Characterizing Swing-Leg Retraction in Human Locomotion

Poggensee, Katherine L.; Sharbafi, Maziar Ahmad; Seyfarth, André; Darmstadt, TU

doi:10.1142/9789814623353_0044

Cited by 10 publications

(9 citation statements)

References 12 publications

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“…However, additional detection rule sets may improve the signal quality and render the thigh a reliable source to differentiate gait phases. When using the additional rule sets for the shank, the leg, and the extended leg, we found a systematic bias of early detection for the heel-strike event (with IMU and Motion capture), which was found to be a typical human gait characteristic in previous work (swing leg retraction; Seyfarth et al, 2003; Poggensee et al, 2014). In comparison, early, on-time and late detection were identified for toe-off.…”

Section: Discussionmentioning

confidence: 51%

Stance and Swing Detection Based on the Angular Velocity of Lower Limb Segments During Walking

et al. 2019

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Lower limb exoskeletons require the correct support magnitude and timing to achieve user assistance. This study evaluated whether the sign of the angular velocity of lower limb segments can be used to determine the timing of the stance and the swing phase during walking. We assumed that stance phase is characterized by a positive, swing phase by a negative angular velocity. Thus, the transitions can be used to also identify heel-strike and toe-off. Thirteen subjects without gait impairments walked on a treadmill at speeds between 0.5 and 2.1 m/s on level ground and inclinations between −10 and +10°. Kinematic and kinetic data was measured simultaneously from an optical motion capture system, force plates, and five inertial measurement units (IMUs). These recordings were used to compute the angular velocities of four lower limb segments: two biological (thigh, shank) and two virtual that were geometrical projections of the biological segments (virtual leg, virtual extended leg). We analyzed the reliability (two sign changes of the angular velocity per stride) and the accuracy (offset in timing between sign change and ground reaction force based timing) of the virtual and biological segments for detecting the gait phases stance and swing. The motion capture data revealed that virtual limb segments seem superior to the biological limb segments in the reliability of stance and swing detection. However, increased signal noise when using the IMUs required additional rule sets for reliable stance and swing detection. With IMUs, the biological shank segment had the least variability in accuracy. The IMU-based heel-strike events of the shank and both virtual segment were slightly early (3.3–4.8% of the gait cycle) compared to the ground reaction force-based timing. Toe-off event timing showed more variability (9.0% too early to 7.3% too late) between the segments and changed with walking speed. The results show that the detection of the heel-strike, and thus stance phase, based on IMU angular velocity is possible for different segments when additional rule sets are included. Further work is required to improve the timing accuracy for the toe-off detection (swing).

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Section: Discussionmentioning

confidence: 51%

Stance and Swing Detection Based on the Angular Velocity of Lower Limb Segments During Walking

et al. 2019

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“…In general, the efficiencies of an actuator for doing positive and negative work can be different (1) . For example, human muscles have about 25% and 120% efficiency for positive and negative (2) work, respectively. 12,28 If the positive quantities 1/c 1 and 1/c 2 are the efficiencies of positive and negative work, respectively, or equivalently c 1 and c 2 are the cost of unit positive and unit negative work, then the net energetic cost of doing W + positive work and W − negative work (W − < 0) is…”

Section: Energetic Cost Of Impulsive Push-off Force and Retraction Tomentioning

confidence: 99%

“…In a normal walking or running step of humans and animals, the non-contact leg swings forward then is rapidly decelerated and, in most cases, begins to move rearward shortly before the swing foot contacts the ground. 1,2 This rearward rotation of the swing leg prior to touch-down, known as swing-leg retraction, is visible in most slow motion videos of running. 3 It is more difficult to see in walking due to the short duration of the retraction phase and small angular velocities of the leg at the end of swing.…”

Section: Introductionmentioning

confidence: 99%

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Energy-optimal relative timing of stance-leg push-off and swing-leg retraction in walking

2015

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SUMMARYSwing-leg retraction in walking is the slowing or reversal of the forward rotation of the swing leg at the end of the swing phase prior to ground contact. For retraction, a hip torque is often applied to the swing leg at about the same time as stance-leg push-off. Due to mechanical coupling, the push-off force affects leg swing, and hip torque affects the stance-leg extension. This coupling makes the energetic costs of retraction and push-off depend on their relative timing. Here, we find the energy-optimal relative timing of these actions. We first use a simplified walking model with non-regenerative actuators, a work-based energetic-cost, and impulsive actuations. Depending on whether the late-swing hip torque is retracting or extending (pushing the leg forward), we find that the optimum is obtained by applying the impulsive hip torque either following or prior to the impulsive push-off force, respectively. These trends extend to other bipedal models and to aperiodic gaits, and are independent of step lengths and walking speeds. In one simulation, the cost of a walking step is increased by 17.6% if retraction torque comes before push-off. To consider non-impulsive actuation and the cost of force production, we add a force-squared (F2) term to the work cost. We show that this cost promotes simultaneous push-off force and retracting torque, but does not change the result that any extending torque should come prior to push-off. A high-fidelity optimization of the Cornell Ranger robot is consistent with the swing-retraction trends from the models above.

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“…Human leg retracts at the end of the swing phase just before the leg collides with ground (i.e., heel-strike) [1]. It was shown that hip retraction exists in human motion for a wide range of walking and running speeds [2]. Leg retraction was also observed in animal locomotion [3].…”

Section: Introductionmentioning

confidence: 99%

Hip retraction enhances walking stability on a ramp: an equilibrium point hypothesis-based study

Bahramian

Shamsi

Towhidkhah

et al. 2019

Preprint

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Hip retraction is a phenomenon observed in human walking. The swing leg rotates 8 backward at the end of the motion. Its positive effect on motion stability was reported in the 9 literature based on some simple models for running or walking. In this study, it is shown that 10 hip retraction angle increases in humans during their ascending and descending walk on a stair. 11In previous studies, hip retraction was modeled by defining a proper motion for the swing leg. 12 According to the equilibrium point hypothesis, the central nervous system (CNS) defines only 13 the equilibrium point(s) and stiffness(es) for body joint(s) to control the human motion. Human 14 body motion emerges as its natural response as a result of the external forces and the defined 15 equilibrium points of joints. Considering the hip torque as a spring-like model with an 16 equilibrium point and stiffness, this study revealed that the hip retraction can be generated by 17 the natural response of the swing leg. Besides, the stabilizing effect of hip retraction was 18 demonstrated by a model for human`s ascending and descending walking on a ramp with a 19 range of positive and negative angles, respectively. The findings suggest that the CNS needs 20 to define equilibrium point just ahead of the stance leg to take advantage of the hip retraction 21 effect on ascending and descending walks on a ramp.22 2

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Characterizing Swing-Leg Retraction in Human Locomotion

Cited by 10 publications

References 12 publications

Stance and Swing Detection Based on the Angular Velocity of Lower Limb Segments During Walking

Stance and Swing Detection Based on the Angular Velocity of Lower Limb Segments During Walking

Energy-optimal relative timing of stance-leg push-off and swing-leg retraction in walking

Hip retraction enhances walking stability on a ramp: an equilibrium point hypothesis-based study

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