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Biomedical subjects

H Rehfeldt

Publications and source records attributed to H Rehfeldt.

At least 19 recordsLinked to original sources
PubMed1992

Fatigue during sustained maximal voluntary contraction of different muscles in humans: dependence on fibre type and body posture.

Nine healthy men, aged between 25 and 35 years, performed sustained maximal voluntary contractions (MVC) of foot plantar, foot dorsal, and finger flexor muscles. Contractions lasted 10 min and were followed by short test contractions at 30% MVC during recovery. Two positions of the working extremity high or low were established by different body postures (supine or sitting). Under these conditions, studies of force, integrated electromyogram (iEMG), blood pressure, and heart rate showed firstly that force decreased throughout the first few minutes of maximal contraction but reached a near steady-state value after 5 to 6 min. Secondly, force decay and steady-state level depended on muscle group and body position. When sitting (low leg), muscles with a high incidence of slow twitch fibres (plantar flexors) showed a slower force decay and a higher relative steady-state force than fast dorsal flexor muscles. When supine (high leg), plantar and dorsal flexor muscles reached about the same low level of relative steady-state force. Changes in iEMG, blood pressure, and heart rate did not differ in the two positions. Thirdly, during recovery, plantar flexor muscles showed higher iEMG values as well as higher values of blood pressure and heart rate when supine than when sitting. Recovery of dorsal flexor muscles was little affected by body posture. Fourthly, force development and recovery of predominantly fast finger flexor muscles were almost independent of arm position. It was concluded that muscle fibre composition was the main factor in determining endurance capacity. However, endurance was influenced by changes in the hydrostatic blood pressure component.(ABSTRACT TRUNCATED AT 250 WORDS)

Adult↗
PubMed1990

[Sex- and age-related differences in blood pressure response to local muscular work during noise].

During noise exposure (90 dB [A]) and during local muscular work (30% MVC) combined with noise (90 db [A]) the blood pressure was measured in 20 men and 20 women (20-29 years; 30-39 years). In the group of younger subjects the blood pressure was taken also during the recovery period of 60 minutes. Age- and sex-related differences in blood pressure response were observed not only during noise exposure but also during combined exposure. The different return of the diastolic blood pressure to the resting value after the period of combined exposure referred to sex-related differences in the response of the cardiovascular system during the recovery period, too.

Adult↗
PubMed1989

[Local muscle work and noise and their effect on the amplitude of the finger pulse].

The finger pulse amplitude of 10 healthy men (aged 20 to 30 years) was measured during noise (70, 80 and 90 dBA) and combined exposure (local muscular work with 30% MVC and noise with 70, 80 or 90 dBA) and during a recovery phase of 60 min. The finger pulse amplitude was reduced only during noise exposure with 90 dBA and was increased during the combined exposures. A continuous decrease of the finger pulse amplitude was observed during the recovery phases. Differences between noise exposure and combined exposure do not exist. The findings were discussed as the risk of hypertension in workers exposed to noise.

Adult↗
PubMed1989

Force, endurance time, and cardiovascular responses in voluntary isometric contractions of different muscle groups.

A study was made to reinvestigate the general validity of the force/endurance relation of isometric contractions. Relative force development, mean bioelectrical muscle activity and circulatory responses (blood pressure, interbeat interval) during isometric contractions of different muscle groups were compared. 6 men performed maximum isometric contractions of foot plantar- and dorsalflexors and hand flexors lasting 10 minutes. The hydrostatic blood pressure was varied by placing subject's arms and legs in two different positions, high and low. 9 Women performed plantarflexion and dorsalflexion with maximum strength and at constant load of 60% MVC to exhaustion. The results confirm that the force/endurance relationship during isometric exercise is not a biological constant, applicable for all muscles. The fibre composition of the muscle and the blood pressure varied by different hydrostatic components are discussed as factors causing differences in force/endurance relationship.

Adult↗
PubMed1983

Physiological responses to sustained isometric contractions during one- and two-armed work. Role of muscle mass on cardiovascular responses to isometric work.

Cardiovascular and ventilatory responses were investigated during one- and two-armed isometric contractions at the same level of maximum voluntary contraction force (MVC). Significant differences were observed in heart rate, blood pressure, pulse arrival time, and oxygen intake in the contractions as compared with each other. These findings contradict the generally accepted view that cardiovascular responses at the same relative force in isometric muscle contractions, irrespective of the size of muscle mass engaged, are equal.

Adult↗
PubMed1983

The measurement of K+e concentration changes in human muscles during volitional contractions.

Changes of extracellular potassium concentration [( K+]e) were measured in human muscles during volitional isometric contractions using liquid ion-exchanger electrodes. In principle, an intramuscular injection needle containing a microelectrode with a side-pore was inserted into the brachioradialis muscle. After insertion of the needle, the glass ion-selective microelectrode (ISM) could be moved out of the protective trocar shield into the muscle tissue. The average values of [K+]e in human muscles during maximal effort rose from 4.5 mmol/l K+ to 9.5 mmol/l K+. These values correspond closely to those previously found in muscles of experimental animals.

Extracellular Space↗
PubMed1982

[Analysis of relationships between physiologic time series in various force loads].

The described analysis of physiological time series gives an example of how the relations between such series can be computed. We had performed force-varied isometric hand-grip contractions. After testing the corresponding prerequisites we investigated the interrelations between the force-induced responses of heart rate, blood pressure, pulse-transit time and force.

Blood Pressure↗