ii MECHANICS OF LOCOMOTOE APPARATUS 127 



ment the movements of the legs by slight rowing movements with 

 the arms. 



Swimming with the abdomen downwards is more difficult, 

 either because the centre of gravity is above the centre of dis- 

 placement or because, as the head and neck are out of water, the 

 weight of the body is consequently greater than that of the water 

 displaced. 



The mechanism of swimming consists essentially in exercising 

 pressure upon the water rhythmically from above downwards, and 

 from before backwards with the surface of the hands and feet, so 

 as to cause a reaction of the water displaced, which is able to raise 

 the body, prevent it from sinking, and impel it forward in the 

 required direction. 



The details of the mechanism of swimming have been little 

 studied since graphic methods cannot be applied, and chrono- 

 photography is difficult. Moreover, swimming is not natural to 

 man, but is an art which he learns and perfects by practice. 

 Accordingly there is no fixed and constant mode of swimming, 

 and the movements of the upper and lower limbs adopted by 

 different swimmers are not exactly alike. Generally speaking, 

 there is an initial thrust forward on the surface of the water by a 

 rapid extension and adduction of the legs, on which the water is 

 displaced backwards and toward the bottom by the feet, producing 

 a reaction which raises the body of the swimmer and jerks it 

 forward. This movement of the lower limbs is accompanied with 

 a forward thrust of the arms, which are brought together in front. 

 The arms are then moved outwards, backwards, and slightly 

 downwards, this being perhaps more efficacious in swimming 

 than the initial movement of the lower limbs. This movement 

 is associated with retraction and abduction of the legs, which 

 completes the natatory cycle. 



If the swimming movements are too strong and rapid, they 

 are fatiguing and of little use. Both hands and feet, which act as 

 the blades of an oar, press on the water with the maximum available 

 surface, and return to the starting position with a slower move- 

 ment, and at the same time present the smallest possible surface 

 to the water. 



BIBLIOGRAPHY 



BORELLI. De motu animalium, etc. Rome, 1680. 



ED. and W. WEBER. Mechanikder menschlichen Gehwerkzeuge. Gottingen, 1836. 

 DUCHENNE. Phys. des mouvements, 1867. 

 CARLET. fitude sur la locomotion humaine, 1872. 

 MAREY. La machine animale, 1879. 



G. H. MEYER. Die Statik und Mechanik des menschlichen Knochengeriistes, 1873. 

 PETTIGREW. La locomotion chez les animaux, 1874. 

 A. FICK. Hermann's Handbuch der Physiol., I., 1879. 



W. BRAUNE and 0. FISCHER. Abhandlungen der math.-phys. Klasse der konig. 

 sachs. Gesellsch. der Wissenschat'ten, 1885-1904. 



