Precision of measurements of physical workload during standardized manual handling part III: Goniometry of the wrists

Goniometry of the wrist is a feasible method for studying wrist movements in most hand-intensive work. The precision and accuracy of the method per se is good. For the knowledge on validity of field measurements, the size of imprecision is of importance. This study evaluated this condition during standardized circumstances.Six women performed three different hand-intensive work tasks: ‘materials picking’, ‘light assembly’, and ‘heavy assembly’, repeated during three different days.Variance components between-days (within subjects) and between-subjects were derived for positions (flexion/extension and deviation) and movements, including angular velocities, % of time with very low velocity (<1°/s), as well as repetitiveness.For positions, the average standard deviations in the three tasks were, both between-days and between-subjects, 3–4°. For movements, the coefficients of variation of angular velocities were about 10% between-days, and could to a great part be explained by differences in work rate. Between-subjects variability was higher, 20–40%. The variability was larger at low velocities than at high ones.The precision of the measured positions was good, expressed as small between-days and between-subjects variability. For movements, the between-days variability was also small, while there was a larger between-subjects variability. The imprecision of goniometry is consequently lower and comparable with inclinometry but lower than for EMG.     

Precision of measurements of physical workload during standardised manual handling. Part I: surface electromyography of m. trapezius, m. infraspinatus and the forearm extensors.

Though surface electromyography (EMG) has been widely used in studies of occupational exposure, its precision in terms of the variance between-days and between-subjects has seldom been evaluated. This study aimed at such an evaluation. Six women performed three different work tasks: 'materials picking', 'light assembly', and 'heavy assembly', repeated on 3 different days. EMG was recorded from m. trapezius, m. infraspinatus and the forearm extensors. Normalisation was made to a maximal (MVE), and a submaximal (RVE), reference contraction. Variance components between days (within subjects) and between subjects were derived for the 10th, 50th and 90th percentiles, as well as for muscular rest parameters. For the task 'heavy assembly', the coefficient of variation between days (CV(BD)) was 8% for m. trapezius (right side, 50th percentile, MVE normalised values). Larger variabilities were found for m. infraspinatus (CV(BD) 15%), and the forearm extensors (CV(BD) 33%). Between-subjects variability (CV(BS)) was greater, 16% for m. trapezius and 57% for m. infraspinatus, 29% for the forearm extensors. RVE normalisation resulted in larger CV(BD), while reducing CV(BS). The between-days and between-subjects variability may be used to optimise sampling strategy, and to assess the bias in epidemiological studies. The bias caused by measurement procedures per se is acceptable.     

Measurements of wrist and forearm positions and movements: effect of, and compensation for, goniometer crosstalk.

Flexible biaxial goniometers are extensively used for measuring wrist positions and movements. However, they display an inherent crosstalk error. The aim was to evaluate the effect, of this error, on summary measures used for characterizing manual work. A goniometer and a torsiometer were combined into one device. An algorithm that effectively compensated for crosstalk was developed. Recordings from 25 women, performing five worktasks, were analyzed, both with and without compensation for crosstalk. The errors in the 10th, 50th and 90th percentiles of the flexion/extension distributions were small, on average <1 degrees. The ulnar/radial deviation distributions were weakly dependent on forearm position. The flexion/extension velocity measures were, for the 50th and 90th percentiles, as well as the mean velocity, consistently underestimated by, on average, 3.9%. For ulnar/radial deviation, the velocity errors were less consistent. Mean power frequency, which is a measure of repetitiveness, was insensitive (error <1%) to crosstalk. The forearm supination/pronation angular distributions were wider, and the velocities higher, than for the wrists. Considering wrist/hand exposure in epidemiologic studies, as well as for establishing and surveillance of exposure limits for prevention of work-related upper extremity musculoskeletal disorders, the crosstalk error can, when considering other errors and sources to variation, be disregarded.     

An upper extremity kinematic model for evaluation of hemiparetic stroke

Quantification of rehabilitation progress is necessary for accurately assessing clinical treatments. A three-dimension (3D) upper extremity (UE) kinematic model was developed to obtain joint angles of the trunk, shoulder and elbow using a Vicon motion analysis system. Strict evaluation confirmed the system's accuracy and precision. As an example of application, the model was used to evaluate the upper extremity movement of eight hemiparetic stroke patients with spasticity, while completing a set of reaching tasks. Main outcome measures include kinematic variables of movement time, range of motion, peak angular velocity, and percentage of reach where peak velocity occurs. The model computed motion patterns in the affected and unaffected arms. The unaffected arm showed a larger range of motion and higher angular velocity than the affected arm. Frequency analysis (power spectrum) demonstrated lower frequency content for elbow angle and angular velocity in the affected limb when compared to the unaffected limb. The model can accurately quantify UE arm motion, which may aid in the assessment and planning of stroke rehabilitation, and help to shorten recovery time.     

Changes in cardiovascular disease risk factors from age 9 to 19 and the influence of television viewing

Objective:

The purpose of this study was to determine if time spent watching television is associated with changes in cardiovascular disease (CVD) risk factors from age 9 to 19.

Design and Methods:

Participants were girls enrolled in the NHLBI Growth and Health Study (n = 1,702), and CVD risk factors were measured at ages 10, 12, 14, 16, and 19. Longitudinal quantile regression was used to determine if television viewing was associated with changes in CVD risk factors over time at the 10th, 25th, 50th, 75th, and 90th percentiles of the CVD risk factors.

Results:

In black girls, television viewing (h/wk) was positively associated with sum of skinfolds (mm) at the 75th (0.22, 99% CI, 0.06‐0.38) and 90th percentiles (0.21, 99% CI, 0.05‐0.36), but not at the 10th, 25th, or 50th percentiles. In white girls, television viewing (h/wk) was positively associated with sum of skinfolds (mm) with the strength of the associations progressively stronger toward the upper tail of the skinfold distribution, adjusting for physical activity and other covariates (10th percentile: 0.08, 99% CI, 0.03‐0.13; 90th percentile: 0.42, 99% CI, 0.24‐0.59). All associations were adjusted for physical activity, dietary factors, sleep, and maturation. No associations were observed between television viewing and changes in systolic blood pressure, triglycerides, or cholesterol levels in black or white girls.

Conclusion:

Girls who spent more time watching television had greater increases in sum of skinfolds from age 9 to 19, independent of physical activity levels and other covariates. The associations observed were stronger at the upper tail of the skinfold distribution.     

De novo mutations producing unstable hemoglobins or hemoglobins M

Summary Hemoglobins M and unstable hemoglobins cause clinical syndromes that are transmitted in autosomal dominant fashion. Pedigrees of 50 probands with de novo mutations producing unstable Hb disease or Hb M disease were compiled. Cases were ascertained (1) by screening the relevant literature published from 1950 through 1980 and (2) through personal communication. Additional pedigree data on several published cases were collected, and a depository containing all available information rekated to de novo Hb mutants was established. The 50 probands were born in 14 countries between 1922 and 1976. Paternity was tested in 36% of the cases, and no instance of false paternity was noted.The data were used to test for an association of advanced parental age with the appearance of de novo mutants. Paternal ages at the probands' births ranged from 20 to 50 years, with a mean of 32.7 years. Maternal ages ranged from 18 to 43 years, with a mean of 28.5 years. For each year and country (or, where necessary, for the nearest possible year and/or a demographically similar country), the cumulative frequency distributions of the ages of parents who had a child in that country and year were computed; the ages of each proband's father and mother were then expressed as percentiles on these distributions. The distribution of paternal age percentiles was shifted toward the upper end of the range, with 11 of the 50 paternal ages falling between the 90th and 100th percentiles. The distribution of maternal age percentiles was more complex, with one peak (10 of 50 ages) falling between the 30th and 40th percentiles and a second peak (10 of 50 ages), between the 90th and 100th percentiles. These distributions, though suggestive of an association of advanced parental age and the appearance of de novo mutations that cause unstable Hb disease or methemoglobinemic cyanosis, were not significantly different from those uniform distributions expected in the absence of a parental age effect.     

Age variation in the upper limit of hearing.

The upper limit of hearing was measured in 6105 otologically normal ears of subjects ranging in age from 5 to 89 years. The results are as follows: in each age group from 5 to 59 years in both sexes, the upper limit of hearing showed an approximately normal distribution if a logarithmic scale was used for the upper limit of hearing axis. The mode of the distribution shifted to a lower frequency with increasing age. Over age 60 years, the distribution became much wider. Standard upper limit age curves were established by calculating 10th, 25th, 50th, 75th and 90th percentiles for each age group. From early childhood where no age variation was recognized in conventional audiometry, deterioration of the upper limit of hearing was already in progress. This deterioration was slight between ages 25 and 39 but at ages over 40 it was accelerated and led to so-called presbycousis. The upper limit of hearing was found to be one of the best parameters for showing the quantitative age-related changes in hearing.     

The accuracy of measuring the kinematics of rising from a chair with accelerometers and gyroscopes

The purpose of this study was to assess the accuracy of measuring angle and angular velocity of the upper body and upper leg during rising from a chair with accelerometers, using low-pass filtering of the accelerometer signal. Also, the improvement in accuracy of the measurement with additional use of high-pass filtered gyroscopes was assessed. Two uni-axial accelerometers and one gyroscope (DynaPort) per segment were used to measure angles and angular velocities of upper body and upper leg. Calculated angles and angular velocities were compared to a high-quality optical motion analysis system (Optotrak), using root mean squared error (RMS) and correlation coefficient (r) as parameters. The results for the sensors showed that two uni-axial accelerometers give a reasonable accurate measurement of the kinematics of rising from a chair (RMS = 2.9, 3.5, and 2.6 degrees for angle and RMS = 9.4, 18.4, and 11.5 degrees /s for angular velocity for thorax, pelvis, and upper leg, respectively). Additional use of gyroscopes improved the accuracy significantly (RMS = 0.8, 1.1, and 1.7 degrees for angle and RMS = 2.6, 4.0 and 4.9 degrees /s for angular velocity for thorax, pelvis and upper leg, respectively). The low-pass Butterworth filter had optimal cut-off frequencies of 1.05, 1.3, and 1.05 for thorax, pelvis, and upper leg, respectively. For the combined signal, the optimal cut-off frequencies were 0.18, 0.2, and 0,38 for thorax, pelvis and upper leg, respectively. The filters showed no subject specificity. This study provides an accurate, inexpensive and simple method to measure the kinematics of movements similar to rising from a chair.     

Concurrent validity and reliability of a mobile tracking technology to measure angular and linear movements of the neck

The neck can be moved in six degrees of freedom. Current 3D-optoelectronic motion-capture systems capable of measuring these movements are inappropriate for use in clinical practice because they are stationary, expensive and time-consuming. We therefore developed a less complex 3D-tracking technology based on Steam®VR to measure six degrees of freedom in a clinical setting. The aim of this study was to assess the validity and reliability of this system.The developed prototype consists of two infrared-emitting lighthouses and sensors, mounted on the participant’s helmet and trunk belt, to detect the orientation of the head and trunk. The system was evaluated by means of an infrared light-reflecting marker tracking system. Twenty healthy participants, equipped with these sensors and markers, performed thirteen neck movement tasks. Linear and angular movements were measured. These tasks were repeated after six to eight days to assess test-retest reliability. Concurrent validity was assessed by the root mean square error, and reliability with generalizability theory.With an average root mean square error between 1.2 and 2.0° in angular and 0.4–0.5 cm in linear movements, the prototype was shown to precisely track these movements. Reliability of the prototype and the reference system was comparable for all tasks. A high contribution of participant’s variability to the observed variance was generally detected, with the exception of joint repositioning error and upper cervical flexion.The reliability was task-specific and did not differ between the systems. The prototype system was shown to be valid, although the reliability of the repositioning and upper cervical flexion tests needs to be reconsidered.     

Cluster-based upper body marker models for three-dimensional kinematic analysis: Comparison with an anatomical model and reliability analysis

Quantifying angular joint kinematics of the upper body is a useful method for assessing upper limb function. Joint angles are commonly obtained via motion capture, tracking markers placed on anatomical landmarks. This method is associated with limitations including administrative burden, soft tissue artifacts, and intra- and inter-tester variability. An alternative method involves the tracking of rigid marker clusters affixed to body segments, calibrated relative to anatomical landmarks or known joint angles. The accuracy and reliability of applying this cluster method to the upper body has, however, not been comprehensively explored. Our objective was to compare three different upper body cluster models with an anatomical model, with respect to joint angles and reliability. Non-disabled participants performed two standardized functional upper limb tasks with anatomical and cluster markers applied concurrently. Joint angle curves obtained via the marker clusters with three different calibration methods were compared to those from an anatomical model, and between-session reliability was assessed for all models. The cluster models produced joint angle curves which were comparable to and highly correlated with those from the anatomical model, but exhibited notable offsets and differences in sensitivity for some degrees of freedom. Between-session reliability was comparable between all models, and good for most degrees of freedom. Overall, the cluster models produced reliable joint angles that, however, cannot be used interchangeably with anatomical model outputs to calculate kinematic metrics. Cluster models appear to be an adequate, and possibly advantageous alternative to anatomical models when the objective is to assess trends in movement behavior.     

Habitat use by yellowheads,Mohoua ochrocephala (Aves: Muscicapidae), in the Hawdon River Valley,Arthur’s Pass National Park. 2. Time budgets and foraging behaviour

Abstract

Instantaneous sampling was used to describe the ecological niche of yellowheads. Observations began during nesting in 1983 and continued until April 1984. Yellowheads spent on average 90% of their time foraging. As daylength decreased, an increasing proportion of time was spent foraging and a decreasing proportion of time was spent on social activities. When feeding nestlings, females spent significantly more time foraging than did males. Yellowheads spent 75% of their time in the upper understorey and the shaded canopy. There was no difference in the relative use of strata in the two canopy tree species, nor a sexual difference in the time spent in each strata. Yellowheads were entirely insectivorous. Prey items were recorded on 33 occasions; most were lepidopteran larvae. The most common foraging method was surface gleaning, most often on foliage and trunks. Time spent foraging on different substrates varied with tree diameter and tree species. Relative use of different foraging methods changed during the study, as did the types of substrates searched for prey and the proportion of time spent in different strata and at different heights in the forest. Presumably these changes were in response to variations in invertebrate availability.     

Greater screen time is associated with adolescent obesity: A longitudinal study of the BMI distribution from Ages 14 to 18

Objective:

Previous research has examined the association between screen time and average changes in adolescent body mass index (BMI). Until now, no study has evaluated the longitudinal relationship between screen time and changes in the BMI distribution across mid to late adolescence.

Design and Methods:

Participants (n = 1,336) were adolescents who were followed from age 14 to age 18 and surveyed every 6 months. Time spent watching television/videos and playing video games was self‐reported (<1 h day^?1, 1 h day^?1, 2 h day^?1, 3 h day^?1, 4 h day^?1, or 5+ h day^?1). BMI (kg m^?2) was calculated from self‐reported height and weight. Longitudinal quantile regression was used to model the 10th, 25th, 50th, 75th, and 90th BMI percentiles as dependent variables. Study wave and screen time were the main predictors, and adjustment was made for gender, race, maternal education, hours of sleep, and physical activity.

Results:

Increases at all the BMI percentiles over time were observed, with the greatest increase observed at the 90th BMI percentile. Screen time was positively associated with changes in BMI at the 50th (0.17, 95% CI: 0.06, 0.27), 75th (0.31, 95% CI: 0.10, 0.52), and 90th BMI percentiles (0.56, 95% CI: 0.27, 0.82). No associations were observed between screen time and changes at the 10th and 25th BMI percentiles.

Conclusions:

Positive associations between screen time and changes in the BMI at the upper tail of the BMI distribution were observed. Therefore, lowering screen time, especially among overweight and obese adolescents, could contribute to reducing the prevalence of adolescent obesity.

     

Eelgrass, Zostera marina, growth along depth gradients: upper boundaries of the variation as a powerful predictive tool

1200 measurements of eelgrass ( Zostera marina ) biomass, shoot density and cover along 19 depth gradients in Øresund, located between Denmark and Sweden, were analysed to characterise growth of eelgrass in relation to depth. The large data set allowed analyses of boundaries of distribution as well as of average trends. Natural variability is large in shallow water where populations are disturbed by wave action and other physical parameters. Models based on average values, therefore, did not adequately describe growth regulation by resources, and only explained a minor part (up to 30%) of the overall variation in data. In contrast, boundary functions, which describe the upper bounds of distributions, focus on the variation produced by the ultimately growth-regulating resource, and therefore provide models with high predictive power. An exponential model explained up to 90% of the variation in upper bounds of eelgrass shoot density as a function of depth and indicated that shoot density was ultimately regulated by light availability. The boundary functions demonstrated that eelgrass shoot density, biomass and cover followed markedly different patterns as functions of depth and were affected differently by the factors governing their distribution. In addition, boundary functions revealed informative spatial structures in data and illustrated whether a given general trend was caused by changes in maximum values, minimum values or both. For example, upper and lower boundaries of biomass-shoot density relations changed markedly with depth, demonstrating depth-related changes in intraspecific succession and competition patterns. Boundary functions are therefore suggested as a promising tool for analysing ultimate regulating factors of distribution and growth of organisms when large data sets are available.     

Characterization and Simulation of Uncertain Frequency Distributions: Effects of Distribution Choice,Variability, Uncertainty,and Parameter Dependence

We use bootstrap simulation to characterize uncertainty in parametric distributions, including Normal, Lognormal, Gamma, Weibull, and Beta, commonly used to represent variability in probabilistic assessments. Bootstrap simulation enables one to estimate sampling distributions for sample statistics, such as distribution parameters, even when analytical solutions are not available. Using a two-dimensional framework for both uncertainty and variability, uncertainties in cumulative distribution functions were simulated. The mathematical properties of uncertain frequency distributions were evaluated in a series of case studies during which the parameters of each type of distribution were varied for sample sizes of 5, 10, and 20. For positively skewed distributions such as Lognormal, Weibull, and Gamma, the range of uncertainty is widest at the upper tail of the distribution. For symmetric unbounded distributions, such as Normal, the uncertainties are widest at both tails of the distribution. For bounded distributions, such as Beta, the uncertainties are typically widest in the central portions of the distribution. Bootstrap simulation enables complex dependencies between sampling distributions to be captured. The effects of uncertainty, variability, and parameter dependencies were studied for several generic functional forms of models, including models in which two-dimensional random variables are added, multiplied, and divided, to show the sensitivity of model results to different assumptions regarding model input distributions, ranges of variability, and ranges of uncertainty and to show the types of errors that may be obtained from mis-specification of parameter dependence. A total of 1,098 case studies were simulated. In some cases, counter-intuitive results were obtained. For example, the point value of the 95th percentile of uncertainty for the 95th percentile of variability of the product of four Gamma or Weibull distributions decreases as the coefficient of variation of each model input increases and, therefore, may not provide a conservative estimate. Failure to properly characterize parameter uncertainties and their dependencies can lead to orders-of-magnitude mis-estimates of both variability and uncertainty. In many cases, the numerical stability of two-dimensional simulation results was found to decrease as the coefficient of variation of the inputs increases. We discuss the strengths and limitations of bootstrap simulation as a method for quantifying uncertainty due to random sampling error.     

Sensitivity of trapezius electromyography to differences between work tasks - influence of gap definition and normalisation methods.

Surface electromyography (EMG) has been used extensively to estimate muscular load in studies of work related musculoskeletal disorders, especially for the trapezius muscle. The occurrences of periods of EMG silence (gaps), the time below a predetermined threshold level (muscular rest) and various percentiles of the amplitude distribution (APDF) are commonly used summary measures. However, the effects of the criteria used to calculate these measures (e.g., gap duration, threshold level, normalisation method) on the sensitivity of these measures to accurately differentiate work loads is not well known.Bilateral trapezius EMG was recorded, for a full workday, for 58 subjects following both maximal (MVE) and submaximal (RVE) reference contractions. Gap frequency, muscular rest, and percentiles were derived for eight fundamental work tasks. The calculations were performed using different gap duration criteria, threshold levels and normalisation methods.A gap duration of less than 1/2 s, and threshold level approximately 0.3% MVE for gap frequency, and approximately 0.5% MVE for muscular rest, were the criteria that optimised sensitivity to task differences. Minimal sensitivity to tasks and a high sensitivity to individuals was obtained using gap frequency with a threshold level of approximately 1% MVE. Normalisation to RVE, rather than MVE, improved sensitivity to differences between tasks, and reduced undesirable variability. Muscular rest was more sensitive to task differences than APDF percentiles.     

Quantification and visualization of coordination during non-cyclic upper extremity motion

There are many design challenges in creating at-home tele-monitoring systems that enable quantification and visualization of complex biomechanical behavior. One such challenge is robustly quantifying joint coordination in a way that is intuitive and supports clinical decision-making. This work defines a new measure of coordination called the relative coordination metric (RCM) and its accompanying normalization schemes. RCM enables quantification of coordination during non-constrained discrete motions. Here RCM is applied to a grasping task. Fifteen healthy participants performed a reach, grasp, transport, and release task with a cup and a pen. The measured joint angles were then time-normalized and the RCM time-series were calculated between the shoulder-elbow, shoulder-wrist, and elbow-wrist. RCM was normalized using four differing criteria: the selected joint degree of freedom, angular velocity, angular magnitude, and range of motion. Percent time spent in specified RCM ranges was used as a composite metric and was evaluated for each trial. RCM was found to vary based on: (1) chosen normalization scheme, (2) the stage within the task, (3) the object grasped, and (4) the trajectory of the motion. The RCM addresses some of the limitations of current measures of coordination because it is applicable to discrete motions, does not rely on cyclic repetition, and uses velocity-based measures. Future work will explore clinically relevant differences in the RCM as it is expanded to evaluate different tasks and patient populations.     

A three-dimensional, six-segment chain analysis of forceful overarm throwing.

A three-dimensional, six-segment model was applied to the pitching motion of three professional pitchers to analyze the kinematics and kinetics of the hips, upper trunk, humerus and forearm plus hand of both the upper limbs. Subjects were filmed at 250 frames per second. An inverse dynamics approach and angular momentum principle with respect to the proximal endpoint of a rigid segment were employed in the analysis. Results showed considerable similarities between subjects in the kinetic control of trunk rotation about the spine's longitudinal axis, but variability in the control of trunk lean both to the side and forward. The kinetics of the throwing shoulder and elbow joint were comparable between subjects, but the contribution of the non-throwing upper limb was minimal and variable. The upper trunk rotators played a key role in accelerating the ball to an early, low velocity near stride foot contact. After a brief pause they resumed acting strongly in a positive direction, though not enough to prevent trunk angular velocity slowing, as the musculature of the arm applied a load at the throwing shoulder. The interaction moment from the proximal segments assisted the forearm extensor in slowing flexion and producing rapid elbow extension near ball release. The temporal onset of muscular torques was not in a strictly successive proximal-to-distal sequence.     

Simulated activities of daily living do not replicate functional upper limb movement or reduce movement variability

Kinematic assessments of the upper limb during activities of daily living (ADLs) are used as an objective measure of upper limb function. The implementation of ADLs varies between studies; whilst some make use of props and define a functional target, others use simplified tasks to simulate the movements in ADLs. Simulated tasks have been used as an attempt to reduce the large movement variability associated with the upper limb. However, it is not known whether simulated tasks replicate the movements required to complete ADLs or reduce movement variability. The aim of this study is to evaluate the use of simulated tasks in upper limb assessments in comparison to functional movements. Therefore answering the following questions: Do simulated tasks replicate the movements required of the upper limb to perform functional activities? Do simulated tasks reduce intra- and inter-subject movement variability? Fourteen participants were asked to perform five functional tasks (eat, wash, retrieve from shelf, comb and perineal care) using two approaches: a functional and a simulated approach. Joint rotations were measured using an optoelectronic system. Differences in movement and movement variability between functional and simulated tasks were evaluated for the thorax, shoulder, elbow/forearm and wrist rotations. Simulated tasks did not accurately replicate the movements required for ADLs and there were minimal differences in movement variability between the two approaches. The study recommends the use of functional tasks with props for future assessments of the upper limb.     

Reproducibility of MUAP properties in array surface EMG recordings of the upper trapezius and sternocleidomastoid muscle

The use of array surface EMG recordings for detailed assessment of motor control and muscle properties is increasing. Motor unit action potentials (MUAPs) and their properties can be extracted from these recordings. The objective of this study was to determine the reproducibility of variables obtained from array surface EMG recordings of the shoulder and neck muscles during different functional tasks.Eight-channel linear arrays were placed on the upper trapezius (UT) and sternocleidomastoid (SCM) muscles of 12 healthy subjects. Subjects performed 3 tasks: shoulder abduction (90°), ironing (repetitively touching two ends of a horizontal bar in front of the subject), and 90° head turning. The protocol was performed twice while electrodes remained on and repeated a third time a week later.Three global and six MUAP-related variables were calculated. Intra-class correlation coefficients (ICC) were calculated to assess reliability and smallest detectable changes (SDC) were calculated to assess agreement.In general, the EMG variables showed high levels of reliability which suggests they may be effective for differentiating between-subjects. SDC was found to be considerably lower for the frequency-related (5–23%) than for the amplitude-related variables (15–78%), indicating that the frequency-related variables may be more suitable for investigating interventions which aim to modify motor control. There was no difference in reproducibility between global and MUAP-related variables, which justifies their complementary use.     

Three-dimensional surfaces for human muscle kinetics

Torque, angular velocity and angular position data were collected on six subjects performing maximum knee extensions at 11 speeds. Three-dimensional (3-D) surfaces were drawn for each subject and for the normalised, averaged data. For each subject, the moment arms of knee extensor and patella excursion were determined from radiographs and averaged across subjects. These data were then used to convert the angular data to linear force, velocity and information on muscle length. Surfaces were plotted for these data and evaluated. Results indicate a major difference between the knee positions for production of peak force or torque. Peak linear force was found to occur at an average of 75 degrees of flexion, while peak torque was found at 57 degrees. It was also suggested that 3-D surfaces provide more information than the traditional methods of presenting dynamic strength results.