Measurement variability and sincerity of effort: clinical utility of isokinetic strength coefficient of variation scores

Uncontrolled HIV and inflammation is associated with intracranial saccular aneurysm presence

OBJECTIVE

To study biomarkers of inflammation in cerebrovascular disease, exploring modifiable and non-modifiable biochemical and clinical risk factors associated with the presence of intracranial saccular aneurysms (ISAs) in an HIV-positive cohort.

DESIGN

A cross-sectional community-based study was used to study blood biomarkers of inflammation as predictors of cerebrovascular disease, specifically the presence of ISAs in persons with HIV. Potential biochemical and clinical predictors of ISA presence were identified.

METHODS

Time of flight magnetic resonance angiography and magnetic resonance imaging data identified the presence of ISAs in an HIV-positive cohort. Quantitative assays for neuroinflammatory biomarkers were performed on plasma blood samples. Lasso regression models were used to identify neuroinflammatory biomarkers and clinical risk factors associated with ISAs.

RESULTS

Eight of 72 participants had radiographically identified ISAs. ISAs were more common in non-Hispanic black participants (18.5% vs. 0% presence in nonblack patients). Participants with well controlled HIV (defined as CD4+ count >200 cells/ml and undetectable viral load at time of magnetic resonance imaging) had lower odds of ISAs (odds ratio: 0.19, 95% confidence interval 0.05-0.79) independent of age, sex, ethnicity and vascular risk factors. Macrophage inflammatory protein-1 p, an HIV- suppressive factor detected in participant blood samples, was inversely associated with aneurysm presence.

CONCLUSION

Well controlled HIV is associated with fewer ISAs. The identification of non-modifiable and modifiable risk factors contributing to ISA formation may provide valuable insight to impact clinical practice and inform the pathophysiology underlying ISA formation.

Effects of Reduced Effort on Mechanical Output Obtained From Maximum Vertical Jumps

The aim of this study was to evaluate the effect of reduced effort on maximum countermovement jumps. Groups of unskilled and skilled jumpers performed countermovement jumps without an arm swing at 100% and 50% effort. The results revealed markedly reduced jump height and work performed at 50% effort, although the maximum force and power output remained virtually unchanged. The observed differences were consistent across individuals with different jumping skills. A possible cause of differences in changes across the tested variables was a reduced countermovement depth associated with the 50% effort jumps. It is known to cause an increase in maximum force and power outputs, but not in jump height. Therefore, the jump height and work performed may be more closely related to our sense of effort when jumping, rather than our maximum force and power output. From a practical perspective, the present findings reiterate the importance of maximizing effort for making valid assessments of muscle mechanical capacities, as tested by maximal vertical jumps and, possibly, other maximum performance tasks.

Consistency of strength curves for determining maximal effort production during isokinetic knee testing of anterior cruciate ligament-deficient patients

The purpose of this investigation was to attempt to establish decision rules for determining maximal effort production during isokinetic strength testing of unilateral anterior cruciate ligament-deficient patients based on the degree of strength curve consistency within a set. Thirty-three participants performed six bilateral knee extension and flexion exertions at maximal effort and at 80% of perceived maximum at testing velocities of 60 and 180°s(-1). Within-set consistency was quantified by computation of the variance ratio across strength curves. Tolerance interval-based cutoff scores covering 99% of the population were calculated for declaring efforts as being maximal or not at confidence levels of 90%, 95%, and 99%. The sensitivity percentages attained for the injured knee for both testing velocities ranged between 9.1% and 27.2%, while specificity percentages ranged between 84.8% and 100%. For the non-injured knee, sensitivity values for both testing velocities ranged between 21.2% and 45.0%, while specificity percentages ranged between 97.0% and 100%. The developed decision rules do not effectively discriminate on an individual patient basis between maximal and non-maximal isokinetic knee musculature efforts. Further research is needed for development of methods that would enable to ascertain maximal effort production in this patient population during knee muscle strength testing.

Discriminating between maximal and feigned isokinetic knee musculature performance using waveform similarity measures

BACKGROUND

Muscle strength test outcomes may aid in determination of impairment or disability rating following injury. In such settings, verification of participant effort during testing is imperative. This investigation explored the utilization of within-set moment waveform similarity measures, namely cross correlation and percent root mean square difference scores, to develop decision rules for discriminating between maximal and feigned efforts during isokinetic testing of the knee joint musculature.

METHODS

A mixed-gender sample of 46 participants performed non-reciprocal sets of maximal or feigned knee extension and flexion concentric and eccentric efforts at testing velocities of 30°s(-1) and 120°s(-1). Logistic regression and Monte Carlo simulations were used to derive decision rules for differentiating between the two effort types.

FINDINGS

Employing cutoff scores corresponding to 100% specificity; sensitivities of the knee extensor's velocity-specific decision rules were 92.4% and 84.8%, respectively. The velocity-specific knee flexor's test sensitivities were 56.5% and 46.7%.

INTERPRETATION

Utilizing the proposed decision rules, substantiating maximal effort performance of the knee extensors may be possible using this specific testing protocol. However, the proposed methods are limited in their ability to verify performance of maximal knee flexor efforts.

Differentiating between types and levels of isokinetic knee musculature efforts

This investigation assessed whether a measure of moment curve shape similarity, and a measure quantifying curve magnitude differences, enables differentiation between types (sincere vs. feigned) and levels (maximal vs. submaximal) of effort exerted during isokinetic testing of the knee. Healthy participants (n=37) performed four sets of six concentric knee extension-flexion repetitions on two occasions. The sets consisted of: (1) maximal effort; (2) self-perceived 75% of maximal effort; (3) self-perceived 50% of maximal effort; and (4) a set attempting to feign injury. Average cross-correlation and percent root mean square difference values were computed between moment curves in each direction. Logistic regression was used to derive decision rules for differentiating between maximal and submaximal effort levels; and between sincere and feigned effort types. Using a cutoff criteria corresponding to 100% specificity, maximal effort production could be ascertained with 96% sensitivity within the sample. Feigned efforts, however, could be ascertained with only 31% sensitivity due to overlap with sincere submaximal effort. Using the proposed models, clinicians may be able to ascertain whether maximal efforts were produced during isokinetic knee musculature testing. Additionally, evidence regarding participant's intentions with regard to influencing test results may be gauged, although to a lesser extent.

The validity and reliability of the 1RM bench press using chain-loaded resistance

The purposes of this study were to determine the validity and test-retest reliability of the 1 repetition maximum (1RM) chain-loaded, free-weight bench press (CBP) and to examine possible learning effects that may occur between the test-retest measurements. Nine resistance-trained men (20.58 +/- 1.31 years, 188.24 +/- 9.29 cm, 92.07 +/- 16.94 kg) and seven resistance-trained women (20.42 +/- 0.98 years, 175.61 +/- 9.32 cm, 73.61 +/- 10.80 kg) participating in Division II college basketball completed this study. Two familiarization sessions took place using light to moderate loads to learn proper technique. The subjects completed a 1RM test on the traditional plate-loaded bench press 4 days before completion of the CBP 1RM, which was followed by 4 days of rest before completing the retest. Intraclass correlation coefficients (ICC) and the percent coefficients of variation (CV) were used to determine relative and absolute test-retest reliability. Concurrent validity was determined from the Pearson correlation coefficients between the CBP and the plate-loaded bench press. Test-retest differences were analyzed with the paired t-test. ICC and CV for the men (r = 0.99, 1.4%) and women (r = 0.93, 3.5%), respectively indicate that highly reproducible 1RM scores can be found with the CBP. High validity was also found with high correlations between the CBP and plate-loaded bench press for the men (r = 0.95) and women (r = 0.80). A statistically significant (p = 0.04) but clinically small (2.57 kg) shift in the mean occurred between the CBP test and retest for the men, whereas no change occurred for the women. The data indicate that valid and reliable 1RM scores can be found after two familiarization sessions in men and women athletes who have previous resistance training experience.

Angular position, range of motion and velocity of arm elevation: a study of consistency of performance

BACKGROUND

To define the normal range, velocity and consistency of the movement of active arm elevation with humerus in neutral or in external rotation using a simplified kinematic model.

METHODS

Nine normal volunteers and the non-involved side of twenty five patients with unilateral shoulder lesion participated. A 3D optoelectronic tracking system was used to register the movement of raising the arm from the normal upright position to maximal elevation in a repetitive way. Peak humeral position, range of movement, velocity of motion and consistency of cycles were analyzed. Descriptive statistics, correlation between variables and with sex, age and side are presented, including differences between performances of movement done in neutral or external rotation.

FINDINGS

Data of the six variables were: maximal abduction 142 degrees [137.4-147.0], range of motion 118.1 degrees [112-124], maximal velocity 238 degrees/s [209-265]; mean velocity 113 degrees/s [96-130]; coefficient of variation of maximal angular abduction was 2.2% [1.7-2.7]; coefficient of variation of maximal velocity 8.6% [7.3-9.9]. No significant differences were observed either on side, sex or between the shoulder of normal volunteers or that of the patients with opposite shoulder lesions. Participants older than 45 years old showed only a significant slightly lower average velocity. The study confirms the weak association between dependent (biomechanical) and independent variables.

INTERPRETATION

As it is described here, analysis of arm elevation has not been previously studied and shows that has a good consistency in angular position, velocity and repeatability of motion in normal conditions which permits a picture of the overall performance of the shoulder.

The sensitivity and specificity of functional capacity evaluations in determining maximal effort: a randomized trial

STUDY DESIGN

Randomized trial.

OBJECTIVES

To determine the sensitivity and specificity of maximal effort testing in functional capacity evaluations.

SUMMARY OF BACKGROUND DATA

Functional capacity evaluations are widely used to determine when an injured worker is able to return to work. The accurate assessment of function is dependent on a patient's willingness to exert maximal effort during evaluation. Although many tests are used to suggest the presence of maximal or submaximal effort, it is unclear whether these tests can actually do what they are hoped to do.

METHODS

Ninety study participants with low back pain were randomized into either a 100% effort group or a 60% effort group. After a thorough evaluation, the blinded tester was asked to give an overall opinion as to whether or not the participant was giving 100% effort or 60% effort.

RESULTS

The tester's opinion on maximal effort tests within the functional capacity evaluation had an overall specificity of 84.1% and a sensitivity of 65.2%. Only 5 of 17 commonly used maximal effort tests were able to individually differentiate between maximal and submaximal effort. The final logistic regression model was able to find three covariates with reasonable explanation of the proportion of variance in the outcome variable of effort (R 3 0.444) with goodness of fit.

CONCLUSIONS

The determination of maximal effort in a functional capacity evaluation is complex. Because of the wide-ranging medicolegal and ethical considerations, caution is recommended in the labeling of patients as exerting either maximal or submaximal effort.

Reliability of isokinetic supine bench press in healthy women using the Ariel Computerized Exercise System

The aim of this study was to assess reliability of the Ariel Computerized Exercise System (ACES) "multifunction exerciser". Twenty-three healthy women completed three sets, three repetitions each, of maximal isokinetic supine bench press at two different velocities, slow (10/s) and moderate (25/s). The following performance parameters were studied: peak and average force, peak and average power, and total work. The experiment was repeated for two days. Intraclass correlation coefficients (ICC[2,1]) varied between 0.947 and 0.755 at 10 degrees/s and between 0.861 and 0.654 at 25 degrees/s. The standard error of the measurement (SEM), the smallest detectable difference (SDD), and the coefficient of variation (CV) indicated that it is possible to achieve reliable and clinically relevant measurements with the ACES.

Identification of feigned shoulder flexion weakness in normal subjects

OBJECTIVE

The purpose of this study was to compare the effect of three related test protocols on the power of a specific index relating to the difference between the eccentric to concentric strength ratios (DEC) to identify feigned shoulder flexion effort.

DESIGN

Seventeen normal subjects were instructed to exert maximal concentric and eccentric shoulder flexion effort and then to feign weakness, pretending the presence of a shoulder injury.

RESULTS

For both range of motions (ROMs), the DEC scores in the feigned effort were significantly greater than their maximal counterparts. A case by case analysis revealed that the DEC correctly identified 100% of the feigned efforts when derived from the 40 and 160 degrees/sec combination.

CONCLUSIONS

The findings indicate that the DEC retains its efficiency even under very short muscle length variation as long as adequate velocity gradients are applied. Consequently, maximality of effort may be tested outside compromised ROMs, particularly where pain or instability denies the performance of a standard full ROM protocol.

Muscle strength and ageing: methodological aspects of isokinetic dynamometry and androgen administration

1. To evaluate interventions aiming to increase muscle strength in older men, it is necessary to use an objective and reproducible method to measure strength. The most reliable method to evaluate muscle strength is isokinetic peak torque (PT) measured by a dynamometer; however, raw PT varies with differences in body size and an optimal scaling for body physique to control confounding effects of body size is necessary to make the most valid comparisons. 2. The present study was designed to estimate the effects of age (part A) and androgen administration (part B) on muscle strength and to estimate reproducibility and evaluate various scaling methods in order to optimize comparisons of isokinetic PT measurements. 3. A single isokinetic exercise protocol was used to compare the muscle strength of 31 healthy men of two age groups (< 40 and > 60 years; part A) and change in strength due to administration of dihydrotestosterone (DHT; 70 mg/day) or placebo gel for 3 months in 35 healthy older (> or = 60 years) men (part B). 4. Muscle strength was assessed by a total of 16 PT measurements using a Cybex NORM dynamometer (Cybex, Ronkonkoma, NY, USA). Age-related differences in muscle strength were estimated by using PT evaluated as raw data or scaled by normalizing methods, including simple ratio (PT/weight), allometric PT (PT/weight(0.67)) and adjustment of PT by weight, height, body mass index and body surface area (BSA). The goodness-of-fit for various scaling methods was compared using the Akaike Information Criterion (AIC) as an objective measure of model-based entropy reduction. 5. The effects of DHT administration according to different scaling methods were estimated by eta-squared measure of effect size in treatment models. In part A, older men were weaker than younger men in five knee PT, consistently by all eight analysis models but not in shoulder PT. In part B, DHT treatment resulted in an increase one knee PT (dominant knee flexion at 120 degrees/s) with the difference consistent in all seven models. 6. The scaling model using BSA proved superior to other comparison models throughout both parts of the present study according to entropy minimization criteria (AIC) for goodness-of-fit of the model or eta-squares for treatment effect size. 7. We conclude that differences in muscle strength due to age or androgen administration in older men are restricted to a minority of lower limb contractions and that use of BSA scaling for PT values is considered the best scaling method for muscle strength comparisons in either cross-sectional or longitudinal studies.

Identifying submaximal muscular effort: reliability of difference scores calculated from isometric and isokinetic measurements

The present investigation examined the reliability of a derived strength measurement and also how variability between test sessions affects the utility of this variable for judging an individual's muscular effort. 31 young healthy men (M age = 25 yr.) completed three isometric and isokinetic concentric contractions of the knee extensors, using maximal and self-selected submaximal efforts, on each of two test sessions. Difference scores between isometric and isokinetic measurements were calculated by subtracting the mean of the three isokinetic peak torques from the mean of the three isometric peak torques for each individual subject for maximal and submaximal efforts performed on both test sessions. For the group of subjects, difference scores were significantly greater during maximal (33 +/- 29 Nm) than submaximal (13 +/- 30 Nm) efforts, suggesting subjects could not maintain the same relationship between isometric and isokinetic muscular actions across the maximal and submaximal conditions. However, the test-retest reliability of the difference scores was only modest even when data were averaged over two test sessions (intraclass correlation coefficients were .82 for maximal, and .58 for submaximal). As a result, the range of scores within which an individual's true score might be expected to lie was large (+/- 25 Nm for maximal, and +/- 37 Nm for submaximal). Although derived strength parameters like difference scores may be effective in distinguishing submaximal from maximal efforts completed by groups of subjects, the test-retest reliability of the present scores suggests that their use in judging an individual's performance may be limited.