ABSTRACT
OBJECTIVE: Obesity and associated low-level local systemic inflammation have been linked to an increased rate of developing knee osteoarthritis (OA). Aerobic exercise has been shown to protect the knee from obesity-induced joint damage. The aims of this study were to determine (1) if resistance training provides beneficial metabolic effects similar to those previously observed with aerobic training in rats consuming a high-fat/high-sucrose (HFS) diet and (2) if these metabolic effects mitigate knee OA in a diet-induced obesity model in rats. DESIGN: Twelve-week-old Sprague-Dawley rats were randomized into 4 groups: (1) a group fed an HFS diet subjected to aerobic exercise (HFS+Aer), (2) a group fed an HFS diet subjected to resistance exercise (HFS+Res), (3) a group fed an HFS diet with no exercise (HFS+Sed), and (4) a chow-fed sedentary control group (Chow+Sed). HFS+Sed animals were heavier and had greater body fat, higher levels of triglycerides and total cholesterol, and more joint damage than Chow+Sed animals. RESULTS: The HFS+Res group had higher body mass and body fat than Chow+Sed animals and higher OA scores than animals from the HFS+Aer group. Severe bone lesions were observed in the HFS+Sed and Chow+Sed animals at age 24 weeks, but not in the HFS+Res and HFS+Aer group animals. CONCLOSION: In summary, aerobic training provided better protection against knee joint OA than resistance training in this rat model of HFS-diet-induced obesity. Exposing rats to exercise, either aerobic or resistance training, had a protective effect against the severe bone lesions observed in the nonexercised rats.
ABSTRACT
BACKGROUND: Mechanical stimulation of joints regulates the biosynthetic activity of chondrocytes. It has been argued that excessive loading might cause chondrocyte death, leading to degeneration of cartilage and cause osteoarthritis. The aims of this study were to apply a high, short-term loading, and a low intensity, long-term loading protocol to intact joints in life animals and determine changes in synovial fluid and the percentage of dead cells in rabbit knee cartilage. METHOD: Nine rabbits were subjected to unilateral exercise loading consisting of five sets of 10 maximal eccentric knee contractions. Another 6 rabbits were subjected to submaximal concentric contractions for 30 min at 20% of the maximum isometric knee extensor force. Contralateral joints served as unloaded controls. Cell viability was assessed using confocal microscopy. Synovial fluid was analyzed for total protein concentration and total number of identifiable proteins and was compared to protein content of control rabbits (n = 4). FINDINGS: Neither the high-intensity, short-term nor the low-intensity, long-term loading protocol caused increased chondrocyte death compared to the unloaded control joints. Total synovial fluid protein concentration was the same before and after exercise. Following the high-intensity exercise protocol, the number of identifiable proteins was decreased, while following the low-intensity exercise protocol, the number of identifiable proteins was increased compared to control. INTERPRETATION: Chondrocytes are well protected in the intact joint and withstood maximal eccentric muscular loading, and maximal endurance loading. Synovial fluid protein content was changed after exercise, and these changes depended crucially on the type of loading.
