The transmission efficiency of backward walking at different gradients

The specialized design of the bipedal system towards forward locomotion has been assessed by measuring the metabolic cost and the mechanical work of b oth forward and backward walking on a treadmill at seven gradients from 0 t o +32%. With respect to forward locomotion, backward walking implies: (1) a higher metabolic cost particularly at level gradient, while at steeper inc lines the difference decreases, (2) the same mechanical internal work despi te an increased stride frequency, (3) higher mechanical external work withi n a gradient range from 0 to +15%, (4) lower "energy recovery", i.e. the ab ility to save mechanical energy by moving as an inverted pendulum, mainly i n level walking, and (5) as a consequence of the above results, a decrease of the efficiency of locomotion particularly at the 0% gradient. The transm ission efficiency of backward walking, relative to the forward progression, was found to be about 65% in level locomotion, while at higher gradients i t increased to and was maintained at a value of about 93%. The poorer econo my of level backward walking could also be explained by an impaired elastic contribution in the last part of the double contact phase, while the simil arity of the two gaits on higher gradients is caused by disruption of the p endulum-like paradigm due to the trajectory geometry of the body's centre o f mass progressively losing its downward portion.