Test-retest reliability of electrical impedance myography in hamstrings of healthy young men.

Several techniques are available to assess muscle tissue status, including electrical impedance myography (EIM). Despite being used in the assessment of neuromuscular status in injury and response to exercise, reliability data for hamstrings muscles are limited. Therefore, this study aimed to determine the test-retest reliability of EIM components on hamstrings. Twenty-one healthy males (25.3 ± 3.4 years; 173 ± 6.7 cm; and 79.7 ± 15.9 kg) volunteered for this study. Subjects completed two visits, separated by seven days to collect EIM components (resistance, reactance, impedance, and phase angle) in the longitudinal and transversal axis of hamstrings in both thighs, using a bioimpedance device and Ag/AgCL adhesive contact electrodes. The electrode arrangement was in the muscular belly, half the distance between origin and insertion of the hamstrings. Reliability was determined by the intraclass correlation coefficient (ICC), minimal detectable change (MDC), and Bland-Altman plots. We observed high to excellent reliability (ICC > 0.85) between all EIM components, except for reactance with MDC ranged from 2.0 to 10.8 and the mean bias in Bland-Altman plots ranged from -0.02 to 2.48 (95% limits of agreement from -9.98 to 11.20). From our findings, the hamstrings assessment using EIM technique is reliable to assess muscle tissue; therefore, it enables the evaluation of changes/adaptations in clinical and applied contexts.

Differentiating maximal and submaximal voluntary strength measures for the purposes of medico-legal assessments and para sport classification: A systematic review.

Measurement of maximum voluntary muscle contractions are effort-dependent - valid measurement requires maximal voluntary effort (MVE) from participants. Submaximal efforts (SMEs) yield invalid and potentially misleading results. This is particularly problematic in medico-legal and Para sport assessments where low strength scores may confer a personal advantage. Therefore, objective methods for accurately differentiating MVE and SME are required. This systematic review aimed to identify, appraise and synthesise evidence from scientific studies evaluating the validity of objective methods for differentiating MVE from SME during maximal voluntary contractions. Four electronic databases were searched for original research articles published in English and secondary references appraised for relevance yielding 25 studies for review. Methods were categorised based on eight distinct underlying theories. For isokinetic strength assessment, methods based on two theories - Strength-measure Ratios and Inter-Trial Strength Consistency - correctly classified 100% MVE and > 92% SME. Consequently, research evaluating the relative suitability of these methods for translation into practice is warranted. During isometric strength assessments, methods based on Deceptive Visual Feedback and Force-length properties warrant further investigation. Both methods yielded statistically significant differences between MVE and SME, with minimal overlap in values, but their sensitivity and specificity have not been evaluated.

Intra- and inter-rater reliability of electrical impedance myography using adhesive electrodes in healthy volunteers.

In spite of the growing use of the electrical impedance myography (EIM) measures for clinical assessment and follow-up of diseased muscle tissue, reliability studies are scarce. We evaluate the reliability of the (EIM) technique using four adhesive electrodes over the muscle of interest. Intra- and inter-rater reliability was studied within the same session and between sessions. Thirty-one healthy and volunteer subjects aged between 20 and 26 years were recruited. Phase angle, reactance and resistance were assessed for each EIM measurement. Intraclass correlation coefficient (ICC) was used to determine the relative reliability. Absolute reliability was expressed as the standard error of measurement and the minimum detectable change. Relative reliability within the same session and between sessions for the EIM technique was excellent (ICCs > 0.9) concerning both intra- and inter-rater reliability, except for the component reactance. The absolute reliability was very high for the three EIM components. EIM measures using four adhesive electrodes over the area of interest is a reliable technique to assess muscle tissue status. This study confirms that these measurement results barely vary depending on the examiner and the moment. The present study also confirms phase angle as the least affected EIM component by examiner and evaluation moment.

Diagnosis Accuracy of Carpal Tunnel Syndrome in Diabetic Neuropathy.

Background and objectives: Carpal tunnel syndrome (CTS) is a common pathology, but sometimes the diagnosis is delayed in patients with diabetic neuropathy (DN). The aim of the study is twofold: first, to compare the accuracy of ultrasound (US) with that of electroneurography (ENG) in the diagnosis of CTS associated with DN, using the clinical diagnosis as a reference standard, and second, to investigate the correlation between morphological US parameters and electrodiagnosis (EDX) measurements in patients with CTS and DN. Materials and Methods: This study included patients with DN. They were divided into two groups: Control (patients without CTS) and Cases (patients with CTS). We performed US and ENG in both hands, totaling 56 wrists, with 28 wrists in each group. Results: We found that the difference in the sensory distal latencies between the median and the ulnar nerves (ring finger) exhibited the highest diagnostic accuracy of all the US and ENG parameters, areas under the receiver operating characteristic (AUC) = 0.99 (95% CI 0.97-1), and it was significantly different from the best US diagnostic method. The wrist cross-sectional area (CSA) had the most accurate US diagnosis, while the wrist-to-forearm ratio had the worst AUC. Moreover, in the group of CTS and DN patients, the wrist CSA enlargement was statistically directly proportional to the median compound muscle action potential (CMAP) distal latency and inversely proportional to the antidromic median nerve conduction study (NCS) and the orthodromic median palm-wrist NCS. Conclusions: Both examinations can be used with confidence in the diagnosis of CTS overlapping with DN, but the EDX examination seems to be more accurate. Furthermore, we found a positive correlation between the US and EDX parameters.

Electrical impedance myography for reducing sample size in Duchenne muscular dystrophy trials.

OBJECTIVE: To evaluate the sensitivity of electrical impedance myography (EIM) to disease progression in both ambulatory and non-ambulatory boys with DMD. METHODS AND PARTICIPANTS: A non-blinded, longitudinal cohort study of 29 ambulatory and 15 non-ambulatory boys with DMD and age-similar healthy boys. Subjects were followed for up to 1 year and assessed using the Myolex® mViewTM EIM system as part of a multicenter study. RESULTS: In the ambulatory group, EIM 100 kHz resistance values showed significant change compared to the healthy boys. For example, in lower extremity muscles, the average change in EIM 100 kHz resistance values over 12 months led to an estimated effect size of 1.58. Based on these results, 26 DMD patients/arm would be needed for a 12-month clinical trial assuming a 50% treatment effect. In non-ambulatory boys, EIM changes were greater in upper limb muscles. For example, biceps at 100kHz resistance gave an estimated effect size of 1.92 at 12 months. Based on these results, 18 non-ambulatory DMD patients/arm would be needed for a 12-month clinical trial assuming a 50% treatment effect. Longitudinal changes in the 100 kHz resistance values for the ambulatory boys correlated with the longitudinal changes in the timed supine-to-stand test. EIM was well-tolerated throughout the study. INTERPRETATION: This study supports that EIM 100 kHz resistance is sensitive to DMD progression in both ambulatory and non-ambulatory boys. Given the technology's ease of use and broad age range of utility it should be employed as an exploratory endpoint in future clinical therapeutic trials in DMD. TRIAL REGISTRATION: Clincialtrials.gov registration #NCT02340923.

Head magnetomyography (hMMG): A novel approach to monitor face and whole head muscular activity.

Muscular activity recording is of high basic science and clinical relevance and is typically achieved using electromyography (EMG). While providing detailed information about the state of a specific muscle, this technique has limitations such as the need for a priori assumptions about electrode placement and difficulty with recording muscular activity patterns from extended body areas at once. For head and face muscle activity, the present work aimed to overcome these restrictions by exploiting magnetoencephalography (MEG) as a whole head myographic recorder (head magnetomyography, hMMG). This is in contrast to common MEG studies, which treat muscular activity as artifact in electromagnetic brain activity. In a first proof-of-concept step, participants imitated emotional facial expressions performed by a model. Exploiting source projection algorithms, we were able to reconstruct muscular activity, showing spatial activation patterns in accord with the hypothesized muscular contractions. Going one step further, participants passively observed affective pictures with negative, neutral, or positive valence. Applying multivariate pattern analysis to the reconstructed hMMG signal, we were able to decode above chance the valence category of the presented pictures. Underlining the potential of hMMG, a searchlight analysis revealed that generally neglected neck muscles exhibit information on stimulus valence. Results confirm the utility of hMMG as a whole head electromyographic recorder to quantify muscular activation patterns including muscular regions that are typically not recorded with EMG. This key advantage beyond conventional EMG has substantial scientific and clinical potential.

Electrical impedance myography as a biomarker of inclusion body myositis: A cross-sectional study.

OBJECTIVE: To assess the value of electrical impedance myography (EIM) in inclusion body myositis (IBM). METHODS: Patients with clinically defined IBM and healthy controls (HC) of similar age group were recruited. Each participant underwent manual muscle testing (MMT), 6-min walk test (6MWT), handgrip dynamometry, and IBM-functional rating scale assessment (IBM-FRS). EIM measurements were obtained from bilateral deltoid, biceps, forearm-flexors, quadriceps, tibialis anterior, and medial gastrocnemius. RESULTS: Fourteen IBM patients and 12 HCs with mean age 68.6 ± 6 and 67.4 ± 5.4 years were included in the final analysis. Averaged phase value at 50 kHz (EIM50) and ratio of phase value at 50 kHz/200 kHz (EIMPR) from six-muscles were significantly lower in IBM patients when compared to HC (5.23 ± 1.34 vs 7.88 ± 1.9, p-value 0.002, and 0.55 ± 0.09 vs. 0.68 ± 0.09, p-value 0.004, respectively). A strong correlation was noted between IBM-FRS, 6MWT, disease-duration and the averaged value of EIM50 and EIMPR in the IBM patients (Spearman |rho|>0.7, p-values < 0.01). CONCLUSIONS: EIM can differentiate between IBM patients and HCs and EIM parameters correlate with clinical outcome measures. SIGNIFICANCE: EIM may be a potential objective biomarker for IBM. A longitudinal validation study is warranted.

Reliability outcomes and inter-limb differences in ankle joint stiffness in children with unilateral cerebral palsy depend on the method of analysis.

Children with cerebral palsy (CP) present increased passive ankle joint stiffness, measured as the slope of the torque-angle curve relationship. However, large discrepancies in results exist among studies, likely because of various methodologies used. The purpose of this study was to determine the influence of different calculation methods on the outcomes and their inter-session reliability in children with unilateral CP (UCP). Thirteen children (mean age: 9.8 years) with spastic UCP underwent passive ankle mobilization at 2°/s on both legs using a dynamometer, on two occasions separated by one week. Passive ankle joint stiffness was calculated as the slope of the torque-angle curve using linear regression on three different relative ranges of torque (i.e. 30%-100%, 20-80% and 50-90% of maximal torque for method 1, 2 and 3, respectively) for both the paretic and non-paretic legs. Inter-session reliability was significantly lower on paretic leg (mean CV = 13.8%, ICC = 0.62) when compared to non-paretic leg (mean CV = 6%, ICC = 0.85), and method 3 presented lower reliability outcomes (mean CV = 11.7%, ICC = 0.75) than methods 1 (mean CV = 7.5%, ICC = 0.78) and 2 (mean CV = 6.6%, ICC = 0.79). Paretic values (0.24 Nm/°) were not different from the non-paretic leg (0.25 Nm/°), although significantly higher when considering the same angular sector (0.18 Nm/°). Passive ankle joint stiffness measurement can be reliably performed in children with UCP using method 1 and 2 while method 3 should be avoided. The non-paretic leg may be used for comparison with the paretic leg when taking into account differences in maximal dorsiflexion angle between legs. ClinicalTrials.gov Identifier: NCT02960932.

Measurement of maximum tongue protrusion force (MTPF) in healthy young adults.

We propose that tongue protrusive strength and tone may be related to upper airway patency, and when protrusive strength is reduced, individuals are at higher risk of developing sleep apnea, or speech/swallow disorders. The goal of the current study was to determine normative values of maximum tongue protrusion force (MTPF) in healthy young adults, using a unique newly developed device. We hypothesized that MTPF would be greater in males than in females. One hundred and one healthy young adults (mean age: 22.99 years; male: 23, female: 78) participated in this study. The subjects pushed their tongue forward against the device's piston (protrusion) as hard as possible for 2-5 sec and MTPF was recorded in Newtons (N). A minimum of 5 MTPF measurements were obtained with 1-2 min rest between measurements. The average MTPF for all subjects was 15.4 N (SD: ±3.8), with a range of 8-29. The male average MTPF was higher than female (17.8 N, SD: ±3.7 vs. 14.7 N, SD: ±3.5; P = 0.001). There was no significant difference for age between males and females; males had significantly greater height and weight. The results demonstrate our novel device can effectively measure tongue protrusive force in healthy young adults. This study provides normative values for MTPF, and identified significant tongue protrusion strength differences between males and females.

Diagnostic accuracy, validity, and reliability of Tensiomyography to assess muscle function and exercise-induced fatigue in healthy participants. A systematic review with meta-analysis.

Tensiomyography™ (TMG) is a non-invasive method to monitor skeletal muscle mechanical characteristics. This systematic review and meta-analysis reports on diagnostic accuracy, validity, and reliability of TMG (maximal radial displacement [Dm], contraction time [Tc], delay time [Td], and velocity of contraction [Vc]) to assess exercise-induced fatigue in healthy volunteers, with the specific aim to determine the current level of supporting evidence. Systematic literature searches within Medline, Embase and Sportdiscus databases were conducted from January 1990 through November 2018. Methodological quality was evaluated by the Assessment of Diagnostic Accuracy Studies (QUADAS) tool or the Validity and Reliability Critical Appraisal Tool (CAT) or the Quality Appraisal of Diagnostic Reliability checklist (QAREL). Meta-analytical methods were utilised to summarize relative reliabilities of Dm, Tc, Td (95%, CI). The methodological quality of the 19 included studies (n = 373; female = 13.0%) ranged from low to high quality. The analysis revealed insufficient diagnostic accuracy and validity, mixed results regarding absolute reliability, and high to excellent relative reliability for the assessed measures. To conclude, robust evidence for diagnostic accuracy/validity of TMG has yet to be determined, whereas there is substantial evidence for its reliability. Higher methodological standards need to be established, including the avoidance of gender bias.

A review on crosstalk in myographic signals.

PURPOSE: Crosstalk in myographic signals is a major hindrance to the understanding of local information related to individual muscle function. This review aims to analyse the problem of crosstalk in electromyography and mechanomyography. METHODS: An initial search of the SCOPUS database using an appropriate set of keywords yielded 290 studies, and 59 potential studies were selected after all the records were screened using the eligibility criteria. This review on crosstalk revealed that signal contamination due to crosstalk remains a major challenge in the application of surface myography techniques. Various methods have been employed in previous studies to identify, quantify and reduce crosstalk in surface myographic signals. RESULTS: Although correlation-based methods for crosstalk quantification are easy to use, there is a possibility that co-contraction could be interpreted as crosstalk. High-definition EMG has emerged as a new technique that has been successfully applied to reduce crosstalk. CONCLUSIONS: The phenomenon of crosstalk needs to be investigated carefully because it depends on many factors related to muscle task and physiology. This review article not only provides a good summary of the literature on crosstalk in myographic signals but also discusses new directions related to techniques for crosstalk identification, quantification and reduction. The review also provides insights into muscle-related issues that impact crosstalk in myographic signals.

A novel method to assess rate of force relaxation: reliability and comparisons with rate of force development across various muscles.

PURPOSE: The ability to generate quick submaximal muscle forces followed by quick relaxations is essential for various athletic and daily tasks. While force generation has been studied extensively, the studies of force relaxation are scarce. Therefore, we aimed to develop the rate of force relaxation scaling factor (RFR-SF) as a kinetic variable to assess the ability to relax submaximal muscle forces quickly. METHODS: Thirteen young adults performed rapid isometric force pulses to various submaximal levels in two different sessions. We compared RFR-SF with rate of development scaling factor (RFD-SF) in grip force muscles (GF), elbow (EE), and knee extensors (KE) and tested its reliability. Both RFD-SF and RFR-SF were calculated as the slopes of the linear relationship between peak forces and the corresponding peak rates of force development and relaxation, respectively. RESULTS: RFR-SFs were mainly different among the tested muscle groups (GF 8.22 ± 0.76 1/s; EE 7.64 ± 0.92 1/s; KE 6.01 ± 1.75 1/s) and there was no correlation among them (all p > 0.05). Within each tested muscle group, RFR-SF was lower than RFD-SF (GF 9.29 ± 1.05 1/s; EE 10.75 ± 0.87 1/s; KE 9.66 ± 0.89 1/s; all p < 0.001). The reliability of RFR-SF was moderate to good across the tested muscles (ICCs between 0.54 and 0.76 and all CVs < 15%). CONCLUSION: The RFR-SF is a clinically relevant kinetic variable that can reliably quantify the ability to relax a muscle force quickly. Future studies should assess both RFD-SF and RFR-SF as they represent different properties of the neuromuscular system.

A Simple Method for Normalization of Aortic Contractility.

Vascular contractile function changes in proliferative vascular diseases, e.g. atherosclerosis, and is documented using isolated blood vessels; yet, many laboratories differ in their approach to quantification. Some use raw values (e.g., mg, mN); others use a "percentage of control agonist" approach; and others normalize by blood vessel characteristic, e.g. length, mass, etc. A lack of uniformity limits direct comparison of contractility outcomes. To address this limitation, we developed a simple 2-step normalization method: (1) measure blood vessel segment length (mm), area (mm2) and calculate volume (mm3); then, (2) normalize isometric contraction (mN) by segment length and volume. Normalized aortic contractions but not raw values were statistically different between normal chow and high-fat diet-fed mice, supporting the practical utility and general applicability of normalization. It is recommended that aortic contractions be normalized to segment length and/or volume to reduce variability, enhance efficiency, and to foster universal comparisons across isometric myography platforms, laboratories, and experimental settings.

Test-retest reliability of laser displacement mechanomyography in paraspinal muscles while in lumbar extension or flexion.

This study investigated test-retest reliability of mechanomyography (MMG) on lumbar paraspinal muscles. Healthy male and female subjects (mean ±â€¯standard deviation, 25 ±â€¯9.4 years, BMI 21.8 ±â€¯2.99, n = 34) were recruited. Two test sessions (one week apart) consisted of MMG (laser displacement sensor (LDS)) muscle evaluations over the 10 lumbar facet joints, and 2 bilateral sacral sites, in anatomical extension and flexion. Two-way repeated measures ANOVA with Tukey's post hoc showed no significant differences between testing sessions for the same position (p > 0.05). The intra-class correlation coefficients (ICCs) in extension were classified as 'very good' (0.8-0.9) for maximal muscle displacement (Dmax), contraction time (Tc) and velocity of contraction (Vr). Half relaxation time (½Tr) and half relaxation velocity (½Vr) were 'poor' (0.4-0.5) and 'good' (0.7-0.8). In flexion, Dmax, Tc and Vr were 'excellent' (≥0.9) whilst ½Tr and ½Vr were 'fair' (0.6-0.7) and 'very good'. Comparing extension against flexion, significant (p < 0.05) differences in Dmax and ½Vr were found (L1/L2-L5/S1). Tc was significant (p < 0.05) for all sites whilst Vc was for L1/L2 on both sides (p < 0.05). ½Tr showed no significance (p > 0.05). Most MMG-derived parameters thus appear as reliable measures of muscle contractile properties in lumbar extension and flexion, with flexion providing more reliable results (ICCs).

Reliability of tensiomyography and myotonometry in detecting mechanical and contractile characteristics of the lumbar erector spinae in healthy volunteers.

PURPOSE: Tensiomyography™ (TMG) and MyotonPRO® (MMT) are two non-invasive devices for monitoring muscle contractile and mechanical characteristics. This study aimed to evaluate the test-retest reliability of TMG and MMT parameters for measuring (TMG:) muscle displacement (Dm), contraction time (Tc), and velocity (Vc) and (MMT:) frequency (F), stiffness (S), and decrement (D) of the erector spinae muscles (ES) in healthy adults. A particular focus was set on the establishment of reliability measures for the previously barely evaluated secondary TMG parameter Vc. METHODS: Twenty-four subjects (13 female and 11 male, mean ± SD, 38.0 ± 12.0 years) were measured using TMG and MMT over 2 consecutive days. Absolute and relative reliability was calculated by standard error of measurement (SEM, SEM%), Minimum detectable change (MDC, MDC%), coefficient of variation (CV%) and intraclass correlation coefficient (ICC, 3.1) with a 95% confidence interval (CI). RESULTS: The ICCs for all variables and test-retest intervals ranged from 0.75 to 0.99 indicating a good to excellent relative reliability for both TMG and MMT, demonstrating the lowest values for TMG Tc and between-day MMT D (ICC < 0.90). Absolute reliability was suitable for all parameters (CV 2-8%) except for Dm (10-12%). Vc demonstrated to be the most reliable and repeatable TMG parameter (ICC > 0.95, CV < 8%). CONCLUSION: The reliability for TMG Vc could be established successfully. Its further applicability needs to be confirmed in future studies. MMT was found to be more reliable on repeated testing than the two other TMG parameters Dm and Tc.

Mechanomyographic responses for the biceps brachii are associated with failure times during isometric force tasks.

In order to characterize the physiological adjustments within the neuromuscular system that contribute to task failure, this study examined the surface mechanomyographic (MMG) response during maximal and submaximal isometric force tasks of the elbow flexors sustained to failure. The time and frequency components of the MMG signal have shown to be influenced by motor unit activation patterns as well as tetanus. Therefore, it was hypothesized that the rate of change for the MMG response would associate with failure times and would be reduced to a similar degree between the two tasks. The isometric force tasks were performed by the dominant elbow flexors of twenty healthy males (age: 25 ± 4 years) and MMG was collected from the biceps brachii. Regression analyses were used to model the relationships between the rates of change for MMG versus failure times. There were high levels of interindividual variability in the response patterns, yet the models demonstrated significant negative associations between the rate of change for the MMG responses and failure times during both tasks (R2  = 0.41-0.72, P < 0.05). Similarly, the mean MMG amplitude and frequency values were reduced to comparable levels at the failure point of the two tasks. The results of this study demonstrated that force failure is associated with the rate of diminution in the properties of the muscle force twitch.

Characterization of tissue stiffness of the infraspinatus, erector spinae, and gastrocnemius muscle using ultrasound shear wave elastography and superficial mechanical deformation.

The aim of this study was to compare measurement methods of tissue stiffness using ultrasound shear wave elastography (SWE) and superficial mechanical deformation (MyotonPRO) in the infraspinatus, erector spinae, and gastrocnemius muscles. Thirty healthy volunteers were assessed during rest, 40% and 80% maximum voluntary isometric contraction (MVIC). Correlation of the two methods in the three muscle regions was significant (r = 0.23-0.71, p < .05), and strongest in the gastrocnemius. MyotonPRO reliability was excellent (ICC > 0.93), and demonstrated ability to discriminate between the three levels of muscle contraction. SWE demonstrated good reliability in the resting condition (ICC > 0.88), but lower during the 2 MVIC conditions. The utility of SWE during isometric contraction may be limited due to the inability to discriminate between 40% and 80% MVIC.

Comparing electro- and mechano-myographic muscle activation patterns in self-paced pediatric gait.

Electromyography (EMG) is the standard modality for measuring muscle activity. However, the convenience and availability of low-cost accelerometer-based wearables makes mechanomyography (MMG) an increasingly attractive alternative modality for clinical applications. Literature to date has demonstrated a strong association between EMG and MMG temporal alignment in isometric and isokinetic contractions. However, the EMG-MMG relationship has not been studied in gait. In this study, the concurrence of EMG- and MMG-detected contractions in the tibialis anterior, lateral gastrocnemius, vastus lateralis, and biceps femoris muscles were investigated in children during self-paced gait. Furthermore, the distribution of signal power over the gait cycle was statistically compared between EMG-MMG modalities. With EMG as the reference, muscular contractions were detected based on MMG with balanced accuracies between 88 and 94% for all muscles except the gastrocnemius. MMG signal power differed from that of EMG during certain phases of the gait cycle in all muscles except the biceps femoris. These timing and power distribution differences between the two modalities may in part be related to muscle fascicle length changes that are unique to muscle motion during gait. Our findings suggest that the relationship between EMG and MMG appears to be more complex during gait than in isometric and isokinetic contractions.

Electrical impedance myography for assessment of Duchenne muscular dystrophy.

OBJECTIVE: Sensitive, objective, and easily applied methods for evaluating disease progression and response to therapy are needed for clinical trials in Duchenne muscular dystrophy (DMD). In this study, we evaluated whether electrical impedance myography (EIM) could serve this purpose. METHODS: In this nonblinded study, 36 boys with DMD and 29 age-similar healthy boys underwent multifrequency EIM measurements for up to 2 years on 6 muscles unilaterally along with functional assessments. A linear mixed-effects model with random intercept and slope terms was used for the analysis of multifrequency EIM values and functional measures. Seven DMD boys were initiated on corticosteroids; these data were analyzed using a piecewise linear mixed-effects model. RESULTS: In boys > 7.0 years old, a significant difference in the slope of EIM phase ratio trajectories in the upper extremity was observed by 6 months of -0.074/month, p = 0.023, 95% confidence interval (CI) = -0.013, -0.14; at 2 years, this difference was -0.048/month, p < 0.0001, 95% CI = -0.028, -0.068. In boys ≤ 7.0 years old, differences appeared at 6 months in gastrocnemius (EIM phase slope = -0.83 °/kHz/mo, p = 0.007, 95% CI = -0.26, -1.40). EIM outcomes showed significant differences earlier than functional tests. Initiation of corticosteroids significantly improved the slope of EIM phase ratio (0.057/mo, p = 0.00019, 95% CI = 0.028, 0.086) and EIM phase slope (0.14 °/kHz/mo, p = 0.013, 95% CI = 0.028, 0.25), consistent with corticosteroids' known clinical benefit. INTERPRETATION: EIM detects deterioration in muscles of both younger and older boys by 6 months; it also identifies the therapeutic effect of corticosteroid initiation. Because EIM is rapid to apply, painless, and requires minimal operator training, the technique deserves to be further evaluated as a biomarker in DMD clinical therapeutic trials. Ann Neurol 2017;81:622-632.

Reliability of ground reaction forces in the aquatic environment.

The aim of this study was to verify the reliability of the kinetic parameters of gait using an underwater force platform. A total of 49 healthy participants with a median age of 21years were included. The kinetic gait data were collected using a 0.6×0.6×0.1m aquatic force plate (Bertec®), set in a pool (15×13×1.30m) with a water depth of 1.20m and water temperature of 32.5°C. Participants walked 10m before reaching the platform, which was fixed to the ground. Participants were instructed to step onto the platform with their preferred limb and data from three valid attempts were used to calculate the average values. A 48-h interval between tests was used for the test-retest reliability. Data were analyzed using interclass correlation coefficients (ICC) and results demonstrated that reliability ranged from poor to excellent, with ICC scores of between 0.24 and 0.87 and mean differences between (d¯)=-0.01 and 0.002. The highest reliability values were found for the vertical (Fz) and the lowest for the mediolateral components (Fy). In conclusion, the force platform is reliable for assessing the vertical and anteroposterior components of power production rates in water, however, caution should be applied when using this instrument to evaluate the mediolateral component in this environment.