Moderate running exercise augments glycosaminoglycans and thickness of articular cartilage in the knee joint of young beagle dogs

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Abstract
The local influences of physical exercise on thickness and glycosaminoglycan (GAG) content of canine articular cartilage were measured by microspectrophotometry of Safranin O‐ and periodic acid‐Schiff (PAS)‐stained tissue sections. Female Beagle dogs were housed in individual cages (bottom 0.9 × 1.2 m) and divided into runner (n = 6) and control (n = 8) groups. The trainig program started at the age of 15 weeks. During the subsequent 10 weeks, the dogs were accustomed to running on a treadmill inclined 15° uphill. Thereafter, the dogs ran 1 h daily, 5 days a week, at a speed of 4 km/h for 15 weeks. At the age of 40 weeks, the dogs were killed, and the samples for histology were taken from 11 different anatomical locations of the right knee (stifle) joint. The thickness of the uncalcified cartilage increased 19–23% on the lateral condyle and patellar surface of the femur, whereas the enhancement was smaller in other parts of the trained cartilage. The calcified cartilage did not show thickness alterations. Total GAGs were augmented by 28% in the summits on the femoral condyles, more on the medial than lateral side. The increased GAGs appeared to be predominantly chondroitin sulphates and were localized in the intermediate, deep, and even in the calcified zones, whereas the superficial zone did not show changes. There was a concomitant increase of non‐GAG oligosaccharides in the intermediate and deep zones, but not in the calcified cartilage. As judged from the enhanced GAG content and thickness, it is considered that moderate running exercise locally alters the biological properties of young articular cartilage at regions bearing the highest loading surplus.