Biomedical subjects

Jan Lexell

Publications and source records attributed to Jan Lexell.

7 recordsLinked to original sources

PubMed2003

Structure and function of the ankle dorsiflexor muscles in young and moderately active men and women.

The aim was to investigate determinants of ankle dorsiflexor muscle (DF) strength and size in moderately active young men and women (n = 30; age 20-31 yr). Concentric (Con) and eccentric (Ecc) strength were measured isokinetically. Magnetic resonance imaging was used to determine the muscle cross-sectional area (CSA). Multiple biopsies were obtained from the tibialis anterior muscle to determine total numbers, areas (Area I and II) and proportions (Prop I and II) of type I and II fibers, respectively, and relative contents of myosin heavy chain (MHC) isoforms MHC1, MHC2a, and MHC2x. Women had lower Con and Ecc strength (24 and 27%; P < 0.01), smaller CSA (19%; P < 0.001), lower Ecc DF specific strength (strength/CSA) (10%; P < 0.01), and smaller Area I and Area II (21 and 31%; P < 0.01) than men. Prop I, MHC1, estimated total number of fibers, and Con DF specific strength were similar for both sexes. Con DF strength was up to 72% determined by CSA and Prop I, and Ecc DF strength was up to 81% determined by CSA, Prop I, and sex; variables other than CSA explained at most 9%. Body weight and fiber areas explained >50% of the variation in CSA. In conclusion, CSA was the predominant determinant of DF strength, CSA was to a great extent determined by the body weight and the sizes of muscle fibers, and sex differences in Ecc specific strength require further study.

Adult↗

PubMed2003

Effects of superimposed electrical stimulation on perceived discomfort and torque increment size and variability.

Superimposed electrical stimulation techniques can be used to detect central activation failure (CAF), that is, incomplete central nervous system recruitment or suboptimal activation of motor units. The purpose of this study was to evaluate the effects of two stimulation parameters on perceived discomfort and torque increment size and variability. Discomfort was evaluated using a visual analog scale (0-100 mm) for pain. The rectus femoris muscle of the dominant leg of 24 young healthy men was stimulated during submaximal (80% maximal) voluntary contractions. The size and variability of torque increments and perceived discomfort were assessed following stimulation with: (1) pulse trains (100 HZ, 150 V, 0.2-ms pulse duration) of different lengths (50 ms and 100 ms); and (2) pulse trains (100 HZ, 100 ms, 150 V) with different pulse durations (0.2 ms and 0.1 ms). Pulse trains of 100 ms generated larger torque increments and produced less variability, but caused more discomfort than pulse trains of 50 ms. Average discomfort ratings for pulse trains of 100 ms were 43.1 mm, and of 50 ms were 53.2 mm. There was no difference in torque increment size or in variability between pulse trains with pulse durations of 0.1 ms and 0.2 ms, whereas discomfort was less for the shorter pulse durations; average discomfort ratings were 53.1 mm and 58.1 mm for pulse durations of 0.1 ms and 0.2 ms, respectively. Thus, the appropriate selection of stimulation parameters can reduce discomfort but maintain the ability to detect CAF.

Adult↗

PubMed2002

Assessment of contractile and noncontractile components in human skeletal muscle by magnetic resonance imaging.

A magnetic resonance imaging (MRI) technique for the assessment of contractile and noncontractile components of human skeletal muscle is described, and the inter-rater and intra-rater test-retest reliability for repeated measurements from the same MR image are examined. Twenty cross-sectional MR images from the right lower leg were obtained from 30 healthy young men and women (mean age 24.1 years, SD 3.3). The anatomical cross-sectional area (aCSA; cm2), the cross-sectional area of noncontractile components (Noncon; cm2), the contractile cross-sectional area (cCSA = aCSA minus Noncon; cm2), and the relative amount of Noncon (%), of the ankle dorsiflexor muscle compartment were determined for each slice using a computer-based image analysis system. Reliability for repeated measurements of the slice with the largest aCSA for the 30 subjects was analyzed by two raters on two different occasions. Inter-rater reliability on both occasions, assessed by the intraclass correlation coefficient (ICC), was excellent for cCSA (ICC3.1 = 0.99) and Noncon (ICC(3.1) > 0.82). Intra-rater (between occasions) reliability was excellent for the two raters for measurements of cCSA (ICC1.1 = 0.99) and Noncon (ICC1.1 > 0.94). Bland and Altman analyses did not identify any clinically relevant bias in the measurements. Method errors were acceptable: within subjects coefficients of variation (CV) was less than 1.8% for cCSA and less than 16.3% for Noncon. It is concluded that repeated measurements of contractile and noncontractile components of the ankle dorsiflexor muscle compartment, obtained from the same MR image, are highly reliable.

Adult↗

PubMed2002

Biopsy sampling requirements for the estimation of muscle capillarization.

The aim of this study was to determine the number of tibialis anterior biopsy samples and muscle fibers required to estimate the capillary supply of individual muscle fibers (C:F(i)). C:F(i) was calculated for 25 type 1 fibers in each of 8 images from 3 biopsies of 5 young healthy individuals. Sequential estimation analysis indicated that 50 fibers from one biopsy are sufficient to characterize the C:F(i) of the tibialis anterior for a group of subjects. Thus, when analyzing the capillarization of the tibialis anterior, the requirements of only one biopsy sample and 50 fibers means a great reduction in time for analysis and in the invasiveness of the procedure.

Adult↗

PubMed2002

Serotonin agents in the treatment of acquired brain injury.

BACKGROUND: The development of novel serotonin agents has led to an increased use of these medications throughout medical practice. An understanding of the basic pharmacological function of these agents is key to understanding their usefulness. Among persons with brain injury, serotonin agents have been used for the treatment of depression, panic disorder, obsessive-compulsive disorders, agitation, sleep disorders, and motor dysfunction. CONCLUSION: This article will review the mechanisms, efficacy, and side effects of serotonin agents with a focus on persons with brain injury.

Brain Injuries↗

PubMed2002

Reliability of concentric ankle dorsiflexion fatigue testing.

The purpose of this study was to determine the reliability of an isokinetic test for ankle dorsiflexion fatigue on a Biodex dynamometer. Young (21 to 32 years), recreationally active men (n = 10) and women (n = 10) performed 50 concentric (60 degrees.s-1) dorsiflexion contractions, on two different occasions. Total work (TW), losses in work (work fatigue; WF), as well as relative losses in peak toruqe, an example being "3-3" which compared the first three to last three repetitions, were measured. The intra-class correlation coefficients (ICC2.1) and coefficients of variation (CV), as well as the Bland-Altman plots and analyses showed that the variables using peak torque and TW were more reliable than WF, with WF having a CV of 11.3% and the best peak torque variable, 3-3, having a CV of 5.6%. In conclusion, ankle dorsiflexion fatigue can be reliably assessed on a Biodex dynamometer.

Adult↗

PubMedDate not supplied

Ginseng.

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