Biomedical subjects

J Winkel

Publications and source records attributed to J Winkel.

8 recordsLinked to original sources

PubMed1992

Can occupational guidelines for work-rest schedules be based on endurance time data?

Within the European Community, work is in progress to establish occupational guidelines for physical workload, including work-rest schedules. A model has been proposed which relies upon endurance time as a valid estimate of the short- and long-term physiological responses to continuous and intermittent exercise. On the basis of recent results from several Scandinavian research groups, the present paper questions the use of this model as a contribution to occupational guidelines. It is believed that the proposed model has a limited validity as a predictor of endurance time, as an indicator of short-term physiological responses, and as an estimator of risk for musculoskeletal disorders.

Adult↗

PubMed1991

Significance of skin temperature changes in surface electromyography.

Differing results have been reported concerning the direction and quantity of the electromyogram (EMG) amplitude response to changes in tissue temperature. The EMG signals from the soleus muscle of six healthy human subjects were therefore recorded during dynamic exercise (concentric contractions) at ambient temperatures of 30 degrees C and 14 degrees C. The mean skin temperature (Tsk) above the muscle investigated was 32.9 degrees C and 21.7 degrees C, respectively. The core temperature, estimated by rectal temperature, was unchanged. The cooling of the superficial tissues caused approximately a doubling of the EMG amplitude. For the probability level 0.9 in the amplitude probability distribution function, the average signal level increased from 73 microV to 135 microV (P = 0.02). The average mean power frequency of the EMG signal was reduced from 142 Hz to 83 Hz (P = 0.004). The amplitude increase was not due to shivering but other possible explanations are presented. As the changes in Tsk investigated were within the range which may occur normally during the working hours, it was concluded that Tsk should be carefully controlled in vocational EMG studies.

Adult↗

PubMed1991

Hand strength: the influence of grip span and grip type.

The maximal force from each of the fingers II-V (FF) and the resultant force between the jaws of the tool (RF), due to contribution from all fingers, were measured using a pair of modified pairs. The RF was measured at 21 handle separations and the FF was measured at seven handle separations for each finger. A traditional grip type was compared with a 'reversed' grip where the little finger was closest to the head of the tool. Sixteen subjects (8 females and 8 males) participated in the study. Both the RF and FF varied according to the distance between the handles. For both grip types, the highest RF was obtained at a handle separation of 50-60 mm for females and 55-65 mm for males. For wide handle separations, the RF was reduced by 10% (cm increase in handle separation). The force-producing ability of the hand was influenced by the grip type and the highest RF was obtained when using the traditional grip. An interaction was found between the fingers, i.e., the maximal force of one finger depended not only on its own grip span, but also on the grip spans of the other fingers. About 35% of the sex difference in hand strength was due to hand size differences.

Adult↗

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↗