QUICK SEARCH:   [advanced] Author: Keyword(s):
Home     Help     Feedback     Subscriptions     Archive     Search     Table of Contents

Help viewing high resolution images Return to article

Fig. 3. (A) The Individual Limbs Method (ILM), proposed by Donelan et al. (2002), models the legs as two rigid struts joined by the centre of mass (COM). Single support is considered as a pendular phase during which the COM moves over the stiff supporting limb. Energy exchange is allowed between E_p and E_k. Double support is a transition state during which the COM is redirected from one pendular arc to the next. To maintain a constant walking speed, the propulsive back leg (black lines) has to perform work to overcome the braking action of the front leg (grey lines) on the COM. When using the classical method of calculating work performed on the COM (i.e. by integration of the resultant of forces underneath both feat) simultaneous positive (W_y,back) and negative (W_y,front) work is cancelled out and work during double contact is underestimated. The ILM calculates the amount of positive work performed by the front and back limb separately, consequently opposite work of both limbs during double contact is not cancelled out. (B) Bastien et al. (2003) proposed an alternative method for calculating internal work during double contact (W_int,dc). The legs are seen as two oscillating actuators performing work on the COM. Since both are performing work on the same structure, they can also perform work on each other. Consequently the energy absorbed when the downward movement of the COM is slowed down after foot contact, (W_v is decreasing during the first half of double support) can be used by the propulsive back limb to accelerate the COM forward (transfer of energy from W_v to W_y,back). Also, the energy absorbed by the front limb (W_y,front) can be used during the second half of double support to lift the COM against gravity (transfer from W_y,front to W_v, which is increasing during the second half of double support). Allowing for this energy transfer between the front and back limb will reduce the amount of work that has to be performed by the back limb to overcome the braking action of the front limb. F, force component.

Return to article