Biomechanical energy harvesting from human motion: theory, state of the art, design guidelines, and future directions

Table 3 Summary of total work done by the muscles at each joint or segment of the body during the walking cycle

joint	work [J]	power [W]	max torque [Nm]	negative work
				%	J
Heel strike	1-5	2-20		50	1-10
Ankle	33.4	66.8	140	28.3	19
Knee	18.2	36.4	40	92	33.5
Hip	18.96	38	40-80	19	7.2
Center of mass	10**	20**		***
Elbow	1.07	2.1	1-2	37	0.8
Shoulder	1.1	2.2	1-2	61	1.3

(*) Except for calculations for center of mass and heel strike, all other calculations were performed for an 80-kg person, assuming a walking frequency of 1 Hz per cycle (i.e., two steps). We chose to use 1 Hz to simplify the calculation, since it is close to the 0.925 Hz that was measured by Winter et al. [20].
** Energetic cost of transporting a 20-kg payload using two models (walking frequency of 1 Hz per cycle).
*** Center of mass also includes muscle negative work, but the magnitude is not known.

ISSN: 1743-0003