Deficits in rate of torque development are accompanied by activation failure in patients with knee osteoarthritis.

Aim of this study was to investigate if knee extensor maximal voluntary contraction (MVC) torque and rate of torque development (RTD) deficits are accompanied by neuromuscular activation failure in patients with knee osteoarthritis (KOA). Nineteen patients with unilateral KOA completed gradual MVCs, from which MVC torque, voluntary activation and maximal EMG activity were recorded, and explosive MVCs, from which RTD and rate of EMG rise were recorded. For gradual MVCs, MVC torque (-28%), voluntary activation (-6%) and maximal EMG activity (-30%) were lower on the involved than on the uninvolved side (p < 0.001). Asymmetries in MVC torque and maximal EMG activity were positively correlated (r = 0.70; p < 0.001). For explosive MVCs, involved-side RTD (-19%) and rate of EMG rise (-20%) were lower compared to the uninvolved side (p < 0.05-0.001). Asymmetries in RTD and rate of EMG rise were positively correlated (r = 0.61-0.80; p < 0.01). Deficits in isometric knee extensor strength were accompanied by neuromuscular activation failure during gradual MVCs and, more importantly, during the early phase of explosive MVCs. Such inability to rapidly activate the quadriceps may have functional consequences and warrants greater attention in the evaluation and rehabilitation of patients with KOA.

[Development and adaptation of tensile strength by bones in the extremities in response to physical training exemplified by the tibia]. / Entwicklung und Anpassung der Biegefestigkeit des Extremitätenskelettes durch Training am Beispiel der Tibia.

Results from an in vivo assessment of the bending stiffness of human tibiae with a new method demonstrate that bone mineral measurements are not a suitable predictor to evaluate changes of mechanical properties of long bones. In a study on 559 male military recruits, the bone mineral at tibial shaft resulted in a mean increase of +1.8% during 15 weeks of exercise. The bending stiffness however increased about 25%. An additional test 24 months later on a sample indicated that the increase of bone mineral content was only due to the natural maturation of bone. The bending stiffness however, decreased by about 6% demonstrating the earlier training effect. No correlation between bone mineral and bending stiffness could be found neither in absolute values nor in difference between the three measurements. At the same time first results of a normative study on children (9 to 18 years old, male and female) and on women (up to 80 years old) are presented.