In vivo behaviour of human muscle architecture and mechanomyographic response using the interpolated twitch technique

This study investigated the origin of curvilinear change in the superimposed mechanomyogram (MMG) amplitude of the human medial gastrocnemius muscle (MG) with increasing contraction intensity. The superimposed twitch amplitude, the superimposed MMG amplitude and the extent of fascicle shortening were measured using ultrasonic images of electrical stimulation during isometric plantar flexions at levels 20%, 40%, 60%, 80%, and 100% of the maximal voluntary contraction (MVC). The superimposed twitch amplitude, the superimposed MMG amplitude and the extent of fascicle shortening decreased with increasing contraction intensity. The superimposed MMG amplitude and the extent of fascicle shortening showed a curvilinear decrease, while the superimposed twitch amplitude showed a linear decrease at levels up to 80% of the MVC. There was a linear relationship between the superimposed MMG amplitude and the extent of fascicle shortening at different contraction intensities. These results indicate that the superimposed MMG amplitude reflects changes in the extent of fascicle shortening at different contraction intensities better than the superimposed twitch amplitude. Our study suggests that the origin of the curvilinear decrease of superimposed MMG amplitude is associated with a curvilinear decrease of the extent of fascicle shortening with increasing contraction intensity in the human MG.     

Variability in the interpolated twitch torque for maximal and submaximal voluntary contractions.

The superimposed twitch technique is frequently used to study the degree of motor unit activation during voluntary effort. This technique is one of the preferred methods to determine the activation deficit (AD) in normal, athletic, and patient populations. One of the limitations of the superimposed twitch technique is its variability under given contractile conditions. The objective of this research was to determine the source(s) of variability in the superimposed twitch force (STF) for repeat measurements. We hypothesized that the variability in the AD measurements may be caused by the timing of the twitch force relative to the onset of muscle activation, by force transients during the twitch application, by small variations in the actual force from the nominal target force, and by variations in the resting twitch force. Twenty-eight healthy subjects participated in this study. Sixteen of these subjects participated in a protocol involving contractions at 50% of their maximal voluntary contraction (MVC) effort, whereas the remaining 12 participated in a protocol involving contractions at 100% of their MVC. Doublet-twitch stimuli were superimposed onto the 50 and 100% effort knee extensor muscle contractions, and the resting twitch forces, voluntary knee extensor forces, and STFs were then measured. The mean resting twitch forces obtained before and after 8 s of 50% of MVC were the same. Similarly, the mean STFs determined at 1, 3, 5, and 7 s into the 50% MVC were the same. The variations in twitch force were significantly smaller after accounting for the actual force at twitch application than those calculated from the prescribed forces during the 50% MVC protocol (P < 0.05). Furthermore, the AD and the actual force showed statistically significant negative correlations for the 50% MVC tests. The interpolated twitch torque determined for the maximal effort contractions ranged from 1 to 70%. In contrast to the protocol at 50% of MVC, negative correlations were only observed in 5 of the 12 subjects during the 100% effort contractions. These results suggest that small variations in the actual force from the target force can account for the majority of the variations in the STFs for submaximal but not maximal effort contractions. For the maximal effort contractions, large variations in the STF exist due to undetermined causes.     

Methodological issues in alpha biofeedback training

Current controversies concerning outcomes of EEG alpha feedback training are at least in part due to methodological differences among different studies. The aim of this paper is to provide future and present researchers in this field with an analysis of methods used in most of the studies published from 1968 to 1976, and to comment on those methodological issues we think most important. These include alpha assessment, training schedules, and uni- versus bidirectional training. This analysis is accomplished in part by a series of tables listing 45 studies and the detailed methodologies used. It is believed that the probabilities of successful feedback enhancement of alpha can be substantially improved by incorporating the following suggestions: (a) employing at least four training sessions, (b) the use of continuous rather than dichotomous feedback, supplemented by periodic quantitative scores of progress, and (c) using training trials of at least 10 minutes' duration.     

Methodological issues unsaid in medical research

Methodology consitutes the study of methods considered as < manners of leading its thought, of establishing or of showing truths according to certain principles and with a certain order >. We will see that medical < truths >, knowledge, could be of an extremely different nature: factual knowledge is a simple observation, often with operational vocation\; theoretical knowledge belongs to a coherent whole, it fascines and facilitates our representations of pathologies\; the causal knowledge is often the subject of extreme interrogations in medical practice\; it is of primarily metaphysical nature. These distinctions are not without consequence in methodological terms. Theories are useful because they facilitate the choice of the assumptions to be tested, the variables to be measured and the interpretation of the results of experiments. The risk however exists to be unable to think apart from their framework, and thus to neglect any source of knowledge which they could not integrate. The cause is inaccessible to science\; it will be necessary, in practice, to be limited to the search for variables of upstream on which action of prevention or cure could be undertaken. To establish, to show this medical knowledge, it is necessary to resort to the scientific method by formulating refutable assumptions by reproducible experiments, and that this process involves a belief in the found results. It appears thus that for the same experimental plan, the level of belief and thus the level of proof of the results is a function of the type of measurement carried out (commonplace measurement or of high technicality), of the medical discipline and the media character or not of studied pathology, even of stakes of being able. The medical reproducibility of experiments is problematic since results of these experiments are in general random. This results from the considerable number of variables entering in the determination of human pathologies, and that the majority of these variables are either unknown, or impossible to control. Randomisation makes it possible to give a probabilistic character to this risk: it is then possible to resort to mathematics to carry out statistical tests, to calculate confidence intervals and to profit from a possibility of making inferences with a known margin of error. In the absence of randomisation, it is possible to resort to models\; they imply however the knowledge of statistical methods, reserve, experience and a great intellectual honesty during the interpretation of the results, finally a replication of the experiments is here, more than elsewhere, essential.     

Vibrotactile thresholds of the Non-Pacinian I channel: I. Methodological issues

Thresholds of the Non-Pacinian I (NP I) channel were measured using a two-interval forced-choice paradigm, a technique independent of the subject's criterion. The studies were performed using the terminal phalanx of the human middle finger with a 40-Hz vibratory stimulus. Unlike most of the previous experiments performed in our laboratory, a contactor surround was not used. This was done to enable comparison with population models of mechanoreceptive fibers in the literature. Since the Pacinian (P) channel and NP I channel have similar vibrotactile thresholds at 40?Hz, a forward-masking procedure was used to elevate the thresholds of the P channel with respect to the NP I channel. While it has been established that the Pacinian fibers are entrained at high stimulus levels, the P channel can be perceptually masked using a 250-Hz stimulus presented prior to the 40-Hz test stimulus. The masking functions were found to be approximately linear on log-log axes and the threshold shifts were found to increase as the masking-stimulus levels increased. The results are discussed in relation to previous studies that were performed at various stimulation sites by using a contactor surround or not. A companion paper presents the variation of NP I-channel thresholds, measured using the methods described herein, and addresses the effects of stimulation along the proximo-distal axis of the phalanx. The companion paper also discusses the predictions of a computational model, recently proposed, in light of the empirical results presented.     

Methodological issues and advances in biological meta-analysis

Meta-analysis has changed the way researchers conduct literature reviews not only in medical and social sciences but also in biological sciences. Meta-analysis in biological sciences, especially in ecology and evolution (which we refer to as ‘biological’ meta-analysis) faces somewhat different methodological problems from its counterparts in medical and social sciences, where meta-analytic techniques were originally developed. The main reason for such differences is that biological meta-analysis often integrates complex data composed of multiple strata with, for example, different measurements and a variety of species. Here, we review methodological issues and advancements in biological meta-analysis, focusing on three topics: (1) non-independence arising from multiple effect sizes obtained in single studies and from phylogenetic relatedness, (2) detecting and accounting for heterogeneity, and (3) identifying publication bias and measuring its impact. We show how the marriage between mixed-effects (hierarchical/multilevel) models and phylogenetic comparative methods has resolved most of the issues under discussion. Furthermore, we introduce the concept of across-study and within-study meta-analysis, and propose how the use of within-study meta-analysis can improve many empirical studies typical of ecology and evolution.     

Autism genetics: Methodological issues and experimental design

Autism is a complex neuropsychiatric disorder of developmental origin, where multiple genetic and environmental factors likely interact resulting in a clinical continuum between affected and unaffected individuals in the general population. During the last two decades, relevant progress has been made in identifying chromosomal regions and genes in linkage or association with autism, but no single gene has emerged as a major cause of disease in a large number of patients. The purpose of this paper is to discuss specific methodological issues and experimental strategies in autism genetic research, based on fourteen years of experience in patient recruitment and association studies of autism spectrum disorder in Italy.     

Methodological issues related to thickness-based muscle size evaluation

The purpose of this study was to highlight the issues related to thickness-based muscle size evaluation that is commonly done in field studies. The cross-sectional area, thickness (the vertical distance from the upper end of the elbow flexors to that of the humerus) and width (the horizontal distance from the left to the right end of the elbow flexors) of the elbow flexors at levels from the reference site (60% of the upper arm length from the acromial process of the scapula to the lateral epicondyle of the humerus) to 5 cm distal to it were determined in 11 young men using magnetic resonance imaging, both at rest and during isometric elbow flexion at 30% of maximal voluntary contraction. During 30% of maximal voluntary contraction, the thickness increased but the width decreased at each measurement site compared with those at rest. This was possibly due to difference in muscle slackness between both conditions. The correlation coefficients between the thickness and cross-sectional area for the elbow flexors were significantly lower at rest (r=0.551-0.856) than during 30% of maximal voluntary contraction (r=0.711-0.922). The present findings indicate that the thickness-based muscle size measurement at rest includes errors owing to the slackness of the resting muscles.     

Model-building with interpolated temporal data

Ecological data can be difficult to collect, and as a result, some important temporal ecological datasets contain irregularly sampled data. Since many temporal modelling techniques require regularly spaced data, one common approach is to linearly interpolate the data, and build a model from the interpolated data. However, this process introduces an unquantified risk that the data is over-fitted to the interpolated (and hence more typical) instances. Using one such irregularly-sampled dataset, the Lake Kasumigaura algal dataset, we compare models built on the original sample data, and on the interpolated data, to evaluate the risk of mis-fitting based on the interpolated data.     

Methodological issues in pooled analysis of biomarker studies

The number of epidemiological studies involving biological markers has dramatically increased in the last years. These studies are generally small sized and this feature has called attention to the need to summarize the individual results, while waiting for the completion of larger studies, designed to answer questions that have been raised by preliminary studies. We describe here some of the methodological issues related to pooling data of biomarker studies, taking advantage of the experience accumulated by conducting two pooled analyses, one of studies of metabolic gene polymorphisms and cancer, the other on cytogenetic damage. Topics that are considered are: data standardization, population selection and bias, statistical analysis, ethical issues.Pooled analysis seems to provide a relevant improvement over meta-analysis in molecular epidemiology studies, though more research on methodology is needed.     

Clustering metagenomic sequences with interpolated Markov models

Background  

Sequencing of environmental DNA (often called metagenomics) has shown tremendous potential to uncover the vast number of unknown microbes that cannot be cultured and sequenced by traditional methods. Because the output from metagenomic sequencing is a large set of reads of unknown origin, clustering reads together that were sequenced from the same species is a crucial analysis step. Many effective approaches to this task rely on sequenced genomes in public databases, but these genomes are a highly biased sample that is not necessarily representative of environments interesting to many metagenomics projects.     

Methodological issues and inconsistencies in the field of omega-3 fatty acids research

There is growing interest into researching omega-3 fatty acids; however, there are considerable variations in the methodologies employed. Many studies add oils to animal feed and under ambient conditions omega-3 fatty acids are particularly unstable and prone to autoxidation and peroxidative damage. It is therefore important to take specific precautions with the stock preparations and when preparing the experimental diets. There is a need for clarity in the reporting of methodologies employed, such as how oil preparations are stored and handled, how experimental diets are prepared, the potential effects of adding additional antioxidants, whether there is a clear rationale for the selection of control/placebo diets, which may be situation dependent, and consistency in expressing the experimental doses. The purpose of this article is to highlight some of these issues in the hope of promoting discussion, and potentially developing guidelines as to what represents best practice.     

Microbial gene identification using interpolated Markov models.

This paper describes a new system, GLIMMER, for finding genes in microbial genomes. In a series of tests on Haemophilus influenzae , Helicobacter pylori and other complete microbial genomes, this system has proven to be very accurate at locating virtually all the genes in these sequences, outperforming previous methods. A conservative estimate based on experiments on H.pylori and H. influenzae is that the system finds >97% of all genes. GLIMMER uses interpolated Markov models (IMMs) as a framework for capturing dependencies between nearby nucleotides in a DNA sequence. An IMM-based method makes predictions based on a variable context; i.e., a variable-length oligomer in a DNA sequence. The context used by GLIMMER changes depending on the local composition of the sequence. As a result, GLIMMER is more flexible and more powerful than fixed-order Markov methods, which have previously been the primary content-based technique for finding genes in microbial DNA.     

Sarcomere dynamics in a spontaneous contraction wave and its effect on the following, electrically triggered twitch in rat myocyte. Comparison with the rested state twitch

A spontaneous contraction (SC) wave propagates among sarcomeres in heart muscle by the mechanism of Ca(++)-induced release of Ca++ from sarcoplasmic reticulum (SR). In the present study, some characteristics of unloaded shortening during the SC and its effect on a subsequent, electrically triggered twitch (Tsc) were examined at a sarcomere level in isolated rat myocytes. The results were compared with those of a rested state twitch (RS), which was accompanied by an action potential. Average shortening velocity from onset to peak of shortening was 3.74 +/- 1.25 (mean +/- SD, n = 18) and 5.35 +/- 2.30 microns/s per sarcomere (n = 54) in SC and RS, respectively. That the former was smaller than the latter (P < 0.01, t test) suggests that Ca++ are released from the SR more slowly in the SC than the RS. There were no differences in either the extent or area of shortening between SC and RS. The extent of shortening increased significantly as shortening velocity increased in all the SC (P < 0.05), RS, Tsc, and triggered twitch (Trs) after the RS (P < 0.001 in the last three). The slope of the line for the regression of the extent upon the velocity of shortening in the SC was approximately 1.5 times greater than the other three. This suggests that the SC has a different time course of change of myoplasmic [Ca++] and therefore a different mode of the causal SR Ca++ release from the electrically triggered twitches (RS, Trs, Tsc). There were positive correlations between the extent and the area of shortening in each of the RS (P < 0.01), the Trs (P < 0.05), and the Tsc (P < 0.001), but not in SC. The slope of the line for the regression of the extent upon the area of shortening in the Tsc was about three times greater than those in the RS and the Trs, suggesting characteristics of the Tsc from different those of the RS and the Trs. An SC inhibited a Tsc in an interval-dependent manner. The shortening velocity in the Tsc recovered fully at a test interval of approximately 0.6 s between the onsets of the two successive contractions. The velocity increased further with further increasing the test interval (up to 0.9 s). At a test interval of 0.8-0.9 s, the shortening velocity in the Tsc was greater than those in the preceding SC and the corresponding Trs by 1.17- and 1.80-fold, respectively, as compared in the same five sarcomeres.(ABSTRACT TRUNCATED AT 400 WORDS)     

Methodological issues in the biological monitoring of urinary benzene and S-phenylmercapturic acid at low exposure levels

Biological monitoring of low level exposure to pollutants is a very challenging analytical activity, and the quality of results is difficult to assess, especially when a certified reference material is unavailable. The aim of this work was to evaluate the reliability of the assays used to measure urinary benzene (Benz-U) and S-phenylmercapturic acid (SPMA), by applying an internal quality control protocol. Urine spot samples from 705 subjects who were either members of the general urban population, gasoline station attendants, or refinery plant workers were assayed for Benz-U and SPMA, using GC/MS and LC/MS/MS, with quantification limits of 15 ng/L and 0.10 μg/L. The median Benz-U concentration was 263 ng/L (60-2789 ng/L, 5th-95th percentile), and the median SPMA concentration was 0.19 μg/L (<0.1-2.5 μg/L, 5th-95th percentile). Linearity of both assays was good, but a less-than-proportional response was found for SPMA concentrations below 1 μg/L. Between-run precision and accuracy for Benz-U concentration determination were assessed using quality controls at 120 ng/L and 1000 ng/L and were 10.3% and 4.8%, and 104.8% and 98.9%, respectively; while the precision and accuracy for SPMA concentration determination at 0.3 μg/L, 2.5 μg/L, and 20 μg/L were 40.3%, 6.2%, and 6.2%, and 48.3%, 96.3%, and 98.8%, respectively. Precision, estimated using duplicates of unknown samples, was 13.4% for Benz-U and 26.5% for SPMA analyses. Control charts for the means of the slope of the linear calibration curve of Benz-U showed good stability of the means over a five-year period. For SPMA, a two-laboratory comparison revealed acceptable agreement between ln-transformed data pairs, with a slope of the linear regression of 0.863 (confidence interval 0.774-0.952), null intercept, and a Pearson's r value of 0.844. Reliable results were obtained for Benz-U analyses over the entire concentration range, and for high and medium SPMA levels. However, the determination of SPMA concentrations at levels close to the limit of quantification was less reliable.     

Methodological issues in studying the anxiety-reducing effects of animals: Reflections from a pediatric dental study

Abstract

This article reports observations made during a study investigating the role of a therapy dog in reducing anxiety in urban children visiting the dentist. The design and execution of the study were affected by methodological issues such as the reaction of urban children to the dog in the clinic, the tools used to measure anxiety in the children, the age and pet-ownership status of the children, and the personality of the therapy dog. Suggestions made for researchers designing similar studies include allowing children to become comfortable with the therapy dog before beginning formal data collection, working with younger children who have made fewer visits to the dentist, and using or developing more accurate tools for measuring behavioral and physiological anxiety.     

Voluntary activation of trapezius measured with twitch interpolation

This study investigated the feasibility of measuring voluntary activation of the trapezius muscle with twitch interpolation. Subjects (n = 8) lifted the right shoulder or both shoulders against fixed force transducers. Stimulation of the accessory nerve in the neck was used to evoke maximal twitches in right trapezius. The twitch-like increments in force (superimposed twitches) evoked during different strength voluntary contractions were linearly related to voluntary force (r = ?0.82 to ?0.99). Hence, voluntary activation could be quantified by twitch interpolation with this stimulus. Comparison of unilateral and bilateral MVCs showed that maximal voluntary force was greater in unilateral than bilateral efforts (92.7 ± 2.9% and 82.3 ± 5.8% MVC, respectively) but voluntary activation was similar (88.6 ± 9.6% and 91.7 ± 5.2%). Trapezius is commonly affected in work-related musculoskeletal disorders. Measurement of voluntary activation will be a useful technique to demonstrate whether the reduced maximal voluntary force reported in such disorders is due to muscular or neural factors.     

Existence of Q gamma in frog cut twitch fibers with little Q beta.

Charge movements were measured in frog cut twitch fibers with the double Vaseline-gap voltage-clamp technique. In most fibers, when a depolarizing pulse to -60 to -40 mV was applied at 13-14 degrees C, the ON segment of a charge movement trace showed an early I beta component and a late I gamma hump component. An ongoing controversy is whether the I gamma hump component triggers calcium release from the sarcoplasmic reticulum or arises as a consequence of the release. Interestingly, a number of cut fibers showed normal I gamma components but greatly diminished, or unresolvable, I beta components. When the amount of charge associated with the current transient was plotted against the membrane potential, the steeply voltage-dependent Q gamma component appeared normal whereas the less steeply voltage-dependent Q beta component was also greatly diminished or unresolvable. These results suggest that I gamma can flow in the absence of I beta, thereby ruling out the possibility that Q beta triggers calcium release which, in turn, causes Q gamma to move. The results, however, do not rule out the positive feedback of calcium release to activate Q gamma, if calcium release is not triggered by Q beta but by Q gamma itself or by some other signal.