The chondrogenic response to exercise in the proximal femur of normal and mdx mice.
“Submaximal exercise is used in the management of muscular dystrophy. The effects of mechanical stimulation on skeletal development are well understood, although its effects on cartilage growth have yet to be investigated in the dystrophic condition. The objective of this study was to investigate the chondrogenic response to voluntary exercise in dystrophin-deficient mice.
Control and dystrophin-deficient (mdx) mice were divided into sedentary and exercise-treated groups and tested for chondral histomorphometric differences at the proximal femur.
Control mice ran 7 km/week further than mdx mice on average, but this difference was not statistically significant. However, exercised control mice exhibited significantly enlarged femur head diameter, articular cartilage thickness, articular cartilage tissue area, and area of calcified cartilage relative to sedentary controls and exercised mdx mic{the enlarged femur head is consistent with articular cartilage endohcondral ossification [and] especially considering the area of calcified cartilage increased as well]. No differences were found between other treatment groups.
Mdx mice exhibit a reduced chondrogenic response to increased mechanical stimulation relative to controls. However, no significant reduction in articular dimensions was found, indicating loss of chondral tissue may not be a clinical concern with dystrophinopathy.”
“Exercise treatment consisted of voluntary access to a running wheel that lasted four weeks.”
“it is conceivable that joint forces in mdx mice failed to provide sufficient mechanical pressure to yield significant chondral expansion. Skeletal muscle of mdx mice of similar age to the ones used in this study have been shown to contain extensive fibrosis and degenerative myocytes with diminished muscle force production”<-maybe being able to generate enough force is a similar limiting factor for our purposes and if we could generate more muscular force we could induce longitudinal bone growth.
“a reduction in joint forces resulting from weaker muscle force production and slower running speeds may explain the diminished chondrogenic response to voluntary running exercise in the proximal femurs of mdx mice.”
The response of bone, articular cartilage and tendon to exercise in the horse.
” For bone, alterations in bone mineral content, mineral density and the morphology of the mineralized tissue are the most common end-points. Apparent bone density increases slightly after athletic training in the cortex, but substantially in the major load paths of the epiphyses and cuboidal bones, despite the lower material density of the new bone, which is deposited subperiosteally and on internal surfaces without prior osteoclastic resorption. With training of greater intensity, adaptive change is supervened by patho-anatomical change in the form of microdamage and frank lesions. In tendon, collagen fibril diameter distribution changes significantly during growth, but not after early training. The exact amount and type of protracted training that does cause reduction in mass average diameter (an early sign of progressive microdamage) have not been defined. Training is associated with an increase in the cross-sectional area of some tendons, possibly owing to slightly greater water content of non-collagenous or newly synthesized matrix. Early training may be associated with greater thickness of hyaline but not calcified articular cartilage, at least in some sites. The age at which adaptation of cartilage to biomechanical influences can occur may thus extend beyond very early life. However, cartilage appears to be the most susceptible of the three tissues to pathological alteration. The effect of training exercise on the anatomical or patho-anatomical features of connective tissue structures is affected by the timing, type and amount of natural or imposed exercise during growth and development which precedes the training.”
“Equine joint cartilage has similar appearance and properties to human articular cartilage”
“At both [phalanx] sites, water, DNA and GAG decreased during maturation whereas collagen content, hydroxylysine content and HP cross-links increased. Postnatal adaptation, resulting in biochemical and therefore biomechanical heterogeneity, which is important for future tissue strength and resistance to injury, occurs early and rapidly, possibly because collagen turnover is extremely low at older ages”
“Exercise influenced calcium content and levels of HP and lysylpyridinoline cross-links at the intermittently loaded site but not at the constantly loaded site of the proximal phalangeal bone, levels of lysyl-hydroxylation and lysylpyridinoline cross-linking being lower at the former than the latter site”
“The epiphyseal bone alters dramatically with exercise and is only arbitrarily separable from the subchondral bone.” the subchondral bone is the bone that is at the end of the articular cartilage and the beginning of epiphyseal bone.