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Abstract
The morphology of the connective tissue may play an important role in locomotor mechanics.
Recent research has revealed an association between increased fascia thickness and
reduced joint flexibility in patients with chronic pain. The present study aimed to
examine the relationship of both factors in healthy individuals, additionally testing
the hypothesis that older subjects display a higher fascia thickness. Young (n = 18,
22 ± 1 years) and old (n = 17, 69 ± 4 years) healthy females were recruited for a
quasi-experimental, cross-sectional trial. All participants underwent standardized
ultrasound-based thickness measurements of the deep fasciae of the trunk and lower
limb. Flexibility was assessed using sit and reach testing (hamstring extensibility)
and the Schober test (lumbar flexion and extension). Systematic between-group differences
of fascia thickness and variable associations (i.e. fascia thickness and flexibility)
were detected using non-parametric data analyses. Young adults exhibited higher fascia
thickness of the anterior and posterior lower leg, anterior thigh and abdominal wall
(+12.3-25.8%, P < 0.05). Conversely, older participants showed higher thickness in
the lumbar spine (+40.0-76.7%, P < 0.05). Correlations of both body mass and fascia
thickness (τ = 0.45-0.75, P < 0.05), as well as flexibility and fascia thickness (τ = 0.38-0.42,
P < 0.05) were found. Age-related changes in fascia thickness may be a contributing
factor of restrictions in joint range of motion. Further study delineating the cause-effect
triangle of body mass index, flexibility and fascia thickness is necessary.
Various theories have been proposed to explain increases in muscle extensibility observed after intermittent stretching. Most of these theories advocate a mechanical increase in length of the stretched muscle. More recently, a sensory theory has been proposed suggesting instead that increases in muscle extensibility are due to a modification of sensation only. Studies that evaluated the biomechanical effect of stretching showed that muscle length does increase during stretch application due to the viscoelastic properties of muscle. However, this length increase is transient, its magnitude and duration being dependent upon the duration and type of stretching applied. Most of these studies suggest that increases in muscle extensibility observed after a single stretching session and after short-term (3- to 8-week) stretching programs are due to modified sensation. The biomechanical effects of long-term (>8 weeks) and chronic stretching programs have not yet been evaluated. The purposes of this article are to review each of these proposed theories and to discuss the implications for research and clinical practice.
Hyaluronan (HA) is a high molecular weight glycosaminoglycan of the extracellular matrix (ECM), which is particularly abundant in soft connective tissues. Solutions of HA can be highly viscous with non-Newtonian flow properties. These properties affect the movement of HA-containing fluid layers within and underlying the deep fascia. Changes in the concentration, molecular weight, or even covalent modification of HA in inflammatory conditions, as well as changes in binding interactions with other macromolecules, can have dramatic effects on the sliding movement of fascia. The high molecular weight and the semi-flexible chain of HA are key factors leading to the high viscosity of dilute solutions, and real HA solutions show additional nonideality and greatly increased viscosity due to mutual macromolecular crowding. The shear rate dependence of the viscosity, and the viscoelasticity of HA solutions, depend on the relaxation time of the molecule, which in turn depends on the HA concentration and molecular weight. Temperature can also have an effect on these properties. High viscosity can additionally affect the lubricating function of HA solutions. Immobility can increase the concentration of HA, increase the viscosity, and reduce lubrication and gliding of the layers of connective tissue and muscle. Over time, these changes can alter both muscle structure and function. Inflammation can further increase the viscosity of HA-containing fluids if the HA is modified via covalent attachment of heavy chains derived from Inter-α-Inhibitor. Hyaluronidase hydrolyzes HA, thus reducing its molecular weight, lowering the viscosity of the extracellular matrix fluid and making outflow easier. It can also disrupt any aggregates or gel-like structures that result from HA being modified. Hyaluronidase is used medically primarily as a dispersion agent, but may also be useful in conditions where altered viscosity of the fascia is desired, such as in the treatment of muscle stiffness.
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