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.     

Tibiofemoral joint forces during maximal isokinetic eccentric and concentric efforts of the knee flexors

OBJECTIVE: The examination of muscular and tibiofemoral joint forces during maximal efforts of the knee flexors. DESIGN: The muscular and tibiofemoral joint knee forces during eccentric and concentric isokinetic efforts of the knee flexors were determined using a two-dimensional mathematical model. BACKGROUND: The examination of joint and muscle loading during isokinetic movements is important for the determination of safety of this exercise. METHODS: Ten healthy males performed three maximal isokinetic concentric and eccentric efforts of the knee flexors at angular velocities of 30 degrees s(-1), 90 degrees s(-1), 120 degrees s(-1) and 150 degrees s(-1). The muscular, tibiofemoral shear and compressive joint forces were determined using a two-dimensional model. RESULTS: The maximum muscular force ranged from 3.44 (Standard deviation, 1.32) times body weight to 6.19 (1.78) times body weight. The tibiofemoral compressive force ranged from 2.62 (1.17) times body weight to 5.89 (1.99) times body weight occurring at angles ranging from 0 degrees to 40 degrees of knee flexion. The posterior shear force ranged from 2.61 (1.33) times body weight to 3.89 (1.62) times body weight and was observed at angles ranging from 50 degrees to 80 degrees of knee flexion. Two-way analysis of variance designs indicated significant effects of type of muscle action and angular velocity on muscle and compressive forces (P<0.05). In contrast, the shear force was not affected by the type of muscle action or the angular velocity (P>0.05). CONCLUSIONS: Isokinetic efforts of the knee flexors induce high tibiofemoral joint forces, especially during high-speed eccentric tests.     

Differences in elbow flexion torque measured concentrically, eccentrically, and isometrically

The purposes of this study were to describe torque-velocity relationships during concentric, eccentric, and isometric testing of elbow flexor muscles and to determine test-retest reliability of a specific isokinetic testing protocol. Thirty healthy women were tested using an isokinetic dynamometer at velocities of 0 degrees, 30 degrees, 120 degrees, and 210 degrees/sec. Reliability was assessed in 20 of the subjects by retesting concentric and eccentric torques at 30 degrees and 120 degrees/sec after a 30-minute rest interval. The highest torque from three maximal efforts was considered to be peak torque. Mean eccentric peak torque was greater than either isometric or concentric peak torque; as isokinetic test velocity increased, the differences between concentric and eccentric torques became larger. Intraclass correlation coefficients ranged from .72 to .83, indicating lack of consistency between test and retest torques. Consecutive concentric-eccentric testing and lack of mechanical stabilization might have contributed to test-retest variability and to the relatively small differences between concentric and eccentric torques. Continued study of reliability of isokinetic testing protocols and further investigation of concentric-eccentric torque-velocity relationships are advocated.     

Chronic pain disability exaggeration/malingering and submaximal effort research

OBJECTIVE: This is the first review of chronic pain (CP) malingering/disease simulation research. The purpose of this review was to determine the prevalence of malingering within CP patients (CPPs), whether evidence exists that malingering can be detected within CPPs, and to suggest some avenues of research for this topic. DESIGN: A computer and manual literature search produced 328 references related to malingering, disease simulation, dissimulation, symptom magnification syndrome, and submaximal effort. Of these, 68 related to one of these topics and to pain. The references were reviewed in detail, sorted into 12 topic areas, and placed into tabular form. These 12 topic areas addressed the following: existence of malingering within the CP setting; dissimulation, identification simulated (faked) facial expressions of pain; identification of malingering by questionnaire; identification of malingered sensory impairment; identification of malingered loss of hand grip strength; identification of submaximal effort by isometric strength testing; identification of submaximal or malingered effort by isokinetic strength testing; identification of submaximal or malingered effort by the method of coefficient of variation; self-deception; symptom magnification syndrome; and miscellaneous malingering identification studies. Each report, in each topic area, was rated for scientific quality according to guidelines developed by the Agency for Health Care, Policy and Research (AHCPR) for rating the level of evidence presented in the reviewed study. The AHCPR guidelines were then used to rate the strength and consistency of the research evidence in each topic area based on the type of evidence the reports represented. All review conclusions were based on the results of these ratings. SETTING: Any medical setting reporting on either malingering or disease simulation, or dissimulation, or submaximal effort and pain. PATIENTS: Normal volunteers, CPPs, or any group asked to produce a submaximal or malingered effort or a malingered test profile. RESULTS: The reviewed studies indicated that malingering and dissimulation do occur within the CP setting. Malingering may be present in 1.25-10.4% of CPPs. However, because of poor study quality, these prevalence percentages are not reliable. The study evidence also indicated that malingering cannot be reliably identified by facial expression testing, questionnaire, sensory testing, or clinical examination. There was no acceptable scientific information on symptom magnification syndrome. Hand grip testing using the Jamar dynamometer and other types of isometric strength testing did not reliably discriminate between a submaximal/malingering effort and a maximal/best effort. However, isokinetic strength testing appeared to have potential for discriminating between maximal and submaximal effort and between best and malingered efforts. Repetitive testing with the coefficient of variation was not a reliable method for discriminating a real/best effort from a malingered effort. CONCLUSIONS: Current data on the prevalence of malingering within CPPs is not consistent, and no conclusions can be drawn from these data. As yet, there is no reliable method for detecting malingering within CPPs, although isokinetic testing shows promise. Claims by professionals that such a determination can be made should be viewed with caution.     

Identification of feigned maximal shoulder external rotation effort

OBJECTIVE: To examine the efficiency of the difference between the isokinetic eccentric to concentric strength ratios at high and low velocities (DEC) for identifying feigned maximal shoulder external rotation effort. BACKGROUND: Previous studies have indicated that the DEC is a powerful identifier of feigned maximal effort. However comparison of maximal versus feigned maximal shoulder external rotation effort has not been undertaken. Due to the high prevalence of rotational shoulder disorders and their chronic ramifications in terms of occupational disability such a study is of specific interest. DESIGN: Maximal and feigned maximal shoulder external rotation isokinetic efforts were compared. SETTING: Functional evaluation unit at an occupational rehabilitation centre. SUBJECTS: Seventeen healthy male volunteers aged between 20 and 40 years old.Main measure: Concentric and eccentric isokinetic tests at 30 degrees /s and 120 degrees /s in maximal and feigned maximal experimental conditions. DEC was calculated by subtracting the 30 degrees /s eccentric/concentric peak torque ratios from the 120 degrees /s ones for both experimental conditions. RESULTS: A case-by-case analysis revealed that the DEC scores derived from the feigned effort were significantly greater than their maximal counterparts in all cases, leading to a cut-off value (0.81) which could distinguish between maximal and feigned performances. CONCLUSIONS: The findings indicate that the DEC is highly effective in identifying feigned shoulder external rotation effort in normal subjects.     

Knee joint forces during isokinetic knee extensions: a case study.

OBJECTIVE: To describe the procedures to obtain knee joint forces during isokinetic knee extensions and evaluate the patellar ligament force, quadriceps tendon force, patellofemoral and tibiofemoral joint forces at different speeds measured from a female subject. DESIGN: A technical note with a case study. BACKGROUND: Two previous studies examined knee joint forces during isokinetic knee extension using different techniques reported inconsistent findings. Also, the highest speed used in these two studies (180 degrees s(-1)) were much lower than the maximum speeds available in modern isokinetic dynamometers. METHODS: The subject performed maximum effort isokinetic knee extensions at 16 different speeds ranged from 25 to 400 degrees s(-1). The gravitational and inertial effects were included in determining the resultant knee torque. Knee radiographs were used to determine the knee joint geometry. A combination of knee torque and geometric data was used to determine different knee joint forces. RESULTS: All knee joint forces were found to decrease with increasing isokinetic speed. The tibiofemoral shears forces indicated that the anterior cruciate ligament was loaded throughout the range of motion. CONCLUSIONS: The magnitudes of knee joint forces are largely depending on the knee torque values. RELEVANCE: Isokinetic knee extensions are considered appropriate for the early part of the rehabilitation for patients with knee dysfunctions due to the lesser demand of coordination. However, to reduce the knee joint forces, submaximal efforts at lower speeds or maximal efforts at higher speeds are recommended.     

Detection of a "faked" strength task effort in volunteers using a computerized exercise testing system.

The objective of this study was to develop an experimental method to separate a "faked" strength effort from a "best" effort in volunteers. Thirty-four pain-free volunteers (18 males, 16 females) performed a shoulder press and pull-down on an isokinetic computerized exercise testing system (CETS), giving a best effort followed by a faked effort. Two months later, a randomly selected subgroup (6 males) repeated the experiment to test the predictive validity of the derived variables. In the statistical analysis, best efforts were first compared with fake efforts by paired ttest for 80 CETS variables for males and females separately. Variables showing a strong difference between the best and faked effort were then selected for further analysis. In the second step of the analysis, the method of multiple correlations (r2 method) was used to reduce the number of redundant CETS variables to five in both the male and female groups. In the third step, a stepwise discriminant analysis was used to select predictor variables for the male and female groups. For the variables selected by the discriminant analysis for both males and females, sensitivities and specificities were calculated. Finally, the developed discriminant formula was used in the predictive validity part of the study to determine the sensitivities and specificities of the developed method. The discriminant analysis selected the following CETS variables for male and female groups, respectively: duty cycle down, work weight/down, peak value up (males); and average power up, 40% repetition down, duty cycle up (females). For males, using their three variables, the discriminant function classified 77.14% of the efforts correctly with 88.9% sensitivity and 64.7% specificity. For females, using their three variables, the discriminant function classified 90.63% of the efforts correctly with 100% sensitivity and 81.3% specificity. In the predictive validity group, the discriminant function classified 75% of the efforts correctly with 83.3% sensitivity and 66.7% specificity. This pilot study indicates that the method developed here may be useful in the experimental study for the discrimination between faked and best efforts on this isokinetic CETS machine. Future studies using this method will need to involve a larger number of volunteers.     

Differentiation of maximal and submaximal knee extension efforts by isokinetic testing

The variability of torque produced during maximal and subject selected submaximal isokinetic knee extension efforst was compared. Subjects were 40 healthy volunteers (20 men and 20 women). Following three warm-up efforts subjects randomly performed one set of both four repeated maximal and submaximal knee extension efforts at 60°/s. Torque was measured at 30 and 45° of flexion and corrected for gravity. Variability of torque was examined by first calculating for each subject the mean, standard deviation (s.d.), and coefficient of variation (CV) for the four trials under the maximal and submaximal conditions. The s.d. was used to represent the absolute variation from the mean, whereas the CV was used to represent the relative variation from the mean. The CVs and s.d.s were compared between the maximal and submaximal efforts using analysis of variance. Variability, as demonstrated by s.d.s, was not consistently greater during submaximal than during maximal efforts. Variability, as demonstrated by CVs, was significantly greater during submaximal than during maximal efforts. In spite of finding statistical differences in the variability of maximal and submaximal efforts, no clear cut-off was identified above and below which performance could be dichotomized into the submaximal and maximal groups based on variability.

Relevance

Although the variability of angle specific knee-extension torques is greater during submaximal than during maximal efforts, the range of variability associated with maximal and submaximal efforts does not appear to be mutually exclusive. Therefore clinicians should exercise caution in judging the sincerity of an individual's maximal effort based solely on isokinetic measurement variability.     

Obtaining reliable measurements of knee extensor torque produced during maximal voluntary contractions: an experimental investigation.

The purpose of this study was to develop and test a protocol that could be used to obtain reliable measurements of knee extensor torque produced during maximal voluntary contractions. On each of 3 days, 10 subjects performed six consecutive maximal voluntary contractions, in the same randomized order, for each of the following 10 conditions: concentric isokinetic contractions at velocities of 30 degrees, 90 degrees, 120 degrees, and 180 degrees/s; eccentric isokinetic contractions at velocities of 30 degrees, 90 degrees, 120 degrees, and 180 degrees/s; and isometric contractions at 40 and 60 degrees of knee flexion. The peak torques produced were examined to determine on which day and during which contraction subjects produced the greatest torques for each condition. This information was used to develop a practice protocol. Fifteen different subjects were tested following this protocol. Subjects participated in two practice sessions, a test session, and a retest session. Intraclass correlation coefficients (ICCs) were calculated to determine the degree of agreement between torques for the test and retest sessions. The ICCs ranged from .87 to .98. The protocol developed appears to be useful for obtaining reliable measurements of knee extensor torque.     

Identification of feigned grip effort using isokinetic dynamometry.

OBJECTIVE: To investigate the feasibility of applying isokinetic dynamometry for identifying submaximal grip strength. DESIGN: Measurement of maximal and feigned concentric and eccentric strength at high and low contraction velocities. BACKGROUND: Identification of feigned grip strength is a highly problematic issue which has been challenged using various techniques, invariably related to isometric efforts. This study is based on recent research which has indicated that isokinetic dynamometry was highly efficient in identifying feigned efforts in other major muscle groups. METHODS: Seventeen healthy women aged 20-25 took part in the study. Prior to executing the feigned effort, subjects were told to exert lower than the maximal grip strength in an attempt to obtain financial compensation for a simulated injury to hand musculature which in fact did not result in weakness of grip. RESULTS: Findings indicated that based on a parameter termed DEC which was defined as the difference between the ratios of the eccentric to concentric strength at the high and low velocities, feigned efforts could very effectively be identified (P<0.0001). Furthermore, a multivariate model enabled this identification to be described in terms of the level of confidence by which a claim concerning weakness of grip may be proclaimed as genuine or insincere. CONCLUSIONS: Though the neuromotor mechanisms responsible for grip strength may differ from those acting with respect to other muscle groups, the inability to adjust the eccentric and concentric force components during submaximal efforts is probably a general feature. RELEVANCE: Isokinetic dynamometry is a powerful method for quantifying various aspects of muscle performance. However, its application in the medicolegal area of muscle weakness has only recently been explored. Combined with previous research, this study strongly indicates that if certain trauma or pathology-related weakness does not result in variations in the force-velocity characteristics of the affected muscles, than this technique has the potential to validly differentiate between patients who have a genuine reason for compensation and those ('symptom magnifiers') who do not.     

Determining the number of repetitions to establish isokinetic knee evaluation protocols specific to angular velocities of 60°/second and 180°/second

IntroductionThis study aims to develop a standard number of repetition at angular velocities of 60°/sec and 180°/sec and define the difference of number of repetitions between genders.MethodOne hundred ninety-six athletes (judo, volleyball, Greco-Roman wrestling, runners, and gymnastics) were involved. Concentric-concentric isokinetic muscle strength of the knee flexor-extensor muscles of the athletes were performed with an ISOMED 2000 isokinetic dynamometer. The evaluation test protocol consisted of 10 repetition of knee flexion-extension at 60°/sec and 30 repetitions at 180°/sec.ResultsAthletes performed with maximal knee flexion strength at their second and third trial at 60°/sec and third-forth trial at 180°/sec. It was found that 2 repetitions and 2–3 repetitions were needed for knee extension peak torque at 60°/sec and 180°/sec respectively. The difference between the genders was significant at 60°/sec for knee flexion and extension on the dominant side; at 180°/sec for knee extension on the dominant and non-dominant side. It was determined that 3 repetitions for 60°/sec, 4 repetitions for 180°/sec were enough to determine peak torque values.DiscussionOptimal number of repetitions is crucial so that athletes could have the opportunity to reach maximal strength without unnecessary workload or waste of time.ConclusionsProtocols involving 3 repetitions for 60°/sec, 4 repetitions for 180°/sec were enough to determine peak torque values. Gender of athletes should be considered when establishing isokinetic knee evaluation protocols.     

Test-retest reliability of isokinetic knee extension and flexion torque measurements in persons with spastic hemiparesis

The purpose of this study was to evaluate and compare the test-retest reliability of isokinetic torque measurements in the involved and uninvolved knee musculature of 20 subjects with spastic hemiparesis. An isokinetic dynamometer was used to measure maximal voluntary knee extension and flexion at 60 degrees and 120 degrees/s. Peak torque (PT) and average peak torque (APT) data were collected from five repetitions on two separate occasions. Average peak torque was defined as the mean of the PT values obtained during each of the five repetitions. Spasticity was measured in the involved knee musculature prior to isokinetic testing using the Ashworth Scale. Pearson Product-Moment Correlation Coefficients and intraclass correlation coefficients (ICCs) were high (greater than or equal to .90) for both knees for PT and APT at both angular velocities. No clinically meaningful differences were found between the Pearson correlation coefficients and the ICCs of the involved versus the uninvolved knee for any testing conditions. We concluded that isokinetic evaluation of torque, as measured by PT and APT in subjects with spastic hemiparesis, can yield reliable results in both extremities.     

Isometric and isokinetic measurement of hamstring and quadriceps strength.

This study evaluates quadriceps strength at varying movement velocities in a group of healthy subjects. Specific objectives included (1) investigating the effect of angular velocity on peak torque (PT) (2) investigating the effect of angular velocity on joint angle at peak torque (JAPT) and (3) evaluating whether the use of a relatively new isokinetic testing device yields new insights to previously accepted relationships between angular velocity and PT or JAPT. Twenty healthy subjects were tested for isometric and isokinetic knee extension and flexion strength on a LIDO Active Isokinetic Rehabilitation System at velocities of 0 degrees, 60 degrees, 120 degrees, and 180 degrees/sec. Isometric PT (0 degrees/sec) was found to be highly correlated with isokinetic PT for both extensors and flexors at all velocities (r = .88-.93, p less than .01). PT declined significantly as angular velocity increased for both extension (p less than .01) and flexion (p less than .05). A relationship between isometric and isokinetic JAPT was significant for extension only at 60 degrees and 180 degrees/sec (r = .48-.52, p less than .05). These results indicate that knee isometric and isokinetic PT as measured on the LIDO Active system are highly related for both extension and flexion. PT declined as isokinetic angular velocity increased. Isometric and isokinetic JAPT are significantly related only for extension.     

Influence of concentric resistance training on concentric and eccentric strength

This study investigated the effects of isokinetic concentric training on isokinetic concentric and eccentric torque outputs. Sixteen female subjects (mean age in years +/- SE = 21 +/- 1) were randomly assigned to either a training or a control group. Concentric and eccentric torques of the right knee extensors were assessed at 1.05rad.s-1 using a KinCom isokinetic dynamometer system. Each test consisted of a set of four maximal concentric and four maximal eccentric contractions of the knee extensors. The peak and average torques for each contraction were calculated using the computer software supplied by the KinCom manufacturer. On a separate day, after abstaining from heavy exercise for at least 12 hours, a single cross-sectional image of the thigh at midfemur was obtained using computer tomography (CT) scanning. From this image, cross-sectional area of the quadriceps femoris group was calculated using the computer software associated with the General Electric 9800 CT Scanning System. Training group subjects trained three days weekly for six weeks on a Cybex II+ isokinetic dynamometer, completing five sets of ten maximal effort knee extensions at an angular velocity of 1.05rad.s-1. Each set of exercise was separated by two minutes of self-selected recovery. Torque outputs were monitored daily to ensure that adequate recovery was provided between sets of exercise, and to document changes in strength as the program progressed. Significant (p less than .01) increases in peak and average concentric torque (11% and 12%, respectively), peak and average eccentric torque (18% and 21%, respectively), and muscle cross-sectional area (3.2%) were observed for training group subjects.(ABSTRACT TRUNCATED AT 250 WORDS)     

Sequential isokinetic and manual muscle testing in patients with neuromuscular disease. A pilot study

The purposes of this study were to compare the value of isokinetic testing and manual muscle testing (MMT) in longitudinal measurements of muscle strength in patients with neuromuscular disease and to identify any consistent pattern demonstrated by the isokinetic testing of patients with specific diagnoses. We measured knee extensor muscle strength at periodic intervals in patients, using MMT and isokinetic testing at angular limb velocities of 30 and 180 degrees/sec. An isokinetic fatigability test also was conducted. The results indicated that in patients who were graded 9 to 10 (ie, within normal limits) by MMT methods, sequential isokinetic strength tests revealed improvement not indicated by MMT. In patients, however, having weakness detectable by MMT and whose course was deteriorating, isokinetic testing did not seem to add clinically significant information for long-term management. Some patients with myotonia demonstrated an increase in peak torque during the fatigability test; this response was unique among the diagnoses we tested. Isokinetic testing may provide, in some patients with neuromuscular disease, valuable information when used in conjunction with MMT for sequential monitoring of strength. Continued research is needed to investigate the value of isokinetic testing in the diagnosis and management of patients with neuromuscular disease.     

Reproducibility and validity of a new test protocol for measuring isokinetic trunk extension strength

OBJECTIVE: To investigate the reproducibility and validity of isokinetic trunk extension strength scores obtained using a range of motion of 20 degrees and velocities of 10 and 40 degrees /s. BACKGROUND: Common protocols for testing trunk extension strength incorporate a range of motion of 40 degrees or more and test velocities of between 30 and 180 degrees/s. These test parameters may be neither necessary for portraying the strength profile of the muscles involved nor suitable for patients impaired with low back dysfunction. DESIGN: Test-retest of maximal concentric and eccentric isokinetic trunk extension strength in healthy subjects. METHODS: 17 women and 18 men were tested twice within 1-2 weeks. Tests were performed with subjects positioned in sitting. RESULTS: The trunk extension strength scores revealed excellent agreement with the expected physiological moment-velocity curve. On average women's trunk extension strength was 62% that of men (range: 59.3-64.4%). The test-retest correlation coefficients were generally higher in women (0.70-0.87) than in men (0.52-0.78) and significant at P=0.01. The standard error of measurement ranged between 13 and 21 N m for women and between 35 and 50 N m for men, which were equivalent to 9% and 15% of the mean strength in women and men, respectively. CONCLUSION: This study indicates that the present protocol may be validly applied in assessing trunk extension strength in normal women. RELEVANCE: Reproducible and valid trunk extension strength findings are essential if measurable strength deficiency of the extensors is to be formally accepted as an impairment. The present protocol incorporates or meets most of the relevant problems associated with trunk concentric and eccentric strength testing, and hence has the potential of becoming a standard method for clinical applications.     

Test-retest reliability of isokinetic muscle strength of the lower extremities in patients with stroke

OBJECTIVE: To i the test-retest reliability of isokinetic strength measurements of 3 muscle groups of the lower extremities in stroke patients. DESIGN: Isokineth tests of bilateral hip flexors, knee extensors, and ankle plantarflexors at 2 angular velocities, performed during 2 sessions scheduled 1 week apart for each subject. SETTING: Outpatilitation clinic of a local hospital in Taiwan. PARTICIPANTS: Nts with mild spastic hemiparesis secondary to stroke and with poststroke onset time of at least 6 months. All subjects could communicate and voluntarily move the affected lower extremity. INTERVENTIONS: Not applicable. MAIN OUTCOME MEASURE: The maximal peak torque, total work, and average power of the 3 muscle groups on the affected side examined during each test were quantified by using the normalization and the deficit methods. The normalization method divides the measured strength value by the patient's body weight, whereas the deficit method divides the difference between the strengths of the unaffected and affected extremities by the strength of the unaffected extremity. RESULTS: The normalized strength measures for muscles on the affected side showed good to excellent test-retest reliability (intraclass correlation coefficient [ICC] range,.62-.94; P<.05), whereas the deficit strength measures did not always show good reliability (ICC range,.13-.91). The knee extensors and ankle plantarflexors, but not the hip flexors, on the affected side showed better test-retest reliability of isokinetic strength generated at faster velocity (ICC range,.73-.94) than that generated at slower velocity (ICC range,.62-.88). The normalized peak torque (ICC range,.76-.94) and total work (ICC range,.83-.91) were more reliable than the normalized average power (ICC range,.62-.90) for all 3 muscle groups on the affected side. CONCLUSIONS: Quantitative assessment of muscle strength of the affected lower extremity in patients with mild spastic hemiparesis secondary to stroke is feasible using isokinetic testing. However, the test-retest reliability of isokinetic strength measures is affected by the quantifying method, testing velocity, and strength measures.     

Clinical application of the DEC variables in assessing maximality of muscular effort: report of 34 patients

OBJECTIVE: To examine maximality of muscular effort in patients with expected muscle strength deficiency using acceptance-rejection cutoff values derived from isokinetic testing of maximal and feigned effort in normal subjects. DESIGN: A retrospective study of 34 patients with orthopedic, rheumatic, or neurologic disorders for which financial compensation was sought. RESULTS: The relevant scores in all patients save one were less than the respective cutoff values that in normal subjects differentiate maximal effort (below cutoff) from feigned weakness (above cutoff) at a 95% level of confidence. CONCLUSIONS: If normal subjects-based cutoff values are accepted as benchmarks for validation of muscle strength deficiency claims, this study indicates that subject to a given protocol, patients performed at a maximal level of effort.     

Correlation between handgrip and isokinetic strength of shoulder muscles in elite sitting volleyball players

The aim of this study was to examine the relationships between isometric handgrip (HG) strength and isokinetic strength data of the glenohumeral rotator muscles. Twelve (Female = 50%) Brazilian Sitting Volleyball (SV) national team players volunteered. Measures of maximal grip strength were obtained by a HG dynamometer Jamar® and isokinetic measures of peak torque (PT) and total work (TW) during shoulder rotations movements were obtained with a Biodex isokinetic dynamometer at speed of 60°/s and 180°/s. Pearson correlation coefficients between isometric HG and isokinetic strength data ranged between 0.23 and 0.72 for the PT and between 0.3 and 0.76 for the isokinetic TW. Results presented positive relationships between HG isometric strength and isokinetic strength of external rotators of the shoulder in SV players. We can suggest that in the absence of isokinetic dynamometers, HG isometric strength measurements could be used to measure strength levels of the external rotator muscles of elite SV players’ shoulder, particularly in the TW values.     

Muscular and tibiofemoral joint forces during isokinetic concentric knee extension

The purpose of this study was the examination of muscular and tibiofemoral forces during concentric isokinetic knee extension at angular velocities ranging from 30 to 210 deg s(-1), using a two-dimensional biomechanical model. Five males without knee joint injury history participated in the study. The maximum moment ranged from 226.2 Nm at 30 deg s(-1) to 166.4 Nm at 210 deg s(-1). The maximum muscular force ranged from 7.5 times body weight at 30 deg s(-1) to 5.7 at 210 deg s(-1). The compressive tibiofemoral force ranged from 7.5 times body weight at 30 deg s(-1) to 5.7 at 210 deg s(-1) and the shear tibiofemoral force ranged from 0.9 to 0.8 times body weight respectively. These results indicate that the forces developed during maximal isokinetic knee extension are significantly reduced relative to other powerful dynamic activities but are higher than joint forces during simple walking and cycling activities. Appropriate precautions and adjustment of the isokinetic protocol are required in the final phases of joint injury rehabilitation. RELEVANCE: Isokinetic dynamometry has widespread applications in rehabilitation and training of muscle function. It is therefore important to examine the joint and muscular forces under different conditions in order to alter rehabilitation and training programmes and prevent exercise-induced injuries.