cell biology and the impact of mechanical load will be provided, with emphasis on the mechanical cues, mechano-transduction pathways, and factors that direct progenitor cells toward the osteoblast lineage. While there are a wide range of clinically available treatments for osteoporosis, the majority act through manipulation of the osteoclast and may have significant disadvantages. Despite the central role of osteoblasts to the deposition of new bone, few therapies directly target osteoblasts for the preservation of bone mass. Improved understanding of the mechanisms leading to osteoblastogenesis may reveal novel targets for translational investigation.

Exercise and Bone Health in Cancer: Enemy or Ally?

Bone health is often threatened in cancer patients. Bone metastasis and osteoporosis frequently occur in patients with cancer and may lead to different skeletal-related events, which may negatively affect patients' quality of life and are associated with high mortality risk. Physical exercise has been recognized as a potential adjunctive strategy in the cancer setting to improve physical function as well as treatment-related side effects. Nevertheless, exercise is often not recommended to patients with bone health impairments due to safety concerns. In the current review, we aimed, through a comprehensive review of the evidence, to explore the impact of exercise in terms of safety profile, bone outcomes, and the effects on other outcomes in patients with cancer affected by bone metastasis or at high risk of losing bone. Additionally, we explored the potential mechanisms by which exercise may act on bone, particularly the impact of mechanical load on bone remodeling. Finally, considerations about exercise prescription and programming in these populations are also discussed.

Выбор методов фиксации костных фрагментов при аутопластике дефектов длинных трубчатых костей

The aim of the study was to analyze the effect of different methods of fixing bone fragments after transplantation of the fibula into a large defect of long tubular bones on the results of treatment. The study included 10 patients (group 1) with major tibia defects in whom the method of postoperative fixation of the segment of the operated limb allowed to give an early mechanical load on the graft itself and 10 patients (group 2) where the impact of mechanical load on the graft was excluded due to its transplantation into the hummers defect (6 cases) or minimized when replacing the tibia defect (4 cases). The degree of graft hypertrophy, the rate of its fusion with the recipient bed, and the number of postoperative complications under different conditions of mechanical stimulation of the fibula graft were studied. The rate of fusion of the graft with the recipient bed in both groups of patients was the same, but the incidence of complete stress fractures of the fibula graft in the second group was three times higher than in the first and was 30%, against the background of a slight degree of graft hypertrophy (from 19% to 45%). The use of the Ilizarov device for fixing fragments of the post-resection bone bed and graft in a stable and dynamic mode allows to give an early postoperative load on the lower limb, stimulates the rate of graft hypertrophy and reduces the likelihood of developing complete stress fractures.

Acoustic method for measurement of crack width in concrete

The article presents the results of research and experimental studies aimed at measurement of crack width in concrete under the impact of mechanical loading. During the research, the author simultaneously measured load, deformation, crack width, acoustic emission gross counting by tensiometric and acoustic methods and obtained full diagrams of concrete deformation. The experiments resulted in regression equations and their combined diagrams showing relation between acoustic emission gross counting and mechanical loading level. The author identified the parameters of macro-crack initiation and their width in lightweight concrete depending on the value of the applied load. The conducted experiments and statistic processing of the data produced the correlation between the crack width and acoustic emission gross counting.

A GENERALIZED THERMOELASTIC DIFFUSION PROBLEM OF THIN PLATE HEATED BY THE ULTRASHORT LASER PULSES

In recent years, ultrashort laser pulses are widely used in the fields of ultra-precision machining, optical storage and microelectronic manufacture due to the advantages of high power density, short duration and high machining accuracy. In the manuscript, the memory-dependent nonlocal generalized thermoelastic diffusion theory is established based on the L-S generalized thermoelastic diffusion theory as well as considering the memory-dependent effect and spatial nonlocal effect. The theory can accurately predict the thermoelastic diffusion responses of structures whose geometry size is equivalent to its internal characteristic scale. The control equations of the theory are derived, and the solution of the control equations are obtained based on the Laplace integral transformation. As a numerical example, the transient thermoelastic diffusion responses of a semi-infinite thin plate subjected to a non-Gaussian laser pulse and a chemical shock are studied. The variation of the temperature, chemical potential, displacement, stresses and concentration with different nonlocal parameters, thermal time delay factors and diffusion time delay factors are obtained. The results show that heat conduction has significant effect on mass transfer, while mass transfer has little effect on heat conduction; nonlocal parameter has significant influence on displacement and stress, but little effect on temperature, chemical potential and concentration. The establishment of this theory and the solution method are aimed at accurately predicting the transient responses of the heat and mass under the impact of mechanical loading, heat and chemical potential.

Spondyloarthritis on the Move: Biomechanical Benefits or Harm.

Physical activity is beneficial in several diseases including spondyloarthritis despite mechanical stress being suggested as a trigger of disease onset or activity. Moreover, there is no clear answer as to where physiological loading of the joints ends and pathological overloading begins. The aim of this review is to provide an overview of what is known about exercise and biomechanical loading in spondyloarthritis. Recent studies focused on the impact of mechanical loading in healthy individuals and spondyloarthritis patients, demonstrating an overlap between the groups and pointing out possible beneficial and detrimental activities. The discovery that several animal models of inflammatory arthritis are dependent on mechanical stress helps unraveling the involved molecular pathways. There is a knowledge gap between the beneficial effect of exercise reported in clinical trials and the harm seen in observational studies and animal models. Imaging studies provide a first step in joining these two opposites by highlighting a wide-ranging spectrum between healthy and diseased joints. Future research is warranted on specific interventions in well-defined patient populations and in animal models in order to understand the pathogenesis. Targeted exercise therapy and prevention should be considered specific goals.

Pathogenesis and clinical management of obesity-related knee osteoarthritis: Impact of mechanical loading.

SummaryObesity-related osteoarthritis (OA) is a complex, multifactorial condition that can cause significant impact on patients’ quality of life. Whilst chronic inflammation, adipocytokines and metabolic factors are considered to be important pathogenic factors in obesity related OA, there has been limited investigation into the biomechanical impact of obesity on OA development. This review aims to demonstrate that mechanical factors are the major pathological cause of obesity-related OA. The effect of obesity on pathological changes to the osteochondral unit and surrounding connective tissues in OA is summarized, as well as the impact of obesity-related excessive and abnormal joint loading, concomitant joint malalignment and muscle weakness. An integrated therapeutic strategy based on this multi-factorial presentation is presented, to assist in the management of obesity related OA.The translational potential of this articleDespite the high prevalence of obesity-related OA, there is no specific guideline available for obesity-related OA management. In this review, we demonstrated the pathological changes of obesity-related OA and summarized the impact of biomechanical factors by proposing a hypothetical model of obesity-related OA change. Therapeutic strategies based on adjusting abnormal mechanical effects are presented to assist in the management of obesity-related OA.

Impact of Mechanical Load on the Expression Profile of Synovial Fibroblasts from Patients with and without Osteoarthritis.

Osteoarthritis (OA) affects the integrity of the entire joint including the synovium. The most abundant cells in the synovium are fibroblasts (SF). Excessive mechanical loading might contribute to OA pathogenesis. Here, we investigate the effects of mechanical loading on SF derived from non-OA (N-SF) and OA patients (OA-SF). We treated N-SF and OA-SF with or without mechanical loading for 48h after 24h of preincubation. Then we assessed gene and protein expression of proinflammatory factors (TNFα, COX-2, PG-E2, IL-6), extracellular matrix (ECM) components (COL1, FN1) and glycosaminoglycans (GAGs) via RT-qPCR, ELISA, DMMB assay and HPLC. Mechanical loading significantly increased TNFα and PG-E2 secretion by N-SF and OA-SF, whereas in OA-SF IL-6 secretion was reduced. COL1 and FN1 secretion were downregulated in N-SF during loading. OA-SF secreted less COL1 compared to N-SF under control conditions. In contrast, OA-SF in general expressed more FN1. GAG synthesis was upregulated in N-SF, but not in OA-SF during loading with OA-SF displaying a higher charge density than N-SF. Mechanical loading enhanced proinflammatory factor expression and GAG synthesis and decreased secretion of ECM components in N-SFs, indicating a contributing role of SF to OA development.

First AC loss test and analysis of a Bi2212 cable-in-conduit conductor for fusion application

The main goal of the Chinese fusion engineering test reactor (CFETR) is to build a fusion engineering tokamak reactor with a fusion power of 50–200 MW, and plan to test the breeding tritium during the fusion reaction. This may require a maximum magnetic field of the central solenoid and toroidal field coils up to 15 T. New magnet technologies should be developed for the next generation of fusion reactors with higher requirements. Bi2Sr2CaCu2Ox (Bi2212) is considered as a potential and promising superconductor for the magnets in the CFETR. R&D activities are ongoing at the Institute of Plasma Physics, Chinese Academy of Sciences for demonstration of the feasibility of a CICC based on Bi2212 round wire. One sub-size conductor cabled with 42 wires was designed, manufactured and tested with limited strand indentation during cabling and good transport performance. In this paper, the first test results and analysis on the AC loss of Bi2212 round wires and cabled conductor samples are presented. Furthermore, the impact of mechanical load on the AC loss of the sub-size conductor is investigated to represent the operation conditions with electromagnetic loads. The first tests provide an essential basis for the validation of Bi2212 CICC and its application in fusion magnets.

In vivo Investigation of Patellofemoral Cartilage Contact Mechanisms- Impact of Mechanical Loading and Patellofemoral Geometry

Aims and Objectives:Today the selection of the procedures for treatment of focal cartilage lesions is standardized to the defect size. Subject specific parameters like individual cartilage contact mechanisms are not taken into account. Aim of the present study therefore was to investigate inter-individual differences in the patellofemoral cartilage contact mechanisms of healthy subjects and to correlate them to the individual patellar joint surface area and patellar and femoral dimensions.Materials and Methods:10 knees of 10 healthy subjects with regular shaped patella and trochlea underwent magnetic resonance imaging at rest and during mechanical loading for simulated weight bearing. Imaging was performed at 30° knee flexion. A custom made pneumatic loading device was used to apply 0 and 200 N axial loading to the leg. Manual segmentation of the patella, the trochlear and the patellofemoral cartilage was performed. Patellar volume, joint surface area and cartilage contact areas were calculated for each loading condition. Moreover patellar height, diameter and femoral epicondylar width were determined. Prospective motion correction was performed to reduce motion artifacts during load application.Results:Mean size of the patellar surface area was 16,08 cm2 (range 13,11-18,07 cm2). Mean patellofemoral contact area (PCA) without loading was 6,15 cm2 (range 5,12-7,33 cm2). During axial loading of the leg with 200N PCA significantly increased to 6,77 cm2 (range 6,05-7,55 cm2) (p<0,05). Patellar surface area and PCA were not correlated (r=0,01; p<0,05). Mean Patella width was 5,4 cm (Range 4,8-6,2 cm) and mean femoral width at the epicondyles was 8,5 cm (Range 7,9-9 cm). The mean patellofemoral cartilage contact area showed poor correlation to patellar geometry (patellar width (r=0,48, p<0,05; patellar cartilage surface r=0,06, p<0,05) but moderate correlation to the femoral width (r=0,75, p<0,05).Conclusion:Main finding of the presented study is that patellofemoral cartilage contact mechanisms are responsive to loading and show relevant inter individual differences. A second important finding is that cartilage contact mechanisms cannot be concluded directly by geometric parameters such as joint surface area or patellofemoral dimensions. Further investigation is needed to identify parameters influencing size of patellofemoral contact area at rest and during loading in order to include them into diagnostics and treatment of the cartilage defects in clinical routine.

Effect of compressive loading and incubation with clodronate on the RANKL/OPG system of human osteoblasts.

In vivo studies have shown that bisphosphonates result in slow rates of orthodontic tooth movement. This study investigated whether clodronate modifies the impact of mechanical loading on the RANKL/OPG system of human osteoblasts. Osteoblasts were cultured in vitro with 0.5 or 5.0 µM clodronate for 48 h and/or subjected to 3 h of compressive loading at 34.9 g/cm(2). Cell viability was determined by MTT assay. Real-time polymerase chain reaction (PCR), enzyme-linked immunosorbent assay (ELISA), and immunocytochemical staining were used to analyze the cells for their production of osteoprotegerin (OPG) and receptor activator of nuclear factor kappa-B ligand (RANKL) at the transcriptional and protein levels. Compressive loading did not affect osteoblast viability in a significant way. Clodronate (5.0 µM) mildly reduced the viability of both compressed and uncompressed cells. Compressive loading induced a 4.2-fold increase in RANKL gene expression, while clodronate led to a concentration-dependent inhibition of this effect (1.8-fold increase at 5.0 µM). OPG gene expression was decreased by compressive loading both in the presence of 0.5 µM clodronate and in the absence of clodronate, and OPG protein synthesis in the compressed cells was significantly decreased in the presence of clodronate. Immunocytochemical staining revealed an increase of RANKL protein synthesis in compressed cells, while clodronate and cell compression reduced this increase. This study demonstrates that clodronate decreases the compression-induced RANKL/OPG ratio expressed by human osteoblasts. Reported in vivo findings of reduced osteoclast numbers on the compression side of orthodontic tooth movement under the action of clodronate-and the associated slow rate of tooth movement-might be attributable not only to a direct impact on osteoclasts but also to changes in osteoblast-osteoclast interaction resulting from the presence of clodronate.

Impact of shear stress and simulated microgravity on osteocytes using a new rotation cell culture device

Osteocytes sense the mechanical loading and weightlessness, and orchestrate bone remodeling by directing both osteoblast and osteoclast functions. Previous studies mostly focused on the impact of mechanical loading or microgravity on the osteocyte changes in themselves. However as the mechanosensors, it is more meaningful to make clear whether and how the mechanosensitivity of osteocytes affected by weightlessness, since the alteration of mechanosensitivity may further affect the mechanotransduction process in osteocytes, and finally altered the bone remodeling process. Whereas until now, this aspect had long been overlooked and was still not clear yet.To investigate how osteocytes respond to shear stress under weightlessness, a novel custom-made device was designed to simulate microgravity and load fluid flow on cells in vitro at the same time. The osteocyte-like cell line MLO-Y4 was loaded by this novel device at 15dyn/cm2 shear stress with 15rpm rotating speed. There were two loading durations for different determinations: 30min of loading for the detection of nitric oxide and Prostaglandin E2, and 6h of loading for the detection of three bone formation biomarkers (alkaline phosphatase, osteocalcin and procollagen type I N propeptide). In order to preliminarily explore the mechanism of this altered response to mechanical loading with different gravity in osteocytes, an observation of cytoskeleton and the determination of the elements in the Wnt/β-catenin signaling pathway were also performed after 6h of loading. The results showed that (1) the mechanical response of both NO and PGE2 were increased higher during 15–30min of shear stress under simulated microgravity than that under normal gravity; (2) the mechanical response of ALP activity was decreased, while that of OC and PINP content were increased by simulated microgravity. Moreover, the ALP activity and the OC content were related to the activity of Wnt signaling pathway, which plays a key role in regulating the bone formation; (3) the exploration for the mechanism of altered mechanical bio-response in osteocytes showed that F-actin filaments enhanced by shear stress under simulated microgravity were not so robust as that showed under normal gravity, and some short dendritic processes at cell periphery were only observed within the simulated microgravity groups; (4) further, the simulated microgravity significantly inhibited the mechanosensitivity of the Wnt/β-catenin signaling pathway on protein level in the osteocytes.These results suggested that the mechanosensitivity of osteocytes was altered by simulated microgravity, and this may be an adverse effect on the osteoblastic bone formation whereas be good for osteoclastogenesis. The findings in this study may provide an important clue for searching an efficient approach to prevent osteocytes from changing the orchestration for bone remodeling under microgravity, and further this prevention may finally make the physical exercises capable against bone loss under microgravity.

The effect of loading on peri-implant bone: a critical review of the literature.

In the 90s, there was a general belief that mechanical overloading was one of the main reasons for late implant failure. This triggered research to assess the role of mechanical loading on the establishment and the maintenance of oral implant osseointegration. Animal experimental studies indeed suggested the potential detrimental effect of excessive mechanical load on peri-implant bone, although randomised or controlled clinical trials of treatment interventions of oral implants designed to study overload are lacking. The lack of quantification of so-called overload at the implant level in the intra-oral setting is one of the main shortcomings in the literature. The level of evidence of the studies on bone response to implant loading is weak and does not indicate that overload can lead to peri-implant bone loss, except in case of inflammation. Clinical and animal experimental studies on early and immediate implant loading, however, provide information on the impact of mechanical loading on the process of osseointegration. It is obvious that micromotion between the implant and host tissues compromises osseointegration. However, in case of an efficient force transfer between implant and surrounding tissues, mechanical loading might even stimulate peri-implant bone formation and therefore osseointegration.

The Impact of Substrate Stiffness and Mechanical Loading on Fibroblast-Induced Scaffold Remodeling

Fibroblasts as many other cells are known to form, contract, and remodel the extracellular matrix (ECM). The presented study aims to gain an insight into how mechanical boundary conditions affect the production of ECM components, their remodeling, and the feedback of the altered mechanical cell environment on these processes. The influence of cyclic mechanical loading (f=1 Hz, 10% axial compression) and scaffold stiffness (E=1.2 and 8.5 kPa) on the mechanical properties of fibroblast-seeded scaffold constructs were investigated in an in vitro approach over 14 days of culture. To do so, a newly developed bioreactor system was employed. While mechanical loading resulted in a clear upregulation of procollagen-I and fibronectin production, scaffold stiffness showed to primarily influence matrix metalloproteinase-1 (MMP-1) secretion and cell-induced scaffold contraction. Higher stiffness of the collagen scaffolds resulted in an up to twofold higher production of collagen-degrading MMP-1. The changes of mechanical parameters like Young's modulus, maximum compression force, and elastic portion of compression force over time suggest that from initially distinct mechanical starting conditions (scaffold stiffness), the construct's mechanical properties converge over time. As a consequence of mechanical loading a shift toward higher construct stiffness was observed. The results suggest that scaffold stiffness has only a temporary effect on cell behavior, while the impact of mechanical loading is preserved over time. Thus, it is concluded that the mechanical environment of the cell after remodeling is depending on mechanical loading rather than on initial scaffold stiffness.

Impact of mechanical loading on the corrosion of steel reinforcement in concrete structures

This paper presents results of an experimental investigation on the effect of mechanical loading on the corrosion of steel reinforcement in concrete. Reinforced concrete beams were cast, subjected to mechanical loadings and then exposed to corrosive environment. Successive drying and wetting cycles using 3% sodium chloride salt solution were used to accelerate the corrosion attack. Electrochemical techniques such as macrocell corrosion current, linear polarization resistance (LPR), corrosion potential (E corr ) and electrochemical impedance spectroscopic (EIS), were used to evaluate the corrosion behavior of the reinforcement. Also, chloride penetration profile and visual inspection of the beam rebars were obtained. The results shows that the pre-exposure mechanical load has no influence on the corrosion initiation or corrosion rate thereafter, unless it reaches to some limit where it develops connected cracks through which the chloride ions flow and depassivate the rebars. The load of 25% of the ultimate capacity seems to be the critical load limit where some microcracks onset to be connected, facilitate the chloride ions flow, and initiate the rebar corrosion.

Dynamic compressive loading influences degradation behavior of PEG‐PLA hydrogels

Biodegradable hydrogels are attractive 3D environments for cell and tissue growth. In cartilage tissue engineering, mechanical stimulation has been shown to be an important regulator in promoting cartilage development. However, the impact of mechanical loading on the gel degradation kinetics has not been studied. In this study, we examined hydrolytically labile gels synthesized from poly(lactic acid)-b-poly(ethylene glycol)-b-poly-(lactic acid) dimethacrylate macromers, which have been used for cartilage tissue engineering. The gels were subject to physiological loading conditions in order to examine the effects of loading on hydrogel degradation. Initially, hydrogels were formed with two different cross-linking densities and subject to a dynamic compressive strain of 15% at 0.3, 1, or 3 Hz. Degradation behavior was assessed by mass loss, equilibrium swelling and compressive modulus as a function of degradation time. From equilibrium swelling, the pseudo-first-order reaction rate constants were determined as an indication of degradation kinetics. The application of dynamic loading significantly enhanced the degradation time for the low cross-linked gels (P < 0.01) while frequency showed no statistical differences in degradation rates or bulk erosion profiles. In the higher cross-linked gels, a 3 Hz dynamic strain significantly increased the degradation kinetics resulting in an overall faster degradation time by 6 days compared to gels subject to the 0.3 and 1 Hz loads (P < 0.0001). The bioreactor set-up also influenced overall degradation behavior where the use of impermeable versus permeable platens resulted in significantly lower degradation rate constants for both cross-linked gels (P < 0.001). The compressive modulus exponentially decreased with degradation time under dynamic loading. Together, our findings indicate that both loading regime and the bioreactor setup influence degradation and should be considered when designing and tuning a biodegradable hydrogel where mechanical stimulation is employed.

Assessment of Mechanobiological Models for the Numerical Simulation of Tissue Differentiation around Immediately Loaded Implants

Nowadays, there is a growing consensus on the impact of mechanical loading on bone biology. A bone chamber provides a mechanically isolated in vivo environment in which the influence of different parameters on the tissue response around loaded implants can be investigated. This also provides data to assess the feasibility of different mechanobiological models that mathematically describe the mechanoregulation of tissue differentiation. Before comparing numerical results to animal experimental results, it is necessary to investigate the influence of the different model parameters on the outcome of the simulations. A 2D finite element model of the tissue inside the bone chamber was created. The differentiation models developed by Prendergast, et al. [“Biophysical stimuli on cells during tissue differentiation at implant interfaces”, Journal of Biomechanics, 30(6), (1997), 539–548], Huiskes et al. [“A biomechanical regulatory model for periprosthetic fibrous-tissue differentiation”, Journal of Material Science: Materials in Medicine, 8 (1997) 785–788] and by Claes and Heigele [“Magnitudes of local stress and strain along bony surfaces predict the course and type of fracture healing”, Journal of Biomechanics, 32(3), (1999) 255–266] were implemented and integrated in the finite element code. The fluid component in the first model has an important effect on the predicted differentiation patterns. It has a direct effect on the predicted degree of maturation of bone and a substantial indirect effect on the simulated deformations and hence the predicted phenotypes of the tissue in the chamber. Finally, the presence of fluid also causes time-dependent behavior. Both models lead to qualitative and quantitative differences in predicted differentiation patterns. Because of the different nature of the tissue phenotypes used to describe the differentiation processes, it is however hard to compare both models in terms of their validity.

Suppressing Cracking in Resistance Welding AA5754 by Mechanical Means

In this paper mechanical aspects of cracking during single- and multi-spot welding of AA5754 was investigated by both experimental and analytical approaches. The impact of mechanical loading on crack initiation and propagation was studied with the consideration of various process parameters including the loading imposed by electrodes, the formation of liquid nugget, and constraining factors during and after welding. Tensile properties of AA5754 and their dependence on the temperature were tested at room and up to solidus temperatures, in order to provide a reference of cracking stress. Thermal-mechanical analysis was conducted based on the temperature field around the nugget and the state of stress encountered during welding. This analysis revealed that tensile stress might build up in the vicinity of the nugget during cooling, as explained in the experimental observation. General guidelines for suppressing cracking were proposed, i.e., to provide sufficient constraint around the weld spot during and after welding.

Impact of mechanical load on functional recovery after muscle reloading.

The purposes of this study included: 1) to determine the impact of reloading after hindlimb suspension on the in vitro isometric contractile properties of the rat soleus muscle (experiment 1), and 2) to determine the impact of altered mechanical load on the recovery of muscle contractile properties after reloading-induced injury (experiment 2). Male Sprague-Dawley rats (240-270 g) were used for both experiments. In experiment 1, all rats were hindlimb suspended for a period of 7 d and studied either immediately afterward (no reloading, 0D-RL), after 1 d (24 h) of reloading (1D-RL), or after 2 d (48 h) reloading (2D-RL). In experiment 2, all rats underwent hindlimb suspension for 7 d followed by reloading for 2 d. Rats were then randomly assigned to one of three groups: 1) cage-bound, 2) treadmill walking (12m x min(-1) x 20 min daily), or 3) resuspended. Rats were then studied 7 or 14 d later. In experiment 1, maximal isometric specific force (force/cross-sectional area, Po) was significantly decreased by approximately 32% and approximately 50% in the ID-RL and 2D-RL groups (P < 0.05) compared with 0D-RL group. During the recovery phase (experiment 2), Po was significantly higher in the cage-bound and treadmill walking groups compared with the resuspended group both at 7 and 14 d. However, there was no significant difference in Po between the cage-bound and treadmill walking groups at either time point. Results from this study indicate that skeletal muscle reloading (after a period of unloading) results in a significant force decrement. Additionally, removal of the load during the recovery phase significantly impairs functional recovery, whereas mild exercise offers no advantage over cage-bound activity.

Impact of Mechanical Load on Recovery from Reloading-Induced Muscle Injury

180 Reloading (RL, i.e. weightbearing) of skeletal muscle following hindlimb suspension (HS) or spaceflight is known to induce muscle damage. The significant reduction in maximal isometric force (Po, N/cm2) of the soleus (SOL) muscle following 7 days HS consequent to 24- or 48 hrs RL is shown below: (Table 1)Table 1The purpose of this study was to determine if altered mechanical load impacted on the rate of recovery of contractile properties following RL-induced muscle injury in male Sprague Dawley rats (250-300 gms). Following 7 days of HS, rats were allowed to RL for 48 hrs. Thereafter, rats were randomly assigned to 1 of 4 groups: re-suspended for 7 days (RS × 7D) or 14 days (RS × 14D), or cage-bound with daily treadmill walking (12 m/min, 20 min/day) for 7 days (TM × 7D) or 14 days (TM × 14D). In vitro isometric contractile properties (25°C) of the SOL muscle were measured. The mean Po (± S.D.) for the 4 groups are shown in in the following table: (Table 2)Table 2Compared with RS, cage-bound activity coupled with daily treadmill walking resulted in a significantly higher Po both 7- and 14-days after reloading-induced muscle injury (P < 0.05). These results indicate that the amount of load post-injury significantly impacts on the rate of recovery. Supported by the University @ Buffalo Moir P. Tanner and Mark Diamond Funds.