By 2020, the increase in life expectancy and the aging of the population should bring arthritis to fourth place in the causes of disability in developed countries .
The knee is one of the most frequent arthrosic locations. In 2002, it represented 1.7% of the health insurance expenses in France . Its therapeutic care relies on the association of pharmacological and nonpharmacological treatments .
Patients suffering from knee osteoarthritis present a muscular weakness in the legs, particularly the quadriceps [4–6]. The extent of quadricep muscle deficiency is linked to the level of gonalgia and functional disability . It has been proven that physical activity and muscular strengthening improves these two factors. On the other hand, we do not know which mode of muscular strengthening is the most efficient. The current recommendations suggest an adapted and personalized rehabilitation program concerning the type of exercises, the intensity, and the frequency . Several studies have shown the interest of isokinetic dynamometers as rehabilitation tools in muscular strengthening and have found an equivalent or superior efficacy of this rehabilitation mode compared to the isometric or isotonic physical exercises more commonly used in current practice [9, 10]. The isokinetic exercises also present an advantage in terms of cardiac tolerance, which is interesting for aged, potentially vascular, arthrosic patients. Indeed, it leads to a smaller increase in heart rate and blood pressure than isometric exercises .
The eccentric contraction of the quadriceps muscles seems to play a fundamental role in walking and other activities of everyday life, allowing control of the bending of the knee (cushioning) and an active joint stability . The protocols for isokinetic muscular strengthening, in combined concentric-eccentric mode, have shown better results than the concentric mode alone in terms of functional improvement in knee osteoarthritis .
To our knowledge no published study has compared isolated eccentric strengthening to concentric strengthening alone in knee osteoarthritis (OA) whereas the superiority of eccentric strengthening in terms of increase in strength has been demonstrated elsewhere for other pathologies . Thus, rehabilitation care currently practiced could be optimized by preferentially using this muscular strengthening contraction mode.