Graduation date: 2007
Previous attempts to understand the factors affecting the energetic
cost of locomotion have found a direct link between the energetic cost and
the mechanical work done during periods when the limb is in contact with
the ground. However, when the limb is not in contact with the ground
during the swing phase, this link between mechanical work and energetic
cost disappears. I examined the mechanics of swing to explore the
possibility of passive mechanisms allowing for the performance of
mechanical work with little to no energetic cost during swing. Previous
studies have ruled out the possibility of a pendulum exchange of
gravitational potential and kinetic energy during human locomotion
because the swing frequencies are too high. I added the accelerations of
the body during stance to the swinging lower limb to determine if the
frequency where the pendulum-like exchange of energy occurs could be
increased. These accelerations increased the frequency where energy
exchange occurs and thereby reduced the work required to swing the
human lower limb. The pendulum-like exchange of energy reduces the
work required for swing, but some work is still required. To explore how
the remaining work for swing was produced I examined two muscles
potentially involved in producing an extension moment about the intertarsal
joint of turkeys during swing. The only muscle providing force for
intertarsal joint extension during swing was the lateral head of the
gastrocnemius (LG). A comparison of the in situ length-tension curve and
in vivo operating lengths during swing revealed the LG operated at long
lengths on the descending limb of the length tension curve during swing.
Finally I characterized the force-velocity curve of the LG and found the
muscle to have mechanical properties within the range previously
determined for other vertebrates. In conclusion, I determined a passive
mechanism which could reduce the required mechanical work of swing and
thereby explain part of the apparent lack of a link between mechanical
work and energetic cost of swing. In addition, results from these studies
suggest the remaining work necessary for swing may be provided by active
contraction of muscle.