| 21. |
- Tveit, P, et al.
(författare)
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Erector spinae lever arm length variations with changes in spinal curvature.
- 1994
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Ingår i: Spine. - 0362-2436 .- 1528-1159. ; 19:2, s. 199-204
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Tidskriftsartikel (refereegranskat)abstract
- Magnetic resonance imaging was used to study the effect of different curvatures in the lumbar spine on lever arm lengths of the erector spinae musculature. Eleven subjects were instructed to simulate static lifts while lying supine in a magnetic resonance camera with the lumbar spine either in kyphosis or lordosis. A sagittal image of the spine was obtained to analyze the lumbosacral angle and to guide the imaging of transverse sections through each disc (L1/L2 to L5/S1). Images were analyzed for lever arm lengths of the erector spinae muscle (ES) and the erector spinae aponeurosis (ESA), the latter functioning as a tendon for superiorly positioned ES muscle portions. The lumbosacral angle (between superior surfaces of S1 and L4) averaged 44 degrees in the lordosed, 26 degrees in the kyphosed and 41 degrees in a neutral supine position. In lordosis, the lever arm lengths were significantly longer than in kyphosis for all levels, averaging 60-63 mm (ES) and 82-86 mm (ESA). The corresponding values for kyphosis were 49-57 mm (ES) and 67-77 mm (ESA), respectively. Thus, there was a considerable effect (10-24%) of lumbar curvature on lever arm lengths for the back extensor muscles. The change in leverage will affect the need for extensor muscle force and thus the magnitude of compression in the lumbar spine in loading situations such as lifting.
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| 22. |
- Westing, Stephen, et al.
(författare)
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Effects of electrical stimulation on eccentric and concentric torque-velocity relationships during knee extension in man
- 1990
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Ingår i: Acta Physiologica Scandinavica. - 0001-6772 .- 1365-201X. ; 140, s. 17-22
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Tidskriftsartikel (refereegranskat)abstract
- The purpose of this study was to examine the effects of electrical stimulation on torque output during knee extension. Nine well-trained males (19-43 years) performed maximal voluntary, electrically evoked and superimposed eccentric and concentric knee extensions at velocities of 60, 180 and 360 degrees s-1, plus an isometric test (torque was always recorded at a 60 degree knee angle). Fifty-hertz stimulation was applied percutaneously at the maximum tolerated voltage (140-200 V). By superimposing electrical stimulation, eccentric torque could be increased by an average of 21-24% above the voluntary level (P less than 0.05). No corresponding differences were observed between superimposed and voluntary torques under isometric or concentric conditions. Electrically evoked torque also exceeded voluntary torque under eccentric conditions (11-12%, P less than 0.05), but was less under isometric and concentric conditions (-10 to -52%, P less than 0.05). Within the limitations of the study, it was concluded that eccentric knee extension torque under maximal voluntary conditions does not represent the maximal torque-producing capacity. The action of a neural inhibitory mechanism was proposed as an explanation for this finding. If active, this mechanism may protect against the extreme muscle tension that could otherwise develop under truly maximal eccentric conditions.
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| 23. |
- Westing, S H, et al.
(författare)
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Muscle activation during maximal voluntary eccentric and concentric knee extension.
- 1991
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Ingår i: European Journal of Applied Physiology and Occupational Physiology. - 0301-5548 .- 1432-1025. ; 62:2, s. 104-8
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Tidskriftsartikel (refereegranskat)abstract
- The aim of this investigation was to study the relationships among movement velocity, torque output and electromyographic (EMG) activity of the knee extensor muscles under eccentric and concentric loading. Fourteen male subjects performed maximal voluntary eccentric and concentric constant-velocity knee extensions at 45, 90, 180 and 360 degrees.s-1. Myoelectric signals were recorded, using surface electrodes, from the vastus medialis, vastus lateralis and rectus femoris muscles. For comparison, torque and full-wave rectified EMG signals were amplitude-averaged through the central half (30 degrees-70 degrees) of the range of motion. For each test velocity, eccentric torque was greater than concentric torque (range of mean differences: 20%-146%, P less than 0.05). In contrast, EMG activity for all muscles was lower under eccentric loading than velocity-matched concentric loading (7%-31%, P less than 0.05). Neither torque output nor EMG activity for the three muscles changed across eccentric test velocities (P greater than 0.05). While concentric torque increased with decreasing velocity, EMG activity for all muscles decreased with decreasing velocity (P less than 0.05). These data suggest that under certain high-tension loading conditions (especially during eccentric muscle actions), the neural drive to the agonist muscles was reduced, despite maximal voluntary effort. This may protect the musculoskeletal system from an injury that could result if the muscle was to become fully activated under these conditions.
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| 24. |
- Westing, Stephen, et al.
(författare)
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Isoacceleration: a new concept of resistive exercise
- 1991
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Ingår i: Medicine & Science in Sports & Exercise. - 0195-9131 .- 1530-0315. ; 23:5, s. 631-635
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Tidskriftsartikel (refereegranskat)abstract
- This study presents the concept of constant (iso-) accelerative and decelerative exercise and compares concentric and eccentric torque output during isoaccelerative and isodecelerative movements with that during comparable constant velocity (isokinetic) conditions. Twelve men (19-42 yr) performed maximal voluntary concentric and eccentric knee extensions at velocities of 120 and 240 degrees.s-1 (isokinetic) and at accelerations of 180 and 720 degrees.s-2 (both isoaccelerative and isodecelerative) between 10 degrees and 90 degrees knee angles. At 50 degrees, the 180 and 720 degrees.s-2 tests had velocities of 120 and 240 degrees.s-1, respectively, and thus torque comparisons could be made at a corresponding position and velocity. No difference was seen among the isoaccelerative, isodecelerative, or isokinetic angle- and velocity-specific torques for either the concentric or eccentric tests (P greater than 0.05). The results demonstrated that, under conditions of maximal voluntary effort, movement speed as such (within the range studied) was the essential determinant of muscle force--not whether this speed was attained during accelerative, decelerative, or constant velocity movements. As a testing and training modality, the controlled acceleration technique, particularly eccentric deceleration and concentric accleration, appears to offer advantages as compared with existing methods, since it more faithfully reflects the contraction conditions during natural strength-requiring movements.
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| 25. |
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| 26. |
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| 27. |
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| 28. |
- Åstrand, PO
(författare)
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J.B. Wolffe Memorial Lecture. "Why exercise?".
- 1992
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Ingår i: Medicine & Science in Sports & Exercise. - 0195-9131 .- 1530-0315. ; 24:2, s. 153-62
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Tidskriftsartikel (refereegranskat)abstract
- There is a pronounced plasticity and adaptability in the structural and/or functional properties of cells, tissues, and organ systems in the human body when exposed to various stimuli. While there is unanimous agreement that regular exercise is essential for optimal function of the human body, it is evident that extrinsic factors, such as diet and exercise habits, are reflected in the morbidity and mortality statistics, especially in the aged. Aging is obligatorily associated with reduced maximal aerobic power and reduced muscle strength, i.e., with reduced physical fitness. As a consequence of diminished exercise tolerance, a large and increasing number of elderly persons will be living below, at, or just above "thresholds" of physical ability, needing only a minor intercurrent illness to render them completely dependent. Physical training can readily produce a profound improvement of functions essential for physical fitness in old age. Adaptability to regular physical activity serves to cause less disruption of the cell's "milieu interieur" and minimizes fatigue, thereby enhancing performance and the economy of energy output during exercise.
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| 29. |
- Åstrand, PO
(författare)
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Physical activity and fitness.
- 1992
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Ingår i: American Journal of Clinical Nutrition. - 0002-9165 .- 1938-3207. ; 55:6 Suppl, s. 1231S-1236S
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Tidskriftsartikel (refereegranskat)abstract
- There is unanimous agreement that regular exercise is essential for optimal function of the human body. It is evident that extrinsic factors, such as diet and exercise habits, are reflected in the morbidity and mortality statistics, especially in aging. Aging is obligatorily associated with reduced maximal aerobic power and reduced muscle strength, ie, with reduced physical fitness. As a consequence of diminished exercise tolerance, a large and increasing number of elderly people will be living below, at, or just above "thresholds" of physical ability, needing only a minor intercurrent illness to render them completely dependent. Physical training can readily produce a profound improvement of functions also essential for physical fitness in old age. From a nutritional viewpoint one advantage of physical activity, and increased metabolic rate, is that a higher energy intake can better secure an adequate intake of essential nutrients.
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