Hip Posture Research Articles

Classification of windswept posture in daily life using tri-axial accelerometers.

An asymmetric windswept posture is often seen in children with severe cerebral palsy (CP). However, it is still unclear how long children with CP remain in the windswept posture in daily life. Thus, we developed a triple-accelerometer system for detecting windswept posture. The aim of this study was to assess the validity of a system for classifying various body postures and movements. We assessed the accuracy of our system in nine healthy young adults (age range, 21-23 years). The participants wore acceleration monitors on the sternum and both thighs, then spent 3 min each in eight different positions and three physical activities. Once accuracy was confirmed, we assessed the posture and movements for 24 h in six healthy young adults (age range, 21-23 years) in their home environments. The body postures and activities were correctly detected: the agreement across the subjects were 100% compatible with the subjects' activity logs at least 68% of the time, and at least 96% of the time for recumbent positions. We concluded that the proposed monitoring system is a reliable and valid approach for assessing windswept hip posture in a free-living setting.

Forelimb muscle activation patterns in American alligators: Insights into the evolution of limb posture and powered flight in archosaurs.

The evolution of archosaurs provides an important context for understanding the mechanisms behind major functional transformations in vertebrates, such as shifts from sprawling to erect limb posture and the acquisition of powered flight. While comparative anatomy and ichnology of extinct archosaurs have offered insights into musculoskeletal and gait changes associated with locomotor transitions, reconstructing the evolution of motor control requires data from extant species. However, the scarcity of electromyography (EMG) data from the forelimb, especially of crocodylians, has hindered understanding of neuromuscular evolution in archosaurs. Here, we present EMG data for nine forelimb muscles from American alligators during terrestrial locomotion. Our aim was to investigate the modulation of motor control across different limb postures and examine variations in motor control across phylogeny and locomotor modes. Among the nine muscles examined, m. pectoralis, the largest forelimb muscle and primary shoulder adductor, exhibited significantly smaller mean EMG amplitudes for steps in which the shoulder was more adducted (i.e., upright). This suggests that using a more adducted limb posture helps to reduce forelimb muscle force and work during stance. As larger alligators use a more adducted shoulder and hip posture, the sprawling to erect postural transition that occurred in the Triassic could be either the cause or consequence of the evolution of larger body size in archosaurs. Comparisons of EMG burst phases among tetrapods revealed that a bird and turtle, which have experienced major musculoskeletal transformations, displayed distinctive burst phases in comparison to those from an alligator and lizard. These results support the notion that major shifts in body plan and locomotor modes among sauropsid lineages were associated with significant changes in muscle activation patterns.

Squat and Countermovement Vertical Jump Dynamics Using Knee Dominant or Hip Dominant Strategies.

This study aimed to investigate squat jump and countermovement jump kinetics in the knee dominant and hip dominant postures. Participants included 12 male sports science students. They were instructed to perform a squat jump and a countermovement jump with two squat postures: knee- and hip-dominant postures. The jumping motion and ground reaction force were recorded using a motion capture system and a force plate, respectively. A p-value of 0.05 was considered statistically significant. There was a significant interaction for the maximal knee joint extension torque, with the knee-countermovement jump being more than twice higher than that of other conditions, but not for mechanical work of the knee joint, which was significantly greater in the knee posture than in the hip posture. No significant interactions were found in mechanical work and maximal extension torque of the hip joint, both of which were significantly greater in the hip posture than in the knee posture, and in the countermovement jump than in the squat jump. This study showed that the effects of countermovement and posture were different for joints and that these effects were independent in the hip joint, but interacted in the knee joint. In the knee joint, the posture increased the effect of countermovement on extension torque, but the effect on mechanical work was small. This suggests that countermovement in the knee posture has little effect on the lifting work, but results in a great load on the knee extensors.

Prevalence of Postural Changes During Pregnancy; A Cross-sectional Study

Background: Pregnant women might experience a lot of physiological and anatomical changes, predominantly postural changes in their bodies. They often report low back pain, leg problems, pelvic girdle pain and urinary incontinence. Pain in the pelvis, lower back and neck might be due to alterations in spinal curvature and postural changes during pregnancy. Anatomical changes occur due to an increase in ligamentous laxity and because of the weight of the fetus during pregnancy. Objective: To estimate the prevalence of postural changes during pregnancy. Methods: This cross-sectional study is approved by the ethical committee of the college in which 113 pregnant women aged between 25 to 45 years were included in the study from different hospitals in Lahore Pakistan, after fulfilling the inclusion criteria using non-probability convenient sampling. Every pregnant woman was given a consent form and after signing that they filled out a questionnaire consisting of questions about their pregnancy, prenatal care, medical problems and pains during the trimester. The pain was rated on a visual analog scale and posture was assessed using a posture score sheet. Although pregnant women who had complications like pre-eclampsia, gestational diabetes, history of trauma, neoplasm or surgery were excluded. For baseline characteristics, percentages and frequencies were calculated. A histogram was plotted for the age variable. Results: In this study, 113 pregnant women with a mean age of 26.3±2.89 years were included. About 24.77% of pregnant females scored poor for lower back postural grading while 20.4% of pregnant females scored poor for upper back postural grading. Conclusion: This study concludes that pregnant females are more likely to develop postural changes during pregnancy due to an increase in ligamentous laxity and weight of the fetus during pregnancy. This study also suggests that the head, shoulder, spine, pelvic and hip posture tilt, head posterior position, lumbar lordosis, lumbar angle and pelvic tilt increases, although the changes and magnitudes of these posture variables are not associated with back pain.

The relationship between objectively measured sitting time, posture, and low back pain in sedentary employees during COVID-19.

The purpose of this study was to examine the relationship between objectively measured sitting time, posture, and low back pain (LBP) in adults with full-time (≥ 40h/week) sedentary "desk" jobs. Physical activity (PA) and sedentary behavior (SB) between work environments (home vs. office) were also compared during COVID-19. Participants (N = 53; M age = 41 ± 12years) were full-time employees in sedentary jobs during COVID-19. A survey with demographic, work environment, and LBP questions was completed; Thomas Test assessed poor hip posture. ActivPAL devices were worn for ≥ 4 valid days (≥ 10h/d) to assess waking sitting time (min/d). Binomial logistic regressions examined sitting as a predictor of poor posture and LBP; ANOVAs compared PA and SB between work environments. Objectively measured sitting (min/day) predicted poor hip posture (β = -0.01, p < 0.046) but was not significant for LBP (β = 0.002, p < 0.43). Participants who worked from home had significantly higher sitting time (569 ± 111 vs. 477 ± 46min/d; p < 0.04), higher muscle strengthening PA (2.2 ± 2 vs. 0.5 ± 1.2d/week p < 0.02), but no difference in aerobic PA (p < 0.15), than those who worked from an office. Given the shift to remote work during COVID-19, employees are at high risk for postural compensations that lead to LBP due to high SB and poor work ergonomics at home. There is a need to develop home-based behavioral and exercise interventions to reduce sitting, help improve posture, and invest in proper ergonomic homework equipment.

Consequences of Juvenile Idiopathic Arthritis on Single Leg Squat Performance in Youth.

Juvenile idiopathic arthritis (JIA) affects body structure and function outcomes that may increase the risk of acute joint injury. The purpose of this study was to examine single leg squat (SLS) biomechanics for youth with JIA and their healthy peers. The study design was a matched pair cohort study. Sixty-five youth (JIA n = 30; control n = 35) participated in this ethics-approved study. Participants performed 3 sets of 5 consecutive SLS tasks. Disease activity and functional status were assessed using the Juvenile Arthritis Disease Activity Score and Child Health Assessment Questionnaire. Indexed (most-affected leg [JIA]; dominant leg [control]) and contralateral extremity biomechanics were obtained using a 12-camera system. Outcomes included hip flexion/extension (FE), adduction/abduction (AA), and internal/external (IE) rotation range of motion (ROM). Data were analyzed using a multivariate random coefficient model in R (α⍺ = 0.05). A total of 29 matched pairs were analyzed. Youth with JIA had low disease activity and performed the SLS with a more internally rotated hip (indexed leg P = 0.023, β = -1.9°). Female participants displayed greater hip FE (indexed leg P = 0.015, β = -4.3°; contralateral leg P = 0.005, β = -4.8°) and IE ROM (indexed leg P = 0.021, β = -2.1°) than male participants. Associations were observed for body mass index and hip IE ROM (contralateral leg P = 0.001, β = -0.4°), knee flexion angle, and hip FE ROM (indexed leg P = 0.001, β = 0.4°; contralateral leg P = 0.001, β = 0.5°) and AA (indexed leg P = 0.010, β = 0.1°; contralateral leg P = 0.002, β = 0.2°). This study identified functional alterations for an SLS in youth with JIA. These findings support the use of physical therapy as part of a multidisciplinary management approach, to restore normal hip posture and movement.

Factors in Ergonomic Design of 6-to-18-month Baby Carriers for Elderly People

The main objective of this study was to formulate an ergonomic design factor for 6-to-18-month baby carrier from simulated loading point data and physical parameters of an average Thai elderly person. The research steps were as follows: (1) reviewing the literature on 6-to-18-month baby carrier designs; (2) simulating the forces acting on a few selected baby carriers and on the body of an average Thai elderly person carrying them; and (3) synthesizing ergonomic design factors based on load-bearing data as well as the physical parameters of an average Thai elderly person. Four ergonomic design factors were synthesized: 1) their shoulder and hip posture while they are using the carrier, 2) the seat and backrest of the baby carrier, 3) the load-bearing points on the body of the carrying person, and 4) the type of baby carrier. Our findings may benefit designers of cushion seat and baby stroller.

Correlations between joint kinematics and dynamic balance control during gait in pregnancy

BackgroundDynamic balance control degrades during pregnancy, but it is not yet understood why. Mechanical aspects of the body should directly affect walking balance control, but we have recently published papers indicating that weight gains during pregnancy explain very little dynamic balance changes. Our goal was to determine if lower extremity joint kinematic changes are an indicator of walking balance control. This information is vital to understanding the route by which pregnancy increases fall risk. MethodsTwenty-three pregnant women were tested at five different times in the 2nd and 3rd trimesters of pregnancy. Participants performed walking trials at a self-selected pace. Motion capture was used to measure joint kinematics (discrete and coordination variables) and body center of mass motion. Changes over time were statistically analyzed. Correlations between kinematics and walking balance were modelled with hierarchical multiple regression models. ResultsAs pregnancy progresses, it appears that a more flexed hip posture could be driving lower extremity kinematic changes toward increased coordination between joints and increased knee and ankle motions. Walking balance changes were also detected through increased COM motion (lateral range of motion and velocity) in the lateral directions. However, there was little correlation between kinematic and balance changes (r2 < 0.4). Strong correlations were only observed when all kinematics (including those that don’t ubiquitously change during pregnancy) were used in the regression model (r2 > 0.7). SignificanceOur findings suggest that walking balance control is not altered by a common kinematic change between all pregnant women. While increased lateral center of mass motion should be expected with pregnancy, the kinematics leading to this increase may be person-specific. The cause of dynamic imbalance in each pregnant women (physiological, mechanical, and neurocognitive) may play an important role in determining the kinematic means by which lateral center of mass motion increases.

Monitoring hip posture in total hip arthroplasty using an inertial measurement unit-based hip smart trial system: An in vitro validation experiment using a fixed pelvis model

Intraoperative measurement of hip posture is the basis for assessing hip range of motion (ROM) and predicting postoperative functional limits allowable for activities of daily living. Although computer navigation for total hip arthroplasty (THA) has improved the accuracy of intraoperative ROM evaluation, it has not gained widespread popularity due to its complex and time-consuming protocol. We therefore developed an inertial measurement unit-based hip smart trial system (IMUHST) for intraoperative monitoring of hip posture. An in vitro validation experiment was conducted using bone models with a three-dimensional measurement model as the reference standard. The absolute mean error, Bland – Altman analysis and intra-class correlation coefficient demonstrated that the validity and reliability of this system meets the requirement for clinical application. Given that monitoring posture is the basis for evaluating the direction(s) of potential impingement, subluxation and dislocation, the IMUHST is a promising development direction of computer assisted surgery in THA.

The role of arthroscopic release of gluteal muscle contracture in improving patellofemoral instability

BackgroundGluteal muscle contracture (GMC) is a notable problem in some developing countries and includes features such as a snapping sound of the hip, abnormal gait, and unusual posture when patients squat with the knees together. Arthroscopic release can not only resolve symptoms, as previously reported, but can also greatly improve accompanying patellofemoral instability. This study was conducted to evaluate the effect of arthroscopic release of GMC on patellofemoral instability and its underlying mechanism.MethodsA total of nearly 500 patients who underwent arthroscopic release of GMC over 2.5 years were filtered, and 54 patients were enrolled in the study. The selected research subjects all had combined patellofemoral instability preoperatively. The Lysholm scores and CT scans of the knee were evaluated pre- and postoperatively.ResultsThe mean follow-up time was 12.2 months. All of the surveyed patients had satisfactory clinical outcomes for hip snapping sounds and abnormal gait. In addition, a significant difference (p < 0.05) was observed between pre- and postoperative Lysholm scores, along with significant knee pain relief. Furthermore, the changes in CT scan parameters were significant as well. The average patellar tilt angle (PTA), patellofemoral index (PFI), and lateral patellar displacement (LPD) were obviously decreased (p < 0.05) after the release. Conversely, the mean lateral patellofemoral angle (LPFA) showed a clear difference (p < 0.05) between preoperative and postoperative CT examinations.ConclusionsArthroscopic release of GMC can reduce the tilt and lateral shift of the patella and enhance its stability due to the release of the iliotibial band.

Trabecular architecture of the great ape and human femoral head.

Studies of femoral trabecular structure have shown that the orientation and volume of bone are associated with variation in loading and could be informative about individual joint positioning during locomotion. In this study, we analyse for the first time trabecular bone patterns throughout the femoral head using a whole-epiphysis approach to investigate how potential trabecular variation in humans and great apes relates to differences in locomotor modes. Trabecular architecture was analysed using microCT scans of Pan troglodytes (n=20), Gorilla gorilla (n=14), Pongo sp. (n=5) and Homo sapiens (n=12) in medtool 4.1. Our results revealed differences in bone volume fraction (BV/TV) distribution patterns, as well as overall trabecular parameters of the femoral head between great apes and humans. Pan and Gorilla showed two regions of high BV/TV in the femoral head, consistent with hip posture and loading during two discrete locomotor modes: knuckle-walking and climbing. Most Pongo specimens also displayed two regions of high BV/TV, but these regions were less discrete and there was more variability across the sample. In contrast, Homo showed only one main region of high BV/TV in the femoral head and had the lowest BV/TV, as well as the most anisotropic trabeculae. The Homo trabecular structure is consistent with stereotypical loading with a more extended hip compared with great apes, which is characteristic of modern human bipedalism. Our results suggest that holistic evaluations of femoral head trabecular architecture can reveal previously undetected patterns linked to locomotor behaviour in extant apes and can provide further insight into hip joint loading in fossil hominins and other primates.

A radiographic assessment of lumbar spine posture in four different upright standing positions

BackgroundApproximately 50% of a sample population will develop prolonged standing induced low back pain. The cause of this pain may be due to their lumbar spine posture. The purpose of this study was to investigate differences in lumbar posture between 17 participants categorized as a pain or non-pain developers during level ground standing. A secondary purpose was to evaluate the influence of two standing aids (an elevated surface to act as a foot rest and declined sloped surface) on lumbopelvic posture. MethodsFour sagittal plane radiographs were taken: a normal standing position on level ground, when using an elevated foot rest, using a declined sloped surface, and maximum lumbar spine extension as a reference posture. Lumbosacral lordosis, total lumbar lordosis, and L1/L2 and L5/S1 intervertebral joint angles were measured on each radiograph. FindingsThere was a significant difference between the lumbosacral lordosis angle and L5/S1 angles in upright versus maximum extension; however, this was independent of pain group. The elevated surface was most effective at causing lumbosacral spine flexion. InterpretationPotentially successful postures for eliminating low back pain during prolonged standing mainly influence the lower lumbar lordosis. Future work should assess the influence of hip posture on low back pain development during standing.

Influence of different stool types on muscle activity and lumbar posture among dentists during a simulated dental screening task

Whereas in the past dental stools typically facilitated a 90° hip angle, a number of currently available alternative designs allow for a more extended hip posture. The present study investigated the influence of different stool types on muscle activity and lumbar posture. Twenty five participants completed a simulated dental procedure on a standard stool, a saddle and the Ghopec. The latter stool comprises a seat pan consisting of a horizontal rear part for the pelvis and an inclinable sloping down front part for the upper legs, with a vertically and horizontally adjustable back rest. Lumbar posture was most close to neutral on the Ghopec, whereas sitting on a standard/saddle stool resulted in more flexed/extended postures respectively. Sitting with a 90° angle (standard stool) resulted in higher activation of back muscles while sitting with a 125° angle (saddle and Ghopec) activated abdominal muscles more, although less in the presence of a backrest (Ghopec). To maintain neutral posture during dental screening, the Ghopec is considered the most suitable design for the tasks undertaken.

The influence of seat height, trunk inclination and hip posture on the activity of the superior trapezius and longissimus.

[Purpose] This study was aimed at investigating the influence of seat height and body posture on the activity of the superior trapezius and longissimus muscles. [Subjects and Methods] Twenty two healthy subjects were instructed to perform a total of eight different body postures, varying according three main factors: seat height (low and high seat); trunk inclination (upright and leaning forward at 45°); and the hips in abduction and adduction. Electromyography of the superior trapezius and longissimus was collected bilaterally, and the average values were obtained and compared across all the postures. [Results] The activity of the superior trapezius and longissimus significantly changes according to the seat height and trunk inclination. For both seat heights, sitting with trunk leaning forward resulted in a significant increase in the activity of both muscles. When sitting in a high seat and the trunk leaning forward, the superior trapezius activity was significantly reduced when compared to the same posture in a low seat. [Conclusion] This study contributes to the knowledge on the influence of the body posture and seat configuration on the activity of postural muscles. Reducing the biomechanical loads on the postural muscles must be targeted in order to improve users’ comfort and safety.

Effects of changes in muscle activation level and spine and hip posture on erector spinae fiber orientation.

During lumbar flexion, the fiber orientation of the lumbar erector spinae (LES) muscle becomes oriented more along the spine compressive axis. It is unknown how changes in LES activation effect fiber orientation. Ultrasound images of LES were collected during 2 sets of experimental conditions: (1) varying levels of LES activation while lying prone; and (2) varying spine and hip angles while seated. Electromyographic activity and lumbar spine and hip angles were also recorded. As LES activation increased, increases in fiber orientation (signifying increased orientation along the posterior shear axis) were found (P<0.001). Compared with the relaxed sitting posture, decreases in fiber orientation were found with full spine flexion and combined spine and hip flexion (P<0.001), but there were no changes with full hip flexion alone. Activation magnitude and spine posture both affect LES fiber orientation, thus modifying its ability to protect the spine against anterior shear forces.

The effect of rollover footwear on pain, disability and lumbar posture in patients with low back pain

Low back pain (LBP) is one of the most common musculoskeletal disorders [1]. Exercise therapy is often advised [2, 3] but requires a significant time commitment, can rely on equipment or health professionals and risks low compliance. As an alternative or adjunct, shoes with a curved sole profile are thought to produce beneficial changes in ankle, knee, hip and back position and posture [4]. Therefore, the aim of this preliminary study was to investigate the effect of rollover footwear on pain, disability and lumbar posture in patients with lumbar pain.

Femoral Head Size of 36 mm against Highly Cross-linked Polyethylene in Patients Younger than 60 Years: Minimun Three Years of Follow Up

Purpose: The purpose of this study was to evaluate the early results of total hip arthroplasty (THA) performed using large diameter femoral head against with highly cross-linked polyethylene as a bearing surface in patients less than sixty years of age. Materials and Methods: Seventy patients were enrolled and retrospectively reviewed. The mean age of patients at index surgery was 49 years and the mean follow-up period was 61 months. Clinical follow-up involved implementing the Harris hip score (HHS) and a radiographic evaluation that included linear radiolucency, osteolysis, and loosening. An annual wear rate was performed at 6 weeks; at 3, 6, and 12 months; and on a yearly basis thereafter. Results: The average HHS at last follow-up was 94 (range: 82-98). Radiographically, no osteolysis in the pelvis or proximal femur was observed in any patient. No acetabular cup or femoral stem failed due to aseptic loosening. No eccentric wear was observed on any liner, and no liner fracture occurred. However, one patient experienced hip dislocation. The average femoral head penetration rate during the fi postoperative year was 0.077±0.026 mm/year, and the average steady-state wear rate was 0.033±0.023 mm/year. Conclusion: THA with a large diameter femoral head of highly cross-linked polyethylene in patients younger than 60 years of age was found to produce results comparable to previous in vitro laboratory hip simulation studies. In particular, patient satisfaction was high due to no limitation in range of motion or hip posture during the early post-operative period. Longer-term follow-up is required to demonstrate the clinical benefi ts of this new material more comprehensively.

Sex and limb differences in hip and knee kinematics and kinetics during anticipated and unanticipated jump landings: implications for anterior cruciate ligament injury

Objectives:In this study, the effects of temporal changes in unanticipated (UN) prelanding stimuli on lower limb biomechanics and the impact of sex and limb dominance on these variables during single-leg...

The influence of prenatal breech presentation on neonatal leg posture

The aim of our study was to examine the effect of prenatal breech presentation on postnatal leg posture. Twelve infants were born after breech presentation and nine infants after cephalic presentation participated. At 2, 4, 6, 12 and 18 weeks postnatal age leg posture was examined during general movements in supine and vertical position. Results Transient differences in hip posture between the groups were observed during the first 6 weeks postnatal age, with significantly more hip flexion and less hip extension in the breech group. For knee extension, differences between the groups were not statistically significant. Changing from supine to vertical position, the breech group demonstrated a significant increase in hip extension, with no significant changes in hip posture for the cephalic group. For both groups the vertical condition resulted in a significant increase in knee extension. Continuity from pre- to postnatal life was found for hip posture in both groups and for knee extension only in the breech group. Conclusions Significant differences between breech and cephalic-born infants were found during the first 6 weeks after birth and mainly concerned hip posture and not knee posture. An increase in gravitational force has more impact on leg posture in the breech than in the cephalic group. The observed differences in hip posture between the studied groups were found to be transient, however, in the long term subtle differences still remain between the groups.

HIP JOINT POSITION AFFECTS VOLITIONAL KNEE EXTENSOR ACTIVITY POST-STROKE.

Purpose/Hypothesis: Individuals post-stroke often exhibit significant functional limitations due to either inadequate or inappropriate volitional muscle activation. In the lower extremity this is particularly apparent during ‘spastic paretic stiff-legged gait’, which has been attributed to excessive quadriceps activity during the stance to swing transition. The mechanism underlying the altered volitional activation of the knee extensors has yet to be elucidated; however, evidence from animal and human models has demonstrated the importance of hip angle sensors in modulating lower extremity muscle activity. Although the hip's position has become a focus for retraining ‘normal’ walking patterns following stroke, there are as of yet, no quantitative studies which examined the influence of hip angle afferent information during isolated volitional muscle activation after stroke. The purpose of this study was therefore to quantify the role of hip joint positioning on the volitional activation of the uniarticular knee extensor muscles after stroke. It was hypothesized that greater hip flexion would yield greater quadriceps activity. Number of Subjects: Fourteen subjects with chronic (> 1 yr) stroke were recruited for testing. Materials/ Methods: Subjects were positioned on a Biodex dynamometer to record the electromyographic (EMG) activity from the uniarticular knee extensor muscles [vastus lateralis (VL) and vastus medialis (VM)] during maximum voluntary isometric knee extension contractions. The knee was fixed at 60°, while hip position was fixed by altering the subject's posture in random order to include: sitting upright (90°), semi-reclined (45°), and supine (0°). EMG data was full wave rectified and low pass filtered to produce a linear envelope. The outcome variable of interest was the integrated EMG activity around peak torque production. A two-way (muscle and hip position) repeated-measures ANOVA (repeated for hip position) was used to determine the effect of varying hip posture on knee extensor activity. Results: Hip position had a substantial effect on the amount of volitional VL and VM muscle activity produced (p=0.07). With the hip positioned in full extension, both muscles were volitionally activated significantly less than when the hip was positioned in flexion (p=0.03). Conclusions: The angle of the hip joint appears to play a significant role in the volitional activation of the uniarticular knee extensors, although more data is required. Patients with stroke tend to walk with the hips in greater flexion, which may facilitate activation of the knee extensors contributing to ‘stiff knee gait’ pattern. Clinical Relevance: Hip joint angle contributes to the modulation of volitional quadriceps activation and likely influences reflexive/spastic activation contributing to inappropriate muscle activity during functional activities. A strong emphasis should therefore be placed on hip joint posturing during gait retraining to assist with appropriate muscle activation patterns.