Static and dynamic assessment of the Biodex dynamometer

Summary The validity and accuracy of the Biodex dynamometer was investigated under static and dynamic conditions. Static torque and angular position output correlated well with externally derived data (r=0.998 andr>0.999, respectively). Three subjects performed maximal voluntary knee extensions and flexions at angular velocities from 60 to 450° · s^–1. Using linear accelerometry, high speed filming and Biodex software, data were collected for lever arm angular velocity and linear accelerations, and subject generated torque. Analysis of synchronized angular position and velocity changes revealed the dynamometer controlled angular velocity of the lever arm to within 3.5% of the preset value. Small transient velocity overshoots were apparent on reaching the set velocity. High frequency torque artefacts were observed at all test velocities, but most noticeably at the faster speeds, and were associated with lever arm accelerations accompanying directional changes, application of resistive torques by the dynamometer, and limb instability. Isokinematic torques collected from ten subjects (240, 300 and 400° · s^–1) identified possible errors associated with reporting knee extension torques at 30° of flexion. As a result of tissue and padding compliance, leg extension angular velocity exceeded lever arm angular velocity over most of the range of motion, while during flexion this compliance meant that knee and lever arm angles were not always identical, particularly at the start of motion. Nevertheless, the Biodex dynamometer was found to be both a valid and an accurate research tool; however, caution must be expercised when interpreting and ascribing torques and angular velocities to the limb producing motion.     

A new dynamometer measuring concentric and eccentric muscle strength in accelerated,decelerated, or isokinetic movements

Summary A new computerized dynamometer (the SPARK System) is described. The system can measure concentric and eccentric muscle strength (torque) during linear or nonlinear acceleration or deceleration, isokinetic movements up to 400° · s^–1, and isometric torque. Studies were performed to assess: I. validity and reproducibility of torque measurements; II. control of lever arm position; III. control of different velocity patterns; IV. control of velocity during subject testing; and, V. intra-individual reproducibility. No significant difference was found between torque values computed by the system and known torque values (p>0.05). No difference was present between programmed and external measurement of the lever arm position. Accelerating, decelerating and isokinetic velocity patterns were highly reproducible, with differences in elapsed time among 10 trials being never greater than 0.001 s. Velocity during concentric and eccentric isokinetic quadriceps contractions at 30° · s^–1, 120° · s^–1 and 270° · s^–1 never varied by more than 3° · s^–1 among subjects (N=21). Over three days of testing, the overall error for concentric and eccentric quadriceps contraction peak torque values for 5 angular velocities between 30° · s^–1 and 270° · s^–1 ranged from 5.8% to 9.0% and 5.8% to 9.6% respectively (N=25). The results indicate that the SPARK System provides valid and reproducible torque measurements and strict control of velocity. In addition, the intra-individual error is in accordance with those reported for other similar devices.     

Development,reliability and validity of a new motorized isometric dynamometer for measuring strength characteristics of elbow flexor muscles

The aim of this study was to develop a new apparatus capable of accurately recording and analysing torque – time curve during isometric muscle contractions of the elbow flexors. A total of 25 (age 29.3 ± 5.0 years) non-athlete male volunteers participated in this study. To establish the measurement precision of the new testing apparatus and to determine possible sources of error in the results, a series of tests was performed. Instrument validity was assessed by comparing each selected measure (lever arm angular position, torque and maximal isometric torque) to a criterion (external inclinometer, calibrated weights and isokinetic dynamometer, respectively), while trial-to-trial and day-to-day comparisons of measurements were made to estimate the reproducibility of the instrument. The statistical outcomes of validity tests demonstrated high agreement between measures and associated criteria (Pearson correlation coefficient's values >.97). Trial-to-trial correlations for maximal isometric torque in different elbow angles showed excellent reproducibility, as values of intraclass correlation coefficient (ICC_[2,1]) ranged from 0.889 to 0.971, with higher value in the middle angle (90°). The value of ICC_[2,1] (day-to-day) for maximal isometric torque in 90 degrees was 0.986 and the respective standard error of measurement (SEM) was 1.5 Nm. Our results indicate that the isometric evaluation of elbow flexor muscles with the new dynamometer is accurate and reproducible.     

Functional torque-velocity and power-velocity characteristics of elite athletes

Summary Technical limitations of some isokinetic dynamometers have called into question the validity of some data on human muscle mechanics. The Biodex dynamometer has been shown to minimize the impact artefact while permitting automatic gravity correction. This dynamometer was used to study quadriceps muscle torque and power generation in elite power (n = 6) and elite endurance (n = 7) athletes over 12 randomly assigned isokinetic velocities from 30° · s^–1 to 300° · s^–1. The angle at peak torque varied as a negative, linear function of angular velocity, with the average angle across test velocities being 59.5° (SD 10.2°). Power athletes developed greater peak torque at each angular velocity (P < 0.05) and experienced a 39.7% decrement in torque over the velocity range tested. En-, durance athletes encountered a 38.8% decline in peak torque. Torques measured at 60° of knee flexion followed a similar trend in both groups; however the greatest torques were recorded at 60° s^–1 rather than at 30° · s^–1 Leg extensor muscle power increased monotonically with angular velocity in both power (r ² = 0.728) and endurance athletes (r ² = 0.839); however these curves diverged significantly so that the power athletes produced progressively more power with each velocity increment. These inter group differences probably reflected a combination of natural selection and training adaptation.     

Evaluation of a dynamometer measuring torque of uni- and bilateral concentric and eccentric muscle action

A dynamometer designed for torque measurements of uni- and bilateral concentric and eccentric muscle actions of the quadriceps and hamstring muscle groups is described. Torque reproducibility and control of lever-arm position were studied using known standards. In vivo measurements assessed angular velocity, lever-arm acceleration, variability of torque between limbs and reproducibility of torque. Torque obtained from left and right leg attachments was equal when using weights and during dynamic in vivo conditions. Static torque recorded at different lever-arm positions and known torque were equal. Likewise, lever-arm position output equated with known angles. In vivo test-retest of peak torque was found to be reliable. Acceleration of the lever arm was greater for concentric bilateral than for unilateral muscle actions but equal during eccentric muscle actions. The dynamometer is suggested to provide valid and reproducible torque measurements up to at least 700 N m at constant angular velocities up to 2.62 rad s-1. Besides being a research tool the dynamometer is useful in clinical settings for rehabilitation and evaluation of skeletal muscle function.     

Effect of prior isometric muscle action on concentric torque output during plantar flexion

The influence of different levels of prior isometric muscle action on the concentric torque output during plantar flexion was examined at two angular velocities (60°·s^–1 and 120°·s^–1) in ten healthy female subjects. The levels of the prior muscle actions were 25%, 50%, 75% and 100% of the maximal voluntary isometric contraction (MVIC). A KINetic-COMmunicator II dynamometer was used to measure torque output during plantar flexion within a range of motion of 78°-120° of the ankle joint. Simultaneous recordings of electromyograms (low-pass filtered and rectified) were obtained from the gastrocnemius medialis muscle and the soleus muscle. Torque-angle curves were made for the plantar flexions using different prior muscle actions. Up to 75% of MVIC, the torque output in the first part of the range of motion increased with the level of the prior isometric muscle action; at higher levels of MVIC the torque did not appear to increase any further. Later in the range of motion, after 24° in the plantar flexion at a velocity of 60°·s^–1 and 31° at 120°·s^–1, the prior muscle actions had no further influence. No increase was found in the electromyograms, with one exception, during the concentric movements when preceded by higher levels of MVIC. It would seem therefore that the increase in torque output early in the range of motion cannot be explained on the basis of differences in electrical muscle activation in this study.     

Accuracy of Biodex system 3 pro computerized dynamometer in passive mode

A specific experimental design has been developed to determine the accuracy of the Biodex system 3 pro dynamometer in passive mode. Five cyclic stretching repetitions were imposed to an elastic rubber band at different velocities using the dynamometer, and the torque produced was measured using both the dynamometer and external force and position sensors. Velocity patterns performed by the dynamometer were also characterized and our results show that these patterns were reliable (ICC=1.00). The torque measured with the dynamometer and the sensors were reliable (ICC=1.00), although significant differences were observed between both methods. However, the measured torque standard error was velocity independent and was lower than 0.33Nm. Moreover, regressions between the two torque measurements were close to the axes-bisector (r=1.00, slope: 1.01+/-0.01, y-intercept: -0.36+/-0.22Nm). Finally, our results showed decreases in torque during the five cycles, but these decreases were not due to the dynamometer. It can be concluded that the dynamometer performed valid torque measurements in passive mode, and was an accurate tool to determine passive mechanical properties of the musculo-articular system. However, some discrepancies between the programmed and the measured speed profiles have been observed when approaching the speed limit of the system.     

Eccentric and concentric torque-velocity characteristics of the quadriceps femoris in man

Summary The primary purpose of this investigation was to study the eccentric and concentric torque-velocity characteristics of the quadriceps femoris in man using a recently developed combined isometric, concentric and eccentric controlled velocity dynamometer (the SPARK System). A secondary purpose was to compare the method error associated with maximal voluntary concentric and eccentric torque output over a range of testing velocities. 21 males (21–32 years) performed on two separate days maximal voluntary isometric, concentric and eccentric contractions of the quadriceps femoris at 4 isokinetic lever arm velocities of 0° · s^–1 (isometric), 30° · s^–1 120° · s^–1 and 270° · s^–1. Eccentric peak torque and angle-specific torques (measured every 10° from 30° to 70°) did not significantly change from 0° · s^–1 to 270° · s^–1 (p>0.05) (with the exception of angle-specific 40° torque, which significantly increased;p<0.05). The mean method error was significantly higher for the eccentric tests (10.6%±1.6%) than for the concentric tests (8.1%±1.7%) (p<0.05). The mean method error decreased slightly with increasing concentric velocity (p>0.05), and increased slightly with increasing eccentric velocity (p>0.05). A tension restricting neural mechanism, if active during maximal eccentric contractions, could possibly account for the large difference seen between the present eccentric torque-velocity results and the classic results obtained from isolated animal muscle.     

The relationships among peak torque, mean power output, mechanomyography, and electromyography in men and women during maximal, eccentric isokinetic muscle actions

The purpose of the present investigation was to examine the velocity-related patterns of peak torque (PT), mean power output (MP), mechanomyographic (MMG) amplitude, and electromyographic (EMG) amplitude of the vastus lateralis (VL) muscle in men and women during maximal, eccentric isokinetic muscle actions of the leg extensors. Eight women [mean (SD)] [aged 23 (3) years] and seven men [aged 23 (2) years] volunteered for this investigation. Their PT was measured on a calibrated dynamometer at randomly ordered velocities of 30, 90, and 150°·s^–1. A piezoelectric MMG recording sensor was placed between bipolar surface EMG electrodes (Ag-AgCl) over the VL muscle. Their MP was determined using the dynamometer software. The results indicated no sex-related differences (P>0.05) for the patterns of PT, MP, MMG amplitude, or EMG amplitude across velocity. The normalized values for MP and MMG amplitude increased (P<0.05) from 30 to 150°·s^–1 (30°·s^–1<90°·s^–1<150°·s^–1), while PT and EMG amplitudes remained unchanged across velocity. The results indicated close associations between the velocity-related patterns of MP and MMG amplitudes as well as PT and EMG amplitudes. Thus, MMG amplitude reflected the velocity-related changes in muscle power output, but not torque production, while EMG amplitude reflected torque production, but not muscle power output. During maximal, eccentric isokinetic muscle actions, EMG and MMG signals provided unique information regarding the electrical and mechanical aspects of muscle strength and power. Electronic Publication     

Test-retest reliability of reciprocal isokinetic knee extension and flexion peak torque measurements

Our purpose in conducting this study was to estimate the reliability of reciprocal concentric knee extension and flexion peak torque obtained in uninjured male athletes using the Biodex isokinetic dynamometer. Twenty-six male intercollegiate athletes (age=19.5+/-4.1 yr; ht=70.3+/-14.9 in; wt=212.9+/-48.5 lb) participated in this study. We used the Biodex to measure peak torque occurring during right knee extension and flexion over 3 consecutive days. Means and standard deviations were calculated for both extension and flexion on each of the 3 days. We observed a significant main effect for days for both extension and flexion. Mean peak torque for the first day was significantly higher (Turkey, p<.05) than the means for the other 2 days, which were not significantly different from each other (Turkey, p>0.05). Intraclass correlation coefficients (ICCs) were estimated for each of the six trials on each of the 3 days. Intraclass correlation coefficients (ICCs) ranged from .88 on trial 1, day 1 for both extension and flexion peak torque to .97 for extension peak torque and .98 for flexion peak torque on day 3, trial 6. The standard error of measurement for extension peak torque was 7.0 ft-lbs and for flexion peak torque was 3.0 ft-lbs. These results indicate that reliable measurements of reciprocal right knee extension and flexion peak torque can be obtained from uninjured male athletes with the Biodex isokinetic dynamometer.     

Torque,total work,power, torque acceleration energy and acceleration time assessed on a dynamometer: reliability of knee and elbow extensor and flexor strength measurements

Isometric torque and isokinetic peak torque, total work, power, torque acceleration energy and acceleration time at 30, 120 and 240° · s^–1 of the knee and elbow extensors and flexors were measured using an isokinetic dynamometer in 24 healthy women. Intra-session variation of the measurements was evaluated and the short-term and long-term reliability was assessed by repeating all procedures after averages of 2 and 30 days, respectively. The effect of learning on peak torque during a session was also evaluated. Moreover, the effect of general warming-up on knee extensor and flexor strength was examined on a separate day. Using correlations, numerous studies have indicated that muscle strength measurements are reliable. Correlations, however, are inappropriate and misleading in studies on reliability. In the present study reliability of each strength variable was expressed as the coefficient of variation (CV). With the protocol used, neither learning nor warming-up had any significant effect on strength. As expected, intra-session variation tended to be less than short-term and long-term inter-session variation. The CVs for strength variables measured 30 days apart exceeded 5% for all variables and rose to 107% for acceleration time. Substantial between-subject variation of individual CVs were found. The study demonstrated that muscle strength measurements may be highly unreliable in the individual subject.     

Development, reliability and validity of a new motorized isometric dynamometer for measuring strength characteristics of elbow flexor muscles

The aim of this study was to develop a new apparatus capable of accurately recording and analysing torque-time curve during isometric muscle contractions of the elbow flexors. A total of 25 (age 29.3+/-5.0 years) non-athlete male volunteers participated in this study. To establish the measurement precision of the new testing apparatus and to determine possible sources of error in the results, a series of tests was performed. Instrument validity was assessed by comparing each selected measure (lever arm angular position, torque and maximal isometric torque) to a criterion (external inclinometer, calibrated weights and isokinetic dynamometer, respectively), while trial-to-trial and day-to-day comparisons of measurements were made to estimate the reproducibility of the instrument. The statistical outcomes of validity tests demonstrated high agreement between measures and associated criteria (Pearson correlation coefficient's values >.97). Trial-to-trial correlations for maximal isometric torque in different elbow angles showed excellent reproducibility, as values of intraclass correlation coefficient (ICC([2,1])) ranged from 0.889 to 0.971, with higher value in the middle angle (90 degrees ). The value of ICC([2,1]) (day-to-day) for maximal isometric torque in 90 degrees was 0.986 and the respective standard error of measurement (SEM) was 1.5 Nm. Our results indicate that the isometric evaluation of elbow flexor muscles with the new dynamometer is accurate and reproducible.     

Use of a Kin-Com dynamometer to study the stretch-shortening cycle during plantar flexion

Summary The aim of this study was to evaluate the Kin-Com II dynamometer in the study of the stretch-shortening cycle (a concentric muscle action preceded by an eccentric muscle action). Measurements were made of plantar flexion at different angular velocities (120° · s^–1 and 240° · s^–1) with the knee at two different angles (0° and 90°). Ten healthy women ranging in age from 22 to 41 years were studied. Torque values were recorded simultaneously with surface electromyograms (EMG); maximal voluntary concentric torque values were recorded and, after a short rest, the torque values of the concentric action which followed immediately after an eccentric action of the same velocity, both with maximal effort. Mean values were taken at different ankle positions and also averaged over different ranges. A concentric action preceded by an eccentric action generated a torque value on an average about 100% larger than a concentric action alone. The EMG activity was lower or unchanged. It was concluded that the present method could be useful in the study of the stretch-shortening cycle in plantar flexion and in the testing of the behaviour of the elastic components in people with disabilities in the lower limbs.     

Smartphone-based accelerometry is a valid tool for measuring dynamic changes in knee extension range of motion

Introduction

Measurement of static joint range of motion is used extensively in orthopaedic and rehabilitative communities to benchmark treatment efficacy. Static measures are, however, insufficient in providing detailed information about patient impairments. Dynamic range of motion measures could provide more detailed information about patient impairments thus leading to better clinical assessments. Reliable and valid methods are available, but due to limitations in the present technology, dynamic measures are seldom performed in clinical settings. The objective of this study was to determine the validity of smartphone-based accelerometry measuring the dynamic range of motion of the knee joint during a passively executed extension movement.

Reliability of concentric ankle dorsiflexion fatigue testing.

The purpose of this study was to determine the reliability of an isokinetic test for ankle dorsiflexion fatigue on a Biodex dynamometer. Young (21 to 32 years), recreationally active men (n = 10) and women (n = 10) performed 50 concentric (60 degrees.s-1) dorsiflexion contractions, on two different occasions. Total work (TW), losses in work (work fatigue; WF), as well as relative losses in peak toruqe, an example being "3-3" which compared the first three to last three repetitions, were measured. The intra-class correlation coefficients (ICC2.1) and coefficients of variation (CV), as well as the Bland-Altman plots and analyses showed that the variables using peak torque and TW were more reliable than WF, with WF having a CV of 11.3% and the best peak torque variable, 3-3, having a CV of 5.6%. In conclusion, ankle dorsiflexion fatigue can be reliably assessed on a Biodex dynamometer.     

Validity and reliability of limits-of-stability testing: a comparison of 2 postural stability evaluation devices

Context:

A lack of published comparisons between measures from commercially available computerized posturography devices and the outcome measures used to define the limits of stability (LOS) makes meaningful interpretation of dynamic postural stability measures difficult.

Objectives:

To compare postural stability measures between and within devices to establish concurrent and construct validity and to determine test-retest reliability for LOS measures generated by the NeuroCom Smart Balance Master and the Biodex Balance System.

Design:

Cross-sectional study.

Setting:

Controlled research laboratory.

Patients or Other Participants:

A total of 23 healthy participants with no vestibular or visual disabilities or lower limb impairments.

Intervention(s):

The LOS were assessed during 2 laboratory test sessions 1 week apart.

Main Outcome Measure(s):

Three NeuroCom LOS variables (directional control, endpoint excursion, and movement velocity) and 2 Biodex LOS variables (directional control, test duration).

Results:

Test-retest reliability ranged from high to low across the 5 LOS measures (intraclass correlation coefficient [2,k] = 0.82 to 0.48). Pearson correlations revealed 4 significant relationships (P < .05) between and within the 2 computerized posturography devices (r = 0.42 to −0.65).

Conclusions:

Based on the wide range of intraclass correlation values we observed for the NeuroCom measures, clinicians and researchers alike should establish the reliability of LOS testing for their own clinics and laboratories. The low to moderate reliability outcomes observed for the Biodex measures were not of sufficient magnitude for us to recommend using the LOS measures from this system as the gold standard. The moderate Pearson interclass correlations we observed suggest that the Biodex and NeuroCom postural stability systems provided unique information. In this study of healthy participants, the concurrent and construct validity of the Biodex and NeuroCom LOS tests were not definitively established. We recommend that this study be repeated with a clinical population to further explore the matter.     

Deltoid muscle volume estimated from ultrasonography: in vitro validation and correlation with isokinetic abduction strength of the shoulder

Accurate prediction of muscle parameters can be used for customization of biomechanical models. A method is presented to estimate the volume of triangular-shaped muscles from ultrasonographic measurements. The deltoid muscle was used to validate the technique in a cadaver study of 12 shoulders. The relationship between isokinetic abduction strength and estimated deltoid muscle volume of the dominant shoulder of 30 healthy male subjects was analysed. Isokinetic joint moments were quantified using the Biodex System 3. A significant relationship (R = 0.87; p < 0.001) between the calculated deltoid volume and the isokinetic abduction peak torque was established.     

Torque loss induced by repetitive maximal eccentric contractions is marginally influenced by work-to-rest ratio

The influence of different work-to-rest (W:R) ratios during fatigue induced by maximal eccentric contractions is unknown. The present study sought to expand the understanding of the task-dependent nature of eccentric contractions, and the associated fatigue, during exercise and acute as well as extended recovery periods. Using a Biodex multi-joint dynamometer, the ankle dorsiflexors of eight men [26 (4) years] were fatigued with 150 maximal eccentric contractions. Set structure was manipulated such that one leg performed 3 sets of 50 repetitions (short rest protocol, SRP), and the other leg performed 15 sets of 10 repetitions (long rest protocol, LRP). A 1-min rest interval separated each set, which resulted in 2 and 14 min of total rest for the SRP and the LRP, respectively. At fatigue, the SRP demonstrated a marginally greater loss of average peak eccentric torque than the LRP (P<0.05). In the acute period following fatigue, isometric peak torque loss and the degree of low-frequency fatigue (LFF) were not recovered (P<0.05) and were equivalent for both protocols. Significant impairment of both eccentric and isometric torque was persistent and equal for each protocol at 96 h of recovery (P<0.05). These findings suggest that the W:R ratio has a modest influence on the fatigue (torque loss) induced by maximal eccentric contractions, but maximal isometric torque during recovery and LFF are insensitive to changes in total rest time.     

Muscular fatigue during repeated isokinetic shoulder forward flexions in young females

Summary Peak torque, work, mean power and electromyographic (EMG) activity were recorded for each of 150 repeated isokinetic maximal shoulder flexions (45°–90°) in 23 healthy females. From the EMG signals of trapezius, deltoid, infraspinatus and biceps brachii the mean power frequency and the signal amplitude were determined in real time. The mechanical output showed a steep decrease during the first 40 contractions, followed by a plateau maintained until the end. In all muscles, except the biceps brachii, significant decreases in mean power frequency occurred during the first 40 contractions, showing a tendency to stabilize around the same absolute frequency value. Signal amplitude increased in the trapezius, the deltoid and the infraspinatus, but was constant in the biceps brachii. For some individuals rather high EMG activity was recorded in the muscles during the time the arm was supposed to be passively extended to the starting position, and this was found to be associated with lower strength and endurance levels. Longitudinal analyses showed that the mean power frequencies correlated better than the signal amplitudes with the three mechanical variables. The results suggest that the initial steep decrease in mechanical performance and mean power frequency is caused by fatiguing of type 2 motor units.     

Motor unit discharge rates of the anconeus muscle during high-velocity elbow extensions

Motor unit recruitment and motor unit discharge rate (MUDR) have been widely studied in isometric conditions but minimally during velocity-dependent contractions. For isometric contractions, surface electromyography (EMG) activity of the elbow extensors plateaus at near maximal torques (Le Bozec et al. 1980; Le Bozec and Maton 1982). One study (Maton and Bouisset 1975) recorded single motor unit (MU) activity at maximal velocities; however, only the rate of the first interspike interval (ISI) was reported and likely was not representative of the average MUDR of the MU train. The purpose was to calculate average MUDRs of the anconeus during loaded velocity-dependent contractions from zero velocity (isometric) up to maximal velocity (V_max25) through a large range of motion. A Biodex dynamometer was used to record elbow extension torque, position, and velocity. Single MU potentials were collected from the anconeus with intramuscular EMG, and surface EMG was sampled from the lateral head of the triceps brachii during maximal voluntary isometric contractions (MVCs) and velocity-dependent contractions loaded at 25% MVC over 120° range of motion at five target velocities (0, 25, 50, 75, 100%V_max25). Elbow extension velocities ranged from 93 to 494°/s and average MUDR ranged from 11.8 Hz at 25%MVC to 39.0 Hz at 100%V_max25. Overall average MUDRs increased as a function of velocity, although the root mean square of triceps brachii surface EMG plateaued at 50%V_max25. Piecewise regression analysis revealed two distinct linear ranges each described by a unique equation, suggesting that MUDRs of the anconeus enter a secondary range of firing, characterized by a steeper slope as velocity approaches maximum.