Much has been written about the cardiovascular benefits of routine exercise (weight reduction, modifications of lipid profile, improvements in coronary arterial blood flow), and these benefits are particularly important for patients with osteoarthritis, as excess weight-bearing directly impacts upon the hips, knees and feet. A 'one size fits all' approach to exercise does not serve patients well, as variations in weight, pain tolerance and aerobic capacity require an individualized program. Muscle strengthening does, however, fit the plan for almost everyone, particularly as increased hamstring strength and quadriceps bulk can help to decrease the force of a weight-bearing load across the knee joint.
Resistance training can be both isometric (flexion/contraction against static resistance) and isotonic (dynamic resistance to range of motion). Patients vary in their tolerance of these strengthening regimens, often preferring static resistance to range of motion exercises. In either case, resistance can be imposed by adding weight to the foot while exercising (boots, strap-on weights), maneuvers which help to build muscle. A single muscle group can be targeted by a specific exercise - leg extension from 90 degrees of flexion to 120 degrees in a seated position - will help to build up the quadriceps while flexion of the knee from a prone position will help to build hamstring strength. Weight bearing in the leg press may produce significant joint stress and is discouraged initially, until both quadriceps and hamstring muscle groups are adequately strengthened.
It is important that resistance (either isotonic or isometric) be increased over time, in efforts to build muscle strength across the joint. Load-bearing should be minimal at the beginning of the strengthening program, then progress to 100% of tolerance over a period of weeks. Beginning with one set of repetitions and progressing to three sets of ten repetitions is frequently advised by therapists, with resistance fixed for one week intervals. Excess resistance will tear (not stretch) muscle, and is to be avoided. Dynamic exercise produces heat, and a cool-down period is advised upon completion of exercises. Note that muscles are 'warmed-up' by aerobic activity, and such activities as bicycling, swimming (especially water aerobics) and, if possible, light jogging are encouraged prior to initiating resistance training. Increasing mobility and cardiovascular fitness are central to the management of osteoarthritis, and will confer long-term benefits which are complimentary to resistance training.