Neurotransmitter system markers in adult barrel field

Abstract

Purpose: Skin contributes to joint position sense (JPS) at multiple joints. Altered cutaneous input at the foot can modulate gait and balance and kinesiology tape can enhance proprioception at the knee, but its effect may be dependent on existing capacity. The effect of texture at the knee, particularly in those with poor proprioception, is unknown. The aim of this study was to determine the effect of textured panels on JPS about the knee.

Materials and methods: Eighteen healthy females were seated in an adjustable chair. Their left leg (target limb) moved passively from 65° to a target of flexion (115° or 90°) or extension (40°). Their right leg (matching limb) was passively moved towards this target angle and participants indicated when their limbs felt aligned. We tested three textured panels over the knee of the matching limb and two control conditions. The target limb maintained a control panel. Directional error, absolute error and variable error in matching between limbs were calculated.

Results: On average textured panels over the knee increased JPS error compared to control pants for participants with poor JPS. These participants undershot the target at 90° of flexion significantly more with textured panels (?11°?±?3°) versus control (?7°?±?3°, p?=?0.04).

Conclusions: For participants with poor JPS accuracy, increased JPS error at 90° with a textured panel suggests these individuals utilised altered cutaneous information to adjust joint position. We propose increased error results from enhanced skin input at the knee leading to the perception of increased flexion.     

The accuracy of measuring glenohumeral motion with a surface humeral cuff

Conclusions about normal and pathologic shoulder motion are frequently made from studies using skin surface markers, yet accuracy of such sensors representing humeral motion is not well known. Nineteen subjects were investigated with flock of birds electromagnetic sensors attached to transcortical pins placed into the scapula and humerus, and a thermoplastic cuff secured on the arm. Subjects completed two repetitions of raising and lowering the arm in the sagittal, scapular and coronal planes, as well as shoulder internal and external rotation with the elbow at the side and abducted to 90°. Humeral motion was recorded simultaneously from surface and bone fixed sensors. The average magnitude of error was calculated for the surface and bone fixed measurements throughout the range of motion. ANOVA tested for differences across angles of elevation, raising and lowering, and differences in body mass index. For all five motions tested, the plane of elevation rotation average absolute error ranged from 0-2°, while the humeral elevation rotation average error ranged from 0-4°. The axial rotation average absolute error was much greater, ranging from 5° during elevation motions to approaching 30° at maximum excursion of internal/external rotation motions. Average absolute error was greater in subjects with body mass index greater than 25. Surface sensors are an accurate way of measuring humeral elevation rotations and plane of elevation rotations. Conversely, there is a large amount of average error for axial rotations when using a humeral cuff to measure glenohumeral internal/external rotation as the primary motion.     

Ageing and joint position sense of the asymptomatic shoulder: An observational study

PurposeThis study aimed to quantify the extent to which age was associated with joint position sense (JPS) of the asymptomatic shoulder as measured by joint position reproduction (JPR) tasks and assess the reproducibility of these tasks.Methods120 Asymptomatic participants aged 18–70 years each performed 10 JPR-tasks. Both contralateral and ipsilateral JPR-tasks were evaluated on accuracy of JPR under active- and passive conditions at two levels within the shoulder forward flexion trajectory. Each task was performed three times. In a subgroup of 40 participants, the reproducibility of JPR-tasks was assessed one week after initial measurement. Reproducibility of JPR-tasks was evaluated by both reliability (intra-class correlation coefficients (ICC’s)) and agreement (standard error of measurement (SEM)) measures.ResultsAge was not associated with increased JPR-errors for any of the contralateral or ipsilateral JPR-tasks. ICC’s ranged between 0.63 and 0.80 for contralateral JPR-tasks, and from 0.32 to 0.48 for ipsilateral tasks, except for one ipsilateral task where the reliability was similar to contralateral tasks (0.79). The SEM was comparable and small for all JPR-tasks, ranging between 1.1 and 2.1.ConclusionNo age-related decline in JPS of the asymptomatic shoulder was found, and good agreement between test and re-test measurements for all JPR-tasks as indicated by the small SEM.     

Central nervous system fatigue alters autonomic nerve activity

AimsFatigue is a common symptom in modern society. In order to clarify the mechanisms underlying fatigue, we examined the association between central nervous system fatigue and autonomic nerve activity.Main methodsThe study group consisted of 20 healthy subjects. They performed the 2-back test for 30 min to induce fatigue. Just before and after the fatigue-inducing session, they completed the advanced trail making test (ATMT) for 30 min as a fatigue-evaluating task session. In order to measure autonomic nerve activity, electrocardiograms were monitored continuously throughout the experiment.Key findingsAfter the fatigue-inducing task session, impaired task performance was demonstrated based on the total trial number and error counts of the ATMT. During the task session, although task performance as measured using the accuracy and the mean reaction time of the 2-back test was almost unchanged, electrocardiographic R-R wave interval analyses showed a decreased high-frequency component power and an increasing trend in the low-frequency component power/high-frequency component power ratio.SignificanceDecreased vagal nerve activity and increased sympathetic nerve activity are associated with central nervous system fatigue.     

Fatigue-induced glenohumeral and scapulothoracic kinematic variability: Implications for subacromial space reduction

Superior humeral head translation and scapula reorientation can reduce the subacromial space. While these kinematic abnormalities exist in injured populations, the effect of muscle fatigue is unclear. Additionally, these mechanisms were typically studied independently, thereby neglecting potential covariance. This research evaluated the influence of upper extremity muscle fatigue on glenohumeral and scapulothoracic kinematics and defined their relationship. Radiography and motion tracking systems captured these kinematic relationships, during scapula plane elevation, both before and after fatigue. Fatigue-induced changes in humeral head position, scapular orientation and the minimum subacromial space width were measured. High inter-subject variability existed for each measure which precluded identification of mean differences at the population level. However, significant scapular upward rotation occurred following fatigue (p = 0.0002). Despite similar population mean results, between 39% and 57% of participants exhibited fatigue-related changes in disadvantageous orientations. Additionally, correlations between measures were generally fair (0.21–0.40) and highly dependent on elevation, likely attributed to the variable fatigue responses. Overall, the data confirms that fatigue-induced changes in kinematics poses highly variable risk of subacromial impingement syndrome across individuals. Thus, solely considering the “average” or mean population response likely underestimates potentially injurious fatigue consequences.     

Joint position reproduction and joint position discrimination at the ankle are not related

Abstract

Purpose: Limited data in current literature can be found on the relation between the two commonly-used active proprioception assessment methods –active joint position reproduction (JPR) and active movement extent discrimination assessment (AMEDA). The current study compared the two active methods, JPR and AMEDA, to investigate their interrelationship over two studies that differed in task difficulty, using active ankle inversion movements made in weight-bearing to maximise ecological validity.

Methods: 50 participants volunteered in this research, 20 of whom on a harder protocol and the other 30 on an easier protocol, were tested by both methods, JPR and AMEDA. Proprioceptive acuity was represented by absolute error (AE) and variable error (VE) for JPR and by AE and the area under the curve (AUC) for AMEDA.

Results: Proprioceptive acuity scores are found to be significantly correlated within test methods but not between methods for either hard or easy tasks, where JPR AE and VE scores were not correlated with either AMEDA AE or AUC. Further, proprioceptive acuity scores were significantly higher on the easy task when tested with the AMEDA method, but not with JPR method.

Conclusion: Scores obtained from the two active movement proprioception tests, movement extent discrimination and joint position reproduction, were not significantly correlated. Taken together with previous findings, these results show that for proprioception, scores from the three classical psychophysical methods for measuring sensitivity (adjustment, limits and constant stimuli) are not correlated with each other. This suggests that each proprioception measurement system assesses a different aspect of proprioception.     

Measuring humeral head translation using fluoroscopy: A validation study

Numerous techniques have been employed to monitor humeral head translation due to its involvement with several shoulder pathologies. However, most of the techniques were not validated. The objective of this study is to compare the accuracy of manual digitization and contour registration in measuring superior translation of the humeral head. Eight pairs of cadaver scapulae and humerii bones were harvested for this study. Each scapula and humerus was secured in a customized jig that allowed for control of humeral head translations and a vise that permitted rotations of the scapula about three axes. Fluoroscopy was used to take images of the shoulder bones. Scapular orientation was manipulated in different positions while the humerus was at 90° of humeral elevation in the scapular plane. Humeral head translation was measured using the two methods and was compared to the known translation. Additionally, accuracy of the contour registration method to measure 2-D scapular rotations was assessed. The range for the root mean square (RMS) error for manual digitization method was 0.27 mm - 0.43 mm and the contour registration method had a RMS error ranging from 0.18 mm - 0.40 mm. In addition, the RMS error for the scapular angle rotation using the contour registration method was 2.4°. Both methods showed acceptable errors. However, on average, the contour registration method showed lesser measurement error compared to the manual digitization method. In addition, the contour registration method was able to show good accuracy in measuring rotation that is useful in 2-D image analysis.     

采用同种异体腓骨植骨重建肱骨近端内侧柱的临床应用及疗效

目的:探讨同种异体腓骨移植重建肱骨近端内侧柱联合锁定钢板治疗肱骨近端骨折的临床疗效。方法:回顾性分析2011年3月至2013年9月于我院行同种异体腓骨移植联合锁定钢板治疗肱骨近端骨折患者38例。根据Neer分型:三部分骨折26例,四部分骨折12例;随访期间测量肱骨头内翻角度、肱骨头高度;患肩功能评分采用Constant肩关节评分标准、美国肩肘协会评分系统(ASES)及加州大学肩关节评分系统(UCLA),同时记录患者并发症。结果:患者随访时间平均15.5±1.8个月;末次随访Constant肩关节评分平均89.0±3.2分;美国肩肘协会评分系统(ASES)评分为平均81.2±14.5分;加州大学肩关节评分系统(UCLA)平均27.6±5.3;根据UCLA评分系统,患者术后优良率为89.4%。患侧肩关节前屈、外展、外旋及内旋运动范围分别是143±20°、138±9°、44±12°、42±9°。影像学结果显示:末次随访肱骨头高度平均丢失1.9 mm,颈干角度平均为128±16°。根据Paavolainen方法,末次随访优30例、良7例、差1例。结论:同种异体腓骨移植重建肱骨近端骨折内侧柱,术中联合肱骨近端锁定钢板能有效支撑肱骨头,预防肱骨头塌陷及螺钉穿出,短期临床疗效满意。     

The assessment of back muscle capacity using intermittent static contractions. Part II: Validity and reliability of biomechanical correlates of muscle fatigue

IntroductionIn a previous paper, standard surface electromyographic (EMG) indices of muscle fatigue, which are based on the lowering of the median or mean frequencies of the EMG power spectrum in time, were applied during an intermittent absolute endurance test and were evaluated relative to criterion validity and test–retest reliability. The aims of this study were to assess mechanical and alternative EMG correlates of muscle fatigue.MethodsHealthy subjects (44 males and 29 females; age: 20–55 yrs) performed three maximal voluntary contractions (MVC) and an endurance test while standing in a static dynamometer. Surface EMG signals were collected from four pairs of back muscles (multifidus at the L5 level, iliocostalis lumborum at L3, and longissimus at L1 and T10). The test, assessing absolute endurance (90 N m torque), consisted of performing an intermittent extension task to exhaustion. Strength was defined as the peak MVC whereas our endurance criterion was defined as the time to reach exhaustion (Tend) during the endurance test. Mechanical indices quantifying physiological tremor and steadiness were computed from the dynamometer signals (L5/S1 extension moments) along with EMG indices presumably sensitive to variable load sharing between back muscle synergists during the endurance test.ResultsMechanical indices were significantly correlated to Tend (r range: −0.47 to –0.53) but showed deceiving reliability results. Conversely, the EMG indices were correlated to Tend (r range: −0.43 to –0.63) with some of them particularly correlated to Strength (r = − 0.72 to –0.81). In addition, their reliability results were acceptable (intra-class correlation coefficient >0.75; standard error of measurement <10% of the mean) in many cases. Finally, several analyses substantiated their physiological relevance. These findings imply that these new EMG indices could be used to predict absolute endurance as well as strength with the use of a single intermittent and time-limited (5–10 min) absolute endurance test, a practical way to assess the back capacity of chronic low back pain subjects.     

The assessment of back muscle capacity using intermittent static contractions. Part I – Validity and reliability of electromyographic indices of fatigue

IntroductionBack muscle capacity is impaired in chronic low back pain patients but no motivation-free test exists to measure it. The aims of this study were to assess the reliability and criterion validity of electromyographic indices of muscle fatigue during an intermittent absolute endurance test.MethodsHealthy subjects (44 males and 29 females; age: 20–55 yrs) performed three maximal voluntary contractions (MVC) and a fatigue test while standing in a static dynamometer. Surface EMG signals were collected from four pairs of back muscles (multifidus at the L5 level, iliocostalis lumborum at L3, and longissimus at L1 and T10). The fatigue test, assessing absolute endurance (90-Nm torque), consisted in performing an intermittent extension task to exhaustion. Strength was defined as the peak MVC whereas our endurance criterion was defined as the time to reach exhaustion (Tend) during the fatigue test. From the first five min (females) or ten min (males) of EMG data, frequency and time-frequency domain analyses were applied to compute various spectral indices of muscle fatigue.ResultsThe EMG indices were more reliable when computed from the time-frequency domain than when computed from the frequency domain, but showed comparable correlation results (criterion validity) with Tend and Strength. Some EMG indices reached moderate to good correlation (range: 0.64–0.69) with Tend, lower correlations (range: 0.39–0.55) with Strength, and good to excellent between-day test-retest reliability results (intra-class correlation range: 0.75–0.83). The quantification of the spectral content more locally in different frequency bands of the power spectrum was less valid and reliable than the indices computed from the entire power spectrum. Differences observed among muscles were interpreted in light of specific neuromuscular activation levels that were observed during the endurance test. These findings supported the use of an intermittent and time-limited (5–10 min) absolute endurance test, that is a practical way to assess the back capacity of chronic low back pain subjects, to assess absolute endurance as well as strength with the use of electromyographic indices of muscle fatigue.     

Delivering RapidArc®: A comprehensive study on accuracy and long term stability

PurposeTo establish the reliability and accuracy of a UNIQUE Linac in delivering RapidArc treatments and assess its long term stability.Materials and methodsUNIQUE performance was monitored and analyzed for a period of nearly two years. 2280 Dynalog files, related to 179 clinical RapidArc treatments were collected. Different tumor sites and dose scheduling were included, covering the full range of our treatment plans. Statistical distributions of MLC motion error, gantry rotation error and MU delivery error were evaluated. The stochastic and systematic nature of each error was investigated together with their variation in time.ResultsAll the delivery errors are found to be small and more stringent tolerances than those proposed by TG142 are suggested. Unlike MLC positional errors, where a linear relationship with leaf speed holds, other Volumetric Modulated Arc Therapy (VMAT) parameters reveal a random nature and, consequently, a reduced clinical relevance. MLC errors are linearly related only to leaf speed no matter the shape of the MLC apertures. Gantry rotation and MU delivery are as accurate as major competing Linacs. UNIQUE was found to be reliable and accurate throughout the investigation period, regardless of the specific tumor sites and fractionation schemes.ConclusionsThe accuracy of RapidArc treatments delivered with UNIQUE has been established. The stochastic nature of delivery errors is proven. Long term statistics of the delivery parameter errors do not show significant variations, confirming the reliability of the VMAT delivery system.     

Oviposition schedules,survivorship curves,and mortality factors within trees of two cerambycid beetles (Coleoptera: Cerambycidae), the Japanese pine sawyer,Monochamus alternatus hope,and sugi bark borer,Semanotus japonicus lacordaire

Summary Oviposition schedules under laboratory conditions, survivorship curves, and mortality factors within trees of two cerambycid beetles, Japanese pine sawyer (JPS),Monochamus alternatus Hope, and sugi bark borer (SBB),Semanotus japonicus Lacordaire, were investigated. Average longevities of reared adults of JPS were 38.1 days for males and 42.3 days for females; those of SBB were 15.7 days for males and 23.8 days for females. It was confirmed that the JPS must feed on the pine branches for full maturation after emergence, but SBB need not; they are able to lay eggs soon after emergence. The average fecundities of JPS and SBB were 32.9 and 90.5, respectively. Thus, the JPS lay fewer eggs for a long time with continuous maturation feeding, whereas the SBB lay more eggs for short time without maturation feeding. Average survivorship curves of JPS within dead pine trees in 8 pine forests were theDeevey's B type, showing a constant mortality through the pre-imaginal stages in the trees. On the other hand those of SBB in 4 cedar stands approached theDeevey's type, suggesting that the high mortality occurred at an early stage in the trees. Average mortalities of JPS between the appearance of oviposition scars and adult emergence in 8 forests ranged from 62.3% to 95.2%. Intraspecific ompetition of JPS resulting from overcrowding in dead pine trees appeared to be main mortality factor. For SBB, as most larvae were killed by resin flow in living trees, this appeared to be the main mortality factor for this species.     

Effect of laterality discrimination on joint position sense and cervical range of motion in patients with chronic neck pain: a randomized single-blind clinical trial

Purpose: The main objective of the present study was to evaluate the effects of laterality discrimination training on neck joint position sense and cervical range of motion (ROM) in patients with chronic non-specific neck pain (NSCNP).

Materials and methods: Forty-eight patients with NSCNP were randomly assigned to the neck group (NG) that observed neck images or the foot group (FG) that observed foot images. Response time, response accuracy, cervical ROM, and joint position error (JPE) were the main variables. The secondary outcome measures included psychosocial variables.

Results: Differences between groups in the cervical ROM for flexion (p?=?.043) were obtained, being NG group the one which obtained greater values. NG showed an improvement in right rotation (p?=?.018) and a decrease in flexion was found in the FG (p?=?.039). In JPE, differences between groups were obtained in the left rotation (p?=?.021) and significant changes were found in the NG for flexion, extension, and left rotation movements (p?<?.05). Moderate associations were found between left and right accuracy regarding to post-intervention flexion and right rotation (r?=?0.46, r?=?0.41; p?<?.05) in NG.

Conclusion: Improvements in cervical range of motion and joint position sense are obtained after the performance of the laterality discrimination task of images of the neck but not the feet. Visualization of images of the painful region presents moderate correlations with the accuracy and response time in the movements of flexion and right rotation.     

Effectiveness of using an unskilled model in action observation combined with motor imagery training for early motor learning in elderly people: a preliminary study

Abstract

Aim of the study: To investigate a more available model for the early phase of motor learning after action observation combined with motor imagery training in elderly people. To address the purpose, we focused on a slow, unskilled model demonstrating an occasional error.

Materials and methods: A total of 36 elderly people participated in the current study and were assigned to either the unskilled or skilled model observation groups (n?=?12, respectively), or the control group (n?=?12). The participants in the observation groups observed the assigned a video clip of an unskilled or skilled model demonstrating a ball rotation task. During the observation, the participants were instructed to imagine themselves as the person in the video clip. The participants in the control group read a scientific paper during the equivalent period of action observation and motor imagery. We measured ball rotation performance (the time required for five rotations, the number of ball drops) in pre- and post-intervention (observation combined with motor imagery training for intervention groups or reading for control group).

Results: Ball rotation performance (ball rotation speed) significantly improved in the unskilled model observation group compared to the other two groups.

Conclusions: Intervention for action observation using unskilled model combined with motor imagery was effective for improving motor performance during the early phase of motor learning.     

The effect of fatigued internal rotator and external rotator muscles of the shoulder on the shoulder position sense

The purpose of this study was to investigate which muscle group, the agonist or antagonist, contributes most to the shoulder position sense (SPS). The SPS was tested under 2 conditions: fatigued shoulder internal rotator (IR) muscles (pectoralis major and latissimus dorsi) and fatigued external rotator (ER) muscles (infraspinatus). In each condition, the SPS was measured before and after a fatiguing task involving the IR or ER muscles by repeating shoulder joint rotation. SPS was measured using a method in which subjects reproduced a memorized shoulder joint rotation angle. The position error values in all conditions (fatigued IR and ER muscles) and measurement periods (before- and after-fatigue task) were compared using 2-way analysis of variance with repeated measures (IR/ER × before/after). Position error increased significantly after both fatigue tasks (before- vs. after-fatigue: IR muscle, 2.68° vs. 4.19°; ER muscle, 2.32° vs. 4.05°). In other words, SPS accuracy decreased when either the agonist or antagonist muscle was fatigued. This finding indicated that SPS may be affected by an integrated information of the afferent signals in the agonist and antagonist muscles.     

Muscle loading and activation of the shoulder joint during humeral external rotation by pulley and variable resistance

BackgroundThe aim of the study was to evaluate differences in the loading of glenohumeral joint muscles between a cable pulley machine (CP) and variable resistance machine (VR) during axial humeral external rotation.MethodsEleven healthy male subjects took part in the study. Intramuscular electromyography from five muscles of the shoulder (medial deltoid, supraspinatus, infraspinatus and upper part of the trapezius), torque and power output was measured at different rotation angles and with different loads (10%, 50% and 100% of 1RM). Also the compressive and shear force in the glenohumeral joint was analyzed at the horizontal level at angles of rotation. External rotation was performed with a self-selected velocity on the scapular plane.FindingsIn the CP the range of movement became narrower than in the VR with increasing workload (P < 0.05). The activity of the infraspinatus did not grow in the CP after 50% load, while it did in the VR (P < 0.01). The upper part of the trapezius was activated less in the CP than in the VR (P < 0.01) machine when using 50% and 100% loads. In comparison with the CP, the shear forces that pull the head of the humerus in a posterior direction were more evenly distributed in the VR than in the CP at different angles of rotation (P < 0.001).InterpretationThe VR seems to make a broader range of motion possible, lager activation the primary external rotators and evenly distributed shear forces than the CP. However, performing the exercise with VR and high load also activates the upper part of the trapezius.RelevanceThese findings can be used in the development of exercise designs, methods and equipment for shoulder injury rehabilitation.     

Accuracy and precision of a wrist movement when vibrotactile prompts inform movement speed

Abstract

Purpose: This study investigated the effect of movement speed on task accuracy and precision when participants were provided temporally oriented vibrotactile prompts. Materials and methods: Participants recreated a simple wrist flexion/extension movement at fast and slow speeds based on target patterns conveyed via vibrating motors affixed to the forearm. Each participant was given five performance-blinded trials to complete the task at each speed. Movement accuracy (root mean square error) and precision (standard deviation) were calculated for each trial in both the spatial and temporal domains. Results: 28 participants completed the study. Results showed temporal accuracy and precision improved with movement speed (both: fast?>?slow, p?<?0.01), while all measures improved across trials (temporal accuracy and precision: trial 1?<?all other trials, p?<?0.05; spatial accuracy: trial 1 and 2?<?all other trials, p?<?0.05; spatial precision: trial 1?<?all other trials, p?<?0.05). Conclusions: Overall, temporal and spatial results indicate participants quickly recreated and maintained the desired pattern regardless of speed. Additionally, movement speed seems to influence movement accuracy and precision, particularly within the temporal domain. These results highlight the potential of vibrotactile prompts in rehabilitation paradigms aimed at motor re-education.     

Decision Tree in Working Memory Task Effectively Characterizes EEG Signals in Healthy Aging Adults

BackgroundThe changes in electroencephalogram (EEG) signals that reflect the changes in physiological structure, cognitive functions, and activities have been observed in healthy aging adults. It is unknown that when the brain aging initiates and whether these age-related alterations can be associated with incipient neurodegenerative diseases in healthy elderly individuals.Materials and methodsWe employed feature extraction and classification methods to classify and compare the EEG signals of middle-aged and elderly age groups. This study included 20 healthy middle-aged and 20 healthy elderly subjects. The EEG signals were recorded during a resting state (eyes-open and eyes-closed) and during a working memory (WM) task using eight electrodes. The minimum redundancy maximum relevance technique was employed in the selection of the optimal feature. Four classification methods, including decision tree, support vector machine, Naïve Bayes, and K-nearest neighbor, were used to distinguish the elderly age group from the middle-aged group based on their EEG signals.ResultsIn the resting state, a good correlation was observed among absolute power delta and theta bands and aging, whereas between beta absolute power and aging, a WM task correlation was observed. The results also indicated that the mean frequency and absolute power might be useful for the prediction and classification of EEG signals in aging individuals. Furthermore, the use of the decision tree method in a WM task state distinguished the elderly group from the middle-aged group with an accuracy of 87.5%.ConclusionsWorking memory could play a vital role in the optimization of classification of EEG signals in aging and discrimination of age-related issues associated with neurodegeneration.     

Estimation of initial rate from discontinuous progress data

Abstract

When using discontinuous assay of reactions, initial rates are often estimated from a limited number of time points. There has been no detailed study of how best to do this. In this work, time courses were simulated by different theoretical equations (including strong product inhibition, first order, Michaelis–Menten and truly linear), but with random error addition to each data point. Various methods were tested to fit an initial rate to the data, and the result compared with the known “true” value. Fitting a simple quadratic generally gives initial rates as accurate as any other curve, and is better than a linear fit if there are about 8 or more time points. For fewer points a linear fit gives less variable and often more accurate rates. The absolute contribution to data point error has a major impact on rate accuracy, and often dominates that due to curvature, so that sampling to at least 10% conversion is preferred. The accuracy of a linear fit can be improved by methods that reject some later points based on curvature tests. Awareness of these effects can help avoid rate inaccuracies of 10% or more due to poor methods of data analysis.     

Inertial Measures of Motion for Clinical Biomechanics: Comparative Assessment of Accuracy under Controlled Conditions - Effect of Velocity

Background

Inertial measurement of motion with Attitude and Heading Reference Systems (AHRS) is emerging as an alternative to 3D motion capture systems in biomechanics. The objectives of this study are: 1) to describe the absolute and relative accuracy of multiple units of commercially available AHRS under various types of motion; and 2) to evaluate the effect of motion velocity on the accuracy of these measurements.

Methods

The criterion validity of accuracy was established under controlled conditions using an instrumented Gimbal table. AHRS modules were carefully attached to the center plate of the Gimbal table and put through experimental static and dynamic conditions. Static and absolute accuracy was assessed by comparing the AHRS orientation measurement to those obtained using an optical gold standard. Relative accuracy was assessed by measuring the variation in relative orientation between modules during trials.

Findings

Evaluated AHRS systems demonstrated good absolute static accuracy (mean error < 0.5^o) and clinically acceptable absolute accuracy under condition of slow motions (mean error between 0.5^o and 3.1^o). In slow motions, relative accuracy varied from 2^o to 7^o depending on the type of AHRS and the type of rotation. Absolute and relative accuracy were significantly affected (p<0.05) by velocity during sustained motions. The extent of that effect varied across AHRS.

Interpretation

Absolute and relative accuracy of AHRS are affected by environmental magnetic perturbations and conditions of motions. Relative accuracy of AHRS is mostly affected by the ability of all modules to locate the same global reference coordinate system at all time.

Conclusions

Existing AHRS systems can be considered for use in clinical biomechanics under constrained conditions of use. While their individual capacity to track absolute motion is relatively consistent, the use of multiple AHRS modules to compute relative motion between rigid bodies needs to be optimized according to the conditions of operation.