Psoas force recruitment in full-body musculoskeletal movement simulations is restored with a geometrically informed cost function weighting.

Simulations of musculoskeletal models are useful for estimating internal muscle and joint forces. However, predicted forces rely on optimization and modeling formulations. Geometric detail is important to predict muscle forces, and greater geometric complexity is required for muscles that have broad attachments or span many joints, as in the torso. However, the extent to which optimized muscle force recruitment is sensitive to these geometry choices is unclear. We developed level, uphill and downhill sloped walking simulations using a standard (uniformly weighted, "fatigue-like") cost function with lower limb and full-body musculoskeletal models to evaluate hip muscle recruitment with different geometric representations of the psoas muscle under walking conditions with varying hip moment demands. We also tested a novel cost function formulation where muscle activations were weighted according to the modeled geometric detail in the full-body model. Total psoas force was less and iliacus, rectus femoris, and other hip flexors' force was greater when psoas was modeled with greater geometric detail compared to other hip muscles for all slopes. The proposed weighting scheme restored hip muscle force recruitment without sacrificing detailed psoas geometry. In addition, we found that lumbar, but not hip, joint contact forces were influenced by psoas force recruitment. Our results demonstrate that static optimization dependent simulations using models comprised of muscles with different amounts of geometric detail bias force recruitment toward muscles with less geometric detail. Muscle activation weighting that accounts for differences in geometric complexity across muscles corrects for this recruitment bias.

Oscillatory work and the step that generates force in single myofibrils from rabbit psoas.

The elementary molecular step that generates force by cross-bridges (CBs) in active muscles has been under intense investigation in the field of muscle biophysics. It is known that an increase in the phosphate (Pi) concentration diminishes isometric force in active fibers, indicating a tight coupling between the force generation step and the Pi release step. The question asked here is whether the force generation occurs before Pi release or after release. We investigated the effect of Pi on oscillatory work production in single myofibrils and found that Pi-attached state(s) to CBs is essential for its production. Oscillatory work is the mechanism that allows an insect to fly by beating its wings, and it also has been observed in skeletal and cardiac muscle fibers, implying that it is an essential feature of all striated muscle types. With our studies, oscillatory work disappears in the absence of Pi in experiments using myofibrils. This suggests that force is generated during a transition between steps of oscillatory work production, and that the states involved in force production must have Pi attached. With sinusoidal analysis, we obtained the kinetic constants around the Pi release steps, established a CB scheme, and evaluated force generated (and supported) by each CB state. Our results demonstrate that force is generated before Pi is released, and the same force is maintained after Pi is released. Stretch activation and/or delayed tension can also be explained with this CB scheme and forms the basis of force generation and oscillatory work production.

Stretch-shortening cycles protect against the age-related loss of power generation in rat single muscle fibres.

Aging is associated with impaired strength and power during isometric and shortening contractions, however, during lengthening (i.e., eccentric) contractions, strength is maintained. During daily movements, muscles undergo stretch-shortening cycles (SSCs). It is unclear whether the age-related maintenance of eccentric strength offsets age-related impairments in power generation during SSCs owing to the utilization of elastic energy or other cross-bridge based mechanisms. Here we investigated how aging influences SSC performance at the single muscle fibre level and whether performing active lengthening prior to shortening protects against age-related impairments in power generation. Single muscle fibres from the psoas major of young (∼8 months; n = 31 fibres) and old (∼32 months; n = 41 fibres) male F344BN rats were dissected and chemically permeabilized. Fibres were mounted between a force transducer and length controller and maximally activated (pCa 4.5). For SSCs, fibres were lengthened from average sarcomere lengths of 2.5 to 3.0 µm and immediately shortened back to 2.5 µm at both fast and slow (0.15 and 0.60 Lo/s) lengthening and shortening speeds. The magnitude of the SSC effect was calculated by comparing work and power during shortening to an active shortening contraction not preceded by active lengthening. Absolute isometric force was ∼37 % lower in old compared to young rat single muscle fibres, however, when normalized to cross-sectional area (CSA), there was no longer a significant difference in isometric force between age groups, meanwhile there was an ∼50 % reduction in absolute power in old as compared with young. We demonstrated that SSCs significantly increased power production (75-110 %) in both young and old fibres when shortening occurred at a fast speed and provided protection against power-loss with aging. Therefore, in older adults during everyday movements, power is likely 'protected' in part due to the stretch-shortening cycle as compared with isolated shortening contractions.

Reliability of Ultrasound Shear Wave Elastography for Evaluating Psoas Major and Quadratus Lumborum Stiffness: Gender and Physical Activity Effects.

OBJECTIVE: We aimed to assess the reliability of quantifying psoas major (PM) and quadratus lumborum (QL) stiffness with ultrasound shear wave elastography (SWE), and to explore the effects of gender and physical activity on muscle stiffness. METHODS: Fifty-two healthy participants (18-32 y) were recruited. To determine reliability, 29 of them underwent repeated SWE measurements of PM and QL stiffness by an operator on the same day. The intra-class correlation coefficients (ICC3,1), standard error of measurement (SEM) and minimal detectable change with 95% confidence interval (MDC95) were calculated. The rest participants underwent a single measurement. Two-way MANCOVA was conducted for the effects of gender and physical activity on muscle stiffness. RESULTS: The observed reliability for PM (ICC3,1 = 0.89-0.92) and QL (ICC3,1 = 0.79-0.82) were good-to-excellent and good, respectively. The SEM (kPa) was 0.79-1.03 and 1.23-1.28, and the MDC95 (kPa) was 2.20-2.85 and 3.41-3.56 for PM and QL, respectively. After BMI adjustment, both gender (PM: F = 10.15, p = 0.003; QL: F = 18.07, p < 0.001) and activity level (PM: F = 5.90, p = 0.005; QL: F = 6.33, p = 0.004) influenced muscle stiffness. The female and inactive groups exhibited higher stiffness in both muscles. CONCLUSION: SWE is reliable for quantifying the stiffness of PM and QL. Female and physical inactivity may elevate PM and QL stiffness, underscoring the importance of accounting for these factors in muscle stiffness investigations. Larger prospective studies are needed to further elucidate their effects.

Activity of deep trunk muscles for postural control to predictable and unpredictable sagittal plane perturbations: Electromyographic analysis.

BACKGROUND: The activity of deep trunk muscles (psoas major; PM, quadratus lumborum; QL, transverse abdominis; TrA, and lumbar multifidus; MF) in response to external perturbation is not clearly known. OBJECTIVE: This study aimed to record the onset and amount of activity of the deep trunk muscles during sagittal plane perturbations. METHODS: Fourteen healthy males participated in this study. The activity of the right deep trunk muscles was recorded using wire electrodes. In standing, the participants performed three tasks: a pendulum impacted from anterior with predictable and unpredictable and posterior with unpredictable. RESULTS: In predictable anterior perturbation, the TrA and PM demonstrated feedforward activation, while all deep trunk muscles demonstrated feedback activation in unpredictable anterior and posterior perturbations. In the anticipatory postural adjustment phase, the activity of the TrA was large in predictable anterior perturbation, while that of all deep trunk muscles was slight in other perturbations. In the compensatory postural adjustment phase, the activity of the PM, QL, and TrA in unpredictable anterior perturbation and those of the PM, QL, and MF in unpredictable posterior perturbation were large. CONCLUSIONS: These results showed that the onset and magnitude of deep trunk muscle activity changed depending on both predictable or unpredictable perturbation and the direction of perturbation.

Passive force enhancement is not abolished by shortening of single rabbit psoas fibres.

Passive force enhancement is defined as the increase in steady-state passive force following deactivation of an actively stretched muscle compared to the corresponding passive force following passive stretching of the muscle. Passive force enhancement has been associated with contributing to the residual force enhancement property, providing stability to sarcomeres, and preventing sarcomeres from over-stretching during eccentric muscle action. Despite its functional importance, the molecular mechanisms underlying passive force enhancement remain unknown. Specifically, it remains unknown how passive force enhancement develops and how it is abolished. Incidental observations on cat soleus muscles led to the speculation that passive force enhancement is abolished when the actively stretched muscle is deactivated and then passively shortened to its pre-stretched length. Here, we tested this hypothesis using skinned fibres from rabbit psoas and rejected it. Rather, we found that passive force enhancement increased following shortening of the fibres to their pre-stretched length (2.4 µm), and furthermore, that the passive force enhancement increased by 70-106% when the shortening and subsequent stretch to the original length (3.6 µm) increased in duration (200 ms, 6 s, and 14 s). These results indicate that passive force enhancement increases during a shortening-stretch cycle, and that this increase is time-dependent. We propose that this increase in passive force enhancement is caused by titin; specifically, with a refolding of titin's immunoglobulin domains that were unfolded during the active fibre stretching that produced the residual and passive force enhancement. Molecular level experiments are required to test this proposal.

Effect of active shortening and stretching on the rate of force re-development in rabbit psoas muscle fibres.

The steady-state isometric force produced by skeletal muscle after active shortening and stretching is depressed and enhanced, respectively, compared with purely isometric force produced at corresponding final lengths and at the same level of activation. One hypothesis proposed to account for these force depression (FD) and force enhancement (FE) properties is a change in cross-bridge cycling kinetics. The rate of cross-bridge attachment (f) and/or cross-bridge detachment (g) may be altered following active shortening and active stretching, leading to FD and FE, respectively. Experiments elucidating cross-bridge kinetics in actively shortened and stretched muscle preparations and their corresponding purely isometric contractions have yet to be performed. The aim of this study was to investigate cross-bridge cycling kinetics of muscle fibres at steady-state following active shortening and stretching. This was done by determining muscle fibre stiffness and rate of active force redevelopment following a quick release-re-stretch protocol (kTR). Applying these measures to equations previously used in the literature for a two-state cross-bridge cycling model (attached/detached cross-bridges) allowed us to determine apparent f and g, the proportion of attached cross-bridges, and the force produced per cross-bridge. kTR, apparent f and g, the proportion of attached cross-bridges and the force produced per cross-bridge were significantly decreased following active shortening compared with corresponding purely isometric contractions, indicating a change in cross-bridge cycling kinetics. Additionally, we showed no change in cross-bridge cycling kinetics following active stretch compared with corresponding purely isometric contractions. These findings suggest that FD is associated with changes in cross-bridge kinetics, whereas FE is not.

Time-course of physical properties of the psoas major muscle after exercise as assessed by MR elastography.

This study aimed to analyze the time-course of the physical properties of the psoas major muscle (PM) before and after exercise using magnetic resonance elastography (MRE). Muscle stiffness is one of the important properties associated with muscle function. However, there was no research on the stiffness of the PM after exercise. In this study, we investigated time-course changes of the shear modulus of the PM after exercise. Furthermore, T2 values and apparent diffusion coefficient (ADC), as the additional information associated with muscular physical properties, were also measured simultaneously. Healthy young male volunteers were recruited in this study (n = 9) and they were required to perform a hand-to-knee isometric and unilateral exercise (left side). At each time-point before and after exercise, a set of 3 types of MR scans to measure multiple physical properties of the PM [shear modulus (MRE), T2 values, and ADC] were repeatedly taken. On day 1, a single set MR scan was taken before exercise (pre-exercise MR scan), and 6 sets MR scans were taken (5.5 to 38.0 min after exercise). After about 10-min rest (46.0 to 56.0 min after exercise), 4 sets MR scans were taken (57.5 to 77.0 min after exercise). About 10-min rest was taken again (85.0-95.0 min after exercise), 4 sets MR scans were taken (96.5 to 116.0 min after exercise). On days 2 and 7, a single set MR scan (MRE, T2 value, and ADC) was taken on each experimental day. The data were analyzed as relative changes (%) of the given parameters to the pre-exercise values. The results indicated significant decreases in PM shear modulus up to about 30 min after exercise. Then, it gradually increased and showed significant increases at about 100 min after exercise compared to that before exercise. T2 values and ADC showed significant increases up to about 65 min after exercise compared to those before exercise, and then returned to the pre-exercise values. On days 2 and 7, all values showed no significant changes compared to the pre-exercise values. This study is the first to report the time-course of the physical properties of the PM after exercise.

Revision of hip flexor anatomy and function in modern humans, and implications for the evolution of hominin bipedalism.

Hip flexor musculature was instrumental in the evolution of hominin bipedal gait and in endurance running for hunting in the genus Homo. The iliacus and psoas major muscles were historically considered to have separate tendons with different insertions on the lesser trochanter. However, in the early 20th century, it became "common knowledge" that the two muscles insert together on the lesser trochanter as the "iliopsoas" tendon. We revisited the findings of early anatomists and tested the more recent paradigm of a common "iliopsoas" tendon based on dissections of hips and their associated musculature (n = 17). We rediscovered that the tendon of the psoas muscle inserts only into a crest running from the superior to anterior aspect of the lesser trochanter, separate from the iliacus. The iliacus inserts fleshly into the anterior portion of the lesser trochanter and into an inferior crest extending from it. We developed 3D multibody dynamics biomechanical models for: (a) the conjoint "iliopsoas" tendon hypothesis and (b) the separate insertion hypothesis. We show that the conjoint model underestimates the iliacus' capacity to generate hip flexion relative to the separate insertion model. Further work reevaluating the primate lower limb (including human) through dissection, needs to be performed to develop those datasets for reconstructing anatomy in fossil hominins using the extant phylogenetic bracket approach, which is frequently used for tetrapods clades outside of paleoanthropology.

Sarcopenia increases the risk of post-operative recurrence in patients with non-small cell lung cancer.

BACKGROUND: Sarcopenia is among the most prevalent and serious cancer-related symptom, and is strongly correlated with a poor prognosis. Moreover, it reportedly predicts poor prognosis after surgery in patients with lung cancer. However, it is unclear whether sarcopenia directly affects post-operative recurrence. The purpose of this study was to evaluate whether sarcopenia can be a risk indicator for post-operative recurrence, and whether it suppresses anti-tumor immunity, in a cohort of patients with resected non-small cell lung cancer. METHODS: This study retrospectively reviewed the data of 256 consecutive patients who underwent curative lobectomy and lymph node dissection for non-small cell lung cancer at our institution. The psoas muscle mass index was calculated as the total psoas muscle area at the third lumbar vertebral level/height2 (cm2/m2). Sarcopenia was defined by a psoas muscle mass index of under 5.03 cm2/m2 and 3.17 cm2/m2 in male and female patients, respectively. Post-operative prognosis and cumulative incidence of recurrence rates were calculated. RESULTS: The 5-year overall survival and disease-free survival rates post-surgery were 59.5% and 38.6%, respectively, in patients with sarcopenia versus 81.1% and 72.1%, respectively, in patients without sarcopenia (p < 0.001). The 5-year cumulative incidence of recurrence rate in patients with sarcopenia was significantly higher than those without sarcopenia (49.9% versus 22.4%, respectively) in every pathological stage. Pathological stages II and III (hazard ratio, 3.36; p = 0.004), histological type (hazard ratio, 2.31; p = 0.025), and sarcopenia (hazard ratio, 2.52; p = 0.001) were independent risk factors for post-operative recurrence according to multivariate analysis. CONCLUSION: Sarcopenia is a risk indicator for post-operative recurrence in patients with non-small cell lung cancer.

Muscle size of individual hip extensors in sprint runners: Its relation to spatiotemporal variables and sprint velocity during maximal velocity sprinting.

Hip extensor muscle size is related to sprint running performance. However, the mechanisms underlying this relationship remain unclear. To gain insights into this issue, the present study examined the relationships between the individual hip extensor sizes, spatiotemporal variables (step frequency and length, and their determinants), and sprint velocity during maximal velocity sprinting. Magnetic resonance images of the hip and right thigh were obtained from 26 male sprinters to determine the volumes of the gluteus maximus, individual hamstrings and adductors, and gracilis. Muscle volumes were normalized to their respective body mass and recorded as relative muscle volumes. The sprinters performed a 100-m sprint with their maximal effort. Their sprint motions were recorded using cameras to calculate the mean sprint velocity and the spatiotemporal variables at 50-60 m interval. The sprint velocity was significantly correlated with the relative volume of the semitendinosus (r = 0.497, P = 0.010), but not with the volumes of the other examined muscles. The relative volume of semitendinosus significantly correlated with the stance distance (r = 0.414, P = 0.036) and the stance distance adjusted by the stance time (r = 0.490, P = 0.011). Moreover, there were significant correlations between the stance distance and step length (r = 0.592, P = 0.001), and between the step length and sprint velocity (r = 0.509, P = 0.008). These results suggest that the semitendinosus contributes to attaining long stance distance and thereby high sprint velocity during maximal velocity sprinting.

Low muscle mass assessed by psoas muscle area is associated with clinical adverse events in elderly patients with heart failure.

BACKGROUND: Acute decompensated heart failure (ADHF) is a growing healthcare burden with increasing prevalence and comorbidities due to progressive aging society. Accumulating evidence suggest that low skeletal muscle mass has a negative impact on clinical outcome in elderly adult population. We sought to determine the significance of psoas muscle area as a novel index of low skeletal muscle mass in elderly patients with ADHF. METHODS: In this single-center retrospective observational study, we reviewed consecutive 865 elderly participants (65 years or older) who were hospitalized for ADHF and 392 were available for analysis (79 years [74-85], 56% male). Cross-sectional areas of psoas muscle at the level of fourth lumbar vertebra were measured by computed tomography and normalized by the square of height to calculate psoas muscle index (PMI, cm2/m2). RESULTS: Dividing the patients by the gender-specific quartile value (2.47 cm2/m2 for male and 1.68 cm2/m2 for female), we defined low PMI as the lowest gender-based quartile of PMI. Multiple linear regression analysis revealed female sex, body mass index (BMI), and E/e', but not left ventricular ejection fraction, were independently associated with PMI. Kaplan-Meier analysis showed low PMI was associated with higher rate of composite endpoint of all-cause death and ADHF re-hospitalization (P = 0.033). Cox proportional hazard model analysis identified low PMI, but not BMI, was an independent predictor of the composite endpoint (Hazard ratio: 1.52 [1.06-2.16], P = 0.024). CONCLUSIONS: PMI predicted future clinical adverse events in elderly patients with ADHF. Further studies are needed to assess whether low skeletal muscle mass can be a potential therapeutic target to improve the outcome of ADHF.

Does the L5 spinal nerve move? Anatomical evaluation with implications for postoperative L5 nerve palsy.

PURPOSE: While palsy of the L5 nerve root due to stretch injury is a known complication in complex lumbosacral spine surgery, the underlying pathophysiology remains unclear. The goal of this cadaveric study was to quantify movement of the L5 nerve root during flexion/extension of the hip and lower lumbar spine. METHODS: Five fresh-frozen human cadavers were dissected on both sides to expose the lumbar vertebral bodies and the L5 nerve roots. Movement of the L5 nerve root was tested during flexion and extension of the hip and lower lumbar spine. Four steps were undertaken to characterize these movements: (1) removal of the bilateral psoas muscles, (2) removal of the lumbar vertebral bodies including the transforaminal ligaments from L3 to L5, (3) opening and removing the dura mater laterally to visualize the rootlets, and (4) removal of remaining soft tissue surrounding the L5 nerve root. Two metal bars were inserted into the sacral body at the level of S1 as fixed landmarks. The tips of these bars were connected to make a line for the ruler that was used to measure movement of the L5 nerve roots. Movement was regarded as measurable when there was an L5 nerve excursion of at least 1 mm. RESULTS: The mean age at death was 86.6 years (range 68-89 years). None of the four steps revealed any measurable movement after flexion/extension of the hip and lower lumbar spine on either side (< 1 mm). Flexion of the hip and lower lumbar spine revealed lax L5 nerve roots. Extension of the hip and lower lumbar spine showed taut ones. CONCLUSION: Significant movement or displacement of the L5 nerve root could not be quantified in this study. No mechanical cause for L5 nerve palsy could be identified so the etiology of the condition remains unclear.

The effect of high, medium and low mobilization forces applied during a hip long-axis distraction mobilization on the strain on the inferior ilio-femoral ligament and psoas muscle: A cadaveric study.

BACKGROUND: Several studies have suggested that the changes in elasticity of the joint capsule and surrounding muscles during a hip long-axis distraction mobilization (LADM) could explain the pain-relieving and mobility-improving effects of the technique. OBJECTIVE: To compare the strain on the inferior ilio-femoral ligament and psoas muscle when applying three different magnitudes of force during LADM. DESIGN: Repeated measures controlled laboratory cadaveric study. METHODS: Eleven hip joints were mobilized from six fresh-frozen cadavers (mean age, 73.4 ± 5.7 years). Three magnitudes of force (low, medium and high) were applied during a hip LADM in open-packed position according to grades of joint mobilization. Strain on the inferior ilio-femoral ligament and psoas muscle were measured with strain gauges. The magnitude of the force applied during LADM was recorded. RESULTS: Strain on the inferior ilio-femoral ligament during a high-force LADM was significantly higher than strain on the inferior ilio-femoral ligament during low (p < 0.001) and medium-force LADM (p < 0.001). The strain on the inferior ilio-femoral ligament during a medium-force LADM was significantly higher than during a low-force LADM (p = 0.004). No changes in strain on psoas muscle were observed. The magnitude of force applied during LADM showed a significant progressive increase from low to high-force LADM. CONCLUSION: The different magnitudes of forces applied during LADM produce different strains on the inferior ilio-femoral ligament but not on the psoas muscle. The strain on the inferior ilio-femoral ligament during LADM depends on the magnitude of the mobilization force.

Fibrous configuration of the fascia iliaca compartment: An epoxy sheet plastination and confocal microscopy study.

BACKGROUND AND OBJECTIVES: The underlying anatomical mechanism of the ultrasound-guided fascia iliaca compartment (FIC) block for anaesthesia and analgesia in the lower limb has not been illuminated and numerous variations were attempted to achieve an optimal needle placement. This study aimed to define the fibrous configuration of the FIC. METHODS: A total of 46 adult cadavers were studied using dissection, latex injection, epoxy sheet plastination and confocal microscopy. RESULTS: (1) The fascia iliaca originated from the peripheral fascicular aponeurotic sheet of the iliopsoas. (2) The FIC was a funnel-shaped adipose space between the fascia iliaca and the epimysium of the iliopsoas, had a superior and an inferior opening and contained the femoral and lateral femoral cutaneous nerves but not obturator nerve. (3) The estimated volume of the FIC in the cadavers was about 23 mls, of which about one third was below the level of the anterior superior iliac spine. CONCLUSIONS: This study revealed that the fascia iliaca was aponeurotic and may be less permeable for the local anesthetics. CONCLUSIONS: The FIC contained only the femoral and lateral femoral cutaneous nerves and communicated with the extraperitoneal space and femoral triangle adipose space via its superior and inferior opening, respectively.

The load dependence and the force-velocity relation in intact myosin filaments from skeletal and smooth muscles.

In the present study we evaluated the load dependence of force produced by isolated muscle myosin filaments interacting with fluorescently labeled actin filaments, using for the first time whole native myosin filaments. We used a newly developed approach that allowed the use of physiological levels of ATP. Single filaments composed of either skeletal or smooth muscle myosin and single filaments of actin were attached between pairs of nano-fabricated cantilevers of known stiffness. The filaments were brought into contact to produce force, which caused sliding of the actin filaments over the myosin filaments. We applied load to the system by either pushing or pulling the filaments during interactions and observed that increasing the load increased the force produced by myosin and decreasing the load decreased the force. We also performed additional experiments in which we clamped the filaments at predetermined levels of force, which caused the filaments to slide to adjust the different loads, allowing us to measure the velocity of length changes to construct a force-velocity relation. Force values were in the range observed previously with myosin filaments and molecules. The force-velocity curves for skeletal and smooth muscle myosins resembled the relations observed for muscle fibers. The technique can be used to investigate many issues of interest and debate in the field of muscle biophysics.

Cross-sectional areas of rectus abdominis and psoas muscles reduces following surgery in rectal cancer patients.

PURPOSE: To evaluate the trophic changes in rectus abdominis and psoas muscles in patients who underwent open or laparoscopic rectum resection for rectal cancer. METHODS: We retrospectively analyzed preoperative staging computerized tomographies (CT) and postoperative first oncological follow-up CTs of the patients who underwent low anterior resection (LAR) for rectal cancer from 2010 through 2015. We measured cross-sectional area of left and right rectus abdominis muscles from two levels (above and below umbilicus) where they are widest and psoas muscle at mid-level of the fourth lumbar vertebral body in axial CT images and compared preoperative and postoperative measurements. We investigated the effects of age, sex, administration of preoperative chemoradiotherapy (CRT), type of surgery (open or laparoscopic), or construction of a diverting ileostomy on cross-sectional muscle area changes. RESULTS: After applying inclusion and exclusion criteria 60 patients found to be eligible for the study. Muscle areas of all measurement sites were reduced postoperatively compared to paired preoperative values. There was no significant effect of age, sex, administration of preoperative CRT, type of surgery (open or laparoscopic), or construction of a diverting ileostomy to muscle cross-sectional area reductions. CONCLUSION: Cross-sectional areas of the rectus abdominis and the psoas muscles of rectal cancer patients reduces following rectum resection which indicates atrophy of these muscles. Clinicians should be aware of this problem and focus on prevention of muscle atrophy during the treatment of rectal cancer patients.

On sarcomere length stability during isometric contractions before and after active stretching.

Sarcomere length (SL) instability and SL non-uniformity have been used to explain fundamental properties of skeletal muscles, such as creep, force depression following active muscle shortening and residual force enhancement following active stretching of muscles. Regarding residual force enhancement, it has been argued that active muscle stretching causes SL instability, thereby increasing SL non-uniformity. However, we recently showed that SL non-uniformity is not increased by active muscle stretching, but it remains unclear if SL stability is affected by active stretching. Here, we used single myofibrils of rabbit psoas muscle and measured SL non-uniformity and SL instability during isometric contractions and for isometric contractions following active stretching at average SLs corresponding to the descending limb of the force-length relationship. We defined isometric contractions as contractions during which mean SL remained constant. SL instability was quantified by the rate of change of individual SLs over the course of steady-state isometric force and SL non-uniformity was defined as deviations of SLs from the mean SL at an instant of time. We found that whereas the mean SL remained constant during isometric contraction, by definition, individual SLs did not. SLs were more stable in the force-enhanced, isometric state following active stretching compared with the isometric reference state. We also found that SL instability was not correlated with the rate of change of SL non-uniformity. Also, SL non-uniformity was not different in the isometric and the post-stretch isometric contractions. We conclude that since SL is more stable but similarly non-uniform in the force-enhanced compared with the corresponding isometric reference contraction, it appears unlikely that either SL instability or SL non-uniformity contribute to the residual force enhancement property of skeletal muscle.

Altered Body Composition of Psoas and Thigh Muscles in Relation to Frailty and Severity of Parkinson's Disease.

Background: To investigate the relationship between fat content and the cross-sectional area of psoas and thigh muscles, and clinical severity in patients with Parkinson's disease. Materials and Methods: Twenty-five patients and 20 age- and sex-matched normal controls were recruited. All subjects underwent MRI study to determine the fat content of the bilateral psoas and thigh muscles. Muscle quality was measured by grasp, walking speed, and cross-sectional area. All patients underwent clinical surveys to evaluate disease severity and frailty, and analyses of the correlations between muscle quality and disease severity were performed. Results: Compared with the controls, patients exhibited higher fatty content in the measured muscles. The higher fat infiltration of measured muscles was significantly correlated with increased disease severity and frailty in patients. The fat fraction of the bilateral medial compartment of the thigh was correlated with the Unified Parkinson Disease Rating Scale-I results and the fat fraction of the bilateral anterior compartment of the thigh was correlated with weakness and exhaustion in patients. Conclusions: Decreased quality in psoas and thigh muscles is prominent in Parkinson's disease which is further associated with disease severity and frailty. Awareness of the risk of sarcopenia and associated sequelae might improve patient care and outcomes.

A discrete element model to predict anatomy of the psoas muscle and path of the tendon: Design implications for total hip arthroplasty.

BACKGROUND: The accurate estimation of a muscle's line of action is a fundamental requirement in computational modelling. We present a novel anatomical muscle wrapping technique and demonstrate its clinical use on the evaluation of the Psoas muscle mechanics in hip arthroplasty. METHODS: A volume preserving, spring model to parameterize muscle anatomy changes during motion is presented. Validation was performed by a CT scan of a cadaver model in multiple positions. The predicted psoas musculotendinous path was compared with the actual imaging findings. In a second stage, psoas kinetics were compared between a conventional versus a resurfacing hip arthroplasty during gait. FINDINGS: Anatomy prediction error was found to be 2.12 mm on average (SD 1.34 mm). When applied to psoas mechanics during walking, the muscle was found to wrap predominantly around the femoral head providing a biomechanically efficient and nearly constant moment arm for flexion during the entire gait cycle. However, this advantage was found to be lost in small diameter hip arthroplasty designs resulting in an important mechanical disadvantage. The moment arm for flexion, was on average 36% (SD 0.03%) lower in the small diameter conventional hip arthroplasty as compared to the large diameter head of the hip resurfacing and this difference was highly significant. (p < 0.001). INTERPRETATION: Despite the shortcomings of an "in silico" and cadaveric study, our findings are in accordance with previous clinical and gait studies. Furthermore, the findings are strongly in favour of large diameter implant designs, warranting their further development and optimisation.