392 MUSCULAR ACTION 



of the trunk is only 0.6 cm. behind it. Altogether the balance is a very 

 perfect one and is maintained with a very small expenditure of effort in 

 comparison with the considerable weight sustained. 



IN SITTING the weight is sustained on the tuberosities of the ischia, and 

 the trunk, leaned either against some surface (as the back of a chair) or 

 else leaned forward, is sustained in balance somewhat as in standing. 



Locomotion consists of some sort of rhythmic alternation of the limbs 

 made in s~uch a way that the body advances as a whole. Aside from 

 jumping and rolling, the chief means of natural human locomotion are 

 walking, running, creeping, and swimming. Of these we need discuss 

 only the first two. 



WALKING AND RUNNING. Braune and Fischer have advanced some- 

 what upon the classic studies of Weber brothers and of Marey into the 

 phenomena of walking and running. By attaching tiny electric lamps 

 to different parts of the body, accurately photographing in the dark the 

 respective courses of these lights, and afterward working them out with 

 mathematical exactness, these researchers have arrived at many of the 

 actual physical conditions of these important motor functions, and with 

 surprising precision. For a general understanding, however, of these 

 processes the instantaneous photographs of Marey (made in part in 

 daylight from a man running and in part in the dark from illuminated 

 lines and lights attached to the man's costume) furnish us the best 

 material. 



The muscles of walking and the process itself are somewhat as follows 

 (Richer) : Pushed forward by a muscular action, which will be noted 

 later on, the leg which is swinging falls again by its own weight on the 

 ground. At this instant it is in a condition of almost complete muscular 

 relaxation or rest. As soon as it begins to support the body's weight 

 again, even before the foot is completely on the ground, the muscular 

 contraction begins. The middle gluteus begins to shorten and its 

 energetic contraction lasts during the time of one-sided support to pre- 

 vent the rotation of the pelvis by the swinging leg attached to it. The 

 middle gluteus and probably also the gluteus minimus directly oppose 

 the lateral fall of the pelvis, and are aided by the upper part of the gluteus 

 maximus and the tensor fasciae latse. The gluteus maximus in its 

 entirety, meanwhile, contracts during the entire posterior step and thus 

 prevents the falling of the trunk forward, but its activity stops at the 

 moment of verticality and does not begin again during the anterior step. 

 The quadriceps also is one of the first muscles of the supporting leg 

 to contract, and maintains thus the extension of the weight-bearing leg 

 which else would bend; like the gluteus maximus, it is quite inactive 

 during the anterior step. The muscles of the (lower) leg are all slightly 

 relaxed during the posterior step, but at the time of verticality the poste- 

 rior and lateral muscles contract vigorously, the contraction increasing to 

 the step's end. The calf-muscles (gastrocnemii and peronei) energetic- 

 ally raise the heel, and the latter, as it leaves the ground, raises and 

 pushes forward the body simultaneously. Hence these muscles are the 



