| 1. |
- Drake, Anna Maria, et al.
(författare)
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Reliability of isokinetic ankle dorsiflexor strength measurements in healthy young men and women
- 1999
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Ingår i: Scandinavian Journal of Rehabilitation Medicine. - : Informa UK Limited. - 0036-5505 .- 1940-2228. ; 31:4, s. 229-239
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Tidskriftsartikel (refereegranskat)abstract
- The purposes of this study were: (i) to determine the test-retest reliability of isokinetic ankle dorsiflexor strength measurements in young healthy adults using the Biodex dynamometer, and (ii) to examine several statistical measures for the interpretation of reliability. Thirty men and women (mean age 23 +/- 3 years) performed three maximal concentric contractions at 30 degrees/s, 60 degrees/s, 90 degrees/s, 120 degrees/s and 150 degrees/s. Reliability of peak torque, work and torque at a specific time were assessed by calculating the intraclass correlation coefficient (ICC 2,1), Pearson product moment correlation coefficient (r), standard error of the measurement (SEM), method error (ME) and coefficient of variation (CV), and by plotting the differences between observations against their means. Isokinetic tests of ankle dorsiflexor strength in healthy young adults using the Biodex dynamometer were highly reliable (ICC 0.61-0.93). It is recommended that test-retest reliability analyses include the ICC and assessments of measurement errors (SEM, ME or CV), as well as graphs to indicate any systematic variations in the data.
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| 2. |
- Lexell, Jan, et al.
(författare)
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A morphometrical comparison of right and left whole human vastus lateralis muscle: how to reduce sampling errors in biopsy techniques
- 1991
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Ingår i: Clinical Physiology. - 1365-2281 .- 0144-5979. ; 11:3, s. 271-276
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Tidskriftsartikel (refereegranskat)abstract
- In studies of the effects of different training programmes, one muscle--most commonly the vastus lateralis--is used for the experiment while the contralateral muscle serves as a control, at the same time as muscle biopsies are taken from both sides. In order to increase the reliability of such studies, the sources and the magnitude of the sampling errors in the biopsy techniques need to be assessed in detail. In this study, cross-sections of whole right and left vastus lateralis muscle from six young sedentary right-handed men were prepared, and the total number and size of fibres and the proportion of the different fibre types were calculated. A significant difference (P less than 0.05-P less than 0.001) between the right and the left muscle was found for at least one of the three variables in each of the six men, but there was no systematic difference and, therefore, no significant right-left difference for the whole group. The maximum difference between the right and the left side for the mean fibre size was 25% and for the fibre type proportion 5%; these differences are much smaller than the known variation within individual muscles. In conclusion, any study involving biopsies from both the right and the left vastus lateralis may use either muscle for the experiment while the contralateral muscle serves as a control without leading to systematic sampling error, whereas the errors involved in taking small samples from each muscle are much more important to control and to reduce.
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| 3. |
- Lexell, Jan
(författare)
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Ageing and human muscle : observations from Sweden
- 1993
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Ingår i: Canadian Journal of Applied Physiology. - : Canadian Science Publishing. - 1066-7814 .- 1543-2718. ; 18:1, s. 2-18
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Tidskriftsartikel (refereegranskat)abstract
- The purposes of this review are to summarize studies of cross-sections of autopsied whole muscles from previously physically healthy males and to focus on the cause of the ageing atrophy. The ageing atrophy begins around 25 years of age and thereafter accelerates. This is caused mainly by a loss of muscle fibres, and to a lesser extent by a reduction in fibre size, mostly of the proportion of the fibre area in the muscle cross-section occupied by type 2 (fast-twitch) fibres. In muscle from old subjects, there is a significant increase in the number of enclosed fibres, indicating an increased incidence of fibre type grouping, a loss of motor neurons in the spinal cord, and a reduction in the number of functioning motor units. These findings strongly suggest a combination of a progressive denervation process and an altered physical activity level as the two major mechanisms underlying the effects of normal ageing on human muscle. These changes have obvious implications for old individuals and their participation in physical activity and in sports, which must be accommodated in rehabilitation regimes or in training programmes.
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| 4. |
- Lexell, Jan, et al.
(författare)
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Differences in fiber number and fiber type proportion within fascicles : A quantitative morphological study of whole vastus lateralis muscle from childhood to old age.
- 1992
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Ingår i: Anatomical Record. - : Wiley. - 0003-276X .- 1097-0185. ; 234:2, s. 183-189
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Tidskriftsartikel (refereegranskat)abstract
- Data are presented on the number of fibers and the proportion of different fiber types within fascicles of whole vastus lateralis muscles from 5 male children, 5 to 15 years of age, and compared with results from 25 male adults, middle aged and old individuals. The results verify a difference in the proportion of fibers with different properties within a fascicle. The proportion of type 2 (fast twitch) fibers on the border of fascicles is larger than the proportion internally: the children have (P less than 0.01) greater difference than the adults and the middle aged, whereas the old have (P less than 0.001) less difference than the other age groups. The mean number of fibers per fascicle increases (P less than 0.05) from childhood to adult age, and thereafter reduces (P less than 0.01). The results imply that fascicles continuously rearrange during the normal growth and development and the normal aging process. It is argued that the causes of the difference in fiber type proportions within fascicles are local factors in the muscle, secondary to the overall age related functional demands put on the fiber population.
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| 5. |
- Lexell, Jan, et al.
(författare)
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Effects of strength training in elderly women
- 1992
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Ingår i: Journal of the American Geriatrics Society. - : Wiley. - 0002-8614 .- 1532-5415. ; 40:2, s. 190-191
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Tidskriftsartikel (refereegranskat)
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| 6. |
- Lexell, Jan
(författare)
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Effekter av styrke- och uthållighetsträning på skelettmuskulaturen hos äldre. Gamla muskler blir som nya!
- 1999
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Ingår i: Läkartidningen. - 0023-7205 .- 1652-7518. ; 96:3, s. 207-209
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Tidskriftsartikel (refereegranskat)abstract
- A well-known effect of increasing age is the gradual reduction of muscle function, and thus of performance in the activity of daily living. Recent research has shown that, even among the very elderly, exercise can improve not only strength and endurance, but also balance and mobility, thus reducing the risk of falls. The possibility of counteracting some of the age-related muscle changes has also been demonstrated. The article reviews current knowledge of strength and endurance training in the elderly, the importance of exercise to improve physical performance, and how lifelong exercise can counteract the effects associated with the ageing of the neuromuscular system.
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| 7. |
- Lexell, Jan
(författare)
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Evidence for nervous system degeneration with advancing age
- 1997
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Ingår i: Journal of Nutrition. - 1541-6100 .- 0022-3166. ; 127:5, s. 1011-1013
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Tidskriftsartikel (refereegranskat)abstract
- Human skeletal muscle undergoes major structural and functional changes with advancing age. A progressive degeneration of the nervous system is now considered a major factor underlying these alterations. This review will briefly describe the changes that occur in the human motor unit with increasing age and focus specifically on the changes that relate to a degeneration of the nervous system.
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| 8. |
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| 9. |
- Lexell, Jan, et al.
(författare)
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Fibre type composition of rabbit tibialis anterior and extensor digitorum longus muscles
- 1994
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Ingår i: Journal of Anatomy. - 0021-8782 .- 1469-7580. ; 185:Pt 1, s. 95-101
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Tidskriftsartikel (refereegranskat)abstract
- Rabbit tibialis anterior (TA) and extensor digitorum longus (EDL) muscles are used extensively in studies of stimulation-induced fibre type transformation, but the proportions and sizes of the 2 main fibre types, and the way in which they are distributed within the muscles, have never been described in any detail. In this study, transverse sections were processed by enzyme histochemical and immunohistochemical techniques and assessed morphometrically. The data were analysed by multivariate methods. In both TA and EDL muscles, the proportion of type 1 fibres varied significantly, and to a similar extent, within a cross-section, from lateral to medial and from superficial to deep parts. The fibre density, an indirect estimate of the mean muscle fibre area, also varied significantly, but not systematically, within a cross-section. For the EDL muscle, the proportion of type 1 fibres was consistently higher in the distal than in the proximal part of the muscle. The proportion of type 1 fibres was also significantly higher in the EDL than in the TA muscle for each of the 6 rabbits. There was no systematic variation between muscles from left and right limbs. The type proportions and fibre densities for both TA and EDL muscles differed significantly between individual rabbits, but not between sexes. The study provides a database that has hitherto been lacking on normal fibre type composition and its variation within and between these experimentally important muscles.
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| 10. |
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