Gait termination on declined compared to level surface; contribution of terminating and trailing limb work in arresting centre of mass velocity.

To terminate gait, the mechanical work-done by the lower-limbs is likely to be predominantly negative but how such work is produced/completed has not previously been investigated. The aim of this study was to determine the amount of negative mechanical (external) work-done by the lower-limbs, along with the associated joints (muscle) work, to terminate gait and how these work contributions were affected by a change in surface angle. Eight males completed terminations on the level floor and a declined ramp. Negative mechanical limb-work (limbW(-ve)) was computed (each orthogonal direction) as the dot-product of the ground-reaction-force and centre-of-mass (CoM) velocity. Inverse dynamics was used to calculate ankle, knee and hip negative joints (muscle) work (Wj(-ve)). Measures were determined for each limb for the two-locomotor steps of gait termination. The trailing-limb did 67% (-0.386 J/kg) of the overall limbW(-ve) to terminate gait on the level; and this increased to 74% (-0.451 J/kg) for ramp trials. Wj(-ve) was greater for the trailing- (ankle -0.315; knee -0.357; hip -0.054 J/kg) compared to terminating- limb (ankle, -0.063; knee -0.051; hip -0.014 J/kg), with the increases in ankle Wj(-ve) being temporally associated with increases in perpendicular limbW(-ve). Wj(-ve) increased on both limbs for declined compared to level surface, particularly at the knee (declined -0.357, level -0.096 J/kg), with such increases being temporally associated with increases in parallel limbW(-ve). These findings provide new perspectives on how the limbs do work on the CoM to terminate gait, and may be helpful in designing prosthetic limbs to facilitate walking on ramps.

Gait termination on a declined surface in trans-femoral amputees: Impact of using microprocessor-controlled limb system.

BACKGROUND: Walking down ramps is a demanding task for transfemoral-amputees and terminating gait on ramps is even more challenging because of the requirement to maintain a stable limb so that it can do the necessary negative mechanical work on the centre-of-mass in order to arrest (dissipate) forward/downward velocity. We determined how the use of a microprocessor-controlled limb system (simultaneous control over hydraulic resistances at ankle and knee) affected the negative mechanical work done by each limb when transfemoral-amputees terminated gait during ramp descent. METHODS: Eight transfemoral-amputees completed planned gait terminations (stopping on prosthesis) on a 5-degree ramp from slow and customary walking speeds, with the limb's microprocessor active or inactive. When active the limb operated in its 'ramp-descent' mode and when inactive the knee and ankle devices functioned at constant default levels. Negative limb work, determined as the integral of the negative mechanical (external) limb power during the braking phase, was compared across speeds and microprocessor conditions. FINDINGS: Negative work done by each limb increased with speed (p < 0.001), and on the prosthetic limb it was greater when the microprocessor was active compared to inactive (p = 0.004). There was no change in work done across microprocessor conditions on the intact limb (p = 0.35). INTERPRETATION: Greater involvement of the prosthetic limb when the limb system was active indicates its ramp-descent mode effectively altered the hydraulic resistances at the ankle and knee. Findings highlight participants became more assured using their prosthetic limb to arrest centre-of-mass velocity.