Between-session Intraclass Correlation Coefficients Research Articles

Reliability of ankle mechanics during jump landings in turned-out and parallel foot positions in professional ballet dancers

This study aimed to determine the within- and between-session reliability of ankle mechanics and vertical ground reaction forces (vGRF) during jump landings in turned-out and parallel foot positions in professional ballet dancers. Twenty-four professional ballet dancers (men = 13, women = 11) attended two data collection sessions where they completed five maximal countermovement jumps in each foot position. The ankle joint mechanics and vGRF of the right limb were recorded via a seven-camera motion capture system and one force platform. Within- and between-session intraclass correlation coefficients (ICC), coefficients of variation (CV), standard error of measurement, and minimal detectable change were calculated for three-dimensional ankle excursion, peak ankle angle, ankle joint velocity, moment, and power, as well as peak landing vGRF, time to peak landing vGRF, loading rate, and jump height. Across both foot positions, within- (ICC: 0.17–0.96; CV: 1.4–82.3%) and between-session (ICC: 0.02–0.98; CV:1.3–57.1%) reliability ranged from poor to excellent, with ankle excursion, peak ankle angle, and jump height demonstrating the greatest ICC values (ICC: 0.65–0.96; CV: 1.4–57%). Jump landings in a turned-out foot position demonstrated better within-session reliability compared to a parallel position, however, no difference in between-session reliability across the foot positions was observed. Most ankle mechanics provide adequate between-session, but not within-session, reliability during jump landings in professional ballet dancers.

Within- and between-session test-retest reliability of pain-free grip strength in individuals with lateral elbow tendinopathy

Introduction: Pain-free grip strength is an important clinical outcome measure in lateral elbow tendinopathy (LET). This study examined the test-retest reliability and minimal detectable change (MDC) for pain-free grip strength between- and within-session in individuals with LET. Methods: Data from 27 individuals (16 males) with LET, recruited for a randomised crossover trial examining the effects of biomechanical tape, were used for this study. Participants underwent three testing sessions, biomechanical tape, control tape, and no tape. During each session pain-free grip strength was measured at three timepoints: baseline, immediately after application, and post-exercise. Baseline measures from the first two data collection sessions, completed between 2 and 28 days apart, were used to examine between-session reliability. The baseline and immediately post-application measures (completed 20 to 30 minutes apart) from the no-tape condition, were used to examine within-session reliability. Pain-free grip strength was assessed in two positions: shoulder neutral, elbow at 90°, forearm pronated (flexed position), and shoulder at 90°, elbow extended, forearm pronated (extended position). Participants were asked to cease gripping as soon as they felt pain and the force (N) was recorded. At each timepoint and position, three trials of pain-free grip strength separated by 30 seconds’ rest were measured using a grip force transducer (ADInstruments, NZ). The mean of the three trials was calculated. To determine test-retest reliability, intraclass correlation coefficients (ICCs) with 95%CI were performed using an absolute agreement, two-way random-effects model (ICC2,3). The MDC at the 95% confidence level was calculated by multiplying the standard error of measurement by 1.96 and then by √2. Results: Between-session ICCs (95%CI) were ICC2,3=0.86 (0.69 - 0.94) and ICC2,3=0.93 (0.84 - 0.97) for the flexed and extended positions, respectively. Within-session ICCs (95%CI) were ICC2,3=0.96 (0.92 - 0.98) and ICC2,3=0.97 (0.93 - 0.98) for the flexed and extended positions, respectively. Between-session MDCs were 97.8 N (flexed) and 94.0 N (extended) and within-session MDCs were 49.3 N (flexed) and 63.8 N (extended). Discussion: The reliability of pain-free grip strength was excellent in both testing positions. Researchers and clinicians should expect to see a change of 94 to 98 N between-session and 49 to 64 N within-session, depending on upper limb position, to be confident a true change has occurred. Conflict of interest statement: The authors have no conflict of interest of relevance to this submission.

Test-retest reliability of force plate-derived measures of reactive stepping

Characterizing reactive stepping is important to describe the response’s effectiveness. Timing of reactive step initiation, execution, and termination have been frequently reported to characterize reactive balance control. However, the test–retest reliabilities of these measures are unknown. Accordingly, the purpose of this study was to determine the between- and within-session test–retest reliabilities of various force plate-derived measures of reactive stepping. Nineteen young, healthy adults responded to 6 small (~8–10% of body weight) and 6 large perturbations (~13–15% of body weight) using an anterior lean-and-release system. Tests were conducted during two visits separated by at least two days. Participants were instructed to recover balance in as few steps as possible. Step onset, foot-off, swing, and restabilization times were extracted from force plates. Relative test–retest reliability was determined through intraclass correlation coefficients (ICCs) and 95% confidence intervals (CIs). Absolute test–retest reliability was assessed using the standard error of the measurement (SEM). Foot-off and swing times had the highest between- and within-session test–retest reliabilities regardless of perturbation size (between-session ICC = 0.898–0.942; within-session ICC = 0.455–0.753). Conversely, step onset and restabilization times had lower ICCs and wider CIs (between-session ICC = 0.495–0.825; within-session ICC = -0.040–0.174). Between-session test–retest reliability was higher (ICC = 0.495–0.942) for all measures than within-session test–retest reliability (ICC = -0.040–0.753). Time to restabilization had the highest SEM, indicating the worst absolute reliability of the measures. These findings suggest multiple baseline sessions are needed for measuring restabilization and step onset times. The minimal detectable changes reported provide an index for measuring meaningful change due to an intervention.

The impact of a familiarization session on the magnitude and stability of active and passive pelvic floor muscle forces measured through intravaginal dynamometry.

The aim of this study was to investigate the impact of task familiarization on (1) the magnitude and (2) the repeatability of active and passive properties of the female pelvic floor muscles (PFMs) measured using automated intra-vaginal dynamometry. Women attended three laboratory sessions at one-week intervals. After receiving initial task instruction and feedback at the start of the first session, standardized instructions were given while women performed maximal effort voluntary contractions of their PFMs with the dynamometer arms open at two different diameters and kept their PFMs relaxed while the dynamometer arms opened to 40 mm at two speeds. Outcomes included baseline force, peak force, relative peak forces (N), rate of force development (N/s) and stiffness. Between session effects were tested for all outcomes using one-way ANOVAs. Intra-class correlation coefficients (ICCs) and minimal detectable change values were computed within each session and between sessions 1 and 2 and sessions 2 and 3. Twenty nulliparous women (mean age = 35 ± 15 years) participated. No differences in the mean values were found across the three visits for any outcomes. Within sessions, neither ICC nor minimal detectable change differed among sessions and between-session ICC values were not different between visits 1 and 2 and visits 2 and 3. There is no evidence of a familiarization effect over a two-week period on the amplitude nor repeatability of dynamometric measures of active or passive PFM properties recorded from nulliparous women.

Assessing gait stability: The influence of state space reconstruction on inter- and intra-day reliability of local dynamic stability during over-ground walking

Estimating local dynamic stability is considered a powerful approach to identify persons with balance impairments. Its validity has been studied extensively, and provides evidence that short-term local dynamic stability is related to balance impairments and the risk of falling. Thus far, however, this relation has only been proven on group level. For clinical use, differences on the individual level should also be detectable, requiring reliability to be high. In the current study, reliability of short-term local dynamic stability was investigated within and between days. Participants walked 500m back and forth on a straight outdoor footpath, on 2 non-consecutive days, and 3D linear accelerations were measured using an accelerometer (DynaPort MiniMod). The state space was reconstructed using 4 common approaches, all based on delay embedding. Within-session intra-class correlation coefficients were good (≥0.70), however between-session intra-class correlation coefficients were poor to moderate (≤0.63) and influenced by the reconstruction method. The same holds for the smallest detectable difference, which ranged from 17% to 46% depending on the state space reconstruction method. The best within- and between-session intra-class correlation coefficients and smallest detectable differences were achieved with a state space reconstruction with a fixed time delay and number of embedding dimensions. Overall, due to the influence of biological variation and measurement error, the short-term local dynamic stability can only be used to detect substantial differences on the individual level.

Reliability of the Developmental Eye Movement Test

This study evaluated the repeatability of the Developmental Eye Movement Test (DEM) with three consecutive administrations on two separate visits to 181 children between the ages of 6 years and 11 years 11 months. Children with visual acuity of ≥ 20/25, normal binocularity, and accommodation were administered three different versions of the DEM test. One to 4 weeks after the first administration of the DEM, the children were tested again using the same order for the three versions of the DEM. Measures of within- and between-session repeatability for the vertical-adjusted time, horizontal-adjusted time, ratio, and error scores were determined. The within-session repeatability for vertical- and horizontal-adjusted time were good to excellent but were poor to good for ratio, and poor to fair for errors. The between-session intraclass correlation coefficients were fair to good for both the vertical and horizontal scores but poor for the ratio and error scores. The repeatability of the pass-fail diagnostic classification within a single session for each subject on test and retest was compared. The percentage of patients who remained in the same classification ranged from 71 to 100% for both vertical and horizontal scores. Wider variability was seen with the ratio and error scores showing between 47 and 100% of the children remaining classified as pass or fail with repeated administrations of the DEM. Such findings would suggest that children in this age range may show improvements in all four test scores without any intervention. Although the DEM is widely used in optometric practice, the results of this study suggest that clinicians should be cautious about using the DEM test in isolation for reaching a diagnosis or monitoring the effectiveness of treatment for saccadic dysfunction.

Simulated work performance tasks in persons with neuropathic and myopathic weakness

Kilmer DD, Aitkens SG, Wright NC, McCrory MA. Simulated work performance tasks in persons with neuropathic and myopathic weakness. Arch Phys Med Rehabil 2000;81:938-43. Objectives: To determine the test-retest reliability of selected simulated work performance tasks in persons with neuropathic and myopathic weakness and control subjects, and the association between muscular performance during these work tasks and conventional isolated muscle group testing. Design: Measurement of three tasks performed on a work simulation device on two different days separated by 1 week. Associations between work task performance and previously reported strength measures in six muscle groups by hand-held dynamometry (HHD) were examined. Setting: Human performance laboratory of a university. Participants: Convenience sample of ambulatory outpatients with hereditary motor and sensory neuropathy, type I (n = 9), myotonic muscular dystrophy (n = 10), and able-bodied controls (n = 11). Main Outcome Measures: For work simulation, isokinetic peak torque and total work; and for HHD, maximal isometric torque. Results: Mean between-session differences for work simulation tasks ranged from −11% to +4% for peak torque and from −12% to +12% for total work; test sessions did not differ significantly for either patient or control groups. All groups had between-session intraclass correlation coefficients usually >.80, indicating good consistency. In general, correlations between peak torque during work simulation and HHD were strongest in the control group. Conclusion: Persons with neuromuscular weakness reliably performed the simulated work tasks examined in this investigation. Work simulation tasks may be a useful tool to assess muscular performance in persons with neuromuscular weakness. © 2000 by the American Congress of Rehabilitation Medicine and the American Academy of Physical Medicine and Rehabilitation