Measuring humeral head translation using fluoroscopy: A validation study

Numerous techniques have been employed to monitor humeral head translation due to its involvement with several shoulder pathologies. However, most of the techniques were not validated. The objective of this study is to compare the accuracy of manual digitization and contour registration in measuring superior translation of the humeral head. Eight pairs of cadaver scapulae and humerii bones were harvested for this study. Each scapula and humerus was secured in a customized jig that allowed for control of humeral head translations and a vise that permitted rotations of the scapula about three axes. Fluoroscopy was used to take images of the shoulder bones. Scapular orientation was manipulated in different positions while the humerus was at 90° of humeral elevation in the scapular plane. Humeral head translation was measured using the two methods and was compared to the known translation. Additionally, accuracy of the contour registration method to measure 2-D scapular rotations was assessed. The range for the root mean square (RMS) error for manual digitization method was 0.27 mm - 0.43 mm and the contour registration method had a RMS error ranging from 0.18 mm - 0.40 mm. In addition, the RMS error for the scapular angle rotation using the contour registration method was 2.4°. Both methods showed acceptable errors. However, on average, the contour registration method showed lesser measurement error compared to the manual digitization method. In addition, the contour registration method was able to show good accuracy in measuring rotation that is useful in 2-D image analysis.     

Within-day and between-days reliability of quadriceps isometric muscle fatigue using mechanomyography on healthy subjects

This study aimed to examine within-day and between-days intratester reliability of mechanomyography (MMG) in assessing muscle fatigue. An accelerometer was used to detect the MMG signal from rectus femoris. Thirty one healthy subjects (15 males) with no prior knee problems initially performed three maximum voluntary contractions (MVCs) using an ISOCOM dynamometer. After 10 min rest, subjects performed a fatiguing protocol in which they performed three isometric knee extensions at 75% MVC for 40 s. The fatiguing protocol was repeated on two other days, two to four days apart for between-days reliability. MMG activity was determined by overall root mean squared amplitude (RMS), mean power frequency (MPF) and median frequency (MF) during a 40 s contraction. RMS, MPF and MF linear regression slopes were also analysed. Intraclass Correlation Coefficients (ICC); ICC1,1 and ICC1,2 were used to assess within-day reliability and between-days reliability respectively. Standard error of measurement (SEM) and smallest detectable difference (SDD) described the within-subjects variability. MMG fatigue measures using linear regression slopes showed low reliability and large between-days error (ICC1,2 = 0.43–0.46; SDD = 306.0–324.8% for MPF and MF slopes respectively). Overall MPF and MF, on the other hand, were reliable with high ICCs and lower SDDs compared to linear slopes (ICC1,2 = 0.79–0.83; SDD = 21.9–22.8% for MPF and MF respectively). ICC1,2 for overall MMG RMS and linear RMS slopes were 0.81 and 0.66 respectively; however, the SDDs were high (56.4% and 268.8% respectively). The poor between-days reliability found in this study suggests caution in using MMG RMS, MPF and MF and their corresponding slopes in assessing muscle fatigue.     

Joint kinematics estimation using a multi-body kinematics optimisation and an extended Kalman filter,and embedding a soft tissue artefact model

To reduce the impact of the soft tissue artefact (STA) on the estimate of skeletal movement using stereophotogrammetric and skin-marker data, multi-body kinematics optimisation (MKO) and extended Kalman filters (EKF) have been proposed. This paper assessed the feasibility and efficiency of these methods when they embed a mathematical model of the STA and simultaneously estimate the ankle, knee and hip joint kinematics and the model parameters. A STA model was used that provides an estimate of the STA affecting the marker-cluster located on a body segment as a function of the kinematics of the adjacent joints. The MKO and the EKF were implemented with and without the STA model. To assess these methods, intra-cortical pin and skin markers located on the thigh, shank, and foot of three subjects and tracked during the stance phase of running were used. Embedding the STA model in MKO and EKF reduced the average RMS of marker tracking from 12.6 to 1.6 mm and from 4.3 to 1.9 mm, respectively, showing that a STA model trial-specific calibration is feasible. Nevertheless, with the STA model embedded in MKO, the RMS difference between the estimated and the reference joint kinematics determined from the pin markers slightly increased (from 2.0 to 2.1 deg) On the contrary, when the STA model was embedded in the EKF, this RMS difference was slightly reduced (from 2.0 to 1.7 deg) thus showing a better potentiality of this method to attenuate STA effects and improve the accuracy of joint kinematics estimate.     

Estimating in vivo passive forces of the index finger muscles: Exploring model parameters

We compared predicted passive finger joint torques from a biomechanical model that includes the exponential passive muscle force–length relationship documented in the literature with finger joint torques estimated from measures in ten adult volunteers. The estimated finger joint torques were calculated from measured right index fingertip force, joint postures, and anthropometry across 18 finger and wrist postures with the forearm muscles relaxed. The biomechanical model predicting passive finger joint torques included three extrinsic and three intrinsic finger muscles. The values for the predicted passive joint torques were much larger than the values calculated from the fingertip force and posture measures with an average RMS error of 7.6 N cm. Sensitivity analysis indicated that the predicted joint torques were most sensitive to passive force–length model parameters compared to anthropometric and postural parameters. Using Monte Carlo simulation, we determined a new set of values for the passive force–length model parameters that reduced the differences between the joint torques calculated from the two methods to an average RMS value of 0.5 N cm, a 94% average improvement of error from the torques predicted using the existing data. These new parameter values did vary across individuals; however, using an average set for the parameter values across subjects still reduced the average RMS difference to 0.8 N cm. These new parameters may improve dynamic modeling of the finger during sub-maximal force activities and are based on in vivo data rather than traditional in vitro data.     

Influence of ankle functional instability on the ankle electromyography during landing after volleyball blocking

The purpose of this study was to describe, interpret and compare the EMG activation patterns of ankle muscles – tibialis anterior (TA), peroneus longus (PL) and gastrocnemius lateralis (GL) – in volleyball players with and without ankle functional instability (FI) during landing after the blocking movement. Twenty-one players with FI (IG) and 19 controls (CG) were studied. The cycle of movement analyzed was the time period between 200 ms before and 200 ms after the time of impact determined by ground reaction forces. The variables were analyzed for two different phases: pre-landing (200 ms before impact) and post-landing (200 ms after impact). The RMS values and the timing of onset activity were calculated for the three studied muscles, in both periods and for both groups. The co-activation index for TA and PL, TA and GL were also calculated. Individuals with FI presented a lower RMS value pre-landing for PL (CG = 43.0 ± 22.0; IG = 26.2 ± 8.4, p < 0.05) and higher RMS value post-landing (CG = 47.5 ± 13.3; IG = 55.8 ± 21.6, p < 0.10). Besides that, in control group PL and GL activated first and simultaneously, and TA presented a later activation, while in subjects with FI all the three muscles activated simultaneously. There were no significant differences between groups for co-activation index. Thus, the rate of contraction between agonist and antagonist muscles is similar for subjects with and without FI but the activation individually was different. Volleyball players with functional instability of the ankle showed altered patterns of the muscles that play an important role in the stabilization of the foot–ankle complex during the performance of the blocking movement, to the detriment of the ligament complex, and this fact could explain the usual complaints in these subjects.     

Spatial reorganisation of muscle activity correlates with change in tangential force variability during isometric contractions

The aim of this study was to quantify the effects of spatial reorganisation of muscle activity on task-related and tangential components of force variability during sustained contractions. Three-dimensional forces were measured from isometric elbow flexion during submaximal contractions (50 s, 5–50% of maximal voluntary contraction (MVC)) and total excursion of the centre of pressure was extracted. Spatial electromyographic (EMG) activity was recorded from the biceps brachii muscle. The centroids of the root mean square (RMS) EMG and normalised mutual information (NMI) maps were computed to assess spatial muscle activity and spatial relationship between EMG and task-related force variability, respectively. Result showed that difference between the position of the centroids at the beginning and at the end of the contraction of the RMS EMG and the NMI maps were different in the medial–lateral direction (P < 0.05), reflecting that muscle regions modulate their activity without necessarily modulating the contribution to the task-related force variability over time. Moreover, this difference between shifts of the centroids was positively correlated with the total excursion of the centre of pressure at the higher levels of contractions (>30% MVC, R² > 0.30, P < 0.05), suggesting that changes in spatial muscle activity could impact on the modulation of tangential forces. Therefore, within-muscle adaptations do not necessarily increase force variability, and this interaction can be quantified by analysing the RMS EMG and the NMI map centroids.     

Alternative methods of normalising EMG during cycling

We evaluated possible methods of normalisation for EMG measured during cycling. The MVC method, Sprint method and 70% Peak Power Output Method were investigated and their repeatability, reliability and sensitivity to change in workload were compared.Thirteen cyclists performed the same experimental protocol on three separate occasions. Each day, subjects firstly performed MVCs, followed by a 10 s maximal sprint on a cycle ergometer. Subjects then performed a Peak Power Output (PPO) test until exhaustion. After which they cycled at 70% of PPO for 5 min at 90 rpm. Results indicated that normalising EMG data to 70% PPO is more repeatable, the intra-class correlation (ICC) of 70% PPO (0.87) was significantly higher than for MVC (0.66) (p = 0.03) and 10 s sprint (0.65) (p = 0.04). The 70% PPO method also demonstrated the least intra-subject variability for five out of the six muscles. The Sprint and 70% PPO method highlighted greater sensitivity to changes in muscle activity than the MVC method. The MVC method showed the highest intra-subject variability for most muscles except VM.The data suggests that normalising EMG to dynamic methods is the most appropriate for examining muscle activity during cycling over different days and for once-off measurements.     

Effect of bolus hardness on the chewing pattern and activation of masticatory muscles in subjects with normal dental occlusion

The aim of the study was to evaluate the effect of bolus hardness on the kinematic of mastication and jaw-elevator muscle activity in subjects with normal dental occlusion and function. The mandibular motion and the surface EMG envelope of the masseter and temporalis anterior muscles were assessed in twelve subjects during mastication of a soft and hard bolus of the same size. When chewing the hard bolus, the chewing pattern in the frontal plane was significantly higher and wider, with smaller closure angle and higher peak velocity than when chewing the soft bolus. EMG peak amplitude of both the masseter and anterior temporalis muscles was higher for the side of the bolus but the contralateral side increased its activity significantly more than the ipsilateral side when the hardness of the bolus increased (for the masseter, mean ± SD: 130.4 ± 108.1% increase for the contralateral side and 29.6 ± 26.9% for the ipsilateral side). Moreover, the peak EMG activity for both muscles occurred more distant from the closure point with hard bolus. The increased activity of the contralateral side may help maintaining the mandibular equilibrium, with indirect participation to the power stroke generated by the chewing-side masseter. The results provide kinematic and EMG adaptations to bolus hardness in healthy subjects and can be used as normative data in the development of methods for early diagnosis of impaired chewing function.     

Uncovering patterns of forearm muscle activity using multi-channel mechanomyography

A coordinated activation of distal forearm muscles allows the hand and fingers to be shaped during movement and grasp. However, little is known about how the muscle activation patterns are reflected in multi-channel mechanomyogram (MMG) signals. The purpose of this study is to determine if multi-site MMG signals exhibit distinctive patterns of forearm muscle activity. MMG signals were recorded from forearm muscle sites of nine able-bodied participants during hand movement. By using 14 features selected by a genetic algorithm and classified by a linear discriminant analysis classifier (LDA), we show that MMG patterns are specific and consistent enough to identify 7 ± 1 hand movements with an accuracy of 90 ± 4%. MMG-based movement recognition required a minimum of three recording sites. Further, by classifying five classes of contraction patterns with 98 ± 3% accuracy from MMG signals recorded from the residual limb of an amputee participant, we demonstrate that MMG shows pattern-specificity even in the absence of typical musculature. Multi-site monitoring of the RMS of MMG signals is suggested as a method of estimating the relative contributions of muscles to motor tasks. The patterns in MMG facilitate our understanding of the mechanical activity of muscles during movement.     

Alternating activation is related to fatigue in lumbar muscles during sustained sitting

The aim of this study was to investigate the relation between variability in muscle activity and fatigue during a sustained low level contraction in the lumbar muscles. Twenty-five healthy participants (13 men 12 women) performed a 30 min sitting task with 5 degrees inclination of the trunk. Surface electromyographic (EMG) signals were recorded bilaterally from the lumbar muscles with 2 high density surface EMG grids of 9 × 14 electrodes. Median frequency (MDF) decrease, amplitude (RMS) increase and the rating of perceived exertion (RPE) were used as fatigue indices. Alternating activation and spatial and temporal variability were computed and relations with the fatigue indices were explored. During sitting, the mono- and bipolar RMS slightly increased while the MDF remained unchanged indicating no systematic muscle fatigue, although the average RPE increased from 6 to 13 on a scale ranging between 6 and 20. Higher frequency of alternating activation between the left and right side was associated with increased RPE (p = 0.03) and decreased MDF (p = 0.05). A tendency in the same direction was seen between increased spatial and temporal variation within the grids and increased RPE and decreased MDF. Present findings provide evidence for a relationship between variability in muscle activity and fatigue.     

Electromyographic analysis of upper limb muscles during standardized isotonic and isokinetic robotic exercise of spastic elbow in patients with stroke

Although it has been reported that strengthening exercise in stroke patients is beneficial for their motor recovery, there is little evidence about which exercise method is the better option. The purpose of this study was to compare isotonic and isokinetic exercise by surface electromyography (EMG) analysis using standardized methods.Nine stroke patients performed three sets of isotonic elbow extensions at 30% of their maximal voluntary isometric torque followed by three sets of maximal isokinetic elbow extensions with standardization of mean angular velocity and the total amount of work for each matched set in two strengthening modes. All exercises were done by using 1-DoF planner robot to regulate exact resistive torque and speed. Surface electromyographic activity of eight muscles in the hemiplegic shoulder and elbow was recorded. Normalized root mean square (RMS) values and co-contraction index (CCI) were used for the analysis.The isokinetic mode was shown to activate the agonists of elbow extension more efficiently than the isotonic mode (normalized RMS for pooled triceps: 96.0 ± 17.0 (2nd), 87.8 ± 14.4 (3rd) in isokinetic, 80.9 ± 11.0 (2nd), 81.6 ± 12.4 (3rd) in isotonic contraction, F[1, 8] = 11.168; P = 0.010) without increasing the co-contraction of muscle pairs, implicating spasticity or synergy.     

Between-day reliability of a hand-held dynamometer and surface electromyography recordings during isometric submaximal contractions in different shoulder positions

Functional shoulder assessments require the use of objective and reliable standardized outcome measures. Therefore, the aim of this study was to examine the between-day reliability of a hand-held dynamometer when measuring muscle strength during flexion, abduction, and internal and external rotation as well as surface electromyography (EMG) when measuring muscle activity from m. trapezius superior and deltoideus anterior. Twenty-four healthy subjects participated and performed four isometric contractions measured with a hand-held dynamometer and EMG. Both relative and absolute reliability were calculated based on the mean of the last three of the four repetitions. EMG amplitude was assessed calculating both absolute and normalized root-mean-square (RMS) values. The reliability of the hand-held dynamometer was high (LOA = 3.2–7.6% and ICC = 0.89–0.98). The absolute reliability for EMG showed similar results for absolute RMS values (LOA = 20.0–68.4%) and normalized RMS values (LOA = 42.4–66.5%). However, the results concerning the relative reliability showed higher ICC for absolute RMS values (ICC = 0.82–0.92) compared with normalized values (ICC = 0.57–0.72).The outcome measurements of this study with healthy subjects were found reliable and, therefore, have the potential to detect changes in muscle strength and muscle activity.     

Bilateral impairments of shoulder abduction in chronic hemiparesis: Electromyographic patterns and isokinetic muscle performance

ObjectiveTo analyze electromyographic (EMG) patterns and isokinetic muscle performance of shoulder abduction movement in individuals who sustained a cerebrovascular accident (CVA).DesignTwenty-two individuals who sustained a CVA and 22 healthy subjects volunteered for EMG activity and isokinetic shoulder abduction assessments. EMG onset time, root mean square (RMS) for upper trapezius and deltoid muscles, as well as the isokinetic variables of peak torque, total work, average power and acceleration time were compared between limbs and groups.ResultsThe paretic side showed a different onset activation pattern in shoulder abduction, along with a lower RMS for both muscles (21.8 ± 13.4% of the maximal voluntary isometric contraction (MVIC) for the deltoid and 25.9 ± 15.3% MVIC for the upper trapezius, about 50% lower than the control group). The non-paretic side showed a delay in both muscles activation and a lower RMS for the deltoid (32.2 ± 13.7% MVIC, about 25% lower than the control group). Both sides of the group of individuals who sustained a CVA presented a significantly lower isokinetic performance compared to the control group (paretic side ～60% lower; non-paretic side ～35% lower).ConclusionsShoulder abduction muscle performance is impaired in both paretic and non-paretic limbs of individuals who sustained a CVA.     

Quantifying ‘normal’ shoulder muscle activity during abduction

The purpose of this experiment was to obtain electromyographic (EMG) activity from a sample of healthy shoulders to allow a reference database to be developed and used for comparison with pathological shoulders. Temporal and intensity shoulder muscle activation characteristics during a coronal plane abduction/adduction movement were evaluated in the dominant healthy shoulder of 24 subjects. Surface and intramuscular fine wire electrodes recorded EMG activity from 15 shoulder muscles (deltoid × 3, trapezius × 3, subscapularis × 2, latissimus dorsi, pectoralis major, pectoralis minor, supraspinatus, infraspinatus, serratus anterior and rhomboids) at 2000 Hz for 10 s whilst each subject performed 10 dynamic coronal plane abduction/adduction movements from 0° to 166° to 0° with a light dumbbell. Results revealed that supraspinatus (?.102 s before movement onset) initiated the movement with middle trapezius (?.019 s) and middle deltoid (?.014 s) also activated before the movement onset. Similar patterns were also found in the time of peak amplitude and %MVC with a pattern emerging where the prime movers (supraspinatus and middle deltoid) were among the first to reach peak amplitude or display the highest %MVC values. In conclusion, the most reproducible patterns of activation arose from the more prime mover muscle sites in all EMG variables analysed and although variability was present, there emerged ‘invariant characteristics’ that were considered ‘normal’ for this group of non pathological shoulders. The authors believe that the methodology and certain parts of the analysis in this study can be duplicated and used by future researchers who require a reference database of muscle activity for use as a control group in comparisons to their respective pathological shoulder group.     

Soft tissue artefacts of skin markers on the lower limb during cycling: Effects of joint angles and pedal resistance

Soft tissue artefacts (STA) are a major error source in skin marker-based measurement of human movement, and are difficult to eliminate non-invasively. The current study quantified in vivo the STA of skin markers on the thigh and shank during cycling, and studied the effects of knee angles and pedal resistance by using integrated 3D fluoroscopy and stereophotogrammetry. Fifteen young healthy adults performed stationary cycling with and without pedal resistance, while the marker data were measured using a motion capture system, and the motions of the femur and tibia/fibula were recorded using a bi-plane fluoroscopy-to-CT registration method. The STAs with respect to crank and knee angles over the pedaling cycle, as well as the within-cycle variations, were obtained and compared between resistance conditions. The thigh markers showed greater STA than the shank ones, the latter varying linearly with adjacent joint angles, the former non-linearly with greater within-cycle variability. Both STA magnitudes and within-cycle variability were significantly affected by pedal resistance (p < 0.05). The STAs appeared to be composed of one component providing the stable and consistent STA patterns and another causing their variations. Mid-segment markers experienced smaller STA ranges than those closer to a joint, but tended to have greater variations primarily associated with pedal resistance and muscle contractions. The current data will be helpful for a better choice of marker positions for data collection, and for developing methods to compensate for both stable and variation components of the STA.     

Reliability of electromyographic amplitude values of the upper limb muscles during closed kinetic chain exercises with stable and unstable surfaces

The purpose of the present study was to evaluate the intra and interday reliability of surface electromyographic amplitude values of the scapular girdle muscles and upper limbs during 3 isometric closed kinetic chain exercises, involving upper limbs with the fixed distal segment extremity on stable base of support and on a Swiss ball (relatively unstable). Twenty healthy adults performed the exercises push-up, bench-press and wall-press with different effort levels (80% and 100% maximal load). Subjects performed three maximal voluntary contractions (MVC) in muscular testing position of each muscle to obtain a reference value for root mean square (RMS) normalization. Individuals were instructed to randomly perform three isometric contraction series, in which each exercise lasted 6 s with a 2-min resting-period between series and exercises. Intra and interday reliabilities were calculated through the intraclass correlation coefficient (ICC 2.1), standard error of the measurement (SEM). Results indicated an excellent intraday reliability of electromyographic amplitude values (ICC ? 0.75). The interday reliability of normalized RMS values ranged between good and excellent (ICC 0.52–0.98). Finally, it is suggested that the reliability of normalized electromyographic amplitude values of the analyzed muscles present better values during exercises on a stable surface. However, load levels used during the exercises do not seem to have any influence on variability levels, possibly because the loads were quite similar.     

Variation the oviposition behavior by the stingless bee,Heterotrigona itama (Hymenoptera,Apidae, Meliponini)

A study to determine the variation of ovipositioning behavior of stingless bees, Heterotrigona itama (Cockerell, 1918) was conducted on three colonies on June 2015. A digital single-lens reflex (DSLR) camera with a macro lens attached was used to record every movement of H. itama in its colonies for 20 min hour between 0800 h and 2000 h for seven days and seven month. The daily egg laying rate and time for laying eggs in colony-B and colony-C were significantly (P ? 0.05) higher than the colony-A. However, time to close the brood was not significantly different among colonies. The fastest egg oviposition time was 4 s by the colony-B and the slowest was 6 s by the colony-A. In addition there are no significant trends on brood produced per day, laying time of eggs, and the closing time of the brood after the oviposition process from June to December 2016. This result is useful for understanding the behavior of egg laying process by the queen bees and necessary to deal with problems of management and reproduction in the near future.     

The development of rhythm regularity, neuromuscular strategies, and movement smoothness during repetitive reaching in typically developing children

IntroductionThis study examined the development of paced coordinated reaching characterized by the successful entrainment of the movement to an external pacer, synchronous muscle activations and movement smoothness.MethodsThirty children, 5–10 years of age, and ten adults were instructed to repeatedly reach for and move an object from a lower shelf to an upper shelf in time to a metronome. Surface electromyography data were recorded. Amplitude and cross-correlations were calculated on three muscle pairs crossing the shoulder and elbow. A motion capture system captured the space curve accelerations of hand, forearm and upper arm segments to quantify movement smoothness.ResultsThe 5–6 year old children showed the greatest amount of temporal variability, followed by 7–10 year olds and then the adults. Correlations between muscle pairs stabilizing the shoulder girdle were higher in each group as compared to the other two muscle pairs but the correlations for all pairs were consistently higher for adults. Movement smoothness for children 9–10 years of age was closer to an adult-like pattern with respect to control of the upper arm, but the hand segment had the greatest variability across groups.ConclusionsThe increased temporal variability and decreased movement smoothness of the hand and forearm segments suggest that control of more distal musculature may be more difficult in children. The neuromuscular strategies adopted by adults were more optimal than those adopted by children as reflected by smoother and more consistent reaching.     

Evidence that pigeons represent both time and number on a logarithmic scale

Pigeons were presented with trials that always began with presentation of a houselight that lasted for 1–16 s. Red and green side keys were presented immediately after the houselight went off. A peck on the red key was reinforced if the houselight duration was 8 s or shorter, and a peck on the green key was reinforced if the houselight duration was 9 s or longer. Plots of asymptotic performance as a function of houselight duration showed bow-shaped curves with higher accuracy at the ends of the scale than in the middle. Training to bisect a scale containing houselight durations of 2–32 s yielded a performance curve that superimposed on the 1–16 s curve. Both curves showed two important asymmetries around the midpoint: pigeons were more accurate at 9 and 10 s than at 7 and 8 s but were more accurate at 1–4 s than at 13–16 s. These findings closely resembled those found in a similar study of number scale bisection [Roberts, W.A., 2005. How do pigeons represent numbers? Studies of number scale bisection. Behav. Process. 69, 33–43]. Theoretical predictions from associative and confusion models showed a good match to the obtained data if it was assumed that time and number scales were logarithmic and that generalization or confusion curves were constant but not if it was assumed that scales were linear and that generalization or confusion curves were scalar.     

High variability in serum estradiol measurements in men and women

To reduce the variability in estradiol (E2) testing and to assure better patient care, standardization of E2 measurements has been recommended. This study aims to assess the accuracy and variability of E2 measurements performed by 11 routine immunological methods and 6 mass spectrometry methods using single donor serum materials and to compare the results to a reference method. The contribution of calibration bias, specificity or matrix effects, and imprecision on the overall variability of individual assays was evaluated.This study showed substantial variability in serum E2 measurements in samples from men and pre- and post-menopausal women. The mean bias across all samples, for each participant, ranged between −2.4% and 235%, with 3 participants having a mean bias of over 100%. The data suggest that calibration bias is the major contributor to the overall variability for nine assays.The analytical performances of most assays measuring E2 concentrations do not meet current needs in research and patient care. Three out of 17 assays would meet performance criteria derived from biological variability of ±12.5% bias at concentrations ⩾20 pg/mL, and a maximum allowable bias of ±2.5 pg/mL at concentrations <20 pg/mL. The sensitivity differs highly between assays. Most assays are not able to measure E2 levels below 10 pg/mL. Standardization, specifically calibration to a common standard by using panels of individual patient samples, can reduce the observed variability and improve the utility of E2 levels in clinical settings.