| 1. |
- Andersson, Eva A, et al.
(författare)
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Intramuscular EMG from the hip flexor muscles during human locomotion.
- 1997
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Ingår i: Acta Physiologica Scandinavica. - 0001-6772 .- 1365-201X. ; 161:3, s. 361-70
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Tidskriftsartikel (refereegranskat)abstract
- The purpose was to investigate the activation pattern of five major hip flexor muscles and its adaptation to changing speed and mode of progression. A total of 11 healthy subjects performed walking and running on a motor-driven treadmill at speeds ranging from 1.0 to 6.0 m s-1. Intramuscular fine-wire electrodes were used to record myoelectric signals from the iliacus, psoas, sartorius, rectus femoris and tensor fascia latae muscles. The basic pattern, with respect to number of activation periods, remained the same irrespective of speed and mode of progression. However, differences in the relative duration and timing of onset of activation occurred between individual muscles. Over the speed range in walking, a progressively earlier onset was generally seen for the activation period related to hip flexion. Changes in EMG amplitude were measured in the iliacus and psoas muscles and showed a marked increase and difference between walking and running at speeds above 2.0 m s-1. Thus, the alternating flexion-extension movements at the hip during locomotion appear to be governed by a rather fixed 'neural program' which normally only needs minor modulations to accomplish the adjustments accompanying an increase in speed of progression as well as a change from walking to running.
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| 2. |
- Carlson, H, et al.
(författare)
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Lumbar back muscle activity during locomotion : effects of voluntary modifications of normal trunk movements.
- 1988
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Ingår i: Acta Physiologica Scandinavica. - 0001-6772 .- 1365-201X. ; 133:3, s. 343-53
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Tidskriftsartikel (refereegranskat)abstract
- The mechanisms of adaptation of the trunk to changed mechanical conditions were studied during locomotion in man. The myoelectrical (EMG) activity in lumbar back muscles and the movements of the trunk were recorded in nine healthy subjects during walking and running on a motor-driven treadmill. Two different types of voluntary modifications of the movement pattern were used: (1) The trunk was kept in an extreme forward or backward tilted position. In both these situations the basic EMG pattern with two periods of activity per stride cycle was maintained during walking, whereas a major shift relative to the stride cycle (25% of the stride cycle duration) occurred in running with the trunk tilted backwards. The synchrony of the back muscle activation at both sides increased when locomotion was performed with the trunk tilted forwards. The relative duration of the EMG bursts was similar to normal locomotion and corresponded to 15-26% of the stride cycle duration in walking and 23-37% in running. (2) In the other type of modification the subjects were instructed to exaggerate the angular trunk movements either in the sagittal or in the frontal plane. The basic EMG pattern and phase relationships remained in most cases unchanged. One exception was running with exaggerated lateral movements, in which only one period of back muscle activity per stride cycle was observed. The relative duration of the bursts was longer in trials with exaggerated trunk movements as compared to normal locomotion. In walking and running with the trunk tilted forwards or backwards the lumbar back muscles were not always involved as prime movers of the trunk. This was in contrast to the more dynamic situations, in which the back muscle activity appeared to be directly involved in braking and reversing the exaggerated trunk movements.
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| 3. |
- Cresswell, A G, et al.
(författare)
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Observations on intra-abdominal pressure and patterns of abdominal intra-muscular activity in man.
- 1992
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Ingår i: Acta Physiologica Scandinavica. - 0001-6772 .- 1365-201X. ; 144:4, s. 409-18
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Tidskriftsartikel (refereegranskat)abstract
- The aim was to investigate possible relationships between activities of the individual muscles of the ventrolateral abdominal wall and the development of pressure within the abdominal cavity. Intra-muscular activity was recorded bilaterally from transversus abdominis, obliquus internus, obliquus externus and rectus abdominis with fine-wire electrodes guided into place using real-time ultrasound. Intra-abdominal pressure was measured intragastrically using a micro tip pressure transducer. Six males were studied during loading and movement tasks with varied levels of intra-abdominal pressure. During both maximal voluntary isometric trunk flexion and extension, transversus abdominis activity and intra-abdominal pressure remained constant, while all other abdominal muscles showed a marked reduction during extension. When maximal isometric trunk flexor or extensor torques were imposed upon a maximal Valsalva manoeuvre, transversus abdominis activity and intra-abdominal pressure remained comparable within and across conditions, whereas obliquus internus, obliquus externus and rectus abdominis activities either markedly increased (flexion) or decreased (extension). Trunk twisting movements showed reciprocal patterns of activity between the left and right sides of transversus abdominis, indicating an ability for torque development. During trunk flexion--extension, transversus abdominis showed less distinguished changes of activity possibly relating to a general stabilizing function. In varied pulsed Valsalva manoeuvres, changes in peak intra-abdominal pressure were correlated with mean amplitude electromyograms of all abdominal muscles, excluding rectus abdominis. It is concluded that the co-ordinative patterns shown between the muscles of the ventrolateral abdominal wall are task specific based upon demands of movement, torque and stabilization. It appears that transversus abdominis is the abdominal muscle whose activity is most consistently related to changes in intra-abdominal pressure.
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| 4. |
- Grillner, S, et al.
(författare)
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Intra-abdominal pressure changes during natural movements in man.
- 1978
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Ingår i: Acta Physiologica Scandinavica. - 0001-6772 .- 1365-201X. ; 103:3, s. 275-83
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Tidskriftsartikel (refereegranskat)abstract
- The weight of the upper part of the trunk is partially transmitted to the pelvis via the vertebral column. If the muscle walls around the abdominal cavity are contracted, a high pressure can be generated within the cavity (greater than 200 mmHg). The abdominal space can them transmit part of weight to, e.g., the upper part of the body, Intra-abdominal pressure recordings have been performed during locomotion and other natural movements with intragastric pressure recordings. With each step, there is a phasic variation in pressure, with its peak coinciding with that of the peak vertical force exerted by the leg against the ground. The peak values increase progressively with the speed of walking/running up to a mean of 38 mmHg and with trough values of 16 mmHg. The phasic variations with each step is due to a phasic activation of the abdominal muscles, with an EMG activity starting 50 ms or more before foot contact. If an extra load is put on the back, the posture changes and at the highest speed of running the pressure values are significantly higher than without this additional load. After a jump down from a moderate height of 0.4 m, the average increase is 89 mmHg and can often exceed 100 mmHg. These pressure changes are large and will presumably act to unload the spine under the prevailing biomechanical conditions and, in addition, there will no doubt be an effect on the circulatory system.
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| 5. |
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| 6. |
- Hultén, B, et al.
(författare)
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Relationship between isometric endurance and fibre types in human leg muscles.
- 1975
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Ingår i: Acta Physiologica Scandinavica. - 0001-6772 .- 1365-201X. ; 93:1, s. 135-8
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Tidskriftsartikel (refereegranskat)abstract
- Relationship between isometric endurance performance at 50% of maximal voluntary isometric contraction (MCV) and skeletal muscle fibre composition has been elucidated in 19 physical education students. This was found to be linear and the equation corresponded to: y=9.35 + 1.093x; r=0.70 (endurance time expressed in seconds and fibre composition as percent slow twitch muscle fibres (ST) of the vastus lateralis muscle). As it is assumed from previous studies that similar isometric tensions preferentially recruit fast twitch muscle fibres (FT) and that the muscle at the point of exhaustion exhibits maximal values for lactate accumulation, it is suggested that lactate formed in FT fibres is released and stored in nonrecruited ST fibres. The ability to sustain similar isometric tension would then be depending on how large the fraction of ST fibres is that can serve as a lactaterecipient for lactate producing FT fibres.
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| 7. |
- Karlsson, J, et al.
(författare)
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LDH isozymes in skeletal muscles of endurance and strength trained athletes.
- 1975
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Ingår i: Acta Physiologica Scandinavica. - 0001-6772 .- 1365-201X. ; 93:2, s. 150-6
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Tidskriftsartikel (refereegranskat)abstract
- Muscle biopsy samples were obtained from arm and leg muscles of endurance and strength trained athletes, respectively. Total LDH activity as well as occurrence and activity of LDH isozymes were determined. Comparing the results from the athletes with those from non-trained subjects with corresponding fibre compositions, it was found that the endurance athletes had a lower total LDH activity, a higher relative activity of the most heart-specific isozymes. LDH (1 + 2), and, on electrophoretic separation, a complete absence of LDH (4 + 5) in both arm and leg muscles. As compared to the untrained material the strength trained athletes tended to have a higher total LDH activity, a similar distribution of relative isozyme activities, and, in the leg muscles, a strong electrophoretic band corresponding to LDH 5, the most skeletal muscle specific isozyme.
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| 8. |
- Komi, P V, et al.
(författare)
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Skeletal muscle fibres and muscle enzyme activities in monozygous and dizygous twins of both sexes.
- 1977
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Ingår i: Acta Physiologica Scandinavica. - 0001-6772 .- 1365-201X. ; 100:4, s. 385-92
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Tidskriftsartikel (refereegranskat)abstract
- Significance of the genetic component in determining the interindividual variation observed in skeletal muscle fibre composition and enzyme activities was investigated in 31 pairs of male and female monozygous (MZ) and dizygous (DZ) twins, whose ages ranged in all but one pair (11 years) from 15 to 24 years. Percent distribution of slow twitch muscle fibres and activities of Ca2+ and Ng2+ stimulated ATPases, creatine phosphokinase, myokinase, phosphorylase, lactate dehydrogenase (LDH) and distribution of its isozyme LDH-1 were all analyzed in biopsy samples taken from the vastus lateralis muscle. The data disclosed that in contrast to DZ twins the MZ twins of both sexes had an essentially identical muscle fibre composition. Calculation of the heritability estimate for this parameter gave the values of 99.5% and 92.8%, respectively for males and females. In contrast to the fibre composition presence of a significant genetic component was not observed in any of the enzyme activities studied. It was concluded that there is a predominant genetic influence on the skeletal muscle fibre composition in man, and thus also on the potential capacity of the muscles to perform work.
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| 9. |
- Löscher, W N, et al.
(författare)
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Electromyographic responses of the human triceps surae and force tremor during sustained submaximal isometric plantar flexion.
- 1994
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Ingår i: Acta Physiologica Scandinavica. - 0001-6772 .- 1365-201X. ; 152:1, s. 73-82
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Tidskriftsartikel (refereegranskat)abstract
- The objective was to investigate electromyographic activity (EMG) and isometric force tremor (IFT) changes during a sustained sub-maximal isometric contraction in two muscles acting upon the same joint but differing in muscle fibre composition. Surface and intra-muscular EMG activity from the gastrocnemius and soleus muscles and IFT were recorded during an exhausting isometric plantar flexion (30% of maximal voluntary contraction). Surface EMG amplitude (RMS) of both gastrocnemius and soleus muscles increased significantly over time. Gastrocnemius EMG RMS increased in a non-linear fashion while soleus EMG RMS increased linearly. A significant linear decrease of surface EMG mean power frequency (MPF) was observed over time for both muscles. The decrease in gastrocnemius MPF was significantly greater than that for soleus. Intra-muscular EMG results showed similar trends. Correlations of intramuscular EMG RMS and MPF with time were, however, characterized by lower correlation coefficients than those from the surface EMG. Isometric force tremor RMS significantly increased non-linearly with duration of contraction, while IFT MPF showed a significant linear decrease with time. Changes in surface EMG RMS were correlated to changes seen in IFT RMS, in particular, for the predominantly fast twitch gastrocnemius muscle. Correlation coefficients of surface EMG MPF and IFT MPF were lower than RMS correlations. The associated changes in IFT and EMG with fatigue indicate alterations in motor unit firing rate, recruitment and synchronization. The muscle specificity of the EMG and IFT changes suggests a coupling to muscle fibre type composition, although differences in the relative force contribution of each muscle could also affect the results.
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| 10. |
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