Subject's Leg Length Research Articles

Toward Generalization of Bipedal Gait Cycle During Stair Climbing Using Learning From Demonstration

Lower limb assistive exoskeletons for rehabilitation is a growing field of study. They allow people with spinal cord injuries and strokes to stand upright and walk. Exoskeleton controls research typically focuses on trajectory generation, motion control over the trajectories, and balance and stability. This work focuses on the generalization of people's joint trajectories climbing a single stair, for an exoskeleton to be developed for people of all leg lengths and be used on variable stair heights. The motion of subjects of different heights, ages, and genders climbing a single stair was collected using motion capture. By using Gaussian mixed regression and Gaussian mixed models, these trajectories were combined to build a model that generalizes individuals with different leg lengths, genders, ages and stair heights. The variability of the subject's leg length is accounted for by tracking a marker on the toe of the subject and using inverse kinematics to calculate the joint angles. The analysis in this paper shows that joint angles can be generalized to climb various stair heights. In addition, an open-source database of motion capture climbing data and an open-source framework for generating joint trajectories has been made available for public use.

Balance responses to lateral perturbations in human treadmill walking

During walking on a treadmill 10 human subjects (mean age 20 years) were perturbed by 100 ms pushes or pulls to the left or the right, of various magnitudes and in various phases of the gait cycle. Balance was maintained by (1) a stepping strategy (synergy), in which the foot at the next step is positioned a fixed distance outward of the 'extrapolated centre of mass', and (2) a lateral ankle strategy, which comprises a medial or lateral movement of the centre of pressure under the foot sole. The extrapolated centre of mass is defined as the centre of mass position plus the centre of mass velocity multiplied by a parameter related to the subject's leg length. The ankle strategy is the fastest, with a mechanical delay of about 200 ms (20% of a stride), but it can displace the centre of pressure no more than 2 cm. The stepping strategy needs at least 300 ms (30% of a stride) before foot placement, but has a range of 20 cm. When reaction time is sufficient, the magnitude of the total response is in good agreement with our hypothesis: mean centre of pressure (foot) position is a constant distance outward of the extrapolated centre of mass. If the reaction time falls short, a further correction is applied in the next step. In the healthy subjects studied here, no further corrections were necessary, so balance was recovered within two steps (one stride).

Effect of seat height and turning direction on the timed up and go test scores of people after stroke

To identify the effect of chair seat height and turning direction on the Timed Up and Go scores of patients after stroke. A cross-sectional study. A geriatric day hospital in Hong Kong. Twenty-five patients with sub-acute stroke. The time taken to complete the Timed Up and Go test with various chair seat heights (65%, 90% and 115% of each subject's leg length - distance from lateral knee joint line to ground in sitting) and turning directions (toward the affected and unaffected side) was recorded using a stopwatch with randomized test order. There were significant differences in Timed Up and Go scores between the 3 levels of chair seat height (p < 0.001), with the lowest Timed Up and Go scores recorded when the seat height was 115% of the subject's leg length and the highest at a seat height of 65% of the subject's leg length. Turning toward the affected side was found to be significantly quicker than turning toward the unaffected side (p < 0.001). Chair seat height and turning direction significantly influence the Timed Up and Go scores of patients after sub-acute stroke. Optimizing chair seat height with reference to subject's leg length and turning direction is essential when using the Timed Up and Go test as an outcome measure in stroke rehabilitation.

Characteristics of a MR-compatible ankle exercise ergometer for a 3.0 T head-only MR scanner

An exercise ergometer, for isometric or dynamic contraction of both dorsiflexion and/or plantarflexion exercise, was designed and constructed for a 3.0 T head-only MR scanner. The principal features of this MR-compatible ergometer include electronic devices for quantification of force (during isometric exercise) and angular displacement (during dynamic exercise), without any significant losses to external motions or frictions. The ergometer was also made to be adjustable for subject leg length and was designed for suspension within the bore of the magnet to eliminate transmission of force and vibration to the MR scanner. A description of the design and construction, as well as the important technical features, is presented herein.

Enhancing the ability of gait analyses to differentiate between groups: scaling gait data to body size.

One goal of gait analysis is to distinguish clearly between a set of abnormal gait values measured from a patient referenced to a comparable population. However, the comparable population is often composed of individuals of various heights and weights, which increases inter-subject gait value variation which reduces the ability of a statistical test to identify a set of gait data outcomes with evaluative properties. Therefore, scaling gait data, based on subject leg length and mass, is commonly used to decrease the inter-subject variation but the efficacy of these methods is unknown. In this paper each of eight scaling strategies (none, ad hoc, dimensionless numbers, and five connected strategies based on similarity, dimensional analysis and muscle properties) were used to modify a set of gait data outcomes acquired from 10 individuals spanning a wide range of height (1.33-1.96 m) and mass (42.3-148.8 kg). These data were then examined to select that strategy and those scaling factors which maximally reduced inter-subject variation. The ad hoc, dimensionless numbers, and dynamic/mechanical/elastic (diameter of a limb (D) proportional to it's length (L) to the 1.5 power; time proportional to L(2) D(-1)) scaling strategies reduced the global inter-subject gait data outcome variation to 44% of its un-scaled value. Considering ten commonly reported gait data outcomes (temporal and spatial (stride time, stride length, progression velocity), kinematic (angles in the sagittal and frontal planes, angles in the transverse plane), external kinetic (ground reaction force and moment), and internal kinetic (joint force, moment, and power)) these three scaling strategies provided the largest number of minimum inter-subject variations (10, 10, and 9, respectively). Reduced inter-subject variation in gait data outcomes increases the ability of a statistical tool to detect a difference between a patient and a comparable group. With a statistically significant difference a clinician can then decide if this patient's gait pattern clinically deviates from that of the comparable group and an appropriate intervention warranted. The ad hoc, dimensionless numbers, and the dynamic/mechanical/elastic scaling strategies all reduce maximally the inter-subject variation in gait data outcomes.

Anticipatory locomotor adjustments for avoiding visible, fixed obstacles of varying proximity

Recent work (McFadyen and Winter 1991) has shown that anticipatory locomotor adjustments (ALA's) for clearing mid-swing obstacles result in the reorganization of lower limb motor strategies towards active knee flexion. The present work studies obstacles set to 10% of each subject's leg length and placed near, mid-way or far from the foot about to clear the obstacle. Results show the robustness of the ALA which shows increased knee flexor involvement as the obstacle is placed closer to the subject. As well, the possibility of a decoupling of ankle control from hip/knee patterning as a function of obstacle proximity is discussed.

脚筋力について (1)

Measurement of leg strength has been an unexplored field of research in Japan. The author devised a leg dynamometer which was so designed as to enable to adjust the angle of knee joint in the sitting posture according to subject's leg length. It became possible to measure the maximum strength of leg extension accurately by this apparatus. It follows from the results obtained on the students of Yamanashi University that Leg strength is greater than either grip strength of both hands together or back lift. 2) There are rather greater individual differences and standard deviations. 3) Strength of right leg tends to be greater than that of the left.