Terahertz wave propagation in one-dimensional periodic dielectrics.

We demonstrate the temporal evolution of terahertz (THz) wave propagation in one-dimensional periodic dielectrics. Distributed Bragg reflectors and a resonant cavity are investigated: The structures involve air gaps interleaved between polymer films. Transmitted and reflected broadband THz waves are measured by means of THz time-domain spectroscopy. The experimental results agree well with transfer matrix calculations.

Effect of active limb movements on symptoms in patients with low back pain.

STUDY DESIGN: A descriptive, correlational study of patients with mechanical low back pain (LBP). OBJECTIVES: To assess the effect of active limb movements on symptoms in patients with LBP and to examine the relationship between symptoms with limb movements and select patient characteristics. BACKGROUND: Limb movements result in forces applied to the spine and, thus, may be important in the examination and treatment of patients with LBP. METHODS AND MEASURES: A total of 188 people with LBP, 84 men and 104 women, participated in a standardized examination. Six of the items required patients to move their limbs and note LBP symptoms as increased, remained the same, or decreased. The prevalence of various symptom responses with each limb movement test was calculated. Relationships between patient characteristics and reports of increased symptoms were examined with Cochran's linear trend statistic and the Spearman and Pearson correlation coefficients. Differences in characteristics of patients with and without increased symptoms were examined with chi2 test, Mann-Whitney U test, or Student's t test for independent groups. RESULTS: An increase in symptoms was reported by 149 patients with at least 1 of the limb movement tests, and 3 of the patients reported a decrease in symptoms. Across the patient sample, the mean number of limb movement tests for which symptoms were reported as increased was 2.30 +/- 1.64. Patients with an increase in symptoms reported higher average pain intensity the week prior to the examination (median = 2; range: 1-5) and higher functional disability (mean = 0.25; SD = 0.15) than those without a change in symptoms (pain intensity: median = 1; range: 0-2 and functional disability: mean = 0.16; SD = 0.12). The correlation between the number of increased symptoms and the person's average pain intensity was r = 0.23; the correlation with the functional disability score was r = 0.36. Patients with a history of LBP tended to report an increase in symptoms with more of the limb movement tests (mean = 3.5; SD = 1.40) than those without a previous history of LBP (mean = 2.0; SD = 1.11). CONCLUSIONS: Active limb movements performed during the examination primarily resulted in increased LBP symptoms. The presence and number of increased symptoms with the active limb movements was related to the patient's report of average pain intensity and functional disability. Tests of symptoms with active limb movements may provide insight into factors contributing to a LBP problem, as well as information to guide the treatment of patients with LBP.

Understanding statistical power.

This article provides an introduction to power analysis so that readers have a basis for understanding the importance of statistical power when planning research and interpreting the results. A simple hypothetical study is used as the context for discussion. The concepts of false findings and missed findings are introduced as a way of thinking about type I and type II errors. The primary factors that affect power are described and examples are provided. Finally, examples are presented to demonstrate 2 uses of power analysis, 1 for prospectively estimating the sample size needed to insure finding effects of a known magnitude in a study and 1 for retrospectively estimating power to gauge the likelihood that an effect was missed.

Reliability of physical examination items used for classification of patients with low back pain.

BACKGROUND AND PURPOSE: The purpose of this study was to examine the interrater reliability of measurements obtained by examiners administering tests proposed to be important for classifying low back pain (LBP) problems. SUBJECTS: Ninety-five subjects with LBP (41 men, 54 women) and 43 subjects without LBP (17 men, 26 women) were examined by 5 therapists trained in the techniques used. METHODS: A manual was developed by the first author that described the clinical examination procedures. The therapists were trained by the first author in the test procedures and definitions. The training included instruction through videotapes, practice and a written examination. Each examination was conducted by a pair of therapists. Within a pair, a therapist was the primary examiner for half of the subjects and an observer was the primary examiner for half of the subjects. Examination findings were recorded independently, without discussion. RESULTS: Percentage of agreement and generalized kappa coefficients were used to analyzed the data. Kappa values were > or = .75 for all 28 items related to the symptoms elicited and > or = .40 for 72% of the 25 items related to alignment and movement. CONCLUSION AND DISCUSSION: The results suggest that experienced therapist who had trained together were able to agree on the results of examinations and obtain an acceptable level of reliability. Future work should focus on testing of reliability when more than one therapist performs the examination and when therapist not trained by the test developer to administer the examination perform the tests. [Van Dillen LR, Sahrmann SA, Norton BJ, et al. Reliability of physical examination items used for classification of patients with low back pain.

The influence of experience with a set of simulated patients on diagnosis of simulated patients not previously diagnosed.

BACKGROUND AND PURPOSE: Diagnoses, to be useful, should be accurate. The purpose of this study using fictitious patients and student judges was to test the theory that diagnostic errors would occur when students saw simulated patients who were similar to previously seen simulated patients. SUBJECTS: Sixty physical therapist (PT) students and 60 non-physical therapist (NPT) students were studied. Subjects were assigned randomly to one of three groups. METHODS: Instructions to the three groups differed in terms of rules provided for diagnoses and instructions to remember the patients. Students first diagnosed the same eight fictitious patients five times. The students then diagnosed eight new patients with similar characteristics interspersed with the original eight patients. Half of the new patients had a diagnosis different from that of the most similar old patient. RESULTS: Students who were given a rule for diagnosis made fewer errors than students who were not given a rule. Students in the PT group took longer but made fewer errors on the critical opposite-diagnosis new cases than did students in the NPT group. CONCLUSION AND DISCUSSION: The results do not provide support for the theory that diagnostic errors would occur when students saw patients who were similar to previously seen patients. Students in the PT group appeared to emphasize accuracy at the expense of speed in making their diagnoses. Given the nature of the simulated patient information and the mode of presentation used in the experiment, however, the conclusion that therapists in actual practice do not make errors because of the similarity between new and previously seen patients is not yet warranted.

Age Group Differences in Postural Adjustments Associated With a Stepping Task.

In this study, differences among age groups in the postural adjustments associated with a stepping task were identified. Twenty subjects from each of 3 age groups, children (8-12 years), young adults (25-35 years), and older adults (65-73 years), performed the task in 2 movement contexts: place and step. In place, the subject simply lifted the foot and placed it on the step. In step, the subject lifted the foot, placed it on the step, and stepped up onto the step. Latencies of postural and focal muscle activation were determined by using surface electromyography and pressure switches. Center of pressure (CP) data were obtained by using a force platform. Subjects in all 3 age groups consistently demonstrated postural adjustments before movement initiation. Children displayed longer postural latencies than young adults as well as disproportionately large values for CP path length. Older adults showed prolonged postural-focal latencies and decreased CP excursions compared with the 2 younger age groups. These results suggest that maturation of coordination between posture and movement may not be fully complete in 8- to 12-year-olds and that increased restraint characterizes the performance of postural adjustments in healthy persons over 65 years of age.

Reliability and concurrent validity of the Metrecom for length measurements on inanimate objects.

BACKGROUND AND PURPOSE: The purpose of this study was to test the reliability and concurrent validity of length measurements (distance between two points) produced by a computer-interfaced, three-dimensional digitizer called the Metrecom. METHODS: A total of 344 points were marked on the surfaces of five different inanimate objects and were digitized in pairs with the Metrecom. On the first three objects, each of two testers digitized each point twice for each of two testing modes (Line Length and 3-D Digitizer); on the last two objects, only one mode (3-D Digitizer) was used. Intraclass correlation coefficients and Pearson Product-Moment Correlation Coefficients were used to assess reliability and concurrent validity, respectively. RESULTS: All of the correlation coefficients were > or = .99. In further analysis of the results, a repeated-measures, one-way analysis of variance (used with reliability data) and repeated-measures t tests (used with validity data) were used to test for differences between repeated measures. After adjustment of the alpha level for the total number of comparisons, two of the t tests for validity comparisons were significant. CONCLUSION AND DISCUSSION: The results indicate that the Metrecom provides reliable length measurements (distance between two points) on inanimate objects and that two different test modes produce consistent measurements. Further study of the validity and reliability of length measurements obtained with the Metrecom on humans under applied conditions is needed before the results of this study can be generalized to applied settings.

Navicular drop as a composite measure of excessive pronation.

The measure of navicular drop has been used as an indicator of pronation at the foot. It is defined as the distance the navicular tuberosity moves in standing, as the subtalar joint is allowed to move from its neutral position to a relaxed position. The purposes of this study were to test the reliability of a method to measure navicular drop and to assess the relationships among measures of forefoot to rearfoot position, subtalar joint neutral position, and navicular drop. The results support traditional biomechanical theory but indicate that other factors contribute significantly to navicular drop.

Reliability of kinematic measurements of rear-foot motion.

The purpose of this study was to examine the ability of a video-based, computer-interfaced motion analysis system to provide reliable data. Ten subjects with no significant orthopedic or neurological dysfunction and ranging in age from 22 to 45 years (mean = 29.6, SD = 7.8) were tested. Retroreflective markers were placed on the posterior shank and foot of each subject. Footswitches were attached to the plantar forefoot and rear foot. A video camera was placed behind the subject, and video data were collected while the subject walked on a treadmill. One representative gait cycle for each subject was selected and processed 10 times with a video processor and analysis software. Three intraclass correlation coefficients (ICCs) were calculated for variables generated by the analysis software, one for two individual measures and one each for the mean of three and five repeated measures. Except for temporal variables, processing data introduced additional variability into the measurement process, particularly for angular velocity data. Measurement of all variables was highly reliable (ICC values greater than or equal to .95) when based on the mean of at least three repeated measures. Although a single measure of temporal and angular position variables may be considered reliable, we recommend using a mean of three trials for angular velocity variables. Additional research is needed to determine tester and subject variability and validity of the measures.

Some cautionary comments on the use of retrospective designs to evaluate treatment efficacy.

This article contrasts the true experimental approach with nonexperimental alternatives, such as retrospective designs, for research on treatment efficacy. The potential problems and limitations of the nonexperimental approach are highlighted so that when deviations from the more desirable experimental methodology are necessary, they can be undertaken with full knowledge of the hazards to be expected. Important issues are illustrated through discussion of a specific type of retrospective design, the case-control design.

Clinical reliability of manual muscle testing. Middle trapezius and gluteus medius muscles.

The purposes of this study were to develop a protocol to examine the reliability of manual muscle testing in a clinical setting and to use that protocol to assess the interrater reliability of manually testing the strength of the middle trapezius and gluteus medius muscles. One hundred ten patients with various diagnoses participated as subjects, and 11 physical therapists participated as examiners in this study. The results showed that interrater reliability for right and left middle trapezius and gluteus medius muscles was low. The percentage of therapists obtaining a rating of the same grade or within one third of a grade ranged from 50% to 60% for the four muscles. This study indicates that using manual muscle testing to make accurate clinical assessments of patient status is of questionable value.

Reliability and validity of goniometric measurements at the knee.

The purposes of this study were to assess the intertester reliability of goniometric measurements at the knee and the validity of the clinical measurements by comparing them to measurements taken from roentgenograms. Thirty healthy subjects between the ages of 20 and 60 years were studied. The subjects were positioned on their right side on a roentgenographic table with their left lower extremity on a stabilizing board that was elevated 15 cm above the table's surface. For standardization of the position, an assistant placed the posterior aspect of the subject's left thigh in contact with two 15-cm pegs, which had been inserted perpendicularly into the stabilizing board. The assistant then moved the left leg to achieve an arbitrary angle of the knee joint and held the limb in that position. Two physical therapists then independently used a standard plastic goniometer to measure the knee joint angle in the sagittal plane using the greater trochanter, the lateral condyle of the femur, the head of the fibula, and the lateral malleolus as bony landmarks. A roentgenogram was taken of the extremity before the subject was moved. Pearson product-moment correlation coefficients (r's) and intraclass correlation coefficients (ICCs) were used to analyze the data. The data analysis revealed that the intertester reliability (r = .98; ICC = .99) and validity (r = .97-.98; ICC = .98-.99) were high. The results of this study indicate that goniometric measurements of the knee joint are both reliable and valid.

Guide for the interpretation of one-way analysis of variance.

In summary, one-way ANOVA for independent groups is used to test whether the group means for a specific dependent variable differ significantly after exposing each group to a unique level of a single factor or independent variable. You may recognize the preceding sentence. We hope it makes more sense to you now than when you first read it at the beginning of this article.

Electromyographic study of the relationship between hamstring and abdominal muscles during a unilateral straight leg raise.

The purposes of this study were 1) to assess the relative participation of the hip extensor and abdominal musculature during unilateral straight leg raising in the naive subject and 2) to examine quantitatively alterations in the pattern of pelvic stabilization when the subject was instructed to relax the contralateral extremity. Surface electrodes were used to record bilaterally the electromyographic activity of the rectus abdominus, external oblique, and medial hamstring muscles. Each healthy subject performed a unilateral straight leg raise three times in each of two modes, Preferred and Relaxed. The electromyographic values for each muscle were normalized to a maximum isometric contraction and analyzed using a three-factor (2 X 2 X 2) mixed design analysis of variance. Results indicate that 9 of the 11 subjects used the tested medial hamstrings and abdominal muscles during a unilateral straight leg raise performed in the Preferred Mode. When instructed to relax the contralateral extremity for the Relaxed Mode, abdominal muscle activity increased significantly (p less than .01). The findings indicate that although most subjects normally stabilize with the contralateral extremity during a unilateral straight leg raise, they can consciously alter the pattern.

Stretch reflex of the biceps and brachioradialis muscles in patients with upper motor neuron syndrome.

The position of elbow flexion commonly observed in patients with upper motor neuron lesions is attributed by many clinicians to hyperactive stretch reflexes. The purpose of this study was to examine the passive stretch reflexes of the biceps and brachioradialis muscles in order to assess their possible relative contributions to the flexion posture. Twenty-one patients with upper motor neuron lesions were tested, using an automated system to produce controlled passive movement strech reflexes. Ratios derived from the electromyographic activity elicited during passive movement were used for quantitative comparisons. The stretch reflex response of the brachioradialis muscle was larger and earlier than the biceps response. A surprising finding was reciprocal activity in these two synergists following phasic stretch.

Reflex and voluntary electromyographic activity in patients with hemiparesis.

The purpose of this study was to quantify the effect of combining voluntary effort with passive muscle stretch in the major flexors and extensors of the elbow and knee joints in order to test the validity of the assumption that stretching a muscle in conjunction with voluntary effort enhances the production of muscle activity more than muscle stretch or voluntary effort alone. This was accomplished by using a computer-controlled test instrument to produce the conditions necessary for measuring stretch reflex activity, voluntary effort, and stretch reflex activity plus voluntary effort, and then quantitatively examining the EMG activity associated with each test condition. In general, greater EMG activity was produced by the combination of muscle stretch and voluntary effort than by either muscle stretch or voluntary effort alone. Clinical implications of these findings are discussed.