An analysis of the popliteus muscle in man, dog, and pig with a reconsideration of the general problems of muscle function.

On the basis of general considerations of muscle functions and by means of mechanical and measuring methods and by computer analysis, it is shown that the popliteus muscle of man, dog, and pig is basically an extensor, regardless of whether femur or tibia are considered as resting. The traditional doctrine claiming a flexor function of the popliteus muscle has to be revised. In spite of the basic extending function, its effect in actual extension, especially against the weight of the entire body, is evidently most doubtful. Never has its rotatory function been doubted. Its role in reversing the compulsory rotation at the beginning of flexion can now easily be explained: since it is an extensor, the flexion would cause its passive elongation, against which its mere tonus causes rotation.