Effect of exercise on osteoarthritis

The popularity of jogging among the population of many countries of the world has recently attracted attention to long-distance running as a risk factor for the development of osteoarthritis. Retrospective and prospective studies have shown that clinical and radiographic criteria of osteoarthritis are found in middle-distance and marathon runners no more often than in people who do not run. However, due to the fact that the design of most of these studies has a number of shortcomings (incorrect statistical analysis, incorrect methods of diagnosis or assessment of osteoarthritis, etc.), their results are questionable. NE Lane et al. (1986, 1987, 1993) attempted to correct the errors of previous researchers. For 9 years, they studied the radiographic signs of osteoarthritis in elderly amateur runners (average age 65 years). It was found that in this category of people, the incidence of osteoarthritis (radiologically confirmed) did not exceed that in a group of people of the same age who are not fond of running. Although in the group of recreational runners, subchondral sclerosis was more often registered in women, and osteophytes were more often detected on X-rays in individuals of both sexes, nevertheless, the authors concluded that amateur athletics is not a risk factor for osteoarthritis. Thus, the presented data indicate that in individuals with "healthy" joints, long-distance running does not cause cartilage degeneration and the development of osteoarthritis.

Studies of the biomechanics of osteoarthritis in animal models support the above conclusion. PM Newton et al. (1997) studied beagles that were trained to run at a speed of 3.3 km/h for 75 min per day for 5 days per week. Each dog carried an additional "exogenous" load of 11.5 kg (130% of body weight). The control group consisted of adult beagles that were not trained and did not have additional load applied. Histological examination of articular cartilage, menisci and ligaments was performed 52 weeks after the start of training. It turned out that the applied load level did not cause degenerative changes in the joint tissues in the dogs. No difference was found between the biomechanical properties of cartilage in trained and untrained dogs.

In another study, young (skeletally immature) beagles were trained on a moderately difficult program (4 km/h on a treadmill with a 15° incline) for 15 weeks. The authors found thickening of the cartilage and increased synthesis of proteoglycans compared with the control (untrained) group of animals. However, most of the proteoglycans in the cartilage of trained animals lost the ability to aggregate with hyaluronic acid and contained more chondroitin-6-sulphates. The authors of the study suggested that this level of load accelerates the maturation of matrix deposits in the articular cartilage of animals.

In a study conducted with young beagles, the training program was slightly more complex: 20 km per day for 15 weeks. This load caused a decrease in collagen concentration, an increase in water content, and a decrease in the ratio of chondroitin-6- and chondroitin-4-sulphates in the articular cartilage of the lateral femoral condyles. Increasing the distance to 40 km per day and the duration of training to 52 weeks was accompanied by a decrease in the content of proteoglycans in the cartilage ECM. The most pronounced loss of glycosaminoglycans was noted at the tips of the femoral condyles, especially in the superficial zone of the cartilage.

Little et al. (1997) demonstrated that chronic intense training can induce changes in proteoglycan metabolism in equine carpal joints. In this study, the authors examined the effects of moderate to vigorous training loads on the synthesis and degradation of a large aggregated proteoglycan (aggrecan) and two small dermatan sulfate-containing proteoglycans (decorin and biglycan). Articular cartilage explants were collected from three highly loaded and commonly injured sites in the third carpus in performance horses. Twelve horses, aged 3 to 5 years, with no clinical or radiographic evidence of middle carpal joint pathology were included in the study. The training program consisted of running at 6 m/s for 2000 m 3 days per week, increasing to 4000 m by the end of the 8th week of the study. Then all animals were divided into two groups - animals of group A continued training in the same mode, and animals of group B had an intensified training mode (running at a speed of 8 m/s over a distance of 4000 m 4 days a week for 17 weeks). 16 weeks after the end of training, material was collected from certain areas of the third carpal bone on both sides.

Histological examination of cartilage from animals of both groups revealed depression of its superficial areas and destruction of calcified cartilage and "wavy border" only in the area of dorsal radial condyle of the third carpal bone. No significant difference in the detected histological changes was found between groups A and B. In the culture of articular cartilage explants from animals of group B, a greater amount of proteoglycans were released from the cartilage of the dorsal radial condyle into the medium than in animals of group A, which indicates a higher level of catabolism in group B. Incorporation of ³⁵ S into proteoglycans was less pronounced in explants obtained from animals of group B; at the same time, an increase in decorin biosynthesis was observed in animals of this group, and no changes in the intensity of biglycan biosynthesis were found. Thus, the obtained results indicate that long-term intensive training of horses induces inhibition of aggrecan synthesis and increased synthesis of dermatan sulfate-containing proteoglycans.

The functional role of decorin in connective tissue in general and cartilage in particular remains a subject of research. Decorin is thought to play a central role in the organization of collagen macromolecules, cell proliferation, and modulation of growth factor activity (e.g., TGF-β). Addition of decorin to a collagen gel resulted in the deposition of more uniform, thin collagen fibrils than in its absence. In postpartum cervical tissue, the disruption of the collagen network correlated with increased decorin levels. Thus, decorin most likely acts as a "conductor" of connective tissue repair and remodeling processes.

The increase in decorin synthesis by equine articular cartilage chondrocytes under high dynamic loads can be interpreted as follows: decorin released from damaged chondrocytes in response to mechanical overload acts as a messenger. This hypothesis is supported by in vitro and in vivo studies, which demonstrated increased decorin production by chondrocytes subjected to supraphysiological mechanical load. T. H. V. Korver et al. (1992) reported that cyclic loading, in vitro, applied for 7 days, increases decorin synthesis in articular cartilage explants by 3 times. Similar results were obtained by N. A. Vissen et al. (1994), who used mature and immature articular cartilage explants. In a model of early (hypertrophic) osteoarthritis induced in dogs by transection of the anterior cruciate ligaments, GS Dourado et al. (1996) observed increased mRNA levels of biglycan, decorin, and fibromodulin in the cartilage of destabilized joints.

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