Isokinetic Velocity Research Articles

Interaction of Velocity and Progression Order During Isokinetic Velocity Spectrum Exercise

Interaction of Velocity and Progression Order During Isokinetic Velocity Spectrum Exercise

Sample withdrawal from a slurry mixing tank

The local solids concentration from a slurry mixing tank has been measured by the withdrawal of a sample from the vessel. It is shown that the sample tube design (shape, diameter and tip angle) and sampling technique (withdrawal velocity and location in the mixing tank) can significantly affect the solids concentration and the particle size distribution of the sample withdrawn. The particle inertia relative to an equal volume of fluid results in solids concentration measurements that vary with particle size and bulk concentration. It is practically impossible to obtain reliable measurements of local solids concentration by sample withdrawal from a mixing tank. Sampling errors can be minimized with the use of fine solids and sampling at as high a velocity as possible. The bulk solids concentration can be accurately measured on the plane of a radial flow impeller by sampling at the isokinetic velocity, with a tapered sampling tube and when the solids concentration does not display a strong in the vertical direction. The fraction of fine sand in a sample obtained from a bimodal mixture of fine and coarse sands was found to be a function of the sample solids concentration.

The effects of pad placement and angular velocity on tibial displacement during isokinetic exercise.

The purpose of this study was to compare the effects of proximal single resistance pad placement (PSPP) and distal single pad placement (DSPP) on tibial displacement during isokinetic exercise on anterior cruciate ligament (ACL)-deficient knees. This study is important to the clinician because it documents tibial displacement during open chain isokinetic knee extension exercise at various isokinetic speeds. In addition, this study documents the range of motion where the greatest amount of anterior tibial displacement occurs. The anterior displacement of the tibia was recorded by a computerized knee laxity testing device during isokinetic exercise. Data were collected from 12 ACL-deficient knees. Each subject was tested on an OSI Knee Signature System for quantifiable tibial displacement during a Lachman's test, anterior drawer test, and active vs. passive knee extension. Following this, each subject was tested on a Biodex isokinetic dynamometer at isokinetic velocities of 60, 180, and 300 degrees/sec with the computerized knee laxity testing device in place. Pad placement consisted of distal single pad placement, which is 1 inch proximal to the medial malleolus, and proximal single pad placement, which is 3 inches proximal to the DSPP location. The testing procedure was standardized, and peak torque was monitored to ensure consistent maximal effort throughout the study. The results indicated that PSPP resulted in less anterior tibial displacement at all three test speeds. The peak anterior tibial displacement occurred in a range from 30 to 15 degrees of knee flexion at both pad placements and all three test speeds.(ABSTRACT TRUNCATED AT 250 WORDS)

Isokinetic trunk extension and flexion strength-endurance relationships

This study examined the relationship between sagittal plane isokinetic trunk extension and flexion strength and endurance using three isokinetic velocities (60, 120, and 180° s −1). Healthy male subjects with no history of low back problems performed 25 consecutive repetitions of a 100° trunk extension-flexion task with encouragement to execute each repetition with maximum effort. Between each isokinetic velocity, 5 min of rest were provided. The traditional isokinetic variables of peak torque and work for trunk extension and flexion were extracted from the torque-position curves and fatigue profiles were generated with linear regression using the mean values of peak torque and work from repetitions 2–4, 7–9, 12–14, 17–19 and 22–24. The linear regression analysis defined the relationship between fatigue and the number of repetitions. The rate of fatigue (given by the slope of the regression equation) and the magnitude of the fatigue was maximum in the 60° condition. The fatigue rate and the magnitude were both related to the absolute strength given by the maximum work output. The trunk flexors were observed to be more susceptible to fatigue than the trunk extensors.

A Three-Dimensional Motion Model of Loads on the Lumbar Spine: II. Model Validation

A three-dimensional motion model has been developed that estimates loads on the lumbar spine under laboratory conditions that simulate manual materials handling conditions. Eleven subjects experienced spinal loading during an experiment in which conditions of trunk velocity, trunk torque output, and trunk asymmetric posture were varied in a series of isokinetic velocity trunk extensions. The electromyographic activity of 10 trunk muscles, subject anthropometry, and trunk kinetics were used as input to a biomechanical simulation model described in Part I of this study. The model calculated estimates of compression, shear, and torsion loading in the lumbar spine, as well as the torque production of the trunk, continuously throughout the exertion. Trunk torque estimates derived from this model were compared with measured trunk torque. The effects of trunk motion, posture, and torque level on spine loading as estimated by the model are discussed. It was concluded that this approach provides a straightforward means of assessing loading of the spine attributable to laboratory simulations of workplace conditions.

SInfluence of Muscle Shortening on the Geometry of Gastrocnemius Medialis Muscle of the Rat

For static and dynamic conditions muscle geometry of the musculus gastrocnemius medialis of the rat was compared at different muscle lengths. The dynamic conditions differed with respect to isokinetic shortening velocity (25, 50 and 75 mm/s) of the muscle-tendon complex and in constancy of force (isotonic) and velocity (isokinetic) during shortening. Muscle geometry was characterized by fibre length and angle as well as aponeurosis length and angle. At high isokinetic shortening velocities (50 and 75 mm/s) small differences in geometry were found with respect to isometric conditions: aponeurosis lengths differed maximally by -2%, fibre length only showed a significant increase (+3.2%) at the highest shortening velocity. The isotonic condition only yielded significant differences of fibre angle (-4.5%) in comparison with isometric conditions. No significant differences of muscle geometry were found when comparing isotonic with isokinetic conditions of similar shortening velocity. The small differences of geometry between isometric and dynamic conditions are presumably due to the lower muscle force in the dynamic condition and the elastic behaviour of the aponeurosis. It is concluded that, unless very high velocities of shortening are used, the relationship between muscle geometry and muscle length in the isometric condition may be used to describe muscle geometry in the dynamic condition.

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

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 degrees.s-1 to 300 degrees.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 degrees (SD 10.2 degrees). Power athletes developed greater peak torque at each angular velocity (P less than 0.05) and experienced a 39.7% decrement in torque over the velocity range tested. Endurance athletes encountered a 38.8% decline in peak torque. Torques measured at 60 degrees of knee flexion followed a similar trend in both groups; however the greatest torques were recorded at 60 degrees.s-1 rather than at 30 degrees.s-1. Leg extensor muscle power increased monotonically with angular velocity in both power (r2 = 0.728) and endurance athletes (r2 = 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.

Trunk Strength during Asymmetric Trunk Motion

It is important to understand how trunk strength varies as a function of workplace factors so that the work environment can be designed to minimize the risk of low back injury. In this study maximal trunk torque production around the lumbosacral junction was measured in 44 subjects as trunk concentric and eccentric isokinetic velocity and trunk asymmetric line of action were varied. Trunk torque decreased by approximately 8.5% of maximum for every 15 deg of asymmetric trunk angle. Increases in concentric velocity decreased trunk strength, whereas increases in eccentric trunk velocity increased strength. Significant interactions were also found, and it was determined that the common finding that eccentric strength exceeds concentric strength is true only for forward trunk angles at all asymmetric angles. These results should have significant implications for the design of manual materials handling tasks.

Calf muscle work and segment energy changes in running

In-situ rat soleus muscles were tetanized and subjected to controlled lengthening and shortening using a Cambridge lever system. Lengthening-shortening cycles similar to those observed in the cat soleus muscle during locomotion confirmed that force-velocity properties may be enhanced in locomotion. Quick release of a tetanized muscle to an isokinetic shortening velocity without prior stretch also enhanced force-velocity properties during the initial stage of shortening. Stretch of a tetanizcd muscle prior to release to an isokinetic shortening produced an elevation of the initial tetanic tension plus an even greater enhancement of force velocity properties. Elevation of tetanic force due to stretch was transient, decaying to normal tetanic levels in approximately 50ms if the stretched position was held. Enhancement without prior stretch may be the result of storage of elastic strain cncrgy in series elastic elements of the skeleto-musculo-tendinous system. Greater enhancement after stretch may be the result of increased force generation within the muscle combined with greater storage of elastic energy possible as a result olr the higher forces achieved under pre-stretch conditions.

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

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 degrees.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 greater than 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 degrees.s-1, 120 degrees.s-1 and 270 degrees.s-1 never varied by more than 3 degrees.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 degrees.s-1 and 270 degrees.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.

Ageing and isokinetic plantar flexion.

Isokinetic torques (Cybex II) of the plantar flexors in 25 healthy men were compared at 5 angular velocities (30, 60, 90, 120 and 180 degrees X s-1). The purposes were to compare plantar flexion torques in young and old subjects, and to determine whether the expected decrease was significantly associated with age, physical activity, or aerobic fitness. Four groups were studied: young (21.7 +/- 2.0 years) and older (63.3 +/- 2.8 years), active and sedentary. Measurements of height, weight, % body fat, VO2max, and daily leisure energy expenditure (questionnaire) were determined for each subject. Statistical measures of analysis of variance were used to determine significant differences among groups; product moment correlation and stepwise regression analysis were used to describe the degree of association between the dependent variable of plantar flexion torque and the independent variables at each velocity. A decline in torque was observed as the isokinetic velocity of angular motion increased. Age alone was a significant determinant of plantar flexion torque, whereas at the slowest speed, when VO2max was used as an explanatory variable, age was not a significant determinant of torque. At 30 degrees X s-1 47% of the variance in torque was explained by VO2max while at 180 degrees X s-1 49% of the variance was explained by age.

The Effect of Electrical Stimulation and Isokinetic Exercise on Muscular Power of the Quadriceps Femoris

The purpose of this study was to compare the power and strength changes, of the quadriceps femoris muscle group, following 6 weeks of training. Twenty-seven moderately trained, female subjects were placed into three equated groups: electrical stimulation plus isokinetic exercise (ES + IE), isokinetic exercise (IE), and electrical stimulation (ES). A CybexQ I1 isokinetic dynamometer was used for testing the quadriceps ' power and strength output at the velocities of 0, 30, 100, and 180 O/ sec. The ES + IE and ES groups received faradic stimulation (progressive from 10- 20 mA) from a Multitone Multifaradic Unit (model F283, Multitone Electric Co., London, England). In addition, the ES + IE group performed isokinetic contractions concurrently with the faradic stimulation. Thigh circumference (TC) and time to peak tension (TPT) were also calculated during the pre-, mid-, and post-tests. Results indicated that a significant power increment was evident between the pre- and posttests and the pre- and mid-tests for the combined groups (p < 0.05). However, there were no significant power increases between the three separate groups at the four velocities. Significant power differences (P c 0.05) for the combined groups between the pre- and post-tests and the pre- and mid-tests at the isokinetic velocities of 30 and OO/sec were also identified. TPT and TC did not change significantly for any group over the 6-week training period. This study indicated that the combined effects of ES + IE, IE, and ES are potentially effective means of improving power and strength; however, data did not reveal one method of training as being significantly superior to another. J Orthop Sports Phys Ther 1986;8(5):260-268.

Prediction of peak torque and contraction work at different isokinetic angular velocities of plantarflexion.

Contraction work (CW) and peak torque (PT) of maximum isokinetic plantar flexions were measured in clinically healthy subjects randomly chosen from the official census list of Umeå, Sweden, in three groups: 40-44, 50-54 and 60-64 years of age, with similar proportions of men and women. Maximum isokinetic plantar-flexions were performed at angular velocities of 30, 60, 120 and 180 degrees X s-1. Body-weight, height and crural circumference were measured. Subjects rated their levels of leisure and occupational activities. To establish formulae to predict CW and PT, stepwise regression procedures were applied. The predictive powers (r2) of the formulae which incorporated age, sex and crural circumference, were higher for PT (30 degrees X s-1: 0.82, 60 degrees X s-1: 0.79, 120 degrees X s-1: 0.75, 180 degrees X s-1: 0.56) than for CW (30 degrees s-1: 0.63, 60 degrees s-1: 0.63, 120 degrees s-1: 0.60, 180 degrees s-1: 0.52). Thus the part of the variance explained decreased with increasing angular velocity, but more than 50% was still explained at 180 degrees s-1. The results indicate that the mechanical output of the plantar flexors is predictable.

Muscular Power in Young Women After Slow and Fast Isokinetic Training

The purpose of this study was to determine, via a pilot study, if training at a fast isokinetic velocity (180 degrees /sec) would result in a greater increase in upper-extremity muscular power than training at a slow isokinetic velocity (60 /sec) while exercising through a specific range of motion (1 80"). Twenty normal young women were randomly selected into one high velocity and one slow velocity experimental group. The exercise protocol consisted of four bouts of five maximal reciprocal isokinetic contractions of the shoulder flexor and extensor muscle groups, three times a week for four weeks. Pre- and post-testing with a Cybex I$ isokinetic dynamometer was performed to determine if significant power gains were elicited within the training range of motion. Aiter training, both fast and slow velocity groups showed significant power gains (p < 0.0005). However, the results indicated that neither fast nor slow isokinetic training is more effective for power production within the 1 80 degrees range of motion of shoulder extension in the young women studied. J Orthop Sports Phys Ther 1986;8(1);1-9.

Isometric, Isotonic, and Isokinetic Torque Variations in Four Muscle Groups Through a Range of Joint Motion

The purpose of this investigation was to describe and examine variations in maximal torque produced by knee extension, knee flexion, elbow extension, and elbow flexion through a range of joint motion. Subjects were young, healthy men (n = 16) and women (n = 15). Torque was measured isometrically and isokinetically using a modified Cybex apparatus. Isotonic torque was calculated from a one-repetition maximum using a modified N-K device. Joint angles were monitored with an electrogoniometer. Torque-joint angle curves were constructed for both men and women for each muscle group. Isometric torque was highest, followed by isotonic and isokinetic torque. Torque declined with increasing isokinetic velocity. The angle of peak torque was found to be highly variable in individual subjects. Variations in torque curves were explained in terms of mechanical characteristics of the musculoskeletal system. Muscle group capability was generally found to be well matched to the mechanical requirements of the movement.

Isokinetic and static plantar flexion characteristics.

Isokinetic and static maximum plantar flexion torques were measured in 135 adults with sedentary professions. Close associations between isokinetic and static peak torques were found. Between the ages 20--49 years strength did not differ. Thereafter strength declined as a function of age. Maximum strength was 35% lower in females than in males. The right plantar flexion strength was slightly lower than the left. Maximum plantar flexion strength was about 15% lower with flexed than with extended knees. A negative exponential model characterized the decline of strength as a function of increased isokinetic velocity of angular motion. Seventy per cent or more of the variations in maximum static and isokinetic strength could be explained by anthropometric variables and by age, and by the extent of physical activity in subjects younger than 50 years. Formulas for estimation of expected static and isokinetic strengths are given.

Evaluation of aerosol aspiration efficiency as a function of stokes number, velocity ratio and nozzle angle

Inertial effects in the aspiration of aerosols from a moving fluid are described in this experimental study. Aspiration coefficients were determined by comparing concentrations collected by two nozzles simultaneously sampling in a 10 cm wind tunnel. The control nozzle was aligned parallel to the axis of the duct and sampled isokinetically. The test nozzle was inserted at angles of 0, 30, 60 and 90° and sampled at a velocity ranging from one half to two times the isokinetic velocity. Particle size, nozzle diameter and free stream velocity were varied to produce a range of Stokes numbers from 0.007 to 3. Data obtained by Belyaev and Levin (1974) were incorporated with experimental data to develop an empirical expression describing the relationship between the aspiration coefficient and the Stokes number as a function of angle of misalignment and velocity ratio. An adjusted Stokes number is described which takes into account the effect of an apparent change in nozzle diameter due to misalignment of the nozzle to the flow stream. Analysis of the probe wash showed that from 15 to 60% of the total particulate matter entering the sampler inlet was lost on the nozzle walls. Implications of this phenomenon are described.

Coolant mixing and subchannel velocities in an LMFBR fuel assembly

Experimental mixing studies were conducted using water with a 91-pin wire-wrapped fuel assembly to establish a data base for calibrating thermal-hydraulic codes and to supplement and clarify existing mixing data. An electrolytic tracer was employed in conjunction with an isokinetic sampling technique which permitted mixed mean subchannel concentrations and flowrates to be measured without incurring errors resulting from local subchannel gradients. Emphasis was placed upon the behavior of peripheral subchannels. A complete set of mixing data was obtained which can be used to calibrate thermal-hydraulic codes. Isokinetic velocity measurements revealed that the pitch-average corner, edge, and central subchannel velocities were nearly equal to the bundle average velocity. It was shown that the average peripheral swirl velocity was approximately 1.2 times greater than predicted assuming the fluid follows the wire-wraps. Also the magnitude of the average swirl flow decreases with increasing bundle size. Parametric studies revealed that neither the velocity nor concentration profiles were sensitive to Reynolds number in the range Re = 9000–24000.