Biomedical subjects
M Kjaer
Publications and source records attributed to M Kjaer.
Determination of markers for collagen type I turnover in peritendinous human tissue by microdialysis: effect of catheter types and insertion trauma.
OBJECTIVES: Previous results from our group have shown that loading of human tendon elevates tendinous type I collagen production measured by microdialysis. However, exclusion of the observed elevation as a response to trauma from inserting the microdialysis catheters or a possible influence from the collagen production in skin was not determined. METHODS: Using the microdialysis method we measured the tissue levels of type I collagen metabolism markers [procollagen I COOH-terminal propeptide (PICP) and COOH-terminal telopeptide of type I collagen (ICTP)] in peritendinous tissue of the Achilles tendon in volunteers at two time points, 0 and 72 h. Using two different catheter types, an investigation of the contribution from the skin in the collagen results obtained was also examined. RESULTS: The data showed no significant changes in the dialysate levels for PICP or ICTP (p>0.05) in either of the catheters. CONCLUSION: Inserting microdialysis fibres around the Achilles tendon twice does not increase the collagen type I metabolism determined 3 days after the initial trauma, and when using microdialysis for measuring peritendinous collagen turnover the skin contribution can be regarded as negligible. These findings support microdialysis as a valid method for the determination of collagen metabolism in peritendinous tissue.
The determination of the three-dimensional structure of barley serine proteinase inhibitor 2 by nuclear magnetic resonance, distance geometry and restrained molecular dynamics.
The solution structure of the 64 residue structured domain (residues 20-83) of barley serine proteinase inhibitor 2 (BSPI-2) is determined on the basis of 403 interproton distance, 34 phi backbone torsion angle and 26 hydrogen bonding restraints derived from n.m.r. measurements. A total of 11 converged structures were computed using a metric matrix distance geometry algorithm and refined by restrained molecular dynamics. The average rms difference between the final 11 structures and the mean structure obtained by averaging their coordinates is 1.4 +/- 0.2 A for the backbone atoms and 2.1 +/- 0.1 A for all atoms. The overall structure, which is almost identical to that found by X-ray crystallography, is disc shaped and consists of a central four component mixed parallel and antiparallel beta-sheet flanked by a 13 residue alpha-helix on one side and the reactive site loop on the other.
Comparison of the solution and X-ray structures of barley serine proteinase inhibitor 2.
A comparison of the solution n.m.r. structures of barley serine protease inhibitor 2 (BSPI-2) with the X-ray structures of both subtilisin complexed and native BSPI-2 is presented. It is shown that the n.m.r. and X-ray structures are very similar in terms of overall shape, size, polypeptide fold and secondary structure. The average atomic rms difference between the 11 restrained dynamics structures on the one hand and the two X-ray structures on the other is 1.9 +/- 0.2 A for the backbone atoms and 3.0 +/- 0.3 A for all atoms. The corresponding values for the restrained energy minimized mean dynamics structure are 1.5 and 2.4 A, respectively.
Biomechanical responses to repeated stretches in human hamstring muscle in vivo.
To examine stiffness, energy, and passive torque in the dynamic and static phases of a stretch maneuver in the human hamstring muscle in vivo we used a test-retest protocol and a repeated stretches protocol. Resistance to stretch was defined as passive torque (in newton-meters) offered by the hamstring muscle group during passive knee extension as measured using an isokinetic dynamometer with a modified thigh pad. In 13 uninjured subjects, the knee was passively extended to a predetermined final position (0.0875 rad/ sec, dynamic phase) where it remained stationary for 90 seconds (static phase). The test-retest protocol included two tests administered 1 hour apart. On a separate occasion, five consecutive static stretches were administered separated by 30 seconds and followed by a sixth stretch 1 hour later. For the test-retest phase, stiffness and energy in the dynamic phase and passive torque in the static phase did not differ and yielded correlations of r = 0.91 to 0.99. During the static phase, passive torque declined in both tests (P < 0.0001). For the repeated stretches, decreases were observed for energy (P < 0.01) and stiffness (P < 0.05) in the dynamic phase and for passive torque (P < 0.0001) in the static phase. However, the decline in the variables returned to baseline within 1 hour. The data show that the method employed is a useful tool for measuring biomechanical variables during a stretch maneuver. This may provide a more detailed method to examine skeletal muscle flexibility.
The effect of strength and flexibility training on skeletal muscle electromyographic activity, stiffness, and viscoelastic stress relaxation response.
The present study examined whether isometric strength training alone or isometric strength training combined with flexibility training of the hamstring muscles altered the viscoelastic response during stretch. Twelve male subjects performed isometric training (strength) on one side and isometric and flexibility training (strength and flexibility) on the other side for 13 weeks; 10 other subjects served as controls. Passive torque offered by the hamstring muscle group was measure during passive knee extension using a dynamometer. The knee was passively extended to a predetermined final position at 0.0875 rad/sec (dynamic phase), where it remained stationary for 90 seconds (static phase). The slope of the line (stiffness) and the area under the curve (energy) in the dynamic phase, and the decline in passive torque (viscoelastic stress relaxation) in the static phase were analyzed. Isometric strength was determined with a dynamometer. A strength test and a stretch maneuver were administered before and after the training period. All variables were unchanged in the control group. Isometric strength increased similarly on both training sides by 43%. The stretch maneuver showed that energy, stiffness, and passive torque increased on both training sides while low-level electromyographic recordings remained constant. Furthermore, the viscoelastic stress relaxation response (31% to 33%) was unaffected by the training. The addition of flexibility exercise had no significant effect on these strength training responses. These data suggest that an increase in isometric strength is accompanied by changes in the material properties of the muscle that are unaffected by flexibility exercises.