II 



MECHANICS OF LOCOMOTOE APPABATUS 117 



able to construct a curve of the movements of various joints and of the head, 

 as also of the movements of the trunk, etc. 



Fig. 80 is a diagram of the cycle of walking constructed by Zimmerman 

 from the chronophotographs of Fischer. 



The tracing (Fig. 79) obtained by Carlet with his exploring 

 shoes shows that in the usual mode of walking the heel is first 

 applied to the ground, then the whole sole of the foot, and lastly 

 the ball of the toes only ; that the time during which both feet 

 are on the ground is less than half the 

 period that each alone rests on it; that 

 the time of the rise and swing of one 

 leg is always shorter than that of the 

 opposite liinb. Carlet demonstrated by 

 the same method that the pressure exer- 

 cised by the foot upon the ground during 

 a step is not equal to the weight of the 

 body, but that in the last stage of the 

 step an additional pressure dependent 

 on the muscular forces, which raises the 

 body and propels it forward, is added. 

 According to Carlet the additional incre- 

 ment of pressure varies with the length 

 of the steps and never exceeds 20 kgrms. 



The length of the step depends on 

 the length of the lower limbs and the 

 degree in which the knee of the limb 

 which bears the weight of the body at 

 the commencement of the step is flexed. 

 Fig. 73, which shows diagrammatically 

 the position of the lower limbs at the 

 commencement of the step, makes it 

 plain that the length of step can only 

 increase when the length of the hypo- 

 tenuse (i.e. the length of the extended 

 limb) is increased, or when the flexion 

 of the knee of the limb on which the weight of the body 

 falls is increased. People who have long legs and long feet 

 naturally take longer steps than short people ; and if they walk 

 together the latter are obliged to quicken their step by a voluntary 

 effort; this is done by increasing the flexion of the knee and 

 dropping the centre of gravity. If the knee is kept rigid and 

 extended, only very short steps are possible, and a greater expendi- 

 ture of energy than usual is required. 



It is also possible to vary the rate of the step, which depends 

 on the duration of the application of one or both feet to the ground, 

 that is, on the forward swing of the inactive limb. The duration of 

 the double application depends on the will ; the more hurried the 



FIG. 77. Subject wearing black 

 clothes to obtain diagram of walk- 

 ing. Chronophotographic method. 

 (Marey.) 



