Maximal Muscle Force Research Articles

Reduced Bone Strength and Muscle Force in Women 27 Years After Anorexia Nervosa.

A substantial body of research findings indicate that muscle mass and bone mass are reduced in populations of anorexic females, even in such populations whose anorexia nervosa had been in remission for longer periods. This study aimed to investigate whether the bone of an anorexia nervosa recovery cohort is adapted to maximal muscle forces and whether there are alterations in the structure of the tibia in this population, as compared with a control group. This was a cross-sectional study of 22 women in Switzerland who have remained in stable recovery from anorexia nervosa for an average of 27 years. The measurements were compared with those of an age- and gender-matched control group (n = 73). There were no interventions. Bone characteristics of the tibia and maximal voluntary ground reaction force (Fm1LH) were measured. The variability in volumetric bone mineral content (vBMC) at the 14% site was explained by 54.7% on the grounds of Fm1LH (P < .001). Formerly anorexic women had an 11.6% lower Fm1LH (P = .001), a significantly lower vBMC at 4% and 14% of tibia length, and an 11.9% (P = .001) lower body mass than the age- and gender-matched control population. Present body mass of the anorexia group correlated positively with vBMC at the 14% site (P < .001). Despite the fact that findings reflected an adaptation of bone to the acting forces, most results indicated that the test cohort generally suffered from a secondary bone defect. In addition, maximal muscle force was also impaired in the formerly anorexic women.

운동유형에 따른 인체 근건복합체 탄성의 급성 변화에 관한 연구

The purpose of this study was to investigate the acute effects of running and weight training on tendon stiffness, muscle strength and neuromuscular acivation on plantarflexor in the young men. Subjects were assigned to running (n=11) and weight training (n=11) groups. Maximal isometric torque (MVC) and muscle force for plantar flexors (PF) were measured. Tendon stiffness for PF was measured using ultrasonography while subjects performed isometric contraction. BR No significant changes occurred in elongation, stiffness in the both group but decrease after training. In th e running group, muscle force decreased significantly after exercise but not for weight group. For muscle activation, significant decreases of lateral gastrocnemius were observed, but not for weight group. BR No significant changes occurred in any measured variables in the both group BR These results indicated that running and weight training brought about decrease of tendon stiffness and strength in medial gastrocnemius in the young men, but it did not affect significantly.

Dynamic muscle quality of the plantar flexors is impaired in claudicant patients with peripheral arterial disease and associated with poorer walking endurance

Peripheral arterial disease and intermittent claudication (PAD-IC) negatively affects physical activity and function. There is evidence for plantarflexor muscle dysfunction and weakness; however, the extent to which this dysfunction can be attributed to reduced muscle size or quality, or both, is not yet known. This study investigated whether in vivo plantarflexor muscle quality during static and dynamic contractions is altered by PAD-IC and whether such changes are associated with impaired walking endurance according to initial and absolute claudication distances. The study recruited 22 participants, consisting of 10 healthy controls and 12 claudicant patients with occlusion of the superficial femoral artery (seven unilateral and five bilateral). Muscle quality of the combined gastrocnemius muscles during static contractions was calculated by normalizing the estimated maximal potential muscle force to the physiological cross-sectional area of the lateral and medial gastrocnemius. Muscle quality during dynamic contractions of the combined plantarflexor muscles was calculated as the ratio of peak voluntary concentric plantarflexor power and the summed volume of lateral and medial gastrocnemius. Dynamic muscle quality was 24% lower in the claudicating-limb and asymptomatic-limb groups compared with controls (P = .017 and P = .023). The differences were most apparent at the highest contraction velocity (180°/s). Dynamic muscle quality was associated with reduced walking endurance (R = 0.689, P = .006 and R = 0.550, P = .042 for initial and absolute claudication distance, respectively). The claudicating-limb group demonstrated a trend toward reduced static muscle quality compared with controls (22%, P = .084). The relative contribution of the soleus muscle to plantarflexion maximum voluntary contraction was significantly higher in the claudicating-limb and asymptomatic-limb groups than in controls (P = .012 and P = .018). The muscle strength of the plantarflexors in those with PAD-IC appears to be impaired at high contraction velocities. This may be explained by some reduction in gastrocnemii muscle quality and a greater reliance on the prominently type I-fibered soleus muscle. The reduced dynamic capability of the plantarflexor muscles was associated with disease severity and walking ability; therefore, efforts to improve plantarflexor power through dynamic exercise intervention are vital to maintain functional performance.

Low muscle strength in late adolescence and Parkinson disease later in life.

To evaluate maximal isometric muscle force at 18 years of age in relation to Parkinson disease (PD) later in life. The cohort consisted of 1,317,713 men who had their muscle strength measured during conscription (1969-1996). Associations between participants' muscle strength at conscription and PD diagnoses, also in their parents, were examined using multivariate statistical models. After adjustment for confounders, the lowest compared to the highest fifth of handgrip strength (hazard ratio [HR] 1.38, 95% confidence interval [CI] 1.06-1.79), elbow flexion strength (HR 1.34, 95% CI 1.02-1.76), but not knee extension strength (HR 1.24, 95% CI 0.94-1.62) was associated with an increased risk of PD during follow-up. Furthermore, men whose parents were diagnosed with PD had reduced handgrip (fathers: mean difference [MD] -5.7 N [95% CI -7.3 to -4.0]; mothers: MD -5.0 N [95% CI -7.0 to -2.9]) and elbow flexion (fathers: MD -4.3 N [95% CI -5.7 to -2.9]; mothers: MD -3.9 N [95% CI -5.7 to -2.2]) strength, but not knee extension strength (fathers: MD -1.1 N [95% CI -2.9 to 0.8]; mothers: MD -0.7 N [95% CI -3.1 to 1.6]), than those with no such familial history. Maximal upper extremity voluntary muscle force was reduced in late adolescence in men diagnosed with PD 30 years later. The findings suggest the presence of subclinical motor deficits 3 decades before the clinical onset of PD.

Exercise Attenuates Age‐Associated Reductions in Muscle Strength and Cardiorespiratory Fitness in Mice

Aging is associated with losses in muscle strength and cardiovascular fitness that may be offset with regular exercise. While exercise adaptations may diminish with age, robust adaptations still occur. We tested the hypothesis that aging reduces muscle function and cardiorespiratory endurance, however voluntary (running wheel, RW) or prescribed (treadmill (TM) training) exercise will attenuate these aging‐associated decreases in strength and fitness. In vivo plantarflexor maximal force and fatigue (% of max force after 10 contractions) were measured in young (4 mo. old) and aged (24 mo. old) sedentary (SED) mice and following 2 wks of RW (24h wheel access) or TM training (45 min/day, 5 day/wk). Cardiorespiratory adaptations were assessed with pre‐ and post‐maximal treadmill tests. Maximal muscle force was lower in aged than young SED mice (1.1±0.04 vs. 1.6±0.07 g/kg BW, respectively, p&lt;0.05). In young groups, neither RW nor TM increased force over SED. In aged groups, RW and TM were associated with respective 22 and 26% higher maximal forces than aged SED mice (p&lt;0.05), but still were lower than young groups. Plantarflexor fatigue resistance was higher in aged than young SED mice (50±3 vs. 35±3% of max, respectively, p&lt;0.05) with no age differences in RW and TM groups. In treadmill pre‐tests, young groups ran longer than aged groups (9:23±0:52 vs. 5:09± 0:51, respectively p&lt;0.05). Increases in treadmill time after training occurred only in young and aged TM with respective 25:34±8:24 and 16:42±2:39 increases from pre to post test (p&lt;0.05). These findings suggest voluntary and prescribed exercise attenuate some age‐associated reductions in muscle force, but prescribed exercise is most effective in improving cardiorespiratory fitness in young and older mice.

Functional Integration During Development Within The Masticatory Apparatus

During development the masticatory apparatus undergoes significant changes; including changes in muscle size and orientation, and in dental form due to replacement and wear. As body size increases during development, absolute masticatory forces are predicted to increase. However the effect of simultaneous changes to muscle lever mechanics and dental topography upon masticatory performance is currently unknown. Cercocebus atys (the sooty mangabey) provides an ideal opportunity to examine this. Over 50% of the diet among all post-weaning individuals centres upon exploiting a mechanically stress resistant seed. Given this dietary consistency, it may be expected that the masticatory system will be integrated across development; such that individuals of all ages are capable of processing this food item. Using virtual modelling techniques, changes in bite pressure along the postcanine dental row were predicted at various stages of development. Results indicate that while maximum muscle force production increase...

The relationship between skull morphology, masticatory muscle force and cranial skeletal deformation during biting

The human skull is gracile when compared to many Middle Pleistocene hominins. It has been argued that it is less able to generate and withstand high masticatory forces, and that the morphology of the lower portion of the modern human face correlates most strongly with dietary characteristics. This study uses geometric morphometrics and finite element analysis (FEA) to assess the relationship between skull morphology, muscle force and cranial deformations arising from biting, which is relevant in understanding how skull morphology relates to mastication. The three-dimensional skull anatomies of 20 individuals were reconstructed from medical computed tomograms. Maximal contractile muscle forces were estimated from muscular anatomical cross-sectional areas (CSAs). Fifty-nine landmarks were used to represent skull morphology. A partial least squares analysis was performed to assess the association between skull shape and muscle force, and FEA was used to compare the deformation (strains) generated during incisor and molar bites in two individuals representing extremes of morphological variation in the sample. The results showed that only the proportion of total muscle CSA accounted for by the temporalis appears associated with skull morphology, albeit weekly. However, individuals with a large temporalis tend to possess a relatively wider face, a narrower, more vertically oriented maxilla and a lower positioning of the coronoid process. The FEAs showed that, despite differences in morphology, biting results in similar modes of deformation for both crania, but with localised lower magnitudes of strains arising in the individual with the narrowest, most vertically oriented maxilla. Our results suggest that the morphology of the maxilla modulates the transmission of forces generated during mastication to the rest of the cranium by deforming less in individuals with the ability to generate proportionately larger temporalis muscle forces.

The muscle–bone interaction in Turner syndrome

ObjectivesTurner syndrome (TS) is associated with an increased fracture rate due to reduced bone strength, which is mainly determined by skeletal muscle force. This study aimed to assess the muscle force–bone strength relationship in TS and to compare it with that of healthy controls. MethodsThis study included 39 girls with TS and 67 healthy control girls. Maximum muscle force (Fmax) was assessed through multiple one-legged hopping with jumping mechanography. Peripheral quantitative computerized tomography assessed the bone strength index at the tibial metaphysis (BSI 4) and the polar strength–strain index at the diaphysis (SSI polar 66). The effect of TS on the muscle–bone unit was tested using multiple linear regression. ResultsTS had no impact on Fmax (p=0.14); however, a negative effect on bone strength (p<0.001 for BSI 4 and p<0.01 for SSI polar 66) was observed compared with healthy controls. Bone strength was lower in the TS group (by 18%, p<0.01, for BSI 4 and by 7%, p=0.027, for SSI polar 66), even after correcting for Fmax. ConclusionsSimilar muscle force induces lower bone strength in TS compared with healthy controls, which suggests altered bone-loading sensitivity in TS.

The Neuro-Immune Pathophysiology of Central and Peripheral Fatigue in Systemic Immune-Inflammatory and Neuro-Immune Diseases.

Many patients with systemic immune-inflammatory and neuro-inflammatory disorders, including depression, rheumatoid arthritis, systemic lupus erythematosus, Sjögren's disease, cancer, cardiovascular disorder, Parkinson's disease, multiple sclerosis, stroke, and chronic fatigue syndrome/myalgic encephalomyelitis, endure pathological levels of fatigue. The aim of this narrative review is to delineate the wide array of pathways that may underpin the incapacitating fatigue occurring in systemic and neuro-inflammatory disorders. A wide array of immune, inflammatory, oxidative and nitrosative stress (O&NS), bioenergetic, and neurophysiological abnormalities are involved in the etiopathology of these disease states and may underpin the incapacitating fatigue that accompanies these disorders. This range of abnormalities comprises: increased levels of pro-inflammatory cytokines, e.g., interleukin-1 (IL-1), IL-6, tumor necrosis factor (TNF) α and interferon (IFN) α; O&NS-induced muscle fatigue; activation of the Toll-Like Receptor Cycle through pathogen-associated (PAMPs) and damage-associated (DAMPs) molecular patterns, including heat shock proteins; altered glutaminergic and dopaminergic neurotransmission; mitochondrial dysfunctions; and O&NS-induced defects in the sodium-potassium pump. Fatigue is also associated with altered activities in specific brain regions and muscle pathology, such as reductions in maximum voluntary muscle force, downregulation of the mitochondrial biogenesis master gene peroxisome proliferator-activated receptor gamma coactivator 1-alpha, a shift to glycolysis and buildup of toxic metabolites within myocytes. As such, both mental and physical fatigue, which frequently accompany immune-inflammatory and neuro-inflammatory disorders, are the consequence of interactions between multiple systemic and central pathways.

Muscle reinnervation with nerve-muscle-endplate band grafting technique: correlation between force recovery and axonal regeneration

BackgroundThis study was designed to determine the correlation between functional recovery and the extent of axonal regeneration after muscle reinnervation with our recently developed nerve-muscle-endplate band grafting (NMEG) technique in a rat model. Materials and methodsThe right experimentally paralyzed sternomastoid (SM) muscle by nerve transection was immediately reinnervated with an NMEG pedicle harvested from a neighboring sternohyoid muscle. The NMEG pedicle contained a muscle block (6 × 6 × 3 mm), a donor nerve branch with nerve terminals, and a motor endplate band. Three months after surgery, the tetanic force of the SM muscle was measured and the regenerated axons in the muscle were detected using neurofilament immunohistochemistry. ResultsThe results showed that the maximal tetanic force (a measure of muscle functional recovery) of the NMEG-reinnervated SM muscle reached up to 66.0% of the normal control. The wet weight of the reinnervated SM muscle (a measure of muscle mass recovery) was 87.2% of the control. The area fraction of the regenerating axons visualized with neurofilament staining within the NMEG-reinnervated SM muscle (a measure of muscle reinnervation) was 42.3%. A positive correlation was revealed between the extent of muscle reinnervation and maximal muscle force. ConclusionsOur newly developed NMEG technique results in satisfactory functional outcomes and nerve regeneration. Further improvement in the functional recovery after NMEG reinnervation could be achieved by refining the surgical procedure and creating an ideal environment that favors axon-endplate connections and accelerates axonal growth and sprouting.

Effects of a multichannel dynamic functional electrical stimulation system on hemiplegic gait and muscle forces.

[Purpose] The purpose of the study was to design and implement a multichannel dynamic functional electrical stimulation system and investigate acute effects of functional electrical stimulation of the tibialis anterior and rectus femoris on ankle and knee sagittal-plane kinematics and related muscle forces of hemiplegic gait. [Subjects and Methods] A multichannel dynamic electrical stimulation system was developed with 8-channel low frequency current generators. Eight male hemiplegic patients were trained for 4 weeks with electric stimulation of the tibia anterior and rectus femoris muscles during walking, which was coupled with active contraction. Kinematic data were collected, and muscle forces of the tibialis anterior and rectus femoris of the affected limbs were analyzed using a musculoskelatal modeling approach before and after training. A paired sample t-test was used to detect the differences between before and after training. [Results] The step length of the affected limb significantly increased after the stimulation was applied. The maximum dorsiflexion angle and maximum knee flexion angle of the affected limb were both increased significantly during stimulation. The maximum muscle forces of both the tibia anterior and rectus femoris increased significantly during stimulation compared with before functional electrical stimulation was applied. [Conclusion] This study established a functional electrical stimulation strategy based on hemiplegic gait analysis and musculoskeletal modeling. The multichannel functional electrical stimulation system successfully corrected foot drop and altered circumduction hemiplegic gait pattern.

Does wearing shoes affect your biomechanical efficiency?

Studies involving minimalist shoes have dramatically increased this past 10 years. While a deeper knowledge of the related modifications has ensued regarding the kinematics, electromyographic, and dynamic patterns, little is known regarding the modifications at the muscle forces and muscle fiber levels. The aim of the present study was to assess at a muscular level the modifications brought up when running barefoot, using 0mm midsole height running shoe, or using classical midsole height running shoes. An EMG-Driven model that combines the kinematics, dynamics, and electromyographic data was used to estimate the Triceps Surae (TS) muscle forces and fiber behavior during running using different footwear conditions. Despite differences at the joint level between barefoot and shod running when looking at ankle joint range of motion, or foot-ground angle at touchdown, the results showed no effect of footwear neither on the maximal muscle forces nor on the relative amount of force produced by each muscle within the TS muscle group when wearing different footwear. On the contrary, different behaviors of muscle fibers were shown with lower amplitudes of fiber lengths for the Gastrocnemii biarticular muscles when running barefoot. This particular results reveal that wearing a shoe, even with a very thin sole, could deeply modify the intricate muscle–tendon mechanics of running.

Effects of countermovement depth on kinematic and kinetic patterns of maximum vertical jumps

Although maximum height (Hmax), muscle force (F), and power output (P), have been routinely obtained from maximum vertical jumps for various purposes, a possible role of the countermovement depth (Hcmd) on the same variables remains largely unexplored. Here we hypothesized that (1) the optimum Hcmd for maximizing Hmax exists, while (2) an increase in Hcmd would be associated with a decrease in both F and P. Professional male basketball players (N=11) preformed maximum countermovement jumps with and without arm swing while varying Hcmd±25cm from its preferred value. Although regression models revealed a presence of optimum Hcmd for maximizing Hmax, Hmax revealed only small changes within a wide range of Hcmd. The preferred Hcmd was markedly below its optimum value (p<.05). However, both F and P sharply decreased with Hcmd, while F also revealed a minimum for Hcmd close to its highest values. Therefore, we conclude that although the optimum Hcmd should exists, the magnitude of its effect on Hmax should be only minimal within a typical Hcmd range. Conversely, F and P of leg muscles assessed through maximum vertical jumps should be taken with caution since both of them could be markedly confounded by Hcmd.

Persons with chronic hip joint pain exhibit reduced hip muscle strength.

Controlled laboratory cross-sectional study. Objectives To assess strength differences of the hip rotator and abductor muscle groups in young adults with chronic hip joint pain (CHJP) and asymptomatic controls. A secondary objective was to determine if strength in the uninvolved hip of those with unilateral CHJP differs from that in asymptomatic controls. Little is known about the relationship between hip muscle strength and CHJP in young adults. Thirty-five participants with CHJP and 35 matched controls (18 to 40 years of age) participated. Using handheld dynamometry, strength of the hip external rotators and internal rotators was assessed with the hip flexed to 90° and 0°. To assess external rotator and internal rotator strength, the hip was placed at the end range of external rotation and internal rotation, respectively. Strength of the hip abductors was assessed in sidelying, with the hip in 15° of abduction. Break tests were performed to determine maximum muscle force, and the average torque was calculated using the corresponding moment arm. Independent-sample t tests were used to compare strength values between (1) the involved limb in participants with CHJP and the corresponding limb in the matched controls, and (2) the uninvolved limb in participants with unilateral CHJP and the corresponding limb in the matched controls. Compared to controls, participants with CHJP demonstrated weakness of 16% to 28% (P<.01) in all muscle groups tested in the involved hip. The uninvolved hip of 22 subjects with unilateral CHJP demonstrated weakness of 18% and 16% (P<.05) in the external rotators (0°) and abductors, respectively, when compared to the corresponding limb of the matched controls. The results of the present study demonstrate that persons with CHJP have weakness in the hip rotator and hip abductor muscles. Weakness also was found in the uninvolved hip of persons with CHJP.

3-D Inverse Dynamics Analysis of the Effect of Maximum Muscle Force Capacities on a Musculoskeletal System

It is known that muscle strength of human body can alter or deteriorate as aging. In this study, we present an inverse dynamics simulation to investigate the effect of muscle strength on performing the daily activities. A 3D musculoskeletal model developed in this study includes several segments of whole body, long and short muscles, ligaments and disc stiffness. Five daily activities such as standing, flexion, finger tip to floor, standing lift close and lifting flexed were simulated with varying the maximum muscle force capacities (MFC) of each muscle fascicles from 30 to <TEX>$90N/cm^2$</TEX> with an increment of <TEX>$30N/cm^2$</TEX>. In the result, no solution can be obtained for finger tip to floor and lifting flexed with <TEX>$30N/cm^2$</TEX>. Even though the solution was available for standing lift close activity in case of <TEX>$30N/cm^2$</TEX> capacity, many of muscle fascicles hit the upper bound of muscle strength which means that it is not physiologically possible to perform the acvities in reality. For lifing flexed, even the case of <TEX>$60N/cm^2$</TEX> capaciy, represents the moderate healthy people, was not able to find the solutions, showing that 18 muscles among 258 muscle fascicles reached 100% of muscle capacity. The estimated results imply that people who have low muscle strength such as elders or rehabilitation patients were required higher muscle work to perform and maintain the same daily activities than healthy one.

THU0221 Pain Predicts Relatively Low Leg Muscle Mass in Knee Osteoarthritis

BackgroundLeg muscle mass is related to development and progression of knee OA, and some studies suggested low leg muscle mass quantified by cross-sectional images of CT or MRI was related...

Sensorimotor function in preschool-aged children with expressive language disorder

The aim of the study was to evaluate functional motor performance and haptic object recognition in 5-year-old children with mild expressive language disorder (ELD) in comparison with age- and gender-matched healthy children. The subjects were classified by speech-language pathologist using The Reynell Developmental Language Scales III and Boehm Test of Basic Concepts: Preschool as children with mild ELD (n=29, incl. 23 boys and 6 girls) and children with typical language development as controls (n=29, incl. 23 boys and 6 girls). The children were examined for manual dexterity, ball skills, static and dynamic balance by Movement-ABC, haptic object recognition (HOR), hand-grip strength (HGS) and vertical jumping performance. Children with mild ELD demonstrated significantly higher scores (i.e., inferior performance) in all subtests of M-ABC (all p values <0.05), in haptic object recognition (p<0.01) and vertical jumping height (p<0.05) compared to controls. However, no statistically significant differences (p>0.05) emerged from HGS. Boys with mild ELD demonstrated higher results in impairment score (p<0.001), ball skills (p<0.01) and balance (p<0.01) of M-ABC, as well as in HOR (p<0.05). Girls with mild ELD showed higher impairment score (p<0.05) with lower percentile (p<0.05) in M-ABC, indicating inferior motor performance, and lower HGS for the non-dominant hand (p<0.05). Seven out of 29 (24.1%) children with mild ELD had definite or borderline motor difficulties, while only one child in control group (3.4%) demonstrated borderline motor difficulties. Children with mild expressive language disorder do not perform as well as controls in tests of functional motor skills, but their results in tests demanding maximal muscle force generation are in level with typically developing children. Boys and girls with mild ELD demonstrated higher impairment scores in M-ABC, indicating the need to follow their overall development more closely.

In vivo deformation of articular cartilage during electrically stimulated contraction

Purpose: In vivo movement of bones comprising synovial joints has been evaluated in various ways and has been calculated theoretically to understand joint biomechanics. In order to assess joint loading and bone movements accurately, the deformation behavior of articular cartilage has been investigated in confined and unconfined compression experiments and indentation tests (references), but to date there exist no data on dynamic in vivo deformation of articular cartilage in intact joints loaded through controlled muscular contraction. The objective of this study was to measure articular cartilage deformations as a function of load in an intact joint of live animals. Methods: In order to achieve the purpose of this study, we developed a novel in vivo testing system that allows for controlled loading of mouse knees through muscular contractions and quantification of the associated, cartilage and chondrocyte deformations. Mice were fixed in a custom-built jig onto the stage of a dual photon microscope. Controlled forces of the knee extensor muscles were produced through direct muscle stimulation using indwelling fine wire electrodes and a Grass (S8800) stimulator. The medial meniscus was excised to provide a direct view of the medial tibio-femoral joint (Figure 1). Imaging of articular cartilage deformation across the entire medial compartment of the knees was performed using a Zeiss 40×0.95 NA water-immersion objective coupled with a Coherent Chameleon IR laser tuned at 780 nm for two-photon excitation. Results: Increases in muscular loading of the knee caused an increase in articular cartilage deformation (Figure 2). Fifty and 80% of the maximal muscular forces produced average peak articular cartilage strains for an 8s contraction of 10 ± 1% to 19 ± 2% respectively (Figure 2). The average overall cartilage thickness was 32 ± 2 μm on the femoral condyles. For slow increasing forces (Figure 3a), the tibio-femoral joint space initially narrowed and reached zero (i.e., the two cartilage surfaces started to touch) when muscle forces reached approximately 40% of maximal isometric values (Figure 3b). Following cartilage contact, cartilage thickness decreased in an approximately exponential manner and reached the deformation peak approximately 5s after initial force application (Figure 3c). Cartilage tissue recovered to its original shape within approximately 30s following force removal (Figure 3c). Discussions And Conclusions: The results of this study suggest that tibio-femoral contact between the articulating surfaces is only achieved with relatively high muscular forces (about 40% of maximal). This may be an artifact of the current setup where the medial meniscus was removed, and physical contact between the two articulating surfaces may occur earlier (i.e., at lower forces) if the meniscus had been left intact. This will need to be investigated further. However, the finding seems to suggest, that at least in the presence of medial meniscectomy, high forces are required to obtain physical cartilage to cartilage contact in the medial tibio-femoral compartment of the mouse knee. Another surprising feature of this work was that cartilage behaves highly visco-elastically. Specifically, peak cartilage deformation is reached much after peak muscle forces have been reached. The delay of about 3s from peak force to peak cartilage deformation suggests that in a normal cyclic movement, such as walking (loading time approximately :800ms) peak steady-state deformation corresponding to the applied force is never reached. Similarly, full cartilage thickness recovery following load removal takes approximately 20s, suggesting that deformation recovery within cyclic movements such as walking, with an unloading time of about 1s, may be neglected. Finally, peak cartilage deformation under the present conditions seems to be maximal at muscle forces of about 70% of the maximal isometric force with further deformations with higher forces not detected by our system. This begs the question of stiffness changes in cartilage with increasing loads and the mechanisms underlying extreme deformation of cartilage under very high joint loading conditions.Figure 2Articular cartilage surface do not touch below approximately 40% of maximal muscle force, then cartilage strain increases exponentially between about 40 – 70% of the maximal force, and remains almost constant beyond about 70 – 80% of maximal force (n = 6).View Large Image Figure ViewerDownload Hi-res image Download (PPT)Figure 3(a) Normalized (relative to maximum = 100%) knee extensor forces as a function of time. Muscles were stimulated for 8 seconds at a voltage and frequency producing approximately 60% and 35% of the maximal isometric force. (b) Medial tibio-femorol joint space as a function of time. Joint space decreased as muscular force increased and reached zero when force reached approximately 40% of maximum. (c) In vivo femoral cartilage thickness changes during loading with 60% of muscular force. No sign of cartilage deformation was noticed at 35% maximal force.View Large Image Figure ViewerDownload Hi-res image Download (PPT)

An experimental study to determine and correlate choline acetyltransferase assay with functional muscle testing after nerve injury

OBJECT Choline acetyltransferase (ChAT) is an enzyme synthesized within the body of a motor neuron whose role is to form the neurotransmitter acetylcholine. Quantification of ChAT levels in motor or mixed nerves has been proposed to provide information regarding the viability of a proximal nerve stump for motor neurotization following brachial plexus injury. To do so requires information regarding normal ChAT levels and those in injured nerves, as well as the correlation of ChAT level determined at surgery with eventual motor recovery. The purpose of this study was to determine ChAT activity in the normal and injured sciatic/peroneal nerve in a rat model, evaluate the correlation between ChAT and motor recovery, find the relationship between ChAT activity and isometric muscle force, and elucidate the parallel between ChAT activity and acetylcholinesterase (AChE) activity. METHODS Sixty animals were divided into 3 groups. The sciatic nerves in Group 1 were transected without repair. Nerves in Group 2 were transected and repaired. Nerves in Group 3 sustained a crush injury followed by transection and reconstruction. All animals were allowed 12 weeks of recovery followed by evaluation of ChAT levels in the peroneal nerve, correlated with measures of maximal isometric tibialis anterior muscle force and muscle weight (the operated side normalized to the control side). Karnovsky AChE staining of peroneal nerve segments was also compared with radiochemical assay of ChAT activity in the same nerve. RESULTS A significant difference in the tibialis anterior isometric tetanic force and the tibialis anterior muscle weight index (TAMI) was noted between Group 1 and Groups 2 and 3 (p < 0.0001); no significant difference was found comparing Group 2 with Group 3. The correlation between the force measurement and the TAMI was 0.382. Both AChE measurement and ChAT activity demonstrated significantly fewer fibers in the operated nerve compared with the contralateral nerve. Intergroup variability could also be illustrated using these tests. The correlation coefficient between the isometric tetanic force measurement and the ChAT analysis in Groups 1 and 2 was 0.468. The correlation for the AChE staining and the isometric tetanic force measurement was 0.111. The correlation between the TAMI and the ChAT levels was 0.773. The correlation between the TAMI and the AChE-stained fibers was 0.640. Correlating AChE staining to the ChAT analysis produced a correlation of 0.712. CONCLUSIONS The great variability in all groups and weak correlations to the functional muscle assessments and the ChAT radiochemical assay made this technique an unreliable method of determining motor nerve viability.

Reliability assesment of the tests for maximal isometric muscle force and rate of force development of m. quadriceps femoris in opened and closed kinetic chain depending on knee angles

The purpose of this study was to assess the reliability of tests for the assessment of maximal isometric muscle force (F(max)) and the explosive force (viewed through the rate of force development - RFD(max)). Tests were carried out for muscle m. quadriceps femoris, in the open (OKL) and closed (CKC) kinetic chain under 6 different angles in the knee joint, ranging from 80˚-130˚ (with changes of at 10˚, 180˚ represents the fully extended leg). The study tested 'intra-assay'(between 3 attempts within a testing session)' and inter-test' (test-retest) reliability presented through ICC coefficients. In addition, differences between the results achieved in different angles for the same test, for Fmax and RFDmax were examined by ANOVA with repeated measures. Nine students of FSPE (23.5±1:38 years) performed each three isometric contractions, by taking tasks of: seated leg extension (OKC) and seated leg press (CKC). Tests were carried out in chronological order: OKC1-OKC2, CKC1-CKC2 (Firstly the OKC test, two times in a span of 72 hours, and then the CKC on the same principle). The results suggest that the CKC is generally more reliable test, but that the reliability of maximal isometric and explosive force varies depending on the selection of the task / test, articulated joint angle and selecting variables for monitoring ('inter' vs 'intra' and 'avg' vs 'max'). The differences in the results of monitored variables among the articular angles indicate that in the OKC m. quadriceps femoris behaves in accordance with F-L (force-length) relation, while the mechanical conditions of the bone-joint levers in the CKC are crucial for the expression of muscle force.