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Biomedical subjects

J Winkel

Publications and source records attributed to J Winkel.

30 records · Page 2Linked to original sources
PubMed1991

Quantifying variation in physical load using exposure-vs-time data.

Variation has in recent years become an important concept in the analysis of loads on the locomotor system in occupational life. Studies of controlled variation in isometric exercise have concentrated on the effects of introducing pauses at regular intervals into an otherwise constant load. A complete description of the cyclic character of such regimens requires a set of three parameters. We suggest the use of the set mean load/cycle time/duty cycle. The design of laboratory studies should more often be based upon the activity patterns found in occupational life. In studies observing exposure, the variation concept introduces problems concerning how to define and how to quantify 'variation'. It is shown that present methods (APDF analysis and contraction frequency analysis) individually fail to pick up important aspects of variation. A new method for exposure variation analysis (EVA) is proposed. Examples are presented of EVA performed on vocational EMG registrations.

Ergonomics↗
PubMed1990

Electromyographic activity in the shoulder-neck region according to arm position and glenohumeral torque.

The electromyographical (EMG) response to isometric ramp contractions of the right arm, the left arm, and both arms was studied using four pairs of surface electrodes above the right upper trapezius muscle (UT) of six men and six women. Contractions were made against gravity with the active arm(s) in eight positions, ranging from flexion to abduction. To describe arm positions, new, simple terminology was developed. Root mean square (rms)-converted EMG-signals were normalized (EMGnorm) with respect to a reference contraction. The EMGnorm corresponding to a 15 N.m torque in the right glenohumeral (GH) joint was strongly related to the position of the right arm (P less than 0.001). The shape of this relationship depended on the electrode position (P less than 0.001). The ratio between EMGnorm at 30 N.m and 15 N.m GH torques was related to arm position (P less than 0.001) and differed between electrodes (P less than 0.001). A left-side GH torque resulted in right-side (contralateral) EMG activity, typically corresponding to 20%-30% of that obtained during similar right-side GH torque. Bilateral GH torque implied 0%-50% increase in EMG activity as compared to that obtained with the right arm alone. The results have shown that signals from one pair of surface electrodes above UT cannot be taken as representative of the EMG activity from electrodes located elsewhere above UT. The EMG recordings reflected a complex pattern of muscular activation, significantly related to both outwardly visible factors (arm position, GH torque), and within-body servosystems (motor control reflexes).

Adult↗
PubMed1989

[Why do musculo-skeletal stress injuries increase?].

The innovation of technologies in the industrial countries in recent decades has involved increased physical monotony and inactivity in working life. Parallel to this development the ergonomic quality of work station design has been improved. But the corresponding reduction in physical stress does not seem to diminish the frequency of symptoms from the locomotor system. On the basis of studies carried out in recent years, a U-shaped relationship between physical stress and symptoms is suggested, i.e. frequency of symptoms may increase not only when the physical stress is high but also when it becomes very low. It is concluded that further research on acceptable physical stress should comprise studies aimed not only at upper but also at lower limits, including minimal variation of the physical load.

Bone Diseases↗
PubMed1988

Effects of leg activity and ambient barometric pressure on foot swelling and lower-limb skin temperature during 8 h of sitting.

Prolonged immobilization in an upright position often leads to discomfort and oedema in the feet of otherwise healthy subjects. To determine the significance of leg activity and ambient pressure on oedema formation, skin temperature (Tsk) and discomfort, 6 volunteers sat for 8 h with one leg immobilized and the other spontaneously active; one day at "sea level" (750 mmHg) and one day at reduced barometric pressure (540 mmHg). Foot swelling was measured by water plethysmography. Leg movements were continuously monitored by a Vitalog computer, and foot discomfort was estimated by analog-visual scales. The 8 hour swelling averaged 5.7% in the inactive foot, and 2.7% in the active foot (p less than 0.001). Tsk of the inactive foot levelled off towards ambient temperature (21 degrees C) within 4 h. For the active foot this fall was reduced by 2-3 degrees C (p less than 0.025). The increase in foot discomfort during the day was lowest in the active foot (p less than 0.005). High foot Tsk was associated with a high foot swelling rate. Reduced ambient barometric pressure had no effects on foot swelling or Tsk. It is concluded that modest leg activity during 8 h of sitting has several effects on the circulation in the feet: some effects promote and some prevent oedema formation. However, the net result is a reduction in foot swelling.

Adult↗
PubMed1986

An evaluation of a tiltable office chair with respect to seat height, backrest position and task.

The amount of spontaneous movement during seated office work was estimated by analysing the tilting movements of a tiltable office chair. Both movement frequency and amplitude range were considered. The seat inclinations and subjective acceptability were also recorded. The seat was moved more frequently and with a greater range when adjusted 6 cm above popliteal level compared to 1 cm below, or when the backrest was pushed anteriorly or posteriorly compared to a middle position. The greatest acceptability occurred with the highest seat adjustment and the backrest in the middle position. Typing or desk-work influenced movement to a similar extent.

Adult↗
PubMed1986

Swelling of the foot, its vascular volume and systemic hemoconcentration during long-term constrained sitting.

Swelling of the left foot and changes in its vascular volume (VV) were studied in seven healthy subjects during 8 h of seated work without leg movements. Changes in total plasma volume (PV) were calculated from hematocrit values. Reference values (r.v.) were obtained during a working day requiring intermittent physical activity (walking). Significant changes during the first 4 h: the foot swelled by 3.5% (r.v.: 2.2%) and VV was reduced by 0.5% of the foot volume (r.v.: increased by 0.3%). Accordingly, the interstitial fluid volume (IFV) of the foot increased by 4.0% (r.v.: 1.9%). The loss of PV was 6.3%. During the last 4 h the only significant change was an increase in foot volume by 1.9%. It is concluded that (1) foot swelling should be corrected for changes in VV to obtain an exact measure of the change in IFV, (2) prolonged elevated pressure, assumed to occur in the feet during relaxed sitting, does not imply distension ("delayed compliance") of the vascular system as previously suggested, (3) hemoconcentration seems to reach complete stability during the initial period of quiet sitting, (4) loss of PV during sedentary work may be avoided by a modest increase in leg activity.

Blood Volume↗
PubMed1986

Muscular performance during seated work elevated by two different EMG methods.

As part of a larger ergonomic survey of seated work, the myoelectric activity of soleus and erector spinae was studied during typing and desk work while sitting on three different office chairs. Muscular performance was evaluated by two EMG methods: (1) the frequently used analysis of the amplitude probability distribution function (APDF) of the EMG signals, and (2) a recently presented method which considers muscular contraction frequencies according to the load levels. The latter indicated significant differences in contraction frequencies which did not appear from the APDF. Moreover, the APDF illustrated differences in load levels which were not evident from the frequency analyses. It is suggested that both EMG methods should be used in evaluations of muscular activity.

Adult↗
PubMed1985

Comparison of office chairs with fixed forwards or backwards inclining, or tiltable seats.

Three adjustments of an office chair seat: one inclining +10 degrees (forwards), one inclining -5 degrees (backwards), and one being freely tiltable from -8 degrees to +19.5 degrees were investigated using two groups of healthy female workers in a field (n = 12), and a laboratory study (n = 10), respectively. The seat adjustments were examined with regard to effects on foot swelling, lumbar muscular load, backrest pressure and subjective acceptability. Desk-work and typing were compared according to lumbar muscular activity, seat movements (tiltable seat), and backrest pressure. Foot swelling tended to increase with increasing seat height but was not influenced by the ability to tilt the seat or not. With the different seat adjustments lumbar muscular activity did not change systematically in spite of greater backrest pressure when the seat inclined backwards. The tiltable seat was preferred to the others. Typing was associated with a more constrained and tens posture than desk work, because movements, transferred to the tiltable seat, decreased and the muscular load increased. Backrest pressure was highest during typing. A tendency towards gradually increasing restlessness (i.e. seat movements) and increasing forward inclination of the tiltable seat with time was observed.

Adult↗
PubMed1984

A method for electromyographic analysis of muscular contraction frequencies.

A method for evaluation of muscular contraction frequencies during prolonged work is presented. It is based upon computer-aided electromyographic (EMG) analyses. Variations in muscular tension, expressed as the relative force of contraction or torque in the joint, are followed using previously described EMG techniques. The number of times muscular tension crosses an amplitude band from below is then estimated. The band represents a predetermined range of amplitude. It is moved in steps from the lowest to the highest force level which occurred during the work task, and the frequency of band-crossings is computed for each band position. The frequencies are then plotted against the force levels at which the upper limit of the band was placed. From this relationship a frequency/force index is computed. The analysis is repeated several times using different band-widths. Thus, the method considers the contraction frequencies according to the load levels. It was developed to study the function of the musculo-venous pump in the legs during prolonged sedentary work, but might also be used to analyse such factors as muscular strain during work.

Adult↗