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Biomedical subjects

A L Hof

Publications and source records attributed to A L Hof.

At least 37 records · Page 2Linked to original sources
PubMed1999

Influence of mandibular length on mouth opening.

Theoretically, mouth opening not only reflects the mobility of the temporomandibular joints (TMJs) but also the mandibular length. Clinically, the exact relationship between mouth opening, mandibular length, and mobility of TMJs is unclear. To study this relationship 91 healthy subjects, 59 women and 32 men (mean age 27.2 years, s.d. 7.5 years, range 13-56 years) were recruited from the patients of the Department of Oral and Maxillofacial Surgery of University Hospital, Groningen. Mouth opening, mobility of TMJs and mandibular length were measured. The mobility of TMJs was measured as the angular displacement of the mandible relative to the cranium, the angle of mouth opening (AMO). Mouth opening (MO) correlated significantly with mandibular length (ML) (r = 0.36) and AMO (r = 0.66). The regression equation MO = C1 x ML x AMO + C2, in which C = 0.53 and C2 = 25.2 mm, correlated well (r = 0.79) with mouth opening. It is concluded that mouth opening reflects both mobility of the TMJs and mandibular length.

Adolescent↗
PubMed1998

From twitch to tetanus for human muscle: experimental data and model predictions for m. triceps surae.

In models describing the excitation of muscle by the central nervous system, it is often assumed that excitation during a tetanic contraction can be obtained by the linear summation of responses to individual stimuli, from which the active state of the muscle is calculated. We investigate here the extent to which such a model describes the excitation of human muscle in vivo. For this purpose, experiments were performed on the calf muscles of four healthy subjects. Values of parameters in the model describing the behaviour of the contractile element (CE) and the series elastic element (SEE) of this muscle group were derived on the basis of a set of isokinetic release contractions performed on a special-purpose dynamometer as well as on the basis of morphological data. Parameter values describing the excitation of the calf muscles were optimized such that the model correctly predicted plantar flexion moment histories in an isometric twitch, elicited by stimulation of the tibial nerve. For all subjects, the model using these muscle parameters was able to make reasonable predictions of isometric moment histories at higher stimulation frequencies. These results suggest that the linear summation of responses to individual stimuli can indeed give an adequate description of the process of human muscle excitation in vivo.

Adult↗
PubMed1998

In vivo measurement of the series elasticity release curve of human triceps surae muscle.

The force-extension characteristic of the series-elastic component of the human triceps surae muscle has been measured in vivo by means of a hydraulic controlled-release ergometer in 12 subjects. The SEC characteristic can be described by a linear relation between muscle moment and extension, with a stiffness K1, preceded by a quadratic 'toe' region at low moments. Stiffness K1 increases with the level of activation of the muscle. At an ankle moment of 100 N m, values range between 250 and 400 N m rad(-1). The elastic stretch corresponds then to about 30, which is considerable compared with the total ankle movement range. At moments of 150 and 180 N m, which correspond to the peak moments in walking and running, respectively, the elastic energy stored in the SEC was 23-37 and 31-57 J. These energy values are amply sufficient to enable the conservation of negative (eccentric) work into a subsequent phase of positive (concentric) work in both walking and running.

Adult↗
PubMed1997

Median power frequency of the surface electromyogram and blood lactate concentration in incremental cycle ergometry.

The electromyogram (EMG) median power frequency of the vastus lateralis and flexor digitorum superficialis muscles was measured in 12 subjects during cycle ergometry with step-wise increasing exercise intensities up to 100% of VO2max. Blood lactate concentration was measured to investigate the relationship between changes in lactate concentration and shifts in the EMG median power frequency of exercising vastus lateralis and non-exercising flexor digitorum superficialis muscles. The results indicated that lactate concentration did not systematically affect median frequency: in spite of a considerable increase in blood lactate concentration, no systematic decrease of the median frequency during exercise was found, either for the vastus lateralis or for the flexor digitorum superficialis muscles. Instead of a decrease of the median frequency during exercise, as seen in isometrical protocols, an increase was seen in most subjects. An interesting finding was a decrease of the median frequency of vastus lateralis muscle during recovery in 8 subjects. The present findings showed that the relationship between EMG frequency decrease, lactate accumulation and fatigue, as observed in isometric protocols, cannot be simply applied to dynamic exercise.

Adult↗
PubMed1997

A controlled-release ergometer for the human ankle.

A hydraulic ergometer for the human foot is described that can apply ankle rotations up to 1 rad at a constant high speed of 10-20 rad/s against moments up to 200 N m. The initial acceleration is damped, so as not to exceed a preset value. With the presented set-up the series elasticity of the intact human m. triceps surae can be measured.

Acceleration↗
PubMed1997

Correcting for limb inertia and compliance in fast ergometers.

In fast moving ergometers for human limbs the acceleration induces transient moments due to the inertia of the limb, in combination with a not perfectly rigid limb fixation. Methods are described by which these effects can be corrected for. The correction of the moment consists of filtering the recorded moment and angular acceleration, and then adding both signals. Inertial transients can thus be reduced to 1/6 or less. The recorded angle can be corrected for the compliance of the limb fixation.

Acceleration↗
PubMed1997

The relationship between electromyogram and muscle force.

Some guidelines are given for the interpretation of the electromyogram (EMG). In static isometric contractions there is, usually a linear, relationship between muscle force and smoothed rectified EMG (SRE). It should be considered, however, that most of the time several muscles are active simultaneously around a joint. This finding implies that the relationship between the SRE of a single muscle and the total joint moment needs not be linear. During movements, the force-length-velocity relationship and the elastic properties of muscle should be taken into account. Also, EMGs during concentric movements are larger than those measured during isometric actions. A further consideration in relating force to EMG is that the force signal has a much lower frequency content than the rectified EMG. Finally, the limited speed of the activation and deactivation process results in a 50 to 200 ms delay of the muscle force relative to the EMG.

Electromyography↗
PubMed1996

Electromyogram median power frequency in dynamic exercise at medium exercise intensities.

The electromyogram (EMG) median power frequency of the calf muscles was investigated during an exhausting treadmill exercise and a 20-min recovery period. The exercise was an uphill run at a speed of 5 km.h-1 and a gradient of 20%. During exercise there was no decrease of EMG median power frequency. In contrast, EMG median power frequency in isometric contractions of the same muscles decreased by 7% for the soleus muscle and 16 to 18% for gastrocnemius muscles immediately after the exercise. During the recovery period the isometric median power frequency of the gastrocnemius muscles increased to pre-exercise levels in about 5 min. The isometric median power frequency of the soleus muscle also increased but had not reached pre-exercise values by 20 min. The observations from this study and from a previous uphill treadmill investigation at a steeper gradient gave evidence that two types of exhaustion can be distinguished during dynamic exercise; exhaustion at lower exercise intensities without a decrease in frequency during exercise and exhaustion at high intensities accompanied by a decline of frequency. The reason for this difference remains unclear.

Adult↗
PubMed1996

Gait analysis of transfemoral amputee patients using prostheses with two different knee joints.

OBJECTIVE: To evaluate the gait of transfemoral amputee patients using a prosthesis with a 4-bar linkage knee joint with either a mechanical swing phase control (Otto Bock 3R20) or a pneumatic swing phase control (Tehlin knee). DESIGN: Randomized cross-over trial. SETTING: Rehabilitation Department of a university hospital in The Netherlands. PATIENTS: Twenty-eight subjects with unilateral transfemoral amputation for reasons other than chronic vascular disease; ages between 16 and 65 years and familiar with the use of the Otto Bock 3R20 knee. SELECTION PROCEDURE: a consecutive sample. INTERVENTION: The Otto Bock 3R20 was used by the subjects before they entered the study. The patients changed to the Tehlin knee at random either after 1 or 2 assessments with the Otto Bock 3R20. MAIN OUTCOME MEASURES: Temporal and kinematic variables in gait analysis (speed recordings were taken before and after the equipment for the measurements of the other parameters was placed on the patients). Subjective scores for comfortable and fast ambulation were obtained by means of 2 questionnaires. Questionnaire A consisted of multiple choice questions (maximum score: 5) and questions using an 8-point rating scale (maximum score: 7). In questionnaire B, the patient was asked to compare the present prosthesis with the previous one. RESULTS: Fast walking speed in gait analysis was higher with the Tehlin knee than with the 3R20 (without equipment 95% confidence interval (CI) .02-.09 m/sec, with equipment CI .04-.11), while comfortable walking speed was not higher with the Tehlin knee (without equipment CI -.20-.20 m/sec, with equipment CI .00-.05). Symmetry of walking as regards swing phase duration was closer to 100% with the Tehlin knee than with the 3R20 (comf. walking CI 4% to 19%, fast walking CI 7% to 17%). Knee joint range of motion during swing phase was smaller with the Tehlin knee than with the 3R20 (comf. walking CI 1.8 degrees-8.7 degrees, fast walking CI 2.0 degrees-9.5 degrees). Knee flexion duration during swing phase was shorter for the Tehlin knee than for the 3R20 at fast walking speed (CI 6-46msec), while knee flexion duration from and to 10 degrees flexion was shorter for the Tehlin knee at comfortable speed (CI 18-67msec) and fast speed (CI 20-64msec). In questionnaire A the amputees reported the Tehlin knee to be better for fast walking (part A1 CI .01-.52, part A2 CI .13-.98) and in questionnaire B for both comfortable and fast walking.

Adolescent↗
PubMed1994

Instrumental straight-leg raising: results in patients.

Straight-leg raising is used as a diagnostic test for both elastogenic (passive muscle stretch test) and nonelastogenic (Lasègue's test) pathology in patients unable to bend forward from the standing position while holding the knees in extension. The test assessment is based on the range of the leg excursion and the type of pain that is provoked. An instrumental version of Lasègue's test (instrumental straight-leg raising) provides information about the extensibility, elasticity and electrical activity of the hamstrings and back muscles and about pelvic rotation. To investigate the diagnostical value of the additional information, both clinical and instrumental straight-leg raising was done by 30 patients who were unable to touch the ground while bending forward from the standing position with the knees extended. In one group of patients, the electrical activity of the muscles was comparable to that observed in the muscles of a control group of healthy volunteers; in a second group, however, the electrical muscle activity was aberrant. Muscle extensibility and passive muscle elasticity was comparable in patients in the first group and the healthy controls. In the patients with aberrant muscle activity, the elasticity of the passive muscles was not different from the control group, but both leg excursion and muscle extensibility were much smaller. Comparison of the clinically and experimentally diagnosed cause (elastogenic or non-elastogenic) of the movement restriction showed a remarkable discrepancy. We conclude that instrumental straight-leg raising provides valuable additional diagnostical information.

Adolescent↗
PubMed1993

The relationship between comfortable and most metabolically efficient walking speed in persons with unilateral above-knee amputation.

Walking is most efficient when the least energy is spent over a certain distance. In six normal male subjects and 11 males with above-knee amputation the comfortable self-selected walking speeds and the most metabolically efficient walking speeds were determined. For that purpose energy expenditure was measured per second and per meter at six incremental walking speeds. Heart and step rate were registrated also at each walking speed. The results showed that in subjects who have not undergone amputation the comfortable walking speed is the same as the most efficient walking speed. However, in the above-knee amputee group, the comfortable walking speed is lower than the most efficient walking speed. When both groups walked at their own efficient walking speed they had the same energy expenditure per second.

Amputation, Surgical↗
PubMed1993

Comparison of gait using a Multiflex foot versus a Quantum foot in knee disarticulation amputees.

The subjective responses and gait patterns of unilateral knee disarticulation amputees wearing prostheses fitted first with the Multiflex foot and then with the Quantum foot were studied. Nine amputees were included in the trial. A questionnaire asked the amputees about their preference for one of the feet. Gait analysis was performed measuring temporal parameters and goniometry of hips, knees and ankles in the sagittal and frontal planes. There was a slight preference for the Quantum foot. Preference seemed not to be related to physical characteristics of the amputees nor to gait parameters. There were no differences in gait as far as the temporal factors were concerned. The main differences in the range of motion of the joints were in the frontal plane: the eversion-inversion movement of the ankle and the adduction-abduction movement of the hip. During walking at comfortable speed with the Multiflex foot the ankle and hip range of motion averaged 2.1 and 3.1 degrees respectively, less than during walking with the Quantum foot.

Adult↗
PubMed1993

Instrumental straight-leg raising: results in healthy subjects.

The instrumental performance of Lasègue's test (instrumental straight-leg raising) provides information about the extensibility, elasticity, and electrical activity of hamstrings and back muscles and about pelvic rotation. Because relevant data on these variables are not known in literature, instrumental straight-leg raising was performed in healthy subjects. Using the toe-touch test, three groups of eight subjects were selected: a flexible group, able to touch the ground with their hands flat, a medium group, able to touch the ground with their finger tips, and a stiff group, not able to touch the ground at all. Measurements showed a considerable difference in the extensibility of the hamstrings between the groups with only a slight difference in the extensibility of the back muscles. They also showed clear differences in elasticity of the hamstrings and the back muscles in the subjects within the groups. Between the groups, however, muscle elasticity was not systematically different. Electromyogram activity was most often present in the subjects of the stiff group, predominantly in the hamstrings. It began only after the leg had been raised to a considerable extent, showed a gradual increase with leg raise, and never reached a high level.

Back↗
PubMed1992

An explicit expression for the moment in multibody systems.

The equations of motion are formulated for a set of interacting rigid bodies. An explicit formulation could be derived for the total moment of the forces on such a system. This is applied to (1) the intersegmental moment in a multisegment rigid-body model, and (2) the interpretation of the 'centre of pressure' as defined in the studies of human posture.

Biomechanical Phenomena↗
PubMed1991

Errors in frequency parameters of EMG power spectra.

Frequency shifts in random signals, e.g., EMG or Doppler ultrasound, can be followed by monitoring one or more parameters of the power spectrum. When such a frequency parameter is determined over a finite length of the signal, a random error and sometimes a systematic error or bias are introduced. Approximate expressions, in terms of moments of the power spectrum, have been derived for bias and standard deviation of the estimates for mean frequency, zero-crossing frequency, and fractile frequency (of which the median frequency is a special case). Experimental results from surface EMG recordings of three human muscles in constant force isometric contractions were in agreement with the theoretical predictions. In this case the mean frequency had the smallest random error. It turned out that the measured values of the zero-crossing frequency can deviate considerably from the predictions by the Rice formula when the amplitude distribution is not exactly Gaussian. In the presence of noise, all frequency parameters show a systematic deviation, depending on the signal-to-noise ratio. In addition to known results on this deviation for mean and zero-crossing frequency, an exact and an approximate expression for the fractile frequency are given. In the case of EMG plus wide-band white noise, the median frequency has the best immunity to noise.

Electromyography↗
PubMed1991

Instrumental straight-leg raising: a new approach to Lasègue's test.

In clinical practice the outcome of Lasègue's test is interpreted with respect to two variables: (1) the maximum angle between the leg and the horizontal plane to which the leg can be lifted, and (2) the pain that is provoked by the movement. For a number of reasons it is difficult in many patients to interpret the test outcome; predominantly, it is because of the lack of information it yields concerning the activity of the muscles. To get more information, an instrumental test was developed that imitates Lasègue's test. In this setup, which is based on a simple biomechanical model, the leg is passively raised in a lift installation. During lifting, the angles between leg and horizontal plane and between leg and pelvis are measured with electrogoniometers; the lift moment is determined with the help of a force transducer; pelvic rotation is assessed with a lordosis meter; and surface electromyography is used to record electric transducer; pelvic rotation is assessed with a lordosis meter; and surface electromyography is used to record electric activity in the erector spinae, the gluteus maximus, and the semimembranosus. The method, called instrumental straight-leg raising, makes it possible to determine the extensibility, elasticity, and electric activity of the hamstrings and back muscles during Lasègue's test. This information provides a better basis for the interpretation of the test outcome.

Adult↗