Test-retest Coefficient Of Variation Research Articles

Reference change value of global longitudinal strain in clinical practice: A test-rest quality implementation project.

Reference change value (RCV) is used to assess the significance of the difference between two measurements after accounting for pre-analytic, analytic, and within-subject variability. The objective of the current study was to define the RCV for global longitudinal strain (GLS) using different semi-automated software in standard clinical practice. Using a test-retest study design, we quantified the median coefficient of variation (CV) for GLS using AutoStrain and Automated Cardiac Motion Quantification (aCMQ) by Philips. Triplane left-ventricular ejection fraction (LVEF) was measured for comparison. Multivariable regression analysis was performed to determine factors influencing test-retest CV including image quality and the presence of segmental wall motion abnormalities (WMA). RCV was reported using a standard formula assuming two standard deviations for repeated measurements; results were also translated into Bayesian probability. Total measurement variation was described in terms of its three different components: pre-analytic (acquisition), analytic (measuring variation), and within-subject (biological) variation. Of the 44 individuals who were screened, 41 had adequate quality for strain quantification. The mean age of the cohort was 56.4±16.8 years, 41% female, LVEF was 55.8±9.8% and the median and interquartile range for LV GLS was -17.2 [-19.3 to -14.8]%. Autostrain was more time efficient (80% less analysis time) and had a lower total median CV than aCMQ (CV=7.4%vs. 17.6%, p <.001). The total CV was higher in patients with WMA (6.4%vs. 13.2%, p=.035). In non-segmental disease, the CV translates to a RCV of 15% (corresponding to a probability of real change of 80%). Assuming a within-subject variability of 4.0%, the component analysis identified that inter-reader variability accounts for 3.7% of the CV, while acquisition variability accounts for 4.0%. Using test-retest analysis and CVs, we find that an RCV of 15% for GLS represents an optimistic estimate in routine clinical practice. Based on our results, a higher RCV of 17%-21% is needed in order to provide a high probability of clinically meaningful change in GLS in all comers. The methodology presented here for determining measurement reproducibility and RCVs is easily translatable into clinical practice for any imaging parameter.

Test-retest reproducibility of atomic force microscopy measurements of human trabecular meshwork stiffness

Purpose: The purpose of the present study was to quantify test-retest reproducibility of measurements of stiffness of the human trabecular meshwork (HTM) by atomic force microscopy (AFM).&#x0D; Methods: Eleven 40 μm radial limbal cryostat sections from a fresh human donor rim were mounted on charged slides and rehydrated at room temperature. Stiffness at four TM locations (anterior to posterior along Schlemm’s canal) was measured by AFM. At each location, a 6 x 6 grid was sampled. Indentation points were evenly distributed over a 20 μm x 20 μm area, with a rate of one load/unload cycle per second. Measurements were then repeated for calculation of test-retest variability.&#x0D; Results: The test-retest coefficients of variation for the four measurement locations (anterior to posterior) were 24.39, 25.28, 12.74, and 14.26%, respectively, with a notable drop in the two posterior locations compared to the anterior. The test-retest coefficient for the sections was 19.17%. For the entire eye, the test-retest coefficient of variation for the measurement of the TM stiffness was 17.13%. Young’s moduli consistently decreased from anterior to posterior location.&#x0D; Conclusions: Wide regional variation suggests that single value does little to fully describe the complex array of TM stiffness levels within the eye, and future studies of TM stiffness assessed by AFM should include multiple tissue samples from each eye, with documentation of the anterior-posterior location of each measurement.

Practical Considerations for Assessing Pulmonary Gas Exchange and Ventilation During Flume Swimming Using the MetaSwim Metabolic Cart.

Lomax, M, Mayger, B, Saynor, ZL, Vine, C, and Massey, HC. Practical considerations for assessing pulmonary gas exchange and ventilation during flume swimming using the MetaSwim metabolic cart. J Strength Cond Res 33(7): 1941-1953, 2019-The MetaSwim (MS) metabolic cart can assess pulmonary gas exchange and ventilation in aquatic environments. The aims of this study were: (a) to determine the agreement between minute ventilation (VE), pulmonary oxygen uptake (VO2), and carbon dioxide output (VCO2) using the MS and Douglas bag (DB) methods during flume swimming; and (b) to assess the repeatability of these and other MS-derived parameters. Sixteen trained swimmers completed a combined incremental and supramaximal verification cardiopulmonary swimming test to determine maximal VO2, 2 progressive intensity swimming tests during which MS and DB measurements were made (agreement protocol), and 3-4 constant-velocity submaximal swimming tests during which only the MS was used (repeatability protocol). Agreement was determined using limits of agreement (LoA), bias, random error, and 95% confidence intervals with systematic bias assessed using paired samples t-tests. Within-trial and between-trial repeatability were determined using the coefficient of variation (CV) and the repeatability coefficient (CR). Where data were heteroscedastic, LoA and CR were log-transformed, antilogged, and displayed as ratios. MetaSwim underestimated peak VO2 and VCO2 (≤0.39 L·min) and VE (9.08 L·min), whereas submaximal values varied between 2 and 5% for CV and ±1.09-1.22 for ratio CR. The test-retest CV during constant-velocity swimming for VE, tidal volume, breathing frequency, VO2, VCO2, and end-tidal pressures of O2 and CO2 was <9% (ratio CR of ±1.09-1.34). Thus, the MS and DB cannot be used interchangeably. Whether the MS is suitable for evaluating ventilatory and pulmonary responses in swimming will depend on the size of effect required.

Evaluation of Pupil Fields Using a Newly Developed Head-mounted Perimeter in Healthy Subjects

The purpose of this study was to evaluate the accuracy of pupil fields and determine the normative pupillary response data by age using a newly developed head-mounted perimeter. A total of 100 healthy subjects (age, 20 to 68 y) were enrolled. The newly developed head-mounted perimeter "imo" was used to measure the percentage pupil constriction (PPC) as response to a stimulus at all 36 test points of the visual field. Goldmann size III and V stimuli at 0, 8, and 11 decibels (dB) under 31.4, 6, and 3 apostilbs (asb) background were presented. The PPC correlations (r) of the right and left eyes were examined. Reproducibility was determined with the coefficient of variation (CV) and a Bland-Altman plot. By a simple bootstrap method, the mean PPC were analyzed as normative data in all 36 test points. Excellent correlation between both eyes was obtained for Goldmann size V stimuli, target luminance of 0 dB, and a background luminance of 31.4 asb (r=0.83; P<0.001). From the test-retest CV peripheral areas have low reproducibility compared with central areas. With a Goldmann size V target, there was a steeper decline of the PPC from the center field to the periphery field, and the temporal field PPC was larger than the nasal field. No major differences were observed between the PPC data and the age groups by decade (eg, center 3 degrees; P=0.223-0.913). Normative PPC data might well be useful for assessing objective visual fields with the newly developed head-mounted perimeter.

Low-dose T1W DCE-MRI for early time points perfusion measurement in patients with intracranial tumors: A pilot study applying the microsphere model to measure absolute cerebral blood flow.

Previous studies have measured cerebral blood flow (CBF) with DSC-MRI using an "early time points" (ET) method based on microsphere theory. To develop and assess a new ET method for absolute CBF estimation using low-dose high-temporal (LDHT) T1W-DCE-MRI. Retrospective cohort study. Seven patients with sporadic vestibular schwannoma (VS) who underwent test-retest imaging; one patient with glioblastoma multiforme (GBM) imaged pretreatment; and 12 neurofibromatosis type 2 (NF2) patients undergoing bevacizumab treatment, imaged pre- and 90 days posttreatment. LDHT-DCE-MRI was performed at 1.5 and 3.0T, using 3D spoiled gradient echo with phase cycling. DSC-MRI performed in one patient, using 3D echo-shifted multi-shot echo-planar imaging (PRESTO) at 3T. Through Monte Carlo simulations, CBF estimation using three newly developed average contrast agent concentration (AC) -based methods (ACrPK, ACrMG, ACcomb), was compared against conventional maximum gradient (MG) approaches, at varying Rician noise levels. Reproducibility and applicability of the ACcomb method was assessed in our sporadic-VS/GBM/NF2 patient cohort, respectively. Reproducibility was measured using test-retest coefficient of variation (CoV). Pre- and posttreatment CBF values were compared using paired t-test with Bonferroni correction. Monte Carlo stimulations demonstrated that AC-based methods, particularly ACcomb, offered superior accuracy to conventional MG approaches. Overall test-retest CoV using the ACcomb method was 5.76 in normal-appearing white matter (NAWM). The new ACcomb method produced gray matter/white matter CBF estimates in the NF2 patient cohort of 55.9 ± 13.9/25.8 ± 3.5 on day 0; compared with 155.6 ± 17.2/128.4 ± 29.1 for the classical MG method. There was a moderate (10% using ACcomb and ACrPK) increase in CBF of NAWM 90 days post therapy (P = 0.03 and 0.005). Our new AC-based method of CBF estimation offers excellent reproducibility, and displays more accuracy in both Monte Carlo analysis and clinical data application, than conventional MG-based approaches. 1 Technical Efficacy: Stage 4 J. MAGN. RESON. IMAGING 2018;48:543-557.

Reliability of Triaxial Accelerometry for Measuring Load in Men's Collegiate Ice Hockey.

Van Iterson, EH, Fitzgerald, JS, Dietz, CC, Snyder, EM, and Peterson, BJ. Reliability of triaxial accelerometry for measuring load in men's collegiate ice hockey. J Strength Cond Res 31(5): 1305-1312, 2017-Wearable microsensor technology incorporating triaxial accelerometry is used to quantify an index of mechanical stress associated with sport-specific movements termed PlayerLoad. The test-retest reliability of PlayerLoad in the environmental setting of ice hockey is unknown. The primary aim of this study was to quantify the test-retest reliability of PlayerLoad in ice hockey players during performance of tasks simulating game conditions. Division I collegiate male ice hockey players (N = 8) wore Catapult Optimeye S5 monitors during repeat performance of 9 ice hockey tasks simulating game conditions. Ordered ice hockey tasks during repeated bouts included acceleration (forward or backward), 60% top-speed, top-speed (forward or backward), repeated shift circuit, ice coasting, slap shot, and bench sitting. Coefficient of variation (CV), intraclass correlation coefficient (ICC), and minimum difference (MD) were used to assess PlayerLoad reliability. Test-retest CVs and ICCs of PlayerLoad were as follows: 8.6% and 0.54 for forward acceleration, 13.8% and 0.78 for backward acceleration, 2.2% and 0.96 for 60% top-speed, 7.5% and 0.79 for forward top-speed, 2.8% and 0.96 for backward top-speed, 26.6% and 0.95 for repeated shift test, 3.9% and 0.68 for slap shot, 3.7% and 0.98 for coasting, and 4.1% and 0.98 for bench sitting, respectively. Raw differences between bouts were not significant for ice hockey tasks (p > 0.05). For each task, between-bout raw differences were lower vs. MD: 0.06 vs. 0.35 (forward acceleration), 0.07 vs. 0.36 (backward acceleration), 0.00 vs. 0.06 (60% top-speed), 0.03 vs. 0.20 (forward top-speed), 0.02 vs. 0.09 (backward top-speed), 0.18 vs. 0.64 (repeated shift test), 0.02 vs. 0.10 (slap shot), 0.00 vs. 0.10 (coasting), and 0.01 vs. 0.11 (bench sitting), respectively. These data suggest that PlayerLoad demonstrates moderate-to-large test-retest reliability in the environmental setting of male Division I collegiate ice hockey. Without previously testing reliability, these data are important as PlayerLoad is routinely quantified in male collegiate ice hockey to assess on ice physical activity.

Clinically Feasible Microstructural MRI to Quantify Cervical Spinal Cord Tissue Injury Using DTI, MT, and T2*-Weighted Imaging: Assessment of Normative Data and Reliability.

DTI, magnetization transfer, T2*-weighted imaging, and cross-sectional area can quantify aspects of spinal cord microstructure. However, clinical adoption remains elusive due to complex acquisitions, cumbersome analysis, limited reliability, and wide ranges of normal values. We propose a simple multiparametric protocol with automated analysis and report normative data, analysis of confounding variables, and reliability. Forty healthy subjects underwent T2WI, DTI, magnetization transfer, and T2*WI at 3T in <35 minutes using standard hardware and pulse sequences. Cross-sectional area, fractional anisotropy, magnetization transfer ratio, and T2*WI WM/GM signal intensity ratio were calculated. Relationships between MR imaging metrics and age, sex, height, weight, cervical cord length, and rostrocaudal level were analyzed. Test-retest coefficient of variation measured reliability in 24 DTI, 17 magnetization transfer, and 16 T2*WI datasets. DTI with and without cardiac triggering was compared in 10 subjects. T2*WI WM/GM showed lower intersubject coefficient of variation (3.5%) compared with magnetization transfer ratio (5.8%), fractional anisotropy (6.0%), and cross-sectional area (12.2%). Linear correction of cross-sectional area with cervical cord length, fractional anisotropy with age, and magnetization transfer ratio with age and height led to decreased coefficients of variation (4.8%, 5.4%, and 10.2%, respectively). Acceptable reliability was achieved for all metrics/levels (test-retest coefficient of variation < 5%), with T2*WI WM/GM comparing favorably with fractional anisotropy and magnetization transfer ratio. DTI with and without cardiac triggering showed no significant differences for fractional anisotropy and test-retest coefficient of variation. Reliable multiparametric assessment of spinal cord microstructure is possible by using clinically suitable methods. These results establish normalization procedures and pave the way for clinical studies, with the potential for improving diagnostics, objectively monitoring disease progression, and predicting outcomes in spinal pathologies.

Testing of Badminton-Specific Endurance.

Madsen, CM, Højlyng, M, and Nybo, L. Testing of badminton-specific endurance. J Strength Cond Res 30(9): 2582-2590, 2016-In the present study, a novel intermittent badminton endurance (B-ENDURANCE) test was developed and tested in elite (n = 17) and skilled (n = 9) badminton players and in age-matched physically active men (nonbadminton players; n = 8). In addition, B-ENDURANCE test-retest reproducibility was evaluated in 9 badminton players. The B-ENDURANCE test is an incremental test where each level consists of repeated sequences of badminton-specific actions toward the 4 corners of the court. The subject starts in the center of the court in front of a computer screen and within each sequence, he must, in a randomized order, complete 8 actions as dictated by the computer, providing the audiovisual input and verifying that the appropriate sensor is activated within the allocated time. Recovery time between each sequence is 10 seconds throughout the test, but the time to complete each sequence is gradually decreased until the subjects cannot follow the dictated tempo. The B-ENDURANCE test performance for elite players was better (p ≤ 0.05) compared with the skilled players and nonbadminton players. In addition, the B-ENDURANCE test performance correlated (r = 0.8 and p < 0.0001) with elite players' national single rankings. Test-retest coefficient of variation was 7.9% between the first 2 trials (i.e., without a familiarization trial) but reduced to 2.5% when comparing the second and third trials. In conclusion, the B-ENDURANCE test is relevant for the evaluation of badminton-specific endurance but at least 1 familiarization trial is recommended if the test is used for evaluation of longitudinal changes, e.g., tracking training effects.

Feasibility and reproducibility of BOLD and TOLD measurements in the liver with oxygen and carbogen gas challenge in healthy volunteers and patients with hepatocellular carcinoma.

To quantify baseline relaxation rates R2* and R1 in the abdomen, their changes after respiratory challenges, and their reproducibility in healthy volunteers and patients with hepatocellular carcinoma (HCC) at 1.5T and 3.0T. R2* measurements were acquired in the liver in 8 volunteers and 27 patients with 34 HCCs using multiecho T2* at baseline and after respiratory challenges with 100% oxygen (O2 ) and carbogen (CB = 95%O2 /5%CO2 ). R1 was measured at 1.5T in one volunteer and 21 patients with 23 HCCs. Test-retest coefficient of variation (CV) was assessed in 10 subjects. Intra- and interobserver variability of R2* and R1 measurements was assessed in 12 and 10 patients, respectively. Parameters for HCC, liver, and muscle were compared between baseline and after gas challenges. We observed that R2* and R1 imaging of HCCs with O2 and CB is feasible and reproducible (test-retest CV R2*<15%/R1 <5%; intra- and interobserver intraclass correlation coefficient R2*>0.88/R1 >0.7 and CV R2*<7%/R1 <3% at 1.5T). R2* measurements were observed to be less reproducible at 3.0T (CV<35%). There was a statistically significant decrease in R2* values in HCC before and after O2 (P = 0.02) and increase in R1 after O2 (P = 0.004). CB had no significant effect (P R2* = 0.47/R1 = 0.278). R2* measurements in HCC and liver parenchyma are more reproducible at 1.5T than at 3.0T, and with O2 than with CB challenge. We observed a decrease in R2* and an increase in R1 of HCCs from baseline in response to O2 challenge, as expected with increased tissue and blood oxygenation.

The reliability, validity and sensitivity of a novel soccer-specific reactive repeated-sprint test (RRST).

The aim of this study was to determine the reliability, validity and sensitivity of a reactive repeated-sprint test (RRST). Elite (n = 72) and sub-elite male (n = 87) and elite female soccer players (n = 12) completed the RRST at set times during a season. Total distance timed was 30 m and the RRST performance measure was the total time (s) across eight repetitions. Competitive match running performance was measured using GPS and high-intensity running quantified (≥ 19.8 km h(-1)). Test-retest coefficient of variation in elite U16 and sub-elite U19 players was 0.71 and 0.84 %, respectively. Elite U18 players' RRST performances were better (P < 0.01) than elite U16, sub-elite U16, U18, U19 and elite senior female players (58.25 ± 1.34 vs 59.97 ± 1.64, 61.42 ± 2.25, 61.66 ± 1.70, 61.02 ± 2.31 and 63.88 ± 1.46 s; ES 0.6-1.9). For elite U18 players, RRST performances for central defenders (59.84 ± 1.35 s) were lower (P < 0.05) than full backs (57.85 ± 0.77 s), but not attackers (58.17 ± 1.73 s) or central and wide midfielders (58.55 ± 1.08 and 58.58 ± 1.89 s; ES 0.7-1.4). Elite U16 players demonstrated lower (P < 0.01) RRST performances during the preparation period versus the start, middle and end of season periods (61.13 ± 1.53 vs 59.51 ± 1.39, 59.25 ± 1.42 and 59.20 ± 1.57 s; ES 1.0-1.1). Very large magnitude correlations (P < 0.01) were observed between RRST performance and high-intensity running in the most intense 5-min period of a match for both elite and sub-elite U18 players (r = -0.71 and -0.74), with the best time of the RRST also correlating with the arrowhead agility test for elite U16 and U18 players (r = 0.84 and 0.75). The data demonstrate that the RRST is a reliable and valid test that distinguishes between performance across standard, position and seasonal period.

Feasibility and precision of transcutaneous very-high resolution ultrasound for quantification of arterial structures in human neonates – Comparison with conventional high resolution vascular ultrasound imaging

BackgroundNon-invasive transcutaneous very-high resolution ultrasound (VHRU, 25–55 MHz) has recently been developed to quantify superficial vascular structures in humans. The performance of the method has yet not been evaluated in vivo in neonates. The aim of the study was to compare VHRU with conventional high-resolution ultrasound (HRU, 7–12 MHz), and to assess the feasibility and precision of VHRU in this population. Methods150 images from central elastic (common carotid, CCA) and peripheral muscular (brachial, BA; femoral, FA) arteries were obtained in 25 neonates of different gestational ages (range 33 + 0 to 41 + 5 gestational weeks) and weights (range 1570–4950 g) with VHRU, and the use of HRU for comparison assessed in five. ResultsImages were captured from CCAs with 35 MHz, FAs using 35 and 55 MHz, and BAs using 55 MHz. 12 MHz was unable to assess FAs and BAs, and the CCA IMT was grossly overestimated compared with 35–55 MHz. IMTs of the smallest BAs and FAs were beyond the axial resolution of VHRU (<0.05 mm), thus immeasurable. For VHRU, the intra-, inter- and test-retest coefficients of variation (CV) were for LDs (range 1.44–2.62 mm, CVs between 1.6 and 4.8%), IMATs (range 0.141–0.161 mm, CVs between 8.8 and 19.9%), and IMTs (range 0.062–0.165 mm, CVs between 12.8 and 24.8%) for the different arteries. ConclusionVHRU is feasible, accurate and precise in the assessment of superficial proximal conduit arteries but unable to assess the abdominal aorta in human neonates HRU-derived neonatal conduit arterial wall layer thicknesses are below the ultrasound axial resolution.

Semi-automatic border detection software for the quantification of arterial lumen, intima-media and adventitia layer thickness with very-high resolution ultrasound

BackgroundThe aim was to evaluate the accuracy, precision and feasibility of semi-automatic border detection software (AMS) in comparison to manual electronic calipers (EC) in the analysis of arterial images obtained with transcutaneous very-high resolution vascular ultrasound (VHRU, 25–55 MHz). Methods100 images from central elastic and peripheral muscular arteries were obtained on two separate imaging occasions from 10 healthy subjects, and independently measured with AMS and EC. ResultsNo bias between AMS and EC was found. The intraobserver coefficients of variation (CV) for carotid lumen dimension (mean dimension 5.60 mm) was lower with AMS compared with EC (0.4 vs. 1.9%, p = 0.033; N = 20). No consistently significant differences in intra, inter or test-retest CVs were observed overall for muscular artery dimensions between AMS and EC. The intra CV for adventitial thickness (AT, mean 0.111 mm; 15.6 vs 24.8%, p = 0.011; N = 41) and inter CV for intima-media thickness (IMT, mean 0.219 mm; 14.3 vs. 21.2%, p = 0.001; N = 58) obtained with AMS in higher quality thin muscular artery images was lower compared with EC. The mean reading time was significantly lower with AMS compared with EC (71.5 s vs. 156.6 s, p < 0.001). ConclusionAMS is accurate, precise, and feasible in the analysis of arterial images obtained with VHRU. Minor, although statistically significant, differences in the precision of AMS and EC-systems were found. The precision of AMS was superior for AT and IMT in higher quality images likely related to a decrease in the technical variability imposed by the observer.

Reproducibility of retinal vessel oxygen saturation measurements in healthy young subjects

An adequate oxygenation and perfusion is essential for the function of the inner retina. Recently, several techniques for the measurement of retinal oxygen saturation became available. We set out to evaluate reproducibility of the measurements using a modified Retinal Vessel Analyzer. A total of 20 healthy female and male subjects aged between 18 and 35 years (22.9 ± 3.9; mean ± SD) were included. The measurement of retinal oxygen saturation with the retinal oximeter employed in this study is based on optical reflectometry using the different absorption characteristics of oxygenated and deoxygenated haemoglobin. The intraclass correlation coefficients and the coefficients of variation (CV) for test-retest, short-term as well as day-to-day measurements were calculated. The intraclass correlation coefficients were between 0.91 and 0.94 for retinal branch arteries and between 0.84 and 0.88 for retinal branch veins. In retinal arteries, we calculated a test-retest CV of 3.24 ± 3.18% for oxygen saturation measurements. In retinal veins, data were slightly less reproducible with a CV of 4.92 ± 3.57%. Short-term reproducibility of both measurement cycles on each study day was in the same range (CV in retinal arteries: 2.91 ± 2.42% and CV in retinal veins: 4.76 ± 3.14%). The day-to-day coefficient of variation was slightly higher (CV in retinal arteries: 3.97 ± 2.87% and CV in retinal veins: 6.18 ± 3.36%). The reproducibility of haemoglobin oxygen saturation measurements using the retinal oximeter is acceptable. Further studies on the validity of the obtained results are, however, required.

The Application of the Yo‐Yo Intermittent Endurance Level 2 Test to Elite Female Soccer Populations

The aim of this study was to evaluate the application of the Yo-Yo intermittent endurance test level 2 (Yo-Yo IE2) to elite female soccer populations. Elite senior (n = 92), youth (n = 42), domestic (n = 46) and sub-elite female soccer players (n = 19) carried out the Yo-Yo IE2 test on numerous occasions across the season. Test-retest coefficient of variation (CV) in Yo-Yo IE2 test performance in domestic female players was 4.5%. Elite senior female players' Yo-Yo IE2 test performances were better (P < 0.01) than elite youth, domestic and sub-elite players (mean ± standard deviation; 1774 ± 532 vs 1490 ± 447, 1261 ± 449, and 994 ± 373 m). For elite senior female players, wide midfielders (2057 ± 550 m) had a higher Yo-Yo IE2 test performance (P < 0.05) than central defenders (1588 ± 534 m) and attackers (1516 ± 401 m), but not central midfielders (1764 ± 473 m) or full-backs (1964 ± 522 m). Large correlations were observed between Yo-Yo IE2 test performance and the total and high-intensity distance covered (r = 0.55; P < 0.05) during elite senior soccer matches (r = 0.70; P < 0.01). A large correlation was also obtained between Yo-Yo IE2 test performance and (r = 0.68; P < 0.01). Performances in the Yo-Yo IE2 test were greater (P < 0.05) in the middle and the end of the season compared with the preparation period for elite youth female players (1767 ± 539 and 1742 ± 503 vs 1564 ± 504 m) and in elite senior female players, Yo-Yo IE2 test performance increased by 14% (P < 0.01) after completing 4 weeks of intense training prior to the FIFA Women's World Cup Finals (2049 ± 283 vs 1803 ± 342 m). The data demonstrate that the Yo-Yo IE2 test is reproducible and is an indicator of the match-specific physical capacity of female soccer players. Furthermore, the Yo-Yo IE2 test illustrates sensitivity by differentiating intermittent exercise performance of female players in various competitive levels, stages of the season and playing positions.

Quantitation of glucose uptake in tumors by dynamic FDG-PET has less glucose bias and lower variability when adjusted for partial saturation of glucose transport

BackgroundA retrospective analysis of estimates of tumor glucose uptake from 1,192 dynamic 2-deoxy-2-(18F)fluoro-D-glucose-positron-emission tomography [FDG-PET] scans showed strong correlations between blood glucose and both the uptake rate constant [Ki] and the metabolic rate of glucose [MRGluc], hindering the interpretation of PET scans acquired under conditions of altered blood glucose. We sought a method to reduce this glucose bias without increasing the between-subject or test-retest variability and did this by considering that tissue glucose transport is a saturable yet unsaturated process best described as a nonlinear function of glucose levels.MethodsPatlak-Gjedde analysis was used to compute Ki from 30-min dynamic PET scans in tumor-bearing mice. MRGluc was calculated by factoring in the blood glucose level and a lumped constant equal to unity. Alternatively, we assumed that glucose consumption is saturable according to Michaelis-Menten kinetics and estimated a hypothetical maximum rate of glucose consumption [MRGlucMAX] by multiplying Ki and (KM + [glucose]), where KM is a half-saturation Michaelis constant for glucose uptake. Results were computed for 112 separate studies of 8 to 12 scans each; test-retest statistics were measured in a suitable subset of 201 mice.ResultsA KM value of 130 mg/dL was determined from the data based on minimizing the average correlation between blood glucose and the uptake metric. Using MRGlucMAX resulted in the following benefits compared to using MRGluc: (1) the median correlation with blood glucose was practically zero, and yet (2) the test-retest coefficient of variation [COV] was reduced by 13.4%, and (3) the between-animal COVs were reduced by15.5%. In statistically equivalent terms, achieving the same reduction in between-animal COV while using the traditional MRGluc would require a 40% increase in sample size.ConclusionsMRGluc appeared to overcorrect tumor FDG data for changing glucose levels. Applying partial saturation correction using MRGlucMAX offered reduced bias, reduced variability, and potentially increased statistical power. We recommend further investigation of MRGlucMAX in quantitative studies of tumor FDG uptake.

Sub-maximal and maximal Yo–Yo intermittent endurance test level 2: heart rate response, reproducibility and application to elite soccer

The aims of this study were to (1) determine the reproducibility of sub-maximal and maximal versions of the Yo-Yo intermittent endurance test level 2 (Yo-Yo IE2 test), (2) assess the relationship between the Yo-Yo IE2 test and match performance and (3) quantify the sensitivity of the Yo-Yo IE2 test to detect test-retest changes and discriminate between performance for different playing standards and positions in elite soccer. Elite (n = 148) and sub-elite male (n = 14) soccer players carried out the Yo-Yo IE2 test on several occasions over consecutive seasons. Test-retest coefficient of variation (CV) in Yo-Yo IE2 test performance and heart rate after 6 min were 3.9% (n = 37) and 1.4% (n = 32), respectively. Elite male senior and youth U19 players Yo-Yo IE2 performances were better (P < 0.01) than elite youth U16s and sub-elite players (2,603 ± 451 and 2,534 ± 549 vs. 1,855 ± 535 vs. 1,749 ± 382 m). The intra- and inter-season CV for Yo-Yo IE2 test performance were 4.2 and 5.6%, respectively. A correlation was observed (P < 0.05) between Yo-Yo IE2 test performance and the total (r = 0.74) and high-intensity (r = 0.58) running distance covered in a match. A correlation was also evident (P < 0.01) between Yo-Yo IE2 test heart rate after 6 min expressed in percentage of maximal heart rate and the peak values for high-intensity running performed by midfielders in 5-min (r = -0.71), 15-min (r = -0.75) and 45-min periods (r = -0.77). The present data demonstrate that the Yo-Yo IE2 test is reproducible and can be used to determine the capacity of elite soccer players to perform intense intermittent exercise. Furthermore, the Yo-Yo IE2 test was shown to be a sensitive tool that not only relates to match performance but can also differentiate between intermittent exercise performance of players in various standards, stages of the season and playing positions.

Reproducibility of black blood dynamic contrast‐enhanced magnetic resonance imaging in aortic plaques of atherosclerotic rabbits

To investigate the short-term reproducibility of black-blood dynamic contrast-enhanced (DCE) magnetic resonance imaging (MRI) in atherosclerotic rabbits to evaluate the potential of this technique to be a reliable readout of plaque progression and/or regression upon therapeutic intervention. Atherosclerotic rabbits were imaged at baseline and 24 hours later with DCE-MRI on a 1.5T MRI system. DCE-MRI images were analyzed by calculating the area under the signal intensity versus time curve (AUC). Intraclass correlation coefficients (ICCs) were used to evaluate interscan, intraobserver, and interobserver reproducibility. In addition, the test-retest coefficient of variation (CoV) was evaluated. Statistical analyses showed excellent interscan, intraobserver, and interobserver agreement. All ICCs were greater than 0.75, P < 0.01 indicating excellent agreement between measurements. Experimental results show good interscan and excellent intra- and interobserver reproducibility, suggesting that DCE-MRI could be used in preclinical settings as a read-out for novel therapeutic interventions for atherosclerosis. This preliminary work encourages investigating the reproducibility of DCE-MRI also in clinical settings, where it could be used for monitoring high-risk patients and in longitudinal clinical drug trials.

The Yo-Yo IR2 Test: Physiological Response, Reliability, and Application to Elite Soccer

To examine the physiological response, reliability, and validity of the Yo-Yo intermittent recovery level 2 test (Yo-Yo IR2). Thirteen normally trained male subjects carried out four Yo-Yo IR2 tests, an incremental treadmill test (ITT), and various sprint tests. Muscle biopsies and blood samples were obtained, and heart rate was measured before, during, and after the Yo-Yo IR2 test. Additionally, 119 Scandinavian elite soccer players carried out the Yo-Yo IR2 test on two to four occasions. Yo-Yo IR2 performance was 591 +/- 43 (320-920) m or 4.3 (2.6-7.9) min. Test-retest coefficient of variation in distance covered was 9.6% (N = 29). Heart rate (HR) at exhaustion was 191 +/- 3 bpm, or 98 +/- 1% HRmax. Muscle lactate was 41.7 +/- 5.4 and 68.5 +/- 7.6 mmol x kg(-1) d.w. at 85 and 100% of exhaustion time, respectively, with corresponding muscle CP values of 40.4 +/- 5.2 and 29.4 +/- 4.7 mmol x kg(-1) d.w. Peak blood lactate was 13.6 +/- 0.5 mM. Yo-Yo IR2 performance was correlated to ITT performance (r = 0.74, P < 0.05) and VO2max (r = 0.56, P < 0.05) but not to 30- and 50-m sprint performance. Yo-Yo IR2 performance was better (P < 0.05) for international elite soccer players than for moderate elite players (1059 +/- 35 vs 771 +/- 26 m) and better (P < 0.05) for central defenders (N = 21), fullbacks (N = 20), and midfielders (N = 48) than for goalkeepers (N = 6) and attackers (N = 24). Fifteen elite soccer players improved (P < 0.05) Yo-Yo IR2 performance by 42 +/- 8% during 8 wk of preseasonal training. This study demonstrates that the Yo-Yo IR2 test is reproducible and can be used to evaluate an athlete's ability to perform intense intermittent exercise with a high rate of aerobic and anaerobic energy turnover. Specifically, the Yo-Yo IR2 test was shown to be a sensitive tool to differentiate between intermittent exercise performance of soccer players in different seasonal periods and at different competitive levels and playing positions.

MR measurement of articular cartilage thickness distribution in the hip

To develop a method to determine the distribution of articular cartilage in the hip and to evaluate the potential of the method in a study of normal weight-bearing effects in asymptomatic young volunteers. Six volunteers were scanned after periods of standing and lying supine, using 3D gradient-echo magnetic resonance imaging (MRI). The protocol was repeated for two successive weeks to determine reproducibility. The femoral and acetabular cartilage layers were segmented as a single unit and thickness distribution maps were calculated using a spherical bone model as a frame of reference. Thickness maps were combined over the population using the bone model and post-weight-bearing and post-resting maps were compared. Mean thickness values were compared using an analysis of variance and a significant increase in cartilage thickness of 0.05 mm (P=0.02) was observed. The reproducibility of the method, assessed using test-retest coefficient of variation was 2.5%. The technique is reproducible, sensitive to sub-millimetre changes in thickness and may be useful in monitoring changes due to disease progression in patients with arthritis of the hip.

Measurement error in short-term power testing in young people

The aim of this study was to examine the consistency or reproducibility of measuring cycling peak power in children and adults. Twenty-seven pre-pubertal girls and boys and 27 female and male physical education students (age 9.8±0.5 and 24.4±4.3 years, respectively; mean±s) participated in the study. All participants performed five tests over 15 days and underwent a habituation session before the study. Each test included four sprints against four different braking forces. We found that braking forces of 7.5% of body weight in children and 10% of body weight in adults were too high for most of the participants to elicit maximal cycling power. Unlike the children, the physical education students improved their performance between session 1 and session 2 (1025±219 vs 1069±243 W; P<0.001). Therefore, to obtain reproducible measures of cycling peak power, a habituation session including a complete test protocol (i.e. warm-up plus three sprints) is highly recommended. When the protocol included three sprints in children and at least two sprints in adults, measurement of cycling peak power was found to be highly reliable (test-retest coefficient of variation ∼3%). Finally, to avoid performance fluctuations, especially over several consecutive evaluations (e.g. longitudinal studies), it is necessary to maintain high motivation in children.