Biomedical subjects

T Aminoff

Publications and source records attributed to T Aminoff.

7 recordsLinked to original sources

PubMed2000

Cardiorespiratory responses to fatiguing dynamic and isometric hand-grip exercise.

In occupational work, continuous repetitive and isometric actions performed with the upper extremity primarily cause local muscle strain and musculoskeletal disorders. They may also have some adverse effects on the cardiorespiratory system, particularly, through the elevation of blood pressure. The aim of the present study was to compare peak cardiorespiratory responses to fatiguing dynamic and isometric hand-grip exercise. The subjects were 21 untrained healthy men aged 24-45 years. The dynamic hand-grip exercise (DHGE) was performed using the left hand-grip muscles at the 57 (SD 4)% level of each individual's maximal voluntary contraction (MVC) with a frequency of 51 (SD 4) grips x min(-1). The isometric hand-grip exercise (IHGE) was done using the right hand at 46 (SD 3)% of the MVC. The endurance time, ventilatory gas exchange, heart rate (HR) and blood pressure were measured during both kinds of exercise. The mean endurance times for DHGE and IHGE were different, 170 (SD 62) and 99 (SD 27) s, respectively (P < 0.001). During DHGE the mean peak values of the breathing frequency [20 (SD 6) breaths x min(-1)] and tidal volume [0.89 (SD 0.34) l] differed significantly (P < 0.01) from peak values obtained during IHGE [15 (SD 5) breaths x min(-1) and 1.14 (SD 0.32) l, respectively]. The corresponding peak oxygen consumptions, pulmonary ventilations, HR and systolic blood pressures did not differ, and were 0.51 (SD 0.06) and 0.46 (SD 0.11) l x min(-1), 17.1 (SD 3.0) and 16.7 (SD 4.7) l x min(-1), 103 (SD 18) and 102 (SD 17) beats x min(-1), and 156 (SD 17) and 161 (SD 17) mmHg, respectively. The endurance times of both DHGE and IHGE were short (< 240 s). The results indicate that the peak responses for the ventilatory gas exchange, HR and blood pressure were similar during fatiguing DHGE and IHGE, whereas the breathing patterns differed significantly between the two types of exercise. The present findings emphasize the importance of following ergonomic design principles in occupational settings which aim to reduce the output of force, particularly in tasks requiring isometric and/or one-sided repetitive muscle actions.

Adult↗

PubMed1999

Physiological strain during kitchen work in relation to maximal and task-specific peak values.

Six female and three male subjects from a hospital kitchen volunteered for the study. The subjects were working on a conveyor belt collecting and sorting dirty plates, glasses and cutlery for cleaning. In the study, a medical examination, a maximal clinical exercise test with a 12-lead electrocardiogram (ECG) and a maximal arm cranking test were performed in the laboratory. Further, each subject was studied for 30 min during a normal work shift in the kitchen. Oxygen uptake (VO2) and heart rate (HR) were continuously registered. During the work period, a rating of perceived exertion (RPE) was asked at the 5th, 15th and 30th minute. Physiological responses were measured by a portable system (K4) both in the laboratory and in the field. VO2 and HR measured in the field were proportioned to corresponding maximal values during cycling and to peak values during arm-cranking. The mean VO2 for the male and the female subjects during kitchen work was 0.65 +/- 0.16 l min-1. This corresponded to 24% of VO2max and to 41% of VO2peak during arm-cranking. The difference was significant (p < 0.001). Owing to a magnetic field at the conveyor belt, reliable HR values were obtained only from the female subjects. The mean HR during work among the female subjects was 101 beats min-1. It corresponded to 55% of HRmax and 67% of HRpeak during arm-cranking (p < 0.05). The present study shows that the relative work intensity is markedly higher when it is expressed relative to the corresponding muscle group's VO2peak instead of the VO2max. Similar difference was also seen in the HR response. More task-specific testing of physical capacity may provide improved evaluation of physical strain in a job.

Adult↗

PubMed1998

Heart rate and blood pressure responses to isometric exercise in young and older men.

The aim of this study was to examine the isometric endurance response and the heart rate and blood pressure responses to isometric exercise in two muscle groups in ten young (age 23-29 years) and seven older (age 54-59 years) physically active men with similar estimated forearm and thigh muscle masses. Isometric contractions were held until fatigue using the finger flexor muscles (handgrip) and with the quadriceps muscle (one-legged knee extension) at 20%, 40%, and 60% of the maximal voluntary contraction (MVC). Heart rate and arterial pressure were related to the the individual's contraction times. The isometric endurance response was longer with handgrip than with one-legged knee extension, but no significant difference was observed between the age groups. The isometric endurance response averaged 542 (SEM 57), 153 (SEM 14), and 59 (SEM 5) s for the handgrip, and 276 (SEM 35), 94 (SEM 10) and 48 (SEM 5) s for the knee extension at the three MVC levels, respectively. Heart rate and blood pressure became higher during one-legged knee extension than during handgrip, and with increasing level of contraction. The older subjects had a lower heart rate and a higher blood pressure response than their younger counterparts, and the differences were more apparent at a higher force level. The results would indicate that increasing age is associated with an altered heart rate and blood pressure response to isometric exercise although it does not affect isometric endurance.

Adult↗

PubMed1998

Prediction of acceptable physical work loads based on responses to prolonged arm and leg exercise.

Nine healthy men (aged 54-59 years) performed arm crank and leg cycle exercises for 30 min at relative work loads of 50 and 75% of peak oxygen uptake (VO2) for the corresponding muscle group, and for 60 min at a relative work load of 30% of peak VO2 for the corresponding muscle group. In the tests, heart rate (HR), blood pressure, gas exchange variables, rating of perceived exertion (RPE) and blood lactate were measured. At the 75% target exercise level, four subjects interrupted the arm-cranking test, and one subject interrupted the leg-cycle test. Owing to differences in peak values during arm-cranking and leg-cycling, the work load and the VO2 were higher during leg-cycling than during arm-cranking. There was no difference in HR between the work modes, but the HR increased to a greater extent during arm-cranking compared to leg-cycling at the 30% (NS) and 50% (P < 0.05) exercise levels. Similarly, the RPE increased more during arm-cranking compared to leg-cycling at each exercise level. The blood lactate concentration was higher after arm-cranking than after leg-cycling; at the 50% exercise level the difference was statistically significant. The results indicate a higher physiological strain with time during arm exercise than during leg exercise at the same muscle group-specific relative work load. The acceptable physical work load, expressed as the percentage peak VO2 for the corresponding muscle group, should thus be lower during arm exercise than during leg exercise. The RPE and the relative HR, expressed as percentage of peak HR for the corresponding muscle group, however, seem to be comparable indicators for the physiological strain during arm and leg exercise.

Arm↗

PubMed1997

Cardiorespiratory and subjective responses to prolonged arm and leg exercise in healthy young and older men.

Ten young (aged 23-30 years) and nine older (aged 54-59 years) healthy men with a similar size of limb muscle mass performed arm crank and leg cycle exercise for 30 min at relative exercise intensities of 50% and 75% of maximal oxygen uptake for the corresponding muscle group. In the tests, heart rate, blood pressure, gas exchange variables, rating of perceived exertion and blood lactate concentration were measured. The limb muscle mass was determined by anthropometric measurements. At the 75% target exercise level, four of the older men and two of the young men could not complete the arm-cranking test, and one of the older men and two of the young men could not complete the leg-cycle test. During arm-cranking the absolute exercise intensity was similar for the young and older men because of similar maximal values during arm-cranking. But during leg-cycling the absolute exercise intensity was higher for the young men than for the older men due to the difference in corresponding maximal values. During arm-cranking there were no significant differences in the physiological responses between the age groups except that a higher ventilatory response was noted among the older compared to the young men. During leg-cycling the heart rate values were higher among the young compared to the older men. But, when the heart rate values were expressed as a percentage of maximal heart rate in the corresponding maximal tests, no significant differences between the age groups were found. The results indicated that 30-min of arm or leg exercise at the same relative submaximal exercise intensity produces a similar degree of physiological strain in healthy older compared to young men. During armcranking, the young and the older men exercised at the same external intensity, indicating a similar ability to perform prolonged excercise using smaller muscle groups expressed both in absolute and relative terms.

Adult↗

PubMed1997

Motor control and cardiovascular responses during isoelectric contractions of the upper trapezius muscle: evidence for individual adaptation strategies.

Ten females (25-50 years of age) performed isometric shoulder flexions, holding the right arm straight and in a horizontal position. The subjects were able to see the rectified surface electromyogram (EMG) from either one of two electrode pairs above the upper trapezius muscle and were instructed to keep its amplitude constant for 15 min while gradually unloading the arm against a support. The EMG electrodes were placed at positions representing a "cranial" and a "caudal" region of the muscle suggested previously to possess different functional properties. During the two contractions, recordings were made of: (1) EMG root mean square-amplitude and zero crossing (ZC) frequency from both electrode pairs on the trapezius as well as from the anterior part of the deltoideus, (2) supportive force, (3) heart rate (HR) and mean arterial blood pressure (MAP), and (4) perceived fatigue. The median responses during the cranial isoelectric contraction were small as compared to those reported previously in the literature: changes in exerted glenohumeral torque and ZC rate of the isoelectric EMG signal of -2.81% x min(-1) (P = 0.003) and 0.03% x min(-1) (P = 0.54), respectively, and increases in HR and MAP of 0.14 beats x min(-2) (P = 0.10) and 0.06 mmHg x min(-1) (P = 0.33), respectively. During the contraction with constant caudal EMG amplitude, the corresponding median responses were -2.51% x min(-1) (torque), 0.01% x min(-1) (ZC rate), 0.31 beats x min(-2) (HR), and 0.93 mmHg x min(-1) (MAP); P = 0.001, 0.69, 0.005, and 0.003, respectively. Considerable deviations from the "isoelectric" target amplitude were common for both contractions. Individuals differed markedly in response, and three distinct subgroups of subjects were identified using cluster analysis. These groups are suggested to represent different motor control scenarios, including differential engagement of subdivisions of the upper trapezius, alternating motor unit recruitment and, in one group, a gradual transition towards a greater involvement of type II motor units. The results indicate that prolonged low-level contractions of the shoulder muscles may in general be accomplished with a moderate metabolic stress, but also that neuromuscular adaptation strategies differ significantly between individuals. These results may help to explain why occupational shoulder-neck loads of long duration cause musculoskeletal disorders in some subjects but not in others.

Adaptation, Physiological↗

PubMed1996

Physical work capacity in dynamic exercise with differing muscle masses in healthy young and older men.

Ten young (aged 23-30 years) and nine older (aged 54-59 years) healthy men with similar estimated limb muscle volumes performed, in random order, three different types of ergometer exercise tests (one-arm cranking, two-arm cranking, and two-leg cycling) up to the maximal level. Values for work load (WL), peak oxygen consumption (V0(2)), peak heart rate (HR), peak ventilation (V(E)), respiratory gas exchange ratio (R), recovery blood lactate concentration [La-], and rating of perceived exertion (RPE) were compared between the age-groups in the given exercise modes. No significant age-related differences in WL, peak V0(2), peak HR, R, [La-], or RPE were found in one-arm or two-arm cranking. During one-arm cranking the mean peak V0(2) was 1.65 (SD 0.26)1*min(-1) among the young men and 1.63 (SD 0.10)l*min(-1) among the older men. Corresponding mean peak V0(2) during two-arm cranking was 2.19 (SD 0.32)1*min(-1) and 2.09 (SD 0.18)1*min(-1), respectively. During one-arm cranking peak V(E) was higher (P <0.05) among the older men compared to the young men. During two-leg cycling the young men showed higher values in WL (P <0.001), peak V0(2) (P <0.001), and peak HR (P <0.001). The mean peak V0(2) was 3.54 (SD 0.24)1*min(-1) among the young men and 3.02 (SD 0.20)1 . min(-1) among the older men. Corresponding mean peak HR was 182 (SD 5) beats*min(-1) and 170 (SD 8) beats*min(-1), respectively. During two-leg cycling, peak V(E), R, [La-], and RPE did not differ between the two age-groups. In summary, the older men with similar sizes of estimated arm and leg muscle volumes as the young men had a reduced physical work capacity in two-leg cycling. In one-arm or two-arm cranking, no significant difference in work capacity was found between the age-groups. These results indicate, that in healthy men, age, at least up to the 6th decade of life, is not necessarily associated with a decline in physical work capacity in exercises using relatively small muscle groups, in which the limiting factors are more peripheral than central.

Adult↗