The musculature serves as motor of the human body and hence promotes our movement within our environment. Its organ-specific performance is the translation of force into movement. This force can be described by means of different qualities - maximal force, speed and endurance. These properties are essential for sports activities and also set limits for the achievement of athletic records. Muscular force can be evaluated by different means. Measurement of force via isokinetic systems enables quantitative measurement of effective muscular forces in various body positions which are frequently comparable under conditions specific to different types of sports. The relevance of these measurements in sports and rehabilitation is documented in this article. Two different groups of subjects (72 sportsmen and 73 patients after capsular ligament reconstruction in the knee joint) were examined. The measurement values: dynamic maximal force, energy of acceleration, average performance and the hamstring/quadriceps ratios (H/Q quotient) are measured at different speeds. The maximal force shows intraindividual differences depending on the speed. These differences are due to different conditions of training and different distribution of muscle fibre types. The acceleration energy enables assessment of differences in the ability to exercise force. Likewise, the different muscle performances can be described by means of the appropriate individual performance maximums. In rehabilitation, muscle atrophy caused by immobilization can be measured and described. Measurement of force by means of isokinetic systems enables the analysis of muscular forces with their different properties, and hence to give advice in training matters and to supervise and control popular recreational sports and competitive sports activities.(ABSTRACT TRUNCATED AT 250 WORDS)