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Biomedical subjects

M A Adams

Publications and source records attributed to M A Adams.

175 records · Page 10Linked to original sources
PubMedDate not supplied

The relationship between EMG activity and extensor moment generation in the erector spinae muscles during bending and lifting activities.

The relationship between EMG activity and extensor moment generation in the erector spinae muscles was investigated under isometric and concentric conditions. The full-wave rectified and averaged EMG signal was recorded from skin-surface electrodes located over the belly of the erector spinae at the levels of T10 and L3, and compared with measurements of extensor moment. The effects of muscle length and contraction velocity were studied by measuring the overall curvature (theta) and rate of change of curvature (d theta/dt) of the lumbar spine in the sagittal plane, using the '3-Space Isotrak' system. Isometric contractions were investigated with the subjects pulling up on a load cell attached to the floor. Hand height was varied to produce different amounts of lumbar flexion, as indicated by changes in lumbar curvature. The extensor moment was found to be linearly related to EMG activity, and the 'gradient' and 'intercept' of the relationship were themselves dependent upon the lumbar curvature at the time of testing. Concentric contractions were investigated with the subjects extending from a seated toe-touching position, at various speeds, while the torque exerted on the arm of a Cybex dynamometer was continuously measured. Under these conditions the EMG signal (E) was higher than the isometric signal (E0) associated with the same torque. E and E0 were related as follows: E0 = E/(1 + A d theta/dt), where A = 0.0014 exp (0.045P) and P = percentage lumbar flexion. This equation was used to correct the EMG data for the effect of contraction velocity. The corrected data were then used, in conjunction with the results of the isometric calibrations, to calculate the extensor moment generated by the erector spinae muscles during bending and lifting activities. The extensor moment can itself be used to calculate the compressive force acting on the lumbar spine.

Adult↗
PubMedDate not supplied

Pharmacokinetics and safety of lomefloxacin following multiple doses.

This was a randomized, double-blind, placebo-controlled study comparing the safety and tolerance of 400 mg lomefloxacin, given orally twice daily, to that of placebo administered to eight and four subjects, respectively, for 2 wk. This dose, interval, and duration of dosing were chosen to be identical to the highest anticipated clinical dose for the longest anticipated clinical duration. Subject assessments included ophthalmological examinations performed prior to the study, at midstudy, and after the dosing. No clinically significant differences from baseline were observed for any test result. Analysis of trough plasma concentrations, CMIN, showed that steady state was achieved on Day 4 (Fig. 2). At steady-state, mean plasma concentrations of lomefloxacin ranged from a maximum of 4.86 micrograms/ml to a minimum of 1.47 micrograms/ml. Mean time to maximum plasma concentration on Day 14 was 1.23 hr in the morning and 3.81 hr in the evening. Plasma half-life was approximately 8 hr. Lomefloxacin was well tolerated at 400 mg administered twice daily for 2 wk; plasma concentrations were maintained at a level that is above the MIC of most clinically significant isolates.

4-Quinolones↗
PubMedDate not supplied

The resistance to flexion of the lumbar intervertebral joint.

Cadaveric lumbar intervertebral joints were subjected to physiologic loads to simulate flexion. The resistance to bending was measured first with the joint intact and again after cutting in turn through the supraspinous/interspinous ligaments, the ligamentum flavum, and the capsular ligaments of the apophyseal joints. In this way the part played by each of these structures, and the intervertebral disc, in resisting and limiting flexion was determined. The results show that at the limit of flexion the supraspinous and interspinous ligaments sprain first and that the capsular ligaments and the intervertebral disc offer considerably more resistance than the ligamentum flavum and the supraspinous/interspinous ligaments. The intervertebral joint was found, on average, to be sufficiently stiff to balance about half the bending moment exerted by the trunk in full flexion.

Biomechanical Phenomena↗
PubMedDate not supplied

The relevance of torsion to the mechanical derangement of the lumbar spine.

Cadaveric lumbar intervertebral joints were loaded simultaneously in torsion and compression, and load-deformation curves were obtained. These were repeated after each of the following structures were cut through in turn: the supra/interspinous ligaments, the apophyseal joint in compression, and the apophyseal joint in tension. From the differences in the curves, it was possible to deduce the role of each structure and of the intervertebral disc in resisting and limiting torsion. The results show that torsion of the lumbar spine is resisted primarily by the apophyseal joint that is in compression, although the intervertebral disc does play a major role. The capsular ligaments of the tension facet and the supra/interspinous ligaments are unimportant. The compression facet is the first of rotation in joints with nondegenerated intervertebral discs. Much greater angles are required to damage the intervertebral disc, so torsion seems unimportant in the etiology of disc degeneration and prolapse.

Adolescent↗
PubMedDate not supplied

Can the lumbar spine be crushed in heavy lifting?

Cadaveric lumbar intervertebral joints were wedged to simulate forward flexion and then compressed to failure. The compressive strengths of the young male specimens tested were compared with the forces calculated to act when average young men perform maximum lifts from the flexed posture. It is concluded that the spine has a considerable margin of safety when such lifts are performed.

Adult↗
PubMedDate not supplied

Gradual disc prolapse.

Fifty-two cadaveric lumbar motion segments were subjected to fatigue loading in compression and bending to determine if the intervertebral discs could prolapse in a gradual manner. Prior to testing, the nucleus pulposus of each disc was stained with a small quantity of blue dye and radiopaque solution. This enabled the progress of any gradual prolapse to be monitored by direct observation and by discogram. Six discs developed a gradual prolapse during the testing period. The injury starts with the lamellae of the annulus being distorted to form radial fissures and then nuclear pulp is extruded from the disc and leaks into the spinal canal. Discs most commonly affected were from the lower lumbar spine of young cadavers. Tests on ten older discs with pre-existing ruptures showed that such discs are stable and do not leak nuclear pulp.

Adolescent↗