The MIT Biomechatronics Group recently built an elastic
exoskeleton similar to Yagn's design. However, its
intended application was not for running augmentation,
but for lowering the metabolic demands of continuous
hopping [15,16]. The exoskeleton, shown in Figure 2b,
comprises fiberglass leaf springs that span the entire leg,
and is capable of transferring body weight directly to the
ground during the stance period. In distinction to Yagn's
exoskeleton, the MIT device does not include a clutch to
disengage the exoskeletal leaf spring during the aerial
phase since such a clutching control was deemed unnecessary
for hopping. Without accounting for the added
weight of each exoskeleton, wearing the exoskeleton
reduced net metabolic power for continuous hopping by
an average of 24% compared to normal hopping [16].
When hoppers utilized external parallel springs, they
decreased the mechanical work performed by the legs and
substantially reduced metabolic demand compared to
hopping without wearing an exoskeleton. Since the biomechanics
of hopping are similar to that of running, it
seems plausible that the effects of wearing an exoskeleton
during hopping could predict the biomechanical and metabolic
effects of wearing an exoskeleton during running,
and that substantial energetic advantages might be
achieved while running with a highly elastic, parallel leg
exoskeleton. Clearly, for the goal of augmenting human
running performance, lightweight and highly elastic leg
exoskeletons that act in parallel with the human leg provide
a research area of critical importance.