Biomedical subjects

J Harlaar

Publications and source records attributed to J Harlaar.

23 records · Page 2Linked to original sources

PubMed1994

Two strategies of transferring from sit-to-stand; the activation of monoarticular and biarticular muscles.

In this study, two different strategies of rising from a chair were compared, using integrated biomechanical and electromyographic analyses. Nine healthy subjects were instructed to rise using two different strategies: natural sit-to-stand transfer (NSTS) and a sit-to-stand transfer with full flexion of the trunk (FSTS). Sagittal kinematics and ground reaction forces were registered. Muscle activity of nine muscles of the right leg were recorded by means of surface EMG. All signals were synchronized at seat-off. The results show that no differences occur between the kinematics of knee and ankle, whereas the hip flexion is, as expected, higher during FSTS. The higher moment about the knee during NSTS is shifted to proportionally higher moments about the hip and ankle during FSTS. It is mainly the differences in the EMG-levels of the biarticular hip and knee muscles which might explain the differences in net moment. These results are in accordance with a theory about a particular role of biarticular muscles. On the other hand, the shift from knee to ankle cannot be associated with a particular increase in activity of the biarticular m.gastrocnemius. It is hypothesized that about the ankle, control of stability is preferred over movement control. An important conclusion for rehabilitation medicine is that a lower net moment about the knee in FSTS does not automatically imply that this reduces the load on the knee extensors.

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PubMed1993

The application of generalizability theory to reliability assessment: an illustration using isometric force measurements.

BACKGROUND AND PURPOSE: The objective of this study was to examine the potential use of the generalizability theory for assessing reliability of muscle force measurements in clinical applications. Reliability is expressed in terms of standard error of measurement (SEM) and the indexes derived from the SEM. Using generalizability theory, potential sources of measurement error can be recognized and estimated. SUBJECTS: Ten healthy women, aged 23 to 47 years (means = 29.5, SD = 7.1), participated in the study. METHODS: The method is illustrated by presenting a pilot study. Repeated measurements of maximal isometric knee extension force were carried out by two therapists. The time interval between measurement occasions was 1 week. A functional prototype of a hand-held dynamometer was used, and measurements were carried out according to standardized test protocols. RESULTS: Relatively important sources of measurement error were associated with interaction effects between subject and therapist as well as with interactions including the factor occasion. The SEM of the net knee moment was estimated for various hypothetical applications of the dynamometer. CONCLUSION AND DISCUSSION: It is concluded that the SEM, the corresponding confidence interval, and the smallest detectable difference are practical measures for expressing reliability of measurements on an individual. Generalizability theory is a powerful tool for estimating the magnitude of multiple sources of measurement error and for assessing the reliability of measurements tailored to specific clinical applications.

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PubMed1993

Evaluation of moment-angle curves in isokinetic knee extension.

The purpose of this study was to challenge the notion that the relationship of moment of force to angular velocity, determined in isokinetic knee extension tests, reflects the force-velocity relationship of human knee extensors. For this purpose, maximum-effort isometric knee extension moments were collected at seven different knee joint angles, and maximum-effort isokinetic knee extension moments were measured as a function of knee joint angle at angular velocities of 30, 60, 120, and 210 degrees.s-1. For the isokinetic contractions two protocols were used with a different threshold moment, i.e., the minimum knee extension moment that had to be reached isometrically before knee extension was initiated. In one protocol (LTM, for low threshold moment) the threshold was set at 5% of the maximum isometric knee extension moment produced at the starting angle of 85 degrees (180 degrees being full knee extension), in the second protocol (HTM, for high threshold moment) it was set at 95% of this isometric moment. During all contractions, electromyograms were recorded from m. vastus medialis, m. vastus lateralis, m. rectus femoris, and m. biceps femoris. The EMG signals were rectified and smoothed to yield SREMG. Two hypotheses were specifically tested. The first was that the threshold moment does not affect knee extension moments in the middle of the range of motion. Between knee angles of 100 degrees and 145 degrees, no differences were found between moments produced in the HTM protocol and those produced in the LTM protocol. Thus, the first hypothesis was supported. The second hypothesis was that subjects achieve the same level of muscle excitation at different speeds.(ABSTRACT TRUNCATED AT 250 WORDS)

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PubMed1992

Diagnostic blocks of the tibial nerve in spastic hemiparesis. Effects on clinical, electrophysiological and gait parameters.

The value of a diagnostic block (DB) of the tibial nerve in 17 hemiparetic patients with gait disturbances was investigated. The purpose of this study was to find instruments that help to select patients who will benefit from a long lasting peripheral nerve block. The manually elicited ankle clonus and its abolition after injection of a local anaesthetic appeared to be a useful clinical test for the efficacy of DB. Electrophysiological tests proved valuable when DB failed to produce clinical effects. With a substantial number of blocked nerve fibres walking velocity did not deteriorate. Transient disturbances in sensation can be regarded as unwanted side effects that might adversely affect the walking ability. From the different aspects of gait an improved heelcontact demonstrated the functional gain in patients with a dynamic equinus foot. To differentiate between a dynamic equinus foot and fixed contractures, we recommend the use of a fast acting local anaesthetic for diagnostic nerve blocks.

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PubMed1991

Electromechanical delay during knee extensor contractions.

The purpose of this study was to investigate the magnitude of electromechanical delay (EMD) and its possible dependence on muscle type, type of contraction, fatigue, level of force, initial muscle length, and muscle contraction velocity. This was achieved using an experiment that measured voluntary knee extensor torques and surface EMG activity for a variety of different contractile conditions in seven male subjects. EMD values were obtained using a cross-correlation technique in three experimental KIN-COM dynamometer conditions of vastus medialis, rectus femoris, and vastus lateralis. In the first condition, a series of 10 repetitive submaximal (50% and 70% MVC) isometric knee extensor contractions were performed at knee angles of 90 degrees and 130 degrees extension. In the second condition, 10 maximal isokinetic knee extensor contractions were performed during passive shortening and lengthening. As such, the dynamometer was used to passively move the knee joint at 30 degrees.s-1 and 60 degrees.s-1. Both during lengthening and shortening, the contractions occurred at an angular position of 110 degrees. In the last condition, a repetitive submaximal isometric knee extensor fatigue test was performed for 100 s (150 contractions). At 10, 40, and 90 s during the time course of this fatigue test, a series of 10 contractions were recorded. To avoid a phase lag, which is introduced with one-way filtering, the EMG was processed with a bidirectional low-pass filter application. A significant main effect in EMD for the factor level of force was found. The EMD values obtained at a force level of 50% MVC were longer than at 70% MVC (107 vs 98 ms).(ABSTRACT TRUNCATED AT 250 WORDS)

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