Biomedical subjects

Stuart M McGill

Publications and source records attributed to Stuart M McGill.

23 records · Page 2Linked to original sources

PubMed2003

Lumbar posture--should it, and can it, be modified? A study of passive tissue stiffness and lumbar position during activities of daily living.

BACKGROUND AND PURPOSE: Physical therapists commonly attempt to reduce and prevent low back pain by "improving" individuals' lumbar posture. To investigate the physical therapy clinical practice of attempting to "improve" lumbar posture, measures of passive tissue stiffness and angular deformation during activities of daily living were used. PARTICIPANTS: The lumbar spine posture of 150 university students was measured as the inclinometer angle difference between L1 and S1. Eighteen female participants (6 with hypolordosis, 6 with hyperlordosis, and 6 controls without lumbar spine impairment) were recruited from this lumbar posture database. Hypolordosis and hyperlordosis were clinically classified by physical therapists. METHODS: Lumbar passive tissue stiffness was measured during sitting, standing, and walking before and after a 12-week exercise program, and estimates of lumbar passive tissue strain were calculated from those measurements. RESULTS: The neutral zone (NZ), a range of lumbar positions of low passive tissue stiffness, was identified. Prior to training, the subjects with hypolordosis had more passive tissue strain during sitting than the subjects with hyperlordosis, and the subjects with hyperlordosis stood in extension relative to their NZs while the control subjects and subjects with hypolordosis stood within their NZs. Before and after training, subjects in all 3 groups walked with lumbar spine positions within their NZs. After training, the lumbar posture of the subjects with hypolordosis and the subjects with hyperlordosis changed toward a "mean" (mid-range) lumbar posture. After the exercise program, subjects in all 3 groups stood and walked with their lumbar spines in positions within their NZs, and they sat with their lumbar spines flexed relative to their NZs. DISCUSSION AND CONCLUSION: Knowing that tissue failure can be related to passive tissue strain, the results of this study support the clinical practice of attempting to change individuals' posture-related lumbar spine positions during activities of daily living. Lumbar passive tissue strain, as estimated from the NZ and angular deformation during activities of daily living, can be decreased, but can also be increased, by an exercise program.

Activities of Daily Living↗

PubMed2002

Point of view.

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Abdomen↗

PubMed2002

The frictional properties at the thoracic skin-fascia interface: implications in spine manipulation.

OBJECTIVE: To assess the friction at the thoracic skin-fascia interface to determine the potential reaction force vectors during thoracic manual therapy. DESIGN: A basic in vivo study of human subjects, documenting the frictional properties at the interface between the thoracic skin and underlying fascia. BACKGROUND: Chiropractors, and other spine manipulative therapists, during thoracic manipulation have been attempting to apply force vectors to spine tissues in specific directions in addition to those applied normal to the skin. For obliquely applied forces to be directly transmitted to the underlying vertebrae, either friction is required at the skin-fascia interface or the applied force must "hook" on a bony process. METHODS: Subjects were placed in the prone position with the thoracic skin exposed. The posterior thoracic region was loaded with normal forces, incrementally from 125.3 to 392.9 N. The interface between the load and the skin was either a plexiglass plate or modelled hands. A force was then applied to either apparatus in the cephalad direction. The applied forces and corresponding displacements were measured using a load cell and an optoelectronic camera system, respectively. Chiropractors then performed actual thoracic manipulation to determine if they could maintain their location of contacts (spinous process/transverse process) on the underlying vertebra. RESULTS: Each of the subjects exhibited negligible friction between the thoracic skin and underlying fascia for both the plexiglass and modelled hand contacts. Furthermore, in each case, the apparatus travelled a distance greater than that between two transverse or spinous processes without showing an abrupt change in the slope of the force-displacement curves. The hands of chiropractors performing thoracic manipulation travelled a similar distance during the dynamic thrust. CONCLUSIONS: The skin-fascia interface over the thoracic spine exhibits negligible friction. Therefore, the reaction force from a thoracic vertebra will be normal to the overlying skin. Furthermore, the data show that the ability to "hook" either a thoracic transverse or spinous process in the superior-inferior direction during a manipulative thrust may be greatly over-rated. RELEVANCE: During thoracic spinal manipulation, one cannot direct a force vector to a thoracic vertebra at a given angle by simply directing their thrust in that direction.

Adult↗

PubMed2002

Low-back stiffness is altered with warm-up and bench rest: implications for athletes.

INTRODUCTION: General practice in many team sports is to have the athletes who do not start in a game sit on a bench while waiting to play. The purpose of this study was to examine the effect of a warm-up followed by bench rest on the stiffness of the lumbar spine in athletes. METHODS: Nine varsity-level volleyball players volunteered to have their lumbar-spine stiffness measured. The protocol consisted of an initial stiffness measurement followed by a 30-min warm-up, then another stiffness measurement, then 30 min of bench rest, and finally a third stiffness measurement. RESULTS: In general, lumbar spine stiffness increased as a result of bench rest after a warm-up. This effect was seen in both the spine extension and lateral bend axes but not in the flexion or axial twist axes. However, there was no decrease in stiffness associated with the active warm-up portion of the task. CONCLUSIONS: It was concluded that a warm-up followed by bench rest does lead to an increase in stiffness of the lumbar spine, suggesting this practice is not in the best interest of reducing the risk of back injury or optimal performance.

Adult↗

PubMed1997

Dynamic loading affects the mechanical properties and failure site of porcine spines.

OBJECTIVE: The purpose of this study was to investigate the effect of load rate on the mechanical characteristics of spinal motion segments under compressive loading. DESIGN: An in vitro experiment using a porcine model which ensured a homogeneous population for age, weight, genetic background and physical activity. BACKGROUND: Spinal motion segments comprise of viscoelastic materials, and as a result the rate of loading will modulate mechanical characteristics and fracture patterns of the segments. METHODS: Twenty-six cervical porcine spines were excised immediately post-mortem with all soft tissue intact. Spines were then separated into two specimens each consisting of three vertebral bodies and the two intervening intervertebral discs (C2-C4 and C5-C7) and loaded to failure under five loading rates (100, 1000, 3000, 10 000 and 16 000 N s(-1)). After the specimens failed, they were dissected to determine the mode of failure. RESULTS: Dynamic loading increases the ultimate load compared with quasi-static loading (100 N s(-1)), whereas the magnitude of dynamic loading (1000-16 000 N s(-1)) appears not to have a significant affect. Stiffness behaved in a similar manner. The displacement to failure of specimens decreased as load rate increased, although there was a diminishing effect at high load rates. Furthermore, failure at low load rates occurred exclusively in the endplate, whereas failure of the vertebral body appeared with greater frequency at higher load rates. CONCLUSIONS: The mechanical characteristics and resulting injuries of porcine spinal motion segments were affected as the loading rates changed from quasi-static to dynamic. The modulating factors of the mechanical characteristics of the spine need to be understood if valid models are to be designed which will increase the understanding of spinal function, and are important for choosing better injury prevention and rehabilitation programmes.

Journal Article↗